Doctoral Degrees (Animal, Wildlife and Grassland Sciences)

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Open Access
Alternative management systems to increase beef production under extensive conditions
(University of the Free State, 2016-06) Grobler, Susanna Maria; Scholtz, M. M.; Greyling, J. P. C.; Neser, F. W. C.
South Africa is still a net importer of beef. Therefore, by increasing off take in the beef sector, South Africa can move towards self-sufficiency. With fertility being regarded as one of the main components influencing total beef herd efficiency, it is essential that the quoted calving percentage of 62% in the commercial beef sector of South Africa must be improved. If the long calving seasons can be shortened and the calving percentage increased, more and heavier calves with a more uniform age can be weaned. Cows that calve early also have a better chance of conceiving in the next breeding season and are generally seen as the more fertile animals Development, production and quality of replacement heifers is a crucial component in the extensive beef production system. In general, beef heifers are managed to calve for the first time at three years of age, but in some cases mating of heifers at one year of age have been advocated. All extensive beef production systems in South Africa are dependent on natural veld and it is well documented that veld condition have a huge influence on a number of beef production parameters. Studies conducted on natural veld have concentrated mainly on aspects that affect herd efficiency, including calving percentage, pre-weaning growth and supplementation of cows and calves. However, none of the studies focused on the reproduction performance of beef cattle mated naturally after synchronization, heifer age at breeding and effect of grazing system on veld condition. The aim of the study was to evaluate: the effect of estrous synchronization followed by natural mating on the calving percentage and calving distribution of multiparous beef cows and heifers; effect of breeding heifers at either 14 months or 26 months of age and the evaluation of a high utilized grazing system and controlled selective grazing on veld condition and animal performance. The effects of climate on cow-calf production characteristics over time was also evaluated. The study was conducted from 2009 to 2015 at the Roodeplaat experimental farm (REF) of the ARC-Animal Production Institute (25°34’11.27’’S; 28°22’05.36’’E) on 900 ha of natural rangeland described as Sourish Mixed Bushveld. The experimental herd (n=92) was divided in four sub-herds consisting of 23 cows each at the beginning of the project in 2009. It was ensured that the four sub-herds were as uniform as possible at the beginning of the project e.g. age, weight, previous number of calves. Within each sub-herd, 50% of the cows and heifers were synchronized prior to the commencement of the breeding season. Two sub-herds were subjected to high utilized grazing and two sub-herds were subjected to controlled selective grazing. The two grazing systems were related to the use of 30% or 60% of the available grass dry matter. Half the heifers were mated at 14 months and the other half at 26 months. Results from this study indicated that calving percentage and body condition score did not differ significantly (P=0.54) between cows that was either synchronized or not synchronized followed by natural mating. However, estrous synchronization prior to natural mating did influence the average days to conception with synchronized cows calving earlier, except for 2012 in the calving season. Over the six-year project period 15% more cows from the synchronized group conceived within 293 days after the onset of the breeding season. Calves from the synchronized cows weaned on average 5kg heavier than the cows that were not synchronized although this difference was not significant. Conception rates of heifers mated at 26 months were significantly (P<0.05) higher than heifers mated at 14 months of age. It would seem that it may be more viable to breed Bonsmara heifers in an extensive production system in the Sourish Mixed Bushveld region at 26 months of age for the first time. Synchronization of 14 month old heifers did not improve conception rate over 14 month old heifers bred naturally. However, the calving percentage of synchronized heifers bred at 26 months was 6% higher than the non-synchronized heifers. Almost no veld condition change was recorded except for veld condition scores for both controlled selective grazing and high utilization grazing. In addition, the results indicate a tendency that high utilization grazing improved veld condition score and grass species composition over that of controlled selective grazing, but the duration of the study is too short to make a definite conclusion on the effect of grazing strategy on veld condition. It was also shown that grazing strategy did not have a significant influence on cow weight and calf growth over the six-year period, indicating that both grazing strategies are sustainable in the Sourish Mixed Bushveld if carrying capacity is adhered to. With the significant differences between years (P ≤ 0.05) for calving percentage, cow weight at calving, cow weight at weaning, calf birth weight, calf weaning weight and body condition score over the six-year observation period, the effect of seasonal temperature, relative humidity and rainfall is elucidated. Forward stepwise regression procedures were performed to determine what climatic data were involved in cow and calf weight at birth and weaning as well as calving percentage. In spite of the high standard errors (which were probably due to the small sample size), maximum relative humidity one month prior to the start of the breeding season, made a major contribution to explain calving percentage and minimum temperature within the last month of the 3 month breeding season, had a low negative correlation with calving percentage. It can be speculated that high humidity in the study region (Sourish Mixed Bushveld) is an indication of warm and wet conditions, negatively impacting cow and bull comfort, leading to lower conception rates. The negative correlation between minimum temperature within the last month of the breeding season and calving percentage may indicate that the cows were unable to cool down at night during the warmer summer months of the year, leading to lower conception rates and resorptions. The researcher acknowledge that the available herd size may be a limitation and that a bigger herd or sub-herds’ size combined with bigger land size could benefit the project outcome, possibly resulting in more significant differences and/or enhanced interpretation of results.
Open Access
Breed genetic and heterosis effects on variability of growth and efficiency traits in beef cattle
(University of the Free State, 2024) Pyoos, Georgette Mareé; MacNeil, M. D.; Neser, W. C.; Scholtz, M. M.
The first goal of this investigation was to characterize breed genetic effects for indigenous and exotic breeds of beef cattle under South African conditions. A second goal was to characterize within animal daily variation in partial body weight and feed intake during the postweaning period. It is intended that these characterizations will lead to better choices among breed resources, particularly for emerging farmers. Thus, a crossbreeding trial was conducted in South Africa, Northern Cape, over a period of eight years from 2015 until 2022. Afrikaner, Bonsmara and Nguni dams were mated with Afrikaner, Bonsmara, Nguni, Angus, and Simmentaler sires. Data were collected according to the National Beef Recording and Improvement Scheme in South Africa. There were 212, 324, 303, 179 and 234 calves sired by Afrikaner, Nguni, Bonsmara, Angus and Simmentaler sires, respectively. There were 182, 633 and 437 calves produced by Afrikaner, Nguni and Bonsmara cows, respectively. Birth and 205-day weights were analyzed including effects of year, sex, age of dam, the genetic expectation for breed group, and the interactions of year with the breed direct and maternal effects and individual heterosis. The probability levels (P-values) for the interaction of the genetic effects and year indicate plasticity with respect to the inter-year environment. Plasticity is defined as deviations in an individual’s phenotype in reaction to environmental fluctuations. The P-values for birth weight interactions of Afrikaner, Angus, Nguni and Simmentaler direct effects with year were 0.06, 0.09, 0.01, and < 0.01, respectively. The corresponding P-values for 205-day weight were 0.69, 0.03, 0.15, and 0.10. Thus, birth weight appeared to be more plastic, i.e., more sensitive to the variation among years, than was 205-day weight. The temperature-humidity index during the study period varied between 78.5 and 81.6. Previous studies indicate that heat stress is induced if temperature humidity index ≥ 72 and thus the preweaning environment was very harsh. After weaning, the male calves were transported from Vaalharts to Irene in groups of 25-28 according to their weight. Upon arrival, the animals were given a 2-week adaptation period and were then allocated to pens in the GrowSafe system according to their body weight. This system of allocation resulted in the partial confounding of breed groups, contemporary groups, and the days on feed. The data were analysed with linear models that included the categorical effects of test group and breed group and the continuous effect of days on test. Breed group effects on daily feed intake and partial body weight were not detected (P > 0.05). As expected, the animals ate more and became heavier as the test progressed (P < 0.05). The breed groups differed in their growth rate as evidenced by the significant interaction between the breed group effect and the linear effect of days on test for partial body weight. However, the rate at which animals increased their daily feed intake was invariant to their genotype. In partitioning the interaction of breed group with days on test into single degree of freedom effects, only the effect of individual heterosis on partial body weight (0.99 ± 0.35 kg/day) was significant (P <0.01). Adding the binary indicator of heat stress to the linear model indicated highly significant effects on both daily feed intake (-9.69 ± 1.31 g/day) and partial body weight (48.2 ± 2.1 g/day). Animals that were heavier consumed more feed (37.7 ± 4.8 g/day; P <0.01) and animals that consumed more feed were heavier (57.1 ± 9.3 g/kg; P <0.01) as this is expected. Estimates of the serial correlations of daily feed intake and partial body weight were calculated for each animal. These correlations were transformed to z-statistics before being analysed further. Average estimates for the z-transformed serial correlation of daily feed intake and partial body weight for each animal were 0.1003 and 3.0506, respectively. The 95% confidence interval for daily feed intake was 0.095 < z < 0.106; and for partial body weight it was 3.041 < z < 3.061. However, it does not appear these differences are related to the breed composition of the animals. The high degree of between-animal variation in the estimate of the serial correlation indicates animals differ markedly for feed they consume from day-to-day. In contrast, the estimates of serial correlation of partial body weights were very high and consistent across animals. Thus, there is little need to average values over days to achieve an accurate estimate of partial body weight at any specific point in time. An evaluation of postweaning feed intake that was conducted over a 36-day period would, on average, produce an accuracy of the daily feed intake mean for an individual animal of 0.80. The inter-day variance in feed intake served as a metric for the evaluation of plasticity. These data were analyzed using Friedman’s test based on a non-parametric two-way analysis of variance. The breed groups differ significantly in their plasticity of feed intake. Linear functions of the breed group effects indicated that the Nguni, Simmentaler, Afrikaner, and Angus breed direct effects were more variable over time than was the Bonsmara direct effect. The estimated heterosis effect was small and not significant indicating that crossbred cattle would be no more variable over time in feed intake than their straightbred counterparts. Some commercial producers and probably all subsistence producers might choose a less plastic and more robust set of breed resources, which may perform well, regardless of the current environment. However, resource-rich commercial producers might prefer to utilize more plastic breed resources to capitalize on times when the environment is favorable and mitigate less favorable times.
Open Access
Causes and consequences of fenceline contrasts in Namibian rangeland
(University of the Free State, 2011-02-15) Zimmermann, Ibo; Smit, G. N.
English: This study made use of the opportunity provided by fenceline contrasts in Namibia to measure differences in rangeland and learn from farmers about the inputs and outputs of management on each side of the fence. The 34 measured contrasts were mostly clustered within the Camelthorn and Thornbush Savannas, with three in the Highland and Dwarf shrub Savannas of Namibia. Mean annual rainfall ranges from 235 to 475 mm. Rangeland measurements focussed on well established perennial vegetation to avoid the fluctuating effect of ephemerals. Eight characteristics were measured and significant (P<0.05) differences occurred in at least one of these at each contrast. Two characteristics (distance from sample point to the nearest perennial grass and the species) were combined to determine a rangeland condition index. At 22 of the 34 contrasts the condition index was significantly (P<0.05) higher on one side of the fence. There was no clear method to distinguish between the influences of different management inputs that may have caused the fenceline contrasts. Therefore, subjective judgment was relied upon to identify bush control as the most likely single causative factor at ten contrasts, stocking rate and period of rest at five contrasts each, and stocking density at two contrasts. Management contributed to both causes and consequences of fenceline contrasts. The negative correlation between stocking rate and rangeland condition index was weak (r = −0.2575, P = 0.04, n = 64), suggesting that there may have been more farms where a higher stocking rate was the cause of poorer rangeland than farms where the higher stocking rate was the consequence of better rangeland raising the carrying capacity. The stronger correlation between profit and income (r = 0.9288, P < 0.001, n = 25) than between profit and expenditure (r = 0.0267, P = 0.899, n = 25), suggests that farmers should focus on reducing non-essential expenditure to increase profitability. Game farming can earn high income, but continuous selective grazing by gregarious game animals may lead to poorer rangeland condition. Useful lessons were learnt from the case study of an innovative farmer who adapted his management based upon his keen observations of rangeland dynamics. Many of his interventions were strategically timed in relation to rainfall events. There is much that can be learnt by both scientists and other farmers from the management strategies applied by successful farmers who earn a good profit while sustaining the rangeland.
Open Access
Characterization of rangeland resources and dynamics of the pastoral production systems in the Somali region of eastern Ethiopia
(University of the Free State, 2006-05) Gezahegn, Amaha Kassahun; Snyman, H. A.; Smit, G. N.
The study was conducted in the Somali region of eastern Ethiopia, with an arid to semiarid climate. The study aimed at the characterization of the rangeland resources, assessing the current condition of the rangeland, understanding pastoral perceptions on rangeland degradation and developing drought feeding strategies for livestock. Three experimental sites, representative of the three predominant vegetation types of eastern Ethiopia were selected. They were the arid Asbuli grassland (used as grazing area for large and small ruminants), the arid Aydora open savanna (bush-grassland: entirely used for grazing/browsing by all types of livestock), and the semi-arid Hurso closed savanna (bushland: selected for its importance as browsing for camels and goats). A degradation gradient was identified in each of the three vegetation types, where the botanical composition was surveyed and the rangeland condition assessed. The perceptions of the pastoralist on rangeland degradation were also quantified. The dry matter production of both the herbaceous and woody layer was determined, while the grazing and browsing capacity calculated. Key forage species were identified and the grazing pattern of various livestock species along the degradation gradient studied. The soil seed bank regeneration potential was assessed in a greenhouse experiment and the response of cattle, sheep and goats to a simulated drought, in terms of reduced fodder, was conducted under controlled conditions. The results of the study confirmed the existence of severe rangeland degradation that occurred since 1944 and which was aggravated after the 1974 drought. This contributed to an increase in the number of poor households. The average livestock holding per household declined from 809 Tropical Livestock Units (TLU) before 1974 to 483 TLU after 1974. Livestock holding shifted from a predominance of cattle to small ruminants, which are able to utilize the degraded rangeland more effectively. Camels are now the most important livestock species in terms of milk and meat production, mainly due to their ability to tolerate drought. The abundance of herbaceous plants, basal cover, dry matter production and grazing capacity was found to be higher in the benchmark sites compared to the other rangeland conditions. There was also a corresponding increase in percentage bare ground, soil compaction and soil erosion along the degradation gradients. Over-grazing and overutilization through continuous grazing of the herbaceous layer were identified as the main causes of these differences. Rangeland condition was observed to significantly influence the grazing behaviour of livestock in terms of plant species selection, grazing intensity and intake per animal. When forage sources were adequately available, animals selected fever plant species. As forage resources declined the animals spend more time grazing and more species selected, including less palatable species. The number of bites, intake per bite and intake as a percentage of the animal’s body mass also increased as the rangeland become more degraded. Acacia nubica and A. mellifera were identified as aggressive encroaching species in the Aydora open savanna and Hurso close savanna. The Aydora open savanna experienced extensive encroachment by woody plants with increasing plant densities across the degradation gradient. The Hurso closed savanna experienced an opposite trend where severe deforestation and a loss of valuable browse species occurred, mainly as a results of over cutting of the woody plants for firewood, charcoal making, construction and the clearing of the land for planted crops. The study on the soil seed bank of soil collected along the various degradation gradients showed a high abundance of plant seed present in the soil, confirming the potential of the area for rangeland restoration. As expected the body weight losses of all livestock species in the controlled feeding trial were highly correlated with the reduction in daily dry matter feed. More than 50% of the animals showed pronounced emaciation and physical weakness and 25% of the cattle and goats collapsed and died within ten weeks after the trial started. This explained the large scale mortalities of livestock during prolonged droughts. Drought must be accepted as part of the pastoral life and there should be an adequate early warning system regarding livestock feed availability and strategies of appropriate mitigation strategies. More realistic stocking rates is the obvious solution to the avoidance of stock losses during droughts, but in view of the well established culture of the pastoralists it is highly doubtful if they will be willing to reduce their animal numbers. In conclusion, the experimental results indicated the existence of genetic variability among the various Somali livestock breeds regarding the tolerance to feed shortages and in rates of compensatory growth. This demonstrates the opportunity for improving the genetic composition of the Somali herds through selection.
Open Access
Comparison of genetic and immunological responses to tick infestation between three breeds of sheep in South Africa
(University of the Free State, 2016) Thutwa, Ketshephaone; Van Wyk, J. B.; Cloete, S. W. P.; Dzama, K.
𝑬𝒏𝒈𝒍𝒊𝒔𝒉 The study investigated genetic parameters and immunological responses to tick infestation in three South African sheep breeds (Namaqua Afrikaner [NA], Dorper and SA Mutton Merino [SAMM]). The study aimed to estimate genetic and crossbreeding parameters for tick count (TC) and weaning weight (WW), to examine the histology of tick attachment and control sites, to select reference genes for normalizing gene expression data in this study, to compare cytokines gene expression at tick attachment and control sites and finally to compare cutaneous hypersensitivity reactions to unfed larvae extracts (ULE) of Rhipicephalus evertsi evertsi between NA, Dorper and SAMM sheep. Genetic parameters for WW and TC were estimated using data of lambs maintained on the Nortier Research Farm from 2010 to 2015. Firstly, data of purebred commercial Dorper and SAMM lambs were combined with data of their reciprocal crosses to assess breed effects and the possible effect of non-additive genetic variation on WW and TC. In the second analysis, data of purebred commercial Dorper lambs were combined with data of the unimproved, indigenous NA and the NA x Dorper cross. In Analysis 1 the coefficient of variations (CV) were 24%, 95% and 50% for WW, untransformed total TC and square root transformed total TC, respectively. Genotype affected WW but not TC. A heterosis estimate of approximately 4% was derived for WW. A single-trait h² estimate for TC was 0.11±0.09. A model analysing across-genotype h² yielded a slightly lower h² estimate of 0.08 ± 0.07. In Analysis 2 the CV were 27% and 55% for WW and square root transformed total TC, respectively. WW and TC were affected by genotype. WW exhibited heterosis amounting to 8.5% while the corresponding value for TC amounted to -23%. The single-trait h² estimate for TC was 0.06±0.05. A model analysing across-genotype h² yielded a substantially higher h² estimate of 0.27±0.07. These results suggest that genetic variation in TC was primarily associated with differences among genetic groups while differences between individual animals within genetic groups were not as important. Heterosis estimates for WW were variable between two analyses, but within ranges reported in the literature. This study established significant variation in TC between sheep genotypes when the indigenous NA breed formed part of the analysis. The NA x Dorper cross resembled the improved Dorper breed for WW but the unimproved, resistant NA for TC and exhibited worthwhile levels of heterosis for both traits. Indigenous ovine genetic resources may be instrumental in providing genetic material for adaptive traits in environments susceptible to high levels of tick infestation. Further research is required to elucidate the role that adapted indigenous ovine genetic resources may play in an integrated tick management strategy under conditions characterised by high levels of tick challenge. A histological study was conducted to assess histological features at tick attachment and control sites in pure breeds. Skin biopsies were examined using routine histological techniques for immunological cell infiltration and skin reactions. Marked variation in immunological responses to tick attachment within and between sheep breeds was observed. There were differences between the attachment and control sites in most of the skin changes (defects) except for four skin defects in the NA. However, all breeds had similar frequencies of skin defects at tick attachment sites. Tick attachment sites were more likely to be infiltrated by cells within as well as across breeds. The NA and SAMM breeds tended to demonstrate greater cellular infiltrations of specific leukocytes at tick attachment sites compared to Dorpers. Basophils, mast cells and eosinophils were increasingly recruited at tick attachment site in NA ewes compared to the Dorper and, occasionally, the SAMM breeds. These results suggest the importance of these cells in sheep resistance to tick infestation. Tick genera influenced the recruitment of neutrophils to tick attachment sites. Tick gender, sampling site as well as tick engorgement level did not affect the number of immunological cells. Further studies should be done with one tick species at a time to better comprehend the species-specific impact of tick attachment to animals belonging to divergent sheep breeds. Five genes (18S, GAPDH, YWHAZ, B2M and SDHA) were tested for their stability. SDHA, YWHAZ and B2M were the most suitable reference genes recommended by geNorm analysis for normalizing gene expression data in sheep skin. These findings will assist in normalizing data in gene expression studies at tick attachment and control sites of the NA, Dorper and SAMM breeds. This study suggested that no reference gene is stably expressed in different experimental conditions. The expression of IL-1β, IL-8, CCL2 and CCL26 was quantified in real-time qPCR. IL-1β and IL-8 were more highly expressed at tick attachment than at control sites. NA ewes expressed IL-1β more at tick attachment sites than Dorpers. The NA breed was also more likely to upregulate the expression of the CCL2, CCL26 and IL-8 genes at tick attachment sites compared to control sites than the other breeds. This indicates that IL-1 β, CCL26 and IL-8 may play a part in resistance or susceptibility of sheep to tick infestation. The differences in expression of the two chemokines between the resistant NA and more susceptible SAMM and Dorper imply that the NA breed could be able to overcome the anti-chemokine activity of tick saliva. ULE of R. evertsi evertsi induced hypersensitivity reactions in all the breeds. The indigenous NA displayed stronger reactions, immediate and delayed, than the commercial breeds. The results suggest that cell-mediated immune responses are invoked to fight against tick infestation in the NA. The hypersensitivity reaction may be used as a phenotypic marker to select animals or breeds that are more resistant to tick infestation. It is well-known that challenge-based research for promoting resistance to pathogens is under scrutiny from an ethical and welfare perspective. The methods employed here could be refined to enable routine evaluation of valuable animals without resorting to more invasive strategies, such as allowing adequate natural challenge to accrue over time in selection candidates. Overall, the component studies reported in the thesis increased the present understanding of ovine tick-host interactions and factors contibuting to breed differences in tick loads. ___________________________________________________________________
Open Access
Crude protein and mineral status of forages grown on Pellic Vertisol of Ginchi, Central Highlands of Ethiopia
(University of the Free State, 2002-11) S/gebreal, Lemma Gizachew; Smit, G. N.
The study was conducted at Ginchi, which is situated in the western Shoa zone of the central Ethiopian highlands. The main aim of the study was to assess the crude protein (CP) and mineral status of feeds produced in the Vertisol area of Ginchi by relating them to pasture management, seasonal and/or soil factors. Aspects of the farming systems that relate to feed resource management, utilization, constraints and opportunities were also investigated. The N and mineral element status of the soil and the feeds were evaluated during the dry and wet seasons of 2001 by analysing samples collected from adjacent 18 year round grazed grassland (YRG) plots, 12 seasonally stock excluded grassland (SSE) plots, 10 tef (Eragrostis tef) and 9 grass pea (Lathyrus sativus) plots, and noug (Guizotia abyssinica) seedcake samples obtained from oil extracting plants. The results of the farming systems study demonstrated a strong inter-dependence between crop and livestock subsystems. Livestock rely on crops for their diets as much as the latter do on livestock for traction power and manure. Stored feed supplies are preferentially fed to working oxen, milking cows and animals intended for sale. The period extending from the late dry season (March-May) up until the mid wet season (July) appeared to be the time when feed shortages were most critical. Smallholders try to cope with the problem through efficient use of SSE, grassland, crop residues and crop weeds. Occasionally they also provide domestic herbivores with locally produced supplemental feeds, common salt, mineral rich soil or mineral water. Soil samples were analysed for particle size class, pH, organic matter (OM), cation exchange capacity (CEC), N, P, Ca, Mg, K, Na, Fe, Mn, Cu and Zn. Most of these soil parameters differ markedly (P<0.05) between the different land use systems. Parameters such as OM and total N in particular were very high in grassland soil in comparison to soil under cropping systems (P<0.01). The results also revealed a substantial across site variation of these soil parameters. For native pastures, the type of pasture management had a considerable influence on floristic composition, herbage CP and mineral concentration. Compared to the YRG grassland the SSE grassland contained a higher proportion of herbaceous species with superior CP and mineral concentrations. The CP and mineral contents of YRG grassland exhibited marked changes with the advance of the season (P
Open Access
The demography and population status of lions (Panthera leo) in the Mana Pools National Park, Zimbabwe
(University of the Free State, 2008-11) Monks, Norman John; De Waal, H. O.
English: Demographics of the lion population in the Mana Pools National Park were studied between 2001 and 2007. No detailed work had previously been carried out on this subject in the park. Demographic data was obtained from six prides, with two prides (Chitake and Jesse) being on the Zambezi Valley floor at the base of the Zambezi Escarpment in the south, and four prides on the Zambezi floodplain in the north. The Zambezi floodplain in the Mana Pools National Park is 95.5 km² in extent and in area comprises 11.2% of the park. Approximately 46% of the adult lion population occurs on the floodplain where approximately 63% of the lion prey base in the park is found. Not all prides could be studied at the same intensity, however, demographic data was obtained for all six prides. The Nyamepi pride on the floodplain was the most intensely studied. A population estimate of 67 adult and sub-adult lions was made for the Mana Pools National Park. Overall density throughout the park was 3.05 lions/100 km². Density ranged from 0.65/100 km² in the escarpment which held 0.3% of the prey species taken by lions to 12.7/100 km² on the floodplain. There were 1.8 adult males to 3.3 adult females and all prides were attended by a male. Mean group size (adults and sub-adults) was 7.8 (range 5-11). The adult and sub-adult age class made up 70.7% of the population and large and small cubs made up 29.3% of the population. Cub survival to one year of age was 66.7%. Females produced their first litter between 43-53 months of age and cohorts of cubs were produced on average every 38.5 months. Pride males had an average tenure with the pride of 33.25 months and sub-adult males dispersed from the pride between 36-57 months with a mean of 39.8 months. Home ranges varied on the floodplain from 28.1 km² to 278 km² and from 50.2 km² to 379.3 km² on the valley floor. The floodplain Nyamepi pride males had a home range two and a half times that of the females. Only the Valley floor lions had differences in dry and wet season home range size (dry season 57.7 km² and wet season 379.3 km²). Demographic variables, when compared to other lion populations in similar habitat in protected areas in Africa, did not differ and the Mana Pools National Park lion population appears to be normal. The Mana Pools National Park is surrounded in the west and east by Safari areas (administered by ZPWLMA) and has no man-made or natural barriers between them. No work was carried out on lions in the surrounding Safari areas but it was found that males frequently made excursions into the Safari areas (one collared male was shot in Chewore Safari area 80 km from the darting site in Mana Pools). Lions also frequently crossed the Zambezi River into the Lower Zambezi National Park, Zambia. It is presumed that there is a two-way movement between the Mana Pools National Park and Safari areas and the Park and the Lower Zambezi National Park, but could not be confirmed in this study. The spotted hyaena population in the Mana Pools National Park was found to be in the low-medium category when compared to other populations in protected areas in Africa (Purchase, 1999). All data accrued during the present study showed that this population do not pose a threat to lion conservation in and around the Mana Pools National Park.
Open Access
The development of breeding objectives for Holstein and Jersey cattle in South Africa
(University of the Free State, 2009-11) Banga, Cuthbert Baldwin; Neser, F. W. C.; Garrick, D. J.; van der Westhuizen, J.
A sound breeding objective is the basis for genetic improvement in overall economic merit of animals. Breeding objectives for Holstein and Jersey dairy cattle breeds in South Africa were developed in the current study, using a systematic approach. First, a logical framework with a profit focus was utilised to develop plausible selection goals for the pasture-based and concentrate-fed dairy production systems in South Africa, leading to an exhaustive list of objective traits influencing these goals and subsequently their possible selection criteria. Next, economic values were calculated for those objective traits for which there was adequate bio-economic data, viz.: milk volume, fat yield, protein yield, live weight, longevity, calving interval and somatic cell score. A bioeconomic model, simulating typical South African pasture-based and concentrate-fed herds, was used to calculate economic values by determining changes in profit arising from an independent unit increase in each trait. Alternative payment systems of four major milk buyers in South Africa were used. Relative economic values, standardised to the value of protein, were used to compare the relative importance of traits across breeds, production systems and payment systems. Protein yield, fat yield and longevity consistently had positive economic values and the converse was true for body weight and calving interval. Economic value for volume was positive or negative, depending on whether the payment system paid for it or did not. Economic values were reasonably robust to fluctuations in the cost of feed and price of beef; with the exception of fat, whose value became negative beyond the feed price of ZAR3.50. Protein was, overall, the most important trait, although volume, live weight, longevity and somatic cell score were more important in some situations. Calving interval was the least important trait, its value ranging from 4 to 22% compared to that of protein, probably because the model used underestimated its value. Sire rankings on aggregate EBVs based on these economic values did not differ much across breeds, production systems and payment systems, most rank correlations falling in the range 0.70-0.99. A single breeding objective may therefore be used for both the Holstein and Jersey breeds, across the different production and payment systems. The basis for multiple-trait selection in the major cattle breeds in South Africa has thus been developed. Considerable work, however, needs to be done to enhance this breeding objective as well as facilitate its wide adoption by industry.
Open Access
The development of economic selection indices for the Simmentaler breeds in South Africa
(University of the Free State, 2004-11) Kluyts, Johan Francois; Neser, F. W. C.; Bradfield, M. J.
English: The purpose of the first chapter was to give a short introduction to the study. Although there were exponential increases in knowledge, there are still fields of study where there is little understanding and enormous gaps relating to information. A short history of the development of cattle was presented, with special reference to the Simmentaler breed. The objectives of this study were then stated. These objectives were: the definition of breeding objectives, derivation of economic values and development of economic selection indices for the Simmentaler breed in South Africa. 2. In Chapter 2 the development of breeding objectives and the derivation of economic values were reviewed. There seems to be general consensus that definition of breeding objectives should be the primary step in the design of structured breeding programs. Development of the breeding objective can be described in terms of the following phases: specific ation of the breeding, production and marketing system, identification of sources of income and expense in commercial herds, determination of biological traits that influence income and expense, derivation of economic values, choice of selection criteria, and estimation of phenotypic and genetic parameters. The modeling methods to derive economic values can be divided into simulation, dynamic programming and profit functions. 3. In Chapter 3 the important traits, which should be considered for the development of breeding objectives, as well as the criteria to be included in the selection index were reviewed. Traits were classified as fitness-, production-, product-, input-, type- and behavioural traits. The decision whether or not to include a trait in the breeding objective depends on the relative economic value of the trait, the potential for genetic improvement and the possibility of accurate and cheap measurement. Several traits determine economic efficiency, and the required balance of these traits is likely to differ between different production systems. 4. The purpose of Chapter 4 was the development of a general breeding objective for the Simmentaler breed in Southern Africa as well as the derivation of economic values for beef production traits. Income was partitioned between weaners (steers), surplus heifers and cull cows. Expenses were calculated for all classes and included feed cost, husbandry cost and marketing cost. Economic values for weaning weight (direct), weaning weight (maternal), yearling weight (400 days), final weight (600 days) and mature cow weight were derived as partial derivatives of the profit equation. These values, expressed per genetic standard deviation, in South African Rand per cow, corrected with the discounted gene flow and diffusion coefficient methods (in brackets) are, 25.57 (75.01), 15.21 (47.97), 28.49(83.63), -13.95 (-40.79) and -69.29 (-63.39) respectively. 5. The objectives of Chapter 5 were to expand the Simmentaler breeding objective by inclusion of functional traits and to derive economic values for the functional traits calving rate, days -to-calving, calving-ease (direct) and calving-ease (maternal). It was assumed, for these categorical traits, that there is an unobserved underlying normal distribution of the sum of genetic and environmental values, and that the phenotypic category is defined by threshold values on this distribution. The consequences of a change in fitness included changes in costs, changes in culling rate, number of barren cows and the number of surplus offspring available for sale. Results emphasised the relative importance of fertility. Economic values, expressed per genetic standard deviation in South African Rand per cow, corrected with the discounted gene flow and diffusion coeffic ient methods (in brackets) are, 18.98 (15.27), - 93.82 (- 75.51), 1.08 (1.31) and 1.15 (1.08) for calving rate, days-to-calving, calving-ease (direct) and calving-ease (maternal), respectively. 6. The objectives of Chapter 6 were to expand the Simmentaler breeding objective by the inclusion of product quality traits and to derive economic values for dressing percentage, backfat thickness, tenderness and marbling. A method to derive economic values for these optimum traits was described. It was as sumed, for the categorical traits, that there is an unobserved underlying normal distribution of the sum of genetic and environmental values, and that the phenotypic category is defined by threshold values on this distribution. The consequences of a change in the mean performance of a trait include changes in the number of animals in different quality classes and as a result thereof, changes in the expected value of a carcass. Economic values, expressed per genetic standard deviation in South African Rand per cow, corrected with the discounted gene flow and diffusion coefficient methods (in brackets) are, 20.96 (61.50), 0.39 (1.14), -3.52 (-10.33) and 0.18 ( 0.52) for dressing percentage, backfat thickness, tenderness and marbling respectively. 7. The development of economic selection indices for an integrated Simmentaler production system was described in Chapter 7. The breeding objective was defined in terms of production-, functional- and product quality traits. Criteria included in the total index are birth- and weaning weight (direct and maternal), yearling weight, final weight, mature cow weight, days -to-calving, backfat thickness, tenderness and marbling. The total merit index (IT) for an integrated Simmentaler production system is IT = – 1.65 BWD – 1.99 BWM + 2.28 WWD + 1.76 WWM + 1.48YW – 0.50 FW – 2.02 MCW – 13.21 CD + 4.92 BF – 2.34 T + 12.77 M. The correlation between this index and the breeding objective is 0.987. The economic superiority, over the average progeny, of the progeny from the top 40% of animals selected on their ranking in the total index, is expected to be R116.49.
Open Access
The dynamics of bush thickening by Acacia mellifera in the Highland Savanna of Namibia
(University of the Free State, 2014) Joubert, David Francois; Smit, G. N.; Hoffman, M. T.
The dynamics of bush thickening by Acacia mellifera in the arid Namibian Highland Savanna was investigated. First, a conceptual state-and-transition model was developed, based on preliminary findings, personal observations and resultant insights. In this model it was proposed that two main states exist, an open, grassy state and a bush-thickened state. Each of these is subdivided into other states. An unstable transitional state with A. mellifera seedlings within the grass sward is a crucial juncture between the grassy and bush thickened state. In the model, the transition to this unstable state occurs after at least two, but more likely three, consecutive years of well above-average annual rainfall through seed production followed by germination and establishment. Only an interruption by fire, which has a high probability of coinciding with this establishment if the grass sward is lightly utilised, prevents a further transition to a bush thickened state. Fire returns the vegetation to a grassy state by causing an almost 100 % mortality of seedlings. If fire is absent through a lack of fuel (overgrazing) or fire is deliberately excluded, the transition to a bush-thickened state is a fait accompli, but may take decades to reach. Transitions from the bush-thickened state to a grassy state require drought and the associated fungal dieback, which accelerates the senescence of mature shrubs. The model proposes that a transition towards the unstable transitional state occurs rarely, due to the rarity of suitable climatic conditions (protracted period of consecutive years of above-average annual rainfall). The mechanisms of two key transitions were tested. Firstly, the transition to an unstable state through the en masse production of seeds followed by the successful establishment of seedlings after a protracted period of well above average rainfall was tested during a nine-year period (late 1998 to early 2007). Secondly, the transition back to an open grassy state during a potential establishment event, through the mortality of seedlings after a fire, was tested experimentally (2008 and 2009). Both of these studies confirmed the predictions of the model and the mechanisms proposed for these transitions. Preliminary evidence suggests that browsing by small herbivores, in particular lagomorphs, thins resultant thickets out through herbivory. Preliminary evidence also suggests that competition between grasses and seedlings does not directly stop the transition to a bush thickened state but may prolong the window of opportunity for a fire to be effective, through reducing the growth rate of seedlings and saplings. The findings are of relevance to management, and thus an expert system for rangeland management, with emphasis on bush thickening, was developed, based largely on the findings of this research. Preliminary historical evidence casts doubt upon the prevailing perception that bush thickening is mostly a phenomenon of the last half century, and, consequently, that bush thickening is the primary cause of the loss of rangeland productivity in the arid rangelands of Namibia during this period. The study suggests that fire in arid savannas is as important as it is in mesic savannas. A general principle could be stated as follows: The importance of the timing of fire in savannas increases with increasing aridity, whilst the importance of the frequency of fire in savannas decreases with increasing aridity.
Open Access
An evaluation of socio-economic and biophysical aspects of small-scale livestock systems based on a case study from Limpopo Province: Muduluni Village
(University of the Free State, 2012-04) Munyai, Fhumulani Rachel; Swanepoel, Frans; Ndlovu, Lindela; Wilke, Pieter
Small-scale livestock production systems are an inherent part of communal livestock farming in the Southern African region and require certain interventions and welldeveloped management systems to ensure long-term sustainability. To this end a better understanding of the biophysical and socio-economic features of communal farming communities can contribute to the planning and implementation of better focused agricultural development programmes in these areas. The present study presented a unique opportunity to study and compare two adjacent areas where mainly livestock farming has been practised for generations by, on the one hand, communal farmers who apply limited pasture management, and on the other, the Mara, which uses proven pasture management and rotational grazing, practices. This research presented an opportunity not only to compare livestock production systems but also to determine the impact of communal farming on plant composition and edible plant material production. The study elicited excitement and enthusiasm among local animal and pasture scientists, as well as social scientists, as the outcome of this study could impact directly on future small-scale livestock farming development. The objective of this study was twofold. The first objective was to evaluate the socioeconomic complexities of small-scale ruminant livestock production under communal farming conditions. To this end, fifty farmer households that share a communal grazing area were surveyed. Data analysis was performed using Statistical Package for Social Sciences (SPSS). Most pertinent results of this study are the following: female animals make up the largest proportion of a herd; the majority of farmers sustain their livelihood from off-farm activity and farm for status not for profit; and farmers farm mainly with the Nguni breed owing to its adaptability to the environment. Given the socio-economic scenario, the second objective was to investigate the way socio-economic conditions impact on the natural feed resource base. Twelve fistulated Bonsmara steers were used. Rumen fistulated steers were used to determine the dry matter disappearance and ammonia concentration using nylon bag technique and the Oesophageal fistulated steers were used to determine the chemical composition. Data were analysed with the SAS Statistical package (2002- 2003) and the results indicated that there was no significant difference measured between the two sites in terms of ingested dry matter (DM) disappearance from the rumen and chemical composition of ingested material and ammonia production in the rumen and vegetational measurements were all significantly different between the two sites. The study concludes that differences in the grazing material available in terms of the two systems are a result of the quantity of the dry material available and not the quality. Moreover, livestock farming on its own is declining and is unable to provide sufficient financial returns for the survival of households. Households are consequently compelled to become involved in off-farm activities in order to generate enough income to sustain their livelihoods.
Open Access
FarmRec: 'n geïntegreerde ekstensiewe veeboerdery rekordhoudingstelsel
(University of the Free State, 2003-04) Theron, Johannes Frederick; Smit, G. N.
English: Extensive farmers in South Africa do not generally keep records of their farming activities, and if they do, it only entails financial record keeping for the Receiver of Revenue. Resources for farm record keeping, especially with regard to grazing and animals, are scarce, and the systems that do exist are elementary. Those farmers who do keep records make use of various approaches, ranging from manual and paper-based systems and computer spreadsheets, to specialist software for certain aspects oftheir farming activities. The FarmRec record-keeping system was developed to provide for a wide range of livestock farming activities. With the development of this record-keeping system, existing shortcomings and problems were addressed, taking into consideration all aspects to be included and contained in a record-keeping system in order to provide a purposeful, comprehensive and user-friendly product. Various information categories are integrated in this system, thereby negating the need for several different types of record-keeping systems. The main purpose of record keeping is to gather information from one's own data. The need for specific information makes it necessary for records to be kept of certain resource data. The relation between resources and the information obtained from them is comprehensively discussed. This relation also indicates the flow of data and information between resources. The FarmRec system was designed and developed around these relations. The waterfall and evolutionary development processes were used to develop and test the system, and to make corrections and improvements to the system. By means of this system, records are kept of information relating to paddocks, land, grazing, animal numbers and animal management actions, as well as of animal and plant product quality and quantity, income and cost information, infrastructure, and financial and rainfall information pertaining to the farming unit. The information to be provided for the different record-keeping facets is discussed. Attention is also given to the integration of information. The information is made available in the form of reports. The extent to which these reports are available is determined by the degree to which the user entered the data of the different facets into the computer. This system makes a large number of reports available to the user. The type of report is determined by the grouping of the selected data. The user himself/herself determines the selection criteria, which consist of the reporting period or date, subunit, groupings and sorting order, as well as level of detail in the report. The system was provided to users and then evaluated to gain an indication of the ease with which the functions and reports in the system can be used. From the evaluation it can be deduced that the FarmRec system is user friendly and easy to use. The system offers many more functions and reports than needed or used by any individual user, but the diversity of users means that different combinations of functions and reports are needed. The level of use by users also varies considerably. With the exception of a few isolated reporting functions, respondents indicated that the functions in the system are easy to use and of much value. The FarmRec system succeeds in addressing a wide range of record-keeping facets. The users indicated that the magnitude and integration are more than sufficient. The system resulted in an improvement in the keeping of grazing records - an aspect that otherwise went unrecorded. Record keeping in respect of grazing was made possible for the user by means of simple notes on animal movement. The total record keeping of the users furthermore improved from their original record-keeping systems. The improvement in record keeping occurred without the users having to spend more time on record keeping. This is regarded as a very positive reaction, as many users indicated that the time available for record keeping is extremely limited.
Open Access
The genetic and environmental modelling of production and reproduction in ostrich females within and across breeding seasons
(University of the Free State, 2012-01) Fair, Michael Denis; Van Wyk, J. B.; Cloete, S. W. P.
English: Pedigree and performance data of a well-documented ostrich breeding resource flock was used to (1) investigate the flock structure, (2) estimate variance and (co)variance components for egg and day-old chick weight (individual traits), (3) estimate genetic and environmental parameters for egg and chick production, mean egg and day-old chick weights and hatchability within breeding seasons (hen traits) and (4) investigate early identification of superior animals using random regression models for repeated measures (longitudinal) data over years. The average level of pedigree completeness of 40 074 birds of a pair-breeding ostrich flock maintained from 1978 to 2005 at the Oudtshoorn Research Farm, South Africa was high (99.3%) in the first generation and the average level of inbreeding (F) was low at 0.51%. The estimated measures of variability were: effective genome equivalents = 47.3, effective number of founders = 59 and the effective number of ancestors = 58. The numbers of ancestors responsible for 100%, 50% and 20% of the variation in the reference population (birds with both parents known), were equal to 254, 21 and 6 respectively. The generation interval in years calculated as the average age of parents when their offspring which were kept for reproduction were born, amounted to 7.72 ± 4.79 years. The linear regressions of rate of inbreeding on year of hatch for the two distinct periods, 1995-2002 and 2003-2005, were 0.08% and -0.07% per year respectively. The estimate of effective population size (Ne) computed via the increase in the individual rate of inbreeding was 112.7 animals. The results of this study indicated that the population under study was at an acceptable level of genetic variability. Pedigree and performance data for 71 147 individual egg records collected between 1991 to 2005 were used to estimate genetic parameters for egg weight (EWT), live day-old chick weight (CWT) and hatchability (H). Heritability estimates (±SE) were 0.12 ± 0.02, 0.14 ± 0.04 and 0.09 ± 0.04 for EWT, CWT and H. Corresponding estimates for maternal genetic effects were 0.27 ± 0.08, 0.38 ± 0.08 and 0.13 ± 0.02. The effects of common environment, permanent environment and breeding paddock were significant but relatively low for all traits. Egg weight and CWT were highly correlated at all levels, while H was mostly independent of the weight traits. These results indicated that genetic improvement in these traits would be feasible. Data involving monthly records of egg production (EP), chick production (CP), hatchability (H), mean egg weight (MEW) and mean day-old chick weight (MCW) were analysed as hen traits. Heritability estimates amounted to 0.04 ± 0.02 for EP, 0.05 ± 0.03 for CP, 0.44 ± 0.04 for MEW, 0.02 ± 0.02 for H and 0.67 ± 0.02 for MCW. Permanent environmental effects as a ratio of phenotypic variance (c2 pe) ranged from 0.08 ± 0.03 to 0.11 ± 0.02 for the first four traits (MCW did not exhibit a significant c2 pe effect). Monthly EP and CP were highly correlated at all levels, ranging from 0.74 for the temporary environmental correlation to unity for the genetic correlation. Hatchability was highly correlated with EP and CP at the genetic level (>0.94). Genetic correlations of EP and CP with MEW and MCW were variable and in some cases antagonistic. Genetic correlations of H with MEW and MCW were positive (0.52 and 0.47, respectively). Results indicate that selection for improved reproduction (reproductive output and product quality traits) is feasible. Selection for production is unlikely to be complicated by unfavourable correlations with H, MEW and MCW. Hen traits defined above were further analysed in single-trait mixed models with a random regression fitted as an intercept for the direct animal (a) and a quadratic polynomial with intercept for the permanent environmental (p) effect peculiar to each hen. Heritability (h2) estimates were moderate and remained relatively constant for EP and CP ranging from 0.13-0.14 and 0.07-0.08 respectively for 3- to 10-year old hens. Quality traits MEW and MCW had moderately high h2 estimates ranging from 0.49-0.61 and 0.37-0.45 respectively. Hatchability had h2 estimates ranging from 0.11-0.13 for the 10 hen-ages. Permanent environment variance ratio for EP, CP, MEW, MCW and H ranges were 0.28-0.42, 0.29-0.41, 0.17-0.33, 0.21-0.35 and 0.14-0.24 respectively. Selection of superior hens from three years onwards seems possible. Hens older than eleven years should be replaced with younger, genetically superior hens which would reduce the generation interval and improve EP and CP genetically, without adversely affecting MEW, MCW and H.
Open Access
A genetic evaluation of productive herd life in dairy cattle
(University of the Free State, 2011-11) Du Toit, Jacobus; Van Wyk, J. B.; Maiwashe, A.
English: The length of productive life is of major economic importance in dairy cattle production. Simple breeding objectives such as selection for increased production in dairy cattle have led to a significant decline in fitness traits. A multi-purpose breeding objective that includes other traits such as length of productive life should be considered. Herd life reflects the ability of a cow to avoid being culled for low production, low fertility, or illness. Herd life can be used in breeding programs if genetic parameters are known. The objectives of the study were to: (1) estimate genetic parameters for functional herd life for the South African Jersey breed using a multiple trait linear model, (2) develop a prototype breeding value for functional herd life for the South African Jersey breed, (3) estimate genetic relationships between functional herd life and conformation traits in the South African Jersey breed and (4) assess inbreeding depression for functional herd life in the South African Jersey breed based on level and rate of inbreeding. A measure of herd life called functional herd life was considered in the current study. Functional herd life refers to herd life adjusted for milk production in the first lactation. In this study functional herd life was defined as survival in each of the first three lactations. Functional herd life was denoted by a 1 if a cow survived and 0 otherwise. Analyses to estimate genetic parameters for functional herd life were carried out as follows. Data and pedigree records on purebred Jersey cows that participated in National Milk Recording and Improvement Scheme were analyzed. Data before editing comprised test-day and lactation yields on milk, fat and protein yields from 252 629 Jersey cows born between 1968 and 2005. After editing, 181 269 cow records from 636 herds recorded over 16 years were available for analysis. Estimates of genetic parameters for herd life were obtained using REML procedures fitting a multiple-trait linear animal and sire models. Heritability estimates (0.02 to 0.03) from the two models were somewhat similar for all lactations. However, heritability estimates for lactations 2 and 3 were slightly higher with the sire model compared to the animal model. The genetic correlation between lactations 1 and 2 from both the sire and animal models was higher than that between lactations 2 and 3. Genetic correlations from the sire model ranged from 0.68 to 0.99 and corresponding estimates from the animal model ranged from 0.76 to 0.99. Genetic parameters obtained in the current study suggest that sufficient genetic variation exist for herd life to allow for genetic improvement and that early selection for functional herd life is feasible. The development of a prototype breeding value for functional herd life for the South African Jersey breed was carried out as follows. Test-day and lactation data on cows that participated in the National Dairy Cattle Improvement Scheme were considered. A multiple-trait linear animal model was used to estimate breeding values using Parameter ESTimation (PEST) software package. A complete (co)variance structure for the additive genetic and residual effects for the three traits were used. These (co)variances were estimated in the first objective. Reliabilities were approximated using the effective number of daughters. Estimated breeding values were scaled so that the average breeding value was a 100. Estimated breeding values for sires ranged from 79 to 114. The rate of genetic progress per year for the period 1985 to 2002 was statistically non-significant (b = 0.02±0.05 per year). The mean reliability was 33.43% and reflective of the low heritability of functional herd life. However, it should be noted that while direct selection for functional herd life could lead to genetic progress, this genetic response could be relatively slow due to the low heritability. The genetic relationship between conformation traits and functional herd life of the South African Jersey population was investigated. Data on conformation traits (n = 46 238) and functional herd life (n = 90 530) on registered South African Jersey cows calving between 1989 and 2008 were obtained from the Integrated Registration and Genetic Information System. Conformation traits were scored using a subjective linear scoring system ranging from 1 to 9, except for foot angle with a maximum score of 8. Conformation traits included stature, chest width, body depth, dairy strength, rump angle, thurl width, rear leg side view, foot angle, fore udder attachment, rear udder height, rear udder width, udder support, udder depth, front teat placement, rear teat placement and front teat length. Genetic correlations between conformation traits and functional herd life were estimated using a series of bivariate analyses. The highest correlations were estimated for udder traits. Significant moderate to high positive genetic correlations between most udder traits and functional herd life (0.23 to 0.63) were estimated. The most important udder traits related to functional herd life were fore udder attachment, rear udder height, and udder depth. Correlations between the majority of body structure and functional herd life were variable. Most of the body structure traits had a low to moderate negative correlation with functional herd life (-0.04 to -0.27). The structural body traits of rump angle and foot angle were estimated to have a moderate positive genetic correlation with functional herd life. The genetic relationships between functional herd life and conformation traits in the South African Jersey breed indicate that conformation traits could be used to enhance the accuracy of genetic evaluation for functional herd life. The effect of inbreeding depression on functional herd life in the South African Jersey population based on individual level and rate of inbreeding was investigated. A pedigree file of the South African Jersey breed (n = 912 638) was obtained from the Integrated Registration and Genetic Information System (INTERGIS). The data included registered, grade and imported animals. The percentages of animals in the pedigree file with two, one and zero parents unknown were 22%, 18% and 60%, respectively. The inbreeding coefficient for each animal (Fi) and the rate of individual inbreeding (ΔFi), as an alternative measure of inbreeding which is adjusted for the depth of known pedigree, were calculated. The effect of inbreeding on functional herd life in each of the first three lactations was estimated using a single trait sire model on data collected from 1985 to 2003. Three analyses for survival in each of the first three lactations were conducted. In the first analysis, in addition to fixed and random effects, an individual inbreeding coefficient (Fi) was fitted as a linear covariate. In the second analysis, the inbreeding coefficient was included as a discrete variable with the following classes of inbreeding: 0 < F ≤ 3.125, 3.125 < F ≤ 6.25, 6.25 < F ≤ 12.5 and F > 12.5. In the third analysis, the individual rate of inbreeding (ΔFi) was included in the model as a linear covariate. The level of inbreeding in the SA Jersey population showed a gradual increase for the period 1985 to 1994, while the period 1995 to 2009 showed a rapid increase. The current mean level of inbreeding (for the year 2010) is 4.85% with a minimum and maximum of 0 and 31.34%, respectively. The rate of inbreeding showed a gradual increase from 0.36% to 0.43% between 1985 and 2003. The average rate of inbreeding is currently (for the year 2010) at 0.55%. There was a significant (P<0.05) unfavourable relationship between inbreeding and functional herd life in the first and second lactation. The effect of inbreeding was more pronounced in the second lactation for both measures of inbreeding. Based on the current level of inbreeding, the reduction in functional herd life in the first lactation can be estimated to be 0.68%. The corresponding estimate for the second lactation is 1.70%. These results indicate that the current level or rate of inbreeding has reached levels that are detrimental to functional herd life. Therefore, individual inbreeding coefficient should be considered when breeding decisions are made by the Jersey breeders in addition to genetic merit.
Open Access
Genetic factors affecting milk production, growth and reproduction traits in Bos indicus x Bos taurus crosses in Ethiopia
(University of the Free State, 2002-11) Mulugeta, Sendros Demeke; Schoeman, S. J.; Neser, F. W. C.
English: Five separate studies were conducted to investigate the genetic factors affecting growth, milk production and reproduction traits in Bos indicus x Bos taurus crosses in Ethiopia. The first three studies were based on early growth data collected from the purebred Boran (Bo), Barca (Ba), Horror (Ho) (Bos indicus) and their crosses with the Friesian (F), Jersey (1) and Simmental (S) breeds (Bos taurus). Early growth data were for calves that were representing three purebred Bos indicus and 38 crossbred genotypes and were separated from their dams one day after birth and fed milk from a bucket. The fourth and fifth studies were based on milk and reproduction data collected from cows of two purebreds (Boran and Friesian) and eight crossbred (crosses of Friesian and Jersey with Boran) genotypes. In the first study, five genetic models were evaluated for goodness of fit and estimation of crossbreeding parameters. These models were: 1) Dominance model, 2) Dickerson's model (recombination loss), 3) Additive x dominance interaction model, 4) Dominance x dominance interaction model and 5) Kinghom's model (x). Models 2 to 5 are epistatic models that included all effects in model one plus one type of epistatic interaction based on a two-locus gene model. The models were evaluated using data for birth, weaning, yearling weights and preweaning average daily gain. All five models tested provided high levels of fit, with adjusted R2 values averaging 93% over traits. All the epistatic models fit the data significantly (P<0.05) better than the dominance model for all the traits. Among the epistatic models, Dickerson's model (Model 2) gave significantly (P<0.05) higher R2 values compared to the other epistatic models. Crossbreeding parameters estimated from this model has relatively lower sampling correlations and correspondingly lower standard errors. This model could, therefore, be considered as the most appropriate one for parameter estimation and prediction of performances of untested genotypes for future crossbreeding decisions for the breeds involved in this study. In the second study, breed difference, heterosis and recombination loss were estimated for birth weight (BWT), weaning weight (WWT), preweaning average daily gain (ADG) and yearling weight (YWT), fitting an animal model. Differences between genotypes were significant (P<0.01) for all traits. Genetic group means adjusted for environmental effects ranged from 20 to 30 kg for BWT, 88 to 114kg for WWT, 122 to 157kg for YWT and 358 to 492g for preweaning average daily gain (ADG). The breed additive effect of the F as a deviation from the Bo was significant (P<0.01) and positive for all traits. Relative to the Bo mean, the additional breed additive contribution of the F breed on BWT, WWT, ADG and YWT was 39.3, 16.5, 9.3 and 10.3%, respectively. On the other hand, the breed additive effects of the Ho and J breeds were significantly (P<0.01) negative for all traits. The heterotic effects were significantly negative (P<0.01) for BWT for all F and S crosses, but positive (P<0.01) for all other traits for all types of crosses. The average heterosis estimated within the F, J and S breeds were: -2.1±0.6, 0.2±0.6 (P>0.05) and -2.3±0.6 kg for BWT, 8.8±2.1, 11.8±2.3 and 13.7±2.4 kg for WWT, 60.4±11.3, 64.8±12.3 and 90.6±12.7 g for ADG and 19.8±2.6, 19.5±2.8 and 20.8±2.9kg for YWT, respectively. The recombination effects were significant (P<0.01) for the majority of crosses for all traits. The estimates for the recombination loss were negative for all traits, except for BWT. The average recombination effects estimated within the F, J and S breeds were: 2.6±0.8, 2.9±0.9 and 2.4±1.0 kg for BWT, -13.6±3.2, -4.2±3.4 (P>0.05) and -16.0±4.0 kg for WWT, -88.0±17.1, -39.4±18.4 and -102.2±21.3 g for ADG and -14.4±4.0, -0.1±4.4 (P>0.05) and -17.5±4.9 kg for YWT, respectively. In the third study, variance components and direct and maternal heritabilities were estimated for weight at birth, weaning and yearling and preweaning average daily gain. Data were analysed using six alternative animal models (direct and including or excluding maternal effects). The direct heritability estimates from the "best" model for each trait were: 0.14±0.03 for birth weight, 0.08±0.03 for weaning weight, 0.06±0.02 for preweaning average daily gain and 0.13±0.03 for yearling weight. The direct maternal heritability estimates were small, but significantly different from zero for only birth weight (0.07±0.02), weaning weight (0.04±0.02) and preweaning average daily gain (0.04±0.02). Direct genetic correlations between birth weight and the other three traits were: 0.66±0.08, 0.55±0.19 and 0.50±0.12 with weaning weight, preweaning average daily gain and yearling weight, respectively. The genetic correlation between weaning weight, preweaning average daily gain and yearling weight was high and ranged from 0.82±0.11 to 0.97±0.O1. Small, but non-zero maternal heritabilities estimated for weaning and preweaning average daily gain for artificially reared calves in this study should be interpreted cautiously because of potential bias from unaccounted breed additive and non-additive effects of the dam. Results of this study also showed that estimates of variance components and genetic parameters suitable for general use can be obtained from mixed purebred and crossbred data after appropriately accounting for breed additive and non-additive effects. In the fourth study, breed additive and non-additive effects plus heritabilities and repeatabilities for milk yield per lactation (LMY), milk yield per day (DMY), lactation length (LL), annual milk yield (AMY), annual milk yield per metabolic body weight (AMYBW) and cow weight at calving (BW) were estimated. In addition, genetic, phenotypic and permanent environmental correlations were estimated between AMY and LL, AMY and BW and LL and BW. Data for each trait were analysed, using two equivalent repeatability animal models: first, fitting genotype as a fixed group effect and in the second model substituting genotype with breed additive, heterotic and recombination effects as fixed covariates. Among the genotypes the Bo had the lowest and the F the highest performance for all traits. The least-squares means for the Bo breed were 529±65 kg for LMY, 2.8±0.1 kg for DMY, 193±6 d for LL, 514±61 kg for AMY, 7.8±0.7 for AMYBW and 304±3 kg for BW. Both F and J breed additive effects, measured as a deviation from the Bo breed were significant (P<0.01) for all traits, except for BW of the J. The F and J additive contributions were 2774±89 and 1473±362 kg for LMY, 7.1±0.2 and 4.8±0.8 kg for DMY, 146±8 and 81±7 d for LL, 2345±71 and 1238±319 kg for AMY, 20.6±0.9 and 18.9±4.3 kg for AMYBWand 140±4 and -21±22 kg (P>0.5) for BW, respectively. The heterotic contributions to the crossbred performance were also positive and significant (P<0.01) for all traits, except for BW in the F x Bo crosses. The Fl heterosis expressed as a deviation from the mid-parent values were 22 and 66 % for LMY, 11 and 20% for DMY, 29 and 29% for LL, 21 and 64 % for AMY, 42% (P>0.05) and 42 % for AMYBW and 2% (P>0.5) and 11% for BW for the F x Bo and J x Bo crosses, respectively. The recombination effect estimated for the F x Bo crosses was negative and significant for LMY (-526±192 kg, P<0.01), DMY (- 3.0±0.4 kg, P<0.01)AMY (-349±174, P<0.05) and BW (-68±11 kg, P<0.001). For the J x Bo crosses the recombination loss was only significant and negative for DMY (-2.2±0.7 kg, P<0.05) and BW (-33±17, P<0.05). The direct heritabilities (h2) and repeatabilities (r2) estimated for each trait after correcting for the fixed environmental and breed additive and non-additive effects were 0.24±0.04 and 0.39±0.02 for LMY, 0.19±0.03 and 0.30±0.02 for DMY, 0.13±0.03 and 0.19±0.02 for LL, 0.23±0.04 and 0.37±0.02 for AMY, 0.17±0.05 and 0.39±0.02 for AMYBW and 0.10±0.03 and 0.34±0.02 for BW, respectively. The estimated genetic correlations between AMY and LL, AMY and BW, LL and BW were 0.71±0.08, 0.17±0.18 and 0.23±0.20, respectively. In the fifth study, estimates of breed additive differences, heterosis and recombination loss, as well as heritabilities were obtained for age at first calving (AFC), calving interval (Cl), days open (DO) and number of services per conception (SPC). The genetic parameters were estimated using a repeatability animal model for Cl, DO and SPC and a unitrait animal model for AFC. The overall least-squares means estimated were: 38.3±0.26 months, 435±4 days, 145±10 days and 1.58±0.03 (number) for AFC, Cl, DO and SPC, respectively. The breed additive effects of F and J were only significant (P<0.01) for AFC. Relative to the Bo, both the F and the J additive contributions for AFC were -5.4±0.5 and -5.5±1.9 months, respectively. Crossing the F and J breeds with the Bo breed also resulted in significant heterosis (P<0.05) ranging from I0ta 21% in all traits. The estimated recombination loss was only significant for AFC (2.8±1.0 months) for the F x Bo crosses. Heritability estimates were high for AFC (0.44±0.05) and low for Cl (0.08±0.03), DO (0.04±0.03) and SPC (0.08±0.02). The corresponding estimates for the repeatability (r2 ) were 0.14±0.02 and 0.14±.0.02 for Cl and DO, respectively. The repeatability estimate for SPC was zero.
Open Access
Genetic improvement of beef cattle in a tropical environment with special reference to the Gudali and Wakwa breeds in Cameroon
(University of the Free State, 1999-11) Ebangi, Achenduh Lot; Erasmus, G. J.; Tawah, C. L.
English:In an attempt to genetically Improve Gudali beef cattle JO Cameroon, two selection experiments were conducted between 1968 and 1988 at the Animal Production and Research Stations of Wakwa, Ngaoundere. The one experiment involved a two-breed synthetic beef breed, the Wakwa, obtained from inter se matings of the first filial generation of American Brahman (50%) x Gudali (50%) crosses. The other experiment involved recurrent selection of the indigenous purebred Gudali in an effort to enhance its beef production without any serious detrimental effects to its adaptational qualities.In order to assess the genetic progress of the two experiments, a study using mixed model methodology was carried out. The objectives were to quantify factors affecting growth traits, estimate (eo )variance components, predict genetic merit (breeding values) for direct and maternal performance and determine genetic progress by examining direct and maternal genetic trends for all animals. A total of 2886 records for birth weight (BWT), 2732 for average preweaning daily gain (ADG), 2899 for weaning weight (WWT), 2098 for yearling weight (YWT) and 1957 for eighteen months weight (EWT) of Gudali cattle were used in the study. Corresponding number of records for the Wakwa were 1793, 1656,1838, 1372and 1328. The results indicated that sire, sex, season (S), calf birth year (C), herd (H), HxSxC interaction, cowage group and ages at weaning (WAGE), yearling (YAGE) and eighteen months (EAGE), as well as covariates for weaning, yearling and eighteen month weights, were significant (p<0.05) sources of variation for these traits. Therefore, for reliablegenetic parameter estimations and evaluation of genetic merit of individual candidate animals for selection, these sources of variation should be taken into consideration. Hence the inclusion of these factors in the mixed model for the estimation of genetic parameters and prediction of breeding values.Estimates obtained for direct, maternal and total heritabilities were 0.37, 0.05 and 0.21 for BWT; 0.24, 0.17 and 0.07 for ADG; 0.27,0.19 and 0.11 for WWT; 0.51, 0.20 and 0.22 for YWT; and 0.18, 0.02 and 0.18 for EWT, respectively, in the Gudali. Corresponding estimates in the Wakwa were 0.55, 0.23 and 0.18 for BWT; 0.26, 0.07 and 0.12 for ADG; 0.28, 0.09 and 0.15 for WWT; 0.18, 0.00 and 0.17 for YWT and 0.14, 0.06 and 0.17 for EWT. Estimates for genetic correlations between direct and maternal effects were generally highly negative and ranged from -0.76 for ADG to -0.98 for YWT in the Wakwa and from -0.77 for WWT to - 0.88 for BWT in the Gudali. However, in both breeds the genetic correlation was nil for EWT. These estimates obtained are indicative that there are distinct possibilities of improving direct preweaning and/or postweaning growth in the both breeds through selection. However, a high selection intensity for direct performance may in the long run be detrimental to maternal performance as a result of the generally strong genetic antagonism between them. Although some estimates of genetic parameters for preweaning weight from one to seven months traits were not obtained for the Wakwa breed due to limited data, estimates obtained for the Gudali indicated that the highest, although moderate, estimate for maternal heritability (0.24) was for weight at two months of age. Therefore, an attempt to optimise direct and maternal performance in the Gudali through selection could be mosteffective at two months and at yearling, respectively. It is suggested that the apparent genetic antagonism generally found between direct and maternal ability be specifically investigated using more suitable data.An assessment of genetic progress indicated positive and significant (p
Open Access
Genotype x environment interaction in Afrikaner cattle
(University of the Free State, 2005-05) Beffa, Luigi Mario; Van Wyk, J. B.; Erasmus, G. J.
English: A line x environment interaction study with grade Afrikaner cattle was established at Matopos Research Station, Zimbabwe, in 1956. From a grade pool of 200 cows, two selection lines of 100 cows were reared in different management environments. The non-supplemented (NS) line relied on the range throughout the year and was mated to calve with the onset of the rains (December to February). The supplemented (S) line was offered protein-rich supplements during the dry season and mated to calve prior to the onset of the rains (October to December). Bull selection based on weight at weaning was to develop lines adapted to their respective environments. After approximately 2 generations of selection, lines were sub-divided into 4 sub-lines, consisting of 75 cows each. One sub-line remained within each environment as a control; the remaining sub-lines were interchanged between environments. Bulls were selected within control lines, while replacement heifers were generated within sub-line. Heifers were selected on weight at mating and replacement rates were dictated by the sub-line with the least number of suitable animals (>265kg). Data collected over a 40-year period representing 6 generations of selection were analyzed to determine a) genetic and environmental factors influencing calf growth and survival and cow fertility, b) direct and correlated responses to selection and c) presence and importance of genotype x environment interactions. Productivity in the S environment, in terms of calf growth and cow fertility, was superior compared with the NS environment. While there were no differences in birth weight, calves born early in the S environment were estimated to be 90kg (33%) heavier at 18 months than calves born late in the NS environment. The performance of calf growth from birth to 18 months in this study has emphasized the importance of matching animal physiological status with seasonal changes in the sub-tropics. Given the significant and consistent detrimental effects of previous lactation status of the cow on fertility and calf growth, it is recommended that this effect be considered in routine evaluations. The high generation intervals (6.7 and 5.5 years pre- and post-crossover) reflect the cow age at first calving (4 and 3 years respectively for the two periods). Direct cumulative selection differentials for weaning weight were very low (0.08 and 0.05 standard deviation units/generation for the S and NS lines respectively). The correlated cumulative selection differentials for pre-weaning weight gain were negative for the pre -crossover period and positive for the post-crossover period, and together with the low direct cumulative selection differentials suggest that significant attention was paid to secondary characteristics. Consequently, selection responses were low (2.35+0.045 and 2.22+0.047kg/generation for weaning weight for the S and NS lines respectively). All correlated direct genetic trends were positive and linear, while maternal genetic trends were very low and negative for the S line. Direct and maternal (in parenthesis) heritability estimates for weights at birth, weaning and 18-months were 0.39+0.03 (0.14+0.02), 0.19+0.03 (0.21+0.04) and 0.36+0.06 (0.15+0.04) respectively. Apart from the non-significant direct-maternal genetic correlation for birth weight, other correlations were all moderately negative (-0.35 to –0.57). With the exception of correlations with birth weight which were variable and often close to zero, direct and maternal genetic correlations among traits were high, particularly for traits measured at ages close to each other. The average incidence of calving success (CS: including abortions at term and stillbirths) was 68%. Heritability and repeatability (in parenthesis) estimates for CS and calving date (CD: with a 21 day penalty for censored records) were 0.08+0.02 (0.10+0.02) and 0.09+0.02 (0.17+0.02) respectively. Service sire was important for both traits, but only accounted for <2% of the total phenotypic variation. Favourable genetic trends were shown for both traits (1.2+0.14% and 0.8+0.13%/generation for CS for the S and NS lines respectively, and -0.8+0.09 days/generation for both lines for CD). The genetic correlation between CS and CD was high (-0.95) and the correlation of sires’ estimated breeding values (EBV) indicated that a one-day improvement in CD EBV is associated with a 1% increase in CS EBV. However, correlation estimates of sires’ EBV between measures of fertility and growth were all unfavourable, but not-significantly different from zero. There were no indications of line x environment interaction for all the growth traits. A significant interaction was, however, manifested for CS and was due to the markedly poorer performance of the S line cows in the NS environment. While no sire x environment interactions were manifested, significant sire x year interactions were found for all the growth traits and for CS, which serves to highlight the tremendous seasonal differences experienced in the sub-tropics. Therefore there is a need to consider selection for genotypic stability, particularly for the more extensive farming environments. This study revealed that concomitant genetic improvements in both growth and fertility were attainable. It is recommended that fertility and calf survival be included in routine breed evaluations. There is however an urgent need to implement data collection strategies to ensure that all calving activities are comprehensively recorded, not least the adequate definition of contemporary groups.
Open Access
In vitro embryo production in cattle
(University of the Free State, 2007-08) Rust, Johannes Matthias; Greyling, J. P. C.; Schwallbach, L. M. J.
English: The objective of this study was the development of efficient in vitro embryo production (IVEP) technology for application on fertility-impaired beef and dairy cows. Fertility-impaired implying animals that could neither reproduce nor produce embryos through conventional MOET procedures due to old age, pregnancy, repeated MOET procedure treatments, certain abnormal uterine conditions and general failure to conceive and become pregnant following repeated inseminations or natural services, as well as due to physical injuries. The investigation concentrated on whether it was possible to produce embryos from a donor cow with this profile and additionally other aspects such as - the best logistical approach for IVEP when presented with a fertility-impaired donor cow - whether superovulation could be used as an enhancing tool when presented with a pregnant donor - and the affect of season on all aspects of IVEP from fertility-impaired donor cows. It was established that a period of OPU could enhance the production of higher numbers of embryos additional to eventual slaughter of the donor cow (10 more embryos on average per donor) and that the culturing of a small number of oocytes and embryos does not negatively affect the eventual IVEP result (10 % more embryos were produced from individual donors). result was a good indicator of how to plan the logistical approach when confronted with these types of donor cows and it also suits the practical situation faced when producing in vitro embryos from small numbers of oocytes collected from these donor cows. It was evident that additional superovulation does not enhance the IVEP potential of pregnant dairy cows (0.02 more embryos per donor per OPU session), unless more refined research is undertaken to optimize the actual superovulation protocols and oocyte recovery procedures. The additional cost implication of added hormonal treatment for superovulation may actually act as a deterrent for cattle stud breeders to embrace this technology. However, the mere fact that it was possible to produce embryos from pregnant dairy cows could be utilized as a useful tool for accelerated genetic improvement in the dairy and beef cattle industry in South Africa. It was established that season (recorded as ambient temperature and photoperiod) had a definite effect on all aspects of IVEP in fertility-impaired beef cattle cows, a trend that was evident from literature in some laboratory IVEP trials on slaughterhouse material and also in the normal reproduction pattern of beef cattle cows in the South African context. This trend manifested itself in the IVEP pattern of fertility-impaired cows. There was a definite decrease in IVEP during the period of late summer (5.4 %) and early autumn (0 %) with a definite delayed effect of high temperatures and possibly photoperiod evident. Alternatively, the optimum period for IVEP seemed to be during winter (between 11 % and 20 %) and spring (between 22 % and 26 %) which also indicated a possible temperature and photoperiod affect. This effect on oocyte quality and eventual embryo production results could also serve as an indicator for other management decisions regarding normal reproduction management in beef cattle as well as the planning of conventional superovulation and embryo transfer programmes. From the obtained results it was clear that IVEP is possible from fertility-impaired and pregnant donor cows. However, there are certain aspects that need to be focussed on to ensure that optimum results are obtained when applying IVEP on these animals. Optimum results are a prerequisite for this technology to be accepted by the South African cattle breeding industry. IVEP is still in a preliminary phase of application in the South African cattle industry and is not within the ability of all breeders. This will, however, become a powerful tool for use in accelerated genetic improvement programmes and will also ensure that superior genetic material from animals that would have been lost for breeding will continue to be utilized in the cattle breeding industry.
Open Access
The influence of calcium intake by broiler breeders on bone development and egg characteristics
(University of the Free State, 2005-07-31) Moreki, John Cassius; Van der Merwe, H. J.; Hayes, J. P.
English: 1. A study was conducted to investigate the effects of dietary Ca levels and feed restriction on the bone development of broiler breeder pullets up to 18 weeks of age. Six hundred and forty one-day-old Ross breeder pullets were randomly assigned to 4 treatment groups; namely 1.0% Ca (0.45% Pi), 1.5% Ca (0.7% Pi), 2.0% Ca (0.9% Pi) and 1.0% Ca (0.45% Pi). The first three treatments were feed restricted while the last treatment was fed ad lib. At 6, 12 and 18 weeks of age 20 pullets were randomly selected from each treatment and killed. Treatment effects on bone dimensions (length, width and weight), bone ash, Ca and P contents of tibia, mechanical properties (bone strength and stress) were investigated. Increasing dieta ry Ca levels had no significant (P>0.05) effect on bone measurements. As expected, all the bone measurements significantly (P<0.05) increased with age. Feed restriction significantly (P<0.05) reduced all the bone characteristics. The results suggested that 1.0% Ca (average 0.7 g/hen/day) is sufficient to support bone development and growth for feed restricted broiler breeder pullets up to 18 weeks of age. 2. One hundred and ninety eight Ross broiler breeder pullets were reared on restricted diets with 1.0, 1.5 and 2.0% Ca up to 22 weeks of age. The pullets in each experimental diet were further randomly divided into three treatments with 1.5, 2.5 and 3.5% dietary Ca (66 birds per treatment) fed from 23 to 60 weeks. At 35 and 60 weeks of age, 12 pullets per treatment were randomly selected and killed to obtain tibiae and humeri. Treatment effects on bone dimensions, bone ash, Ca and P content of tibia, mechanical properties, true cortical area (TCA) and percent bone were investigated. The 1.5% Ca diet resulte d in lower (P<.05) feed intake and body weight. Calcium level had no effect on bone dimensions, bone stress, ash content, Ca content of ash, TCA and percent bone. These results suggest that the 2.5% dietary Ca (4 g/hen/day) may be adequate to support bone development and growth of feed restricted broiler breeder pullets. 3. The broiler breeder pullets described in paragraph 2 were used to investigate the effects of three levels of dietary Ca (1.5, 2.5 and 3.5%) during the early lay period (23 to 35 weeks) on egg production and eggshell quality. Increasing dietary Ca level from 1.5 to 3.5% had no significant effect (P>.05) on egg production, egg weight, egg mass, egg surface area and egg contents. Increasing the level of Ca from 1.5 to 2.5% increased shell weight, shell weight per unit surface area, shell percentage and shell thickness. As anticipated, egg weight increased with age. The converse was true for egg production and eggshell parameters. It was concluded that a dietary Ca level of 2.5% and Ca intakes of 3.8, 3.9, and 3.5 g at weeks 27, 30 and 33, respectively were sufficient to sustain good eggshell quality of feed restricted broiler breeder hens. 4. The mentioned broiler breeder hens in paragraph 3 were fed three dietary Ca levels, 1.5, 2.5 and 3.5% from week 36 to 60. Regression analysis suggested that Ca level during the rearing period could positively influence eggshell quality during the later stages of lay (36 to 60 weeks). Increasing dietary Ca level from 1.5 to 2.5% during the laying period significantly (P<.05) increased egg production, egg weight, egg mass, shell weight, egg contents, egg surface area, shell percentage, shell weight per unit surface area and shell thickness. As anticipated, egg weight, shell weight, egg contents and egg surface area increased with age while egg production, egg mass, shell percentage and shell thickness declined. These results suggest that the 2.5% Ca (3.8 g/hen/day) is adequate to support egg production and to improve eggshell quality in feed restricted broiler breeder hens. 5. The effect of dietary Ca intake (1.5, 2.5 and 3.5% dietary Ca) on Ca retention of broiler breeder hens (30 per treatment) and the relationship between Ca retention and egg characteristics was investigated. Shell (r=0.27) and faecal (r=0.50) Ca excretions were significantly (P<.05) positively related to Ca intake of broiler breeders. Proportionally less of the Ca intake was used for eggshell formation as the intake of broiler breeders increased. It seems that a higher Ca intake was mainly accompanied by a higher Ca excretion through the faeces. The net effect of Ca intake and total Ca excretion was that the 2.5% Ca level (3.8 g Ca /hen/day) exhibit a significant (P<.05) higher Ca retention compared to 1.5% Ca. It was concluded from the results that 1.0% dietary Ca (0.7 g /pullet/day) is needed during the rearing period up to 22 weeks. Thereafter 2.5% Ca (3.5 to 4.0 g /hen/day) should be included in broiler breeder diets up to 60 weeks. The possible effect of Ca levels during the rearing period on eggshell quality needs further investigation.
Open Access
The influence of feeding various roughage: concentrate ratios on milk production of Friesland cows
(University of the Free State, 1974-12) Neitz, Martin Heinrich; Smith, A.
1. In a single-lactation 240-day continuous trail, 64 lactating dairy animals were used to study input-output response to complete rations. Nine first-calf heifers and seven cows were allotted by the procedure of balancing to each of the four experimental treatments. Ration treatments were: 80% lucern: 20% concentrate (ration A), 60% lucern: 40% concentrate (ration B), 40% lucern: 60% concentrate (ration C) and 20% lucern: 80% concentrate (ration D). The crude fibre percentages of rations A, B, C and D were 23,16; 19.34; 16,11 and 12.01, respectively. These rations were pelleted and fed ad lib. in addition to 9 kg of maize silage daily. A digestibility trial with four additional lactating dairy animals was carried out simultaneously. 2. With decreasing proportions of lucern, digestibility of the dry matter increased from 55,55 to 65,33 per cent (P<0,05). Increasing the proportion of concentrates in the ration led to an increased concentration of metabolizable energy (P<0,05). The digestible protein in the rations varied very slightly (P>0,05). 3. Changes in body mass of cows and first-calf heifers due to ration treatment were non-significant (P>0,05). Age was the most important factor influencing body mass variations of experimental animals; differences between cows and first-calf heifers being highly significant (P<0,01) in favour of the cows. The individual mean body mass gain of the first-calf heifers during their first lactation was 80,4 kg compared to 9,9 kg of the cows in their second and later lactations. 4. There were non-significant (P>0,05) differences, due to ration treatment, in the daily amount of actual milk, 4% fat corrected milk and solids corrected milk produced by cows. Although first-calf heifers on ration D produced 19,3 to 27,0 percent more actual milk, 14,0 to 23,0 per cent more 4% fat corrected milk and 16,3 to 22,9 per cent more solids corrected milk than heifers on either the A, B or C rations, these differences were non-significant. 5. Cows on ration A, B and C produced more (P<0,05) milk, 4% fat corrected milk and solids corrected milk, during each stage of lactation, than the first-calf heifers. Cows fed ration D showed a significantly (P<0,05) higher production than heifers, during the third to fifth month of lactation and a non-significant difference during the sixth to tenth month. 6. Small non-significant (P>0,05) differences occurred in the mean solids-no-fat content of milk. Solids-not-fat content of milk produced by cows ranged from 8,69 to 9,02 per cent and from 8,90 to 9,16 per cent in the case of first-calf heifers. The milk produced by first-calf heifers had a significantly higher (P<0,01) solids-not-fat content than cows during all stages of lactation, irrespective of ration treatment. 7. Milk fat was non-significantly affected by ration treatment. Decreasing lucern content in the ration was accompanied by a decrease in the fat percentage of milk produced by cows (0,3) and by heifers (0,29). 8. The dry matter and gross energy consumption by cows tended to decrease as the dry matter digestibility of the ration increased, differences being non-significant. Similarly as the metabolizable energy concentration increased (increasing with a decreasing proportion of lucern) the voluntary intake by cows tended to decrease. Metabolizable energy intake between ration treatments was very constant and was related to the mean daily yield of the cows. The intake of dry matter and gross energy by first-calf heifers remained more or less the same for all rations (P>0,05). However, as the dry matter digestibility of the ration increased the metabolizable energy consumption by heifers tended to increase, differences being non-significant. 9. Cows consumed significantly (P<0,01) more dry matter, gross energy and metabolizable energy during certain stages of lactation than first-calf heifers, irrespective of ration treatment. In the case of cows the efficiency of metabolizable energy utilization for milk production increased as the lucern portion in the ration increased, differences non-significant. A very similar tendency was noticed with the first-calf heifers. Irrespective of ration treatment cows produced milk more efficiently (P<0,05) during the third and fourth month of lactation than during the later months. The effect of stage of lactation on efficiency of use of metabolizable energy for milk production by heifers was less pronounced than that obtained with cows, but the differences were non-significant. 10. Irrespective of treatment the cows produced milk more efficiently (P<0,01) durng the third and fourth month of lactation than the first-calf heifers. During the fifth, sixth and seventh month of lactation efficiency of milk production by cows and heifers was very similar. During the eighth and ninth month of lactation heifers were more efficient than the cows. 11. In terms of marketing fresh milk the profit margins over cost of feed was 5,6; 6,0; 6,1 and 6,2 c per litre when cows were fed rations A, B, C and D respectively. The profit margins for first-calf heifers were 4,8; 4,7; 4,8 and 6,0 c per litre for the same rations. Reproduction of cows and first-calf heifers was non-significantly affected by ration treatment. 12. None of the experimental rations caused bloat-, digestive- or general stiffness problems. Seventeen cases of mastitis occurred during the course of three years and seven months. 13. In four switchback trials with 16 lactating dairy animals the pelleted experimental rations were compared with otherwise identical non-pelleted rations (lucern portion being chaffed in 2,5 cm lengths). The method of preparing the rations by either pelleting or non-pelleting did not appreciably influence the dry matter consumption (g DM/W kg 0,75), daily amounts of actual milk produced, solids corrected milk and composition of milk. However, animals receiving ration D in a non-pelleted form, produced significantly (P<0,05) more solids corrected milk and total solids in milk than animals fed the corresponding pelleted ration.