Masters Degrees (Animal, Wildlife and Grassland Sciences)

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Browsing Masters Degrees (Animal, Wildlife and Grassland Sciences) by Advisor "Erasmus, G. J."

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    The effects of breed and housing system on the production and reproduction of weaner piglets in an outdoor pig unit
    (University of the Free State, 1995-08) Visser, Daniël Pieter; Erasmus, G. J.; Botha, T.
    Outdoor pigfarming is a concept which (within the 20th century) had its origin (revival) in the early 1950s in England. Today approximately 15% of all breeding sows in England are kept out of doors while in South Africa probably less than 0,3% of sows (recorded), are kept out of doors. The rationale for outdoor pig farming was motivated from four angles of incidence: firstly an economic viewpoint, secondly the animal's adaptability to the environment, thirdly an ethological viewpoint and finally the new political dispensation - specifically the prospective small-farmer. The ultimate aim of this study was to identify the most suitable genotype and farrowing house of outdoor pigfarming based on the reproduction information of the sow's litters. The effect of genotype was significant (P = 0.0695) only for the trait litter size at birth, implying no significant poorer performance from the other genotypes in terms of relative reproductive efficiency. The three linear models, obtained by ANOV A procedures using SAS, which were specified for the reproductive traits litter size at birth, mortality and weaning mass, could explain very little of the variation for the three traits and Rl values of 0,05, 0,086 and 0,45 were calculated for the three traits respectively. However, the effect of parity was highly significant (P = 0.0001) for all three traits. The effect of house was non-significant (P = 0.3314) for number of piglets born alive, but significant for mortality (P = 0.0548) and highly significant for weaning mass (P = 0.0056). The inferiority of farrowing house 5 was undoubtedly revealed in this study. The importance of sufficient clean and fresh straw which will not only stimulate the sow's natural nesting activities, but will also form a buffer and heating mechanism for the young piglets, was clearly shown, given the significant (P = 0.0548) effect of house on mortality rate, and the highly significant (P = 0.0056) effect of house on weaning mass. In retrospect the reproduction performance of the outdoor breeding sow is measured against the norms applicable to the modern sow, however, the outdoor sow has to reproduce while competing with all the elements of nature (Falconer's paradox). The effect of parity was highly significant (P = 0.0001) for all three traits. This study, especially Tables 4,4; 4.8 and 4.11, showed that three distinctive (significant) phases could be identified during a sow's reproductive lifetime (Figures 4.1; 4.3 and 4.4). The commencing phase (Ist and 2nd litter) where number of piglets born alive, mortality and weaning masses are at its lowest. The optimising phase (3rd to 5th litter) when numbers of piglets born alive, and weaning mass reach their optimum while mortality rate reaches the intermediate stage. The diminishing phase (from the 6th litter onwards) where the number of piglets born alive are less than the optimising phase and more than the commencing phase, and mortality rate reaches its peak and weaning mass declines significantly.
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    Genetic characterization of Southern African sheep breeds using DNA markers
    (University of the Free State, 2006-05-16) Buduram, Pranisha; Van Wyk, J. B.; Erasmus, G. J.; Kotze, A.
    Merino sheep are an important resource for South Afric an farmers, providing meat and wool and thus an important income source. Indigenous and locally developed breeds are an important asset for many reasons, but particularly because, over time, they have developed unique combinations of adaptive traits to respond to the pressures of the local environment. To be able to distinguish between breeds for conservation and utilization purposes, the genetic variability, population structure and phylogenetic relationships were determined. Seven different Merino genotypes were sampled. These included the Dormer, SA Merino, SA Mutton Merino, Landsheep, Letelle, Dohne and Afrino. The indigenous and locally developed breeds comprised of the Damara, Pedi, Blinkhaar Ronderib Afrikaner, Blackhead Persian, Blackhead Speckled Persian, Redhead Persian, Redhead Speckled Persian, Zulu, Namaqua Afrikaner, Karakul, Swazi, Van Rooy and Dorper. The Merino, indigenous and locally developed breeds were assessed for genetic diversity using 24 microsatellites. Different statistical analyses were performed to determine the genetic variation, genetic relationships and genetic differentiation of the breeds. The SA Merino showed a high number of very distinct alleles. This study confirmed a higher variability of the SA Merino when compared with the other breeds. The genetic distance between the SA Merino and SA Mutton Merino, both fine wool breeds, was high indicating that these two breeds are relatively distant from each other. The Afrino known to have 25% SA Merino, 25% Ronderib Afrikaner and 50% SA Mutton Merino, indicated a closer relationship with the SA Mutton Merino. This result confirmed the development of the breed. From the phylogenetic analysis between the seven Merino genotypes, when compared to the other estimates obtained in the study, it was evident that the Merino genotypes in South Africa have more within breed variation than between breed variation. The genetic distance estimates observed for the indigenous fat-tailed breeds were relatively high indicating that even between these breeds genetic differences exist. As expected, a smaller genetic distance between the Persian varieties was observed. Genetic distances between the developed breeds supported their ancestral development. The results of the indigenous and locally developed breeds present the first study of the genetic characterization of these breeds using microsatellite markers in South Africa. Southern Africa is hosting a very large sheep (Merino, indigenous and locally developed) genetic resource. Adapted to the agricultural production systems of the continent, it represents a unique resource that has great potential for further development of its productivity.
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    Genetic parameter estimation of production and reproduction traits of the Elsenburg Dormer stud
    (University of the Free State, 2002-11) Fair, Michael Denis; Van Wyk, J. B.; Erasmus, G. J.
    English: Genetic parameter estimates were compared usmg Gibbs sampling and REML methods. Variance components and resulting heritabilities of birth weight (BW) and weaning weight (WW) in the Elsenburg Dormer sheep stud were estimated using a conventional (REML) and a Bayesian (GIBBS sampling) approach. A sire model with relationships included were fitted in both cases. Data from 10701 lambs recorded from 1943 to 1999 were used in the analyses. Effects fitted as fixed were sex (male, female); birth status (single; twin, triplet); year (1943-1999) and age of dam (two to seven years, and older). Sire and residual were the only random effects fitted. The posterior means (h2) ofBW and WW were 0.24 and 0.15 for REML and 0.23 and 0.16 for the Bayesian method respectively. The heritability estimates obtained were of the same magnitude and in accordance with estimates found in the literature where sire models were used. Genetic parameters for the pre-wearung growth traits BW and WW were also calculated from the (eo )variance components estimated using the ASREML program by fitting univariate animal models. Log likelihood ratio tests were done to determine the appropriate mixed models. Bivariate models were also fitted for BW and WW using as starting values for the (eo)variance components the values obtained from the univariate analysis. Fixed effects fitted were the same as in the previous section. The direct heritability (h2 a) for BW and WW for the bivariate model was 0.22 and 0.12 respectively. The maternal effects (m2 ) were 0.24 and 0.11 for BW and WW respectively. These m2 values fall within the range 0.09 to 0.31 found in literature. The direct-maternal genetic correlations (ram) of -0.38 and -0.38 for BW and WW were similar to those found in literature. Genetic parameter estimates for reproduction traits, i.e. number of lambs born (NLB), number of lambs born alive (NLBA), number of lambs weaned (NL W), total weight weaned (TWW) and survival traits were obtained using the ASREML program fitting univariate animal models. Data for TWW were pre-corrected for fixed and random effects of sex, year and sire respectively. An animal model with only the direct random effect of animal and fixed effects of birth status and birth year of the ewe was fitted. Direct heritability (h2a) estimates of 0.12, 0.14 and 0.10 were obtained for TWW1, TWW2 and TWW3 respectively. Direct heritability (h2 a) and (SE) estimates of0.103 (0.016),0.101 (0.016) and 0.031 (0.011) were obtained for NLB, NLBA and NLW respectively. Permanent maternal environmental variance components as proportions of phenotypic variance for the three traits were 0.013 (0.005), 0.008 (0.009) and 0.023 (0.008) respectively, with service sire variance as a proportion of phenotypic variance of 0.005 (0.004), 0.007(0.004) and 0.006 (0.003) respectively for the traits mentioned. Heritability estimates for direct and maternal effect of survival were 0.03 (0.018) and 0.00 (0.00). Permanent maternal environmental variance as a proportion of phenotypic variance for survival was 0.077 (0.017). It was concluded that Gibbs sampling could be of use to the animal breeder while the question of negative covariances between direct and maternal genetic effects still need further investigation. TWW could be used as selection criteria for reproductive efficiency.
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    Ondersoek na linieêre klassifikasie in die Suid-Afrikaanse Jerseyras
    (University of the Free State, 1999-05) Van Niekerk, Daniel Jacobus; Neser, F. W. C.; Erasmus, G. J.
    English: A total of 36000 records that were obtained from INTERGIS were used in this study to determine genetic parameters for the South African Jersey breed. After editing 9447 records qualified for the analysis. The data set consisted of animals with official first lactation records and linearly scored during their first lactation. The individual animal record contained the following information: identification number, sire, dam, birth date, owner, classification date, classifier, 13 linear type-traits (wither height, strength, dairy form, rump angle, thurl width, rear legs, hoof inclination, fore-udder attachment, rear-udder height, rear-udder width, udder cleft, udder depth and teat placement), final udder class, final class, age at first calving, milk-, butterfat- and protein production, butterfat percentage, protein percentage as well as length of lactation. A variance analysis on 9447 records was conducted by means of the SAS OLM (1988) procedures. The following effects were tested: herd, year of birth, year and season of calving, classifier, classification year, classification month, region, age at first calving and stage of lactation. Effects that were significant at the 1% level were included in the model. Nine models were specified and the resulting heritability estimates were obtained by DFREML procedures (Not all the non-genetical effects were significant for all the traits). Bivariate REML-procedures were done to determine the genetic parameters for the South African Jersey breed. The heritability estimates obtained varied between 0.05 for hoof inclination to 0.32 for wither height. The heritability estimates are in agreement with results reported in the literature. The genetic and phenotypic correlations obtained between the 13 linear type-traits and the three production traits (milk, butterfat, protein) are in agreement with results reported in the literature. The highest positive genetic correlation was found between rear udder height and rear udder width (0.99). The highest positive genetic correlation with protein production was found with rear udder width (0.83). The highest negative correlation was found between rear legs side view and hoof inclination (-0.96). These results could be used to the benefit of the breed, for example in determining estimates breeding values for linear type traits.