Breed genetic and heterosis effects on variability of growth and efficiency traits in beef cattle
| dc.contributor.advisor | MacNeil, M. D. | en_ZA |
| dc.contributor.advisor | Neser, W. C. | en_ZA |
| dc.contributor.advisor | Scholtz, M. M. | en_ZA |
| dc.contributor.author | Pyoos, Georgette Mareé | en_ZA |
| dc.date.accessioned | 2025-01-03T11:19:29Z | |
| dc.date.available | 2025-01-03T11:19:29Z | |
| dc.date.issued | 2024 | en_ZA |
| dc.description | Thesis (Ph.D.(Animal Science))--University of the Free State, 2024 | en_ZA |
| dc.description.abstract | 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. | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/11660/12902 | |
| dc.language.iso | en | |
| dc.publisher | University of the Free State | en_ZA |
| dc.rights.holder | University of the Free State | en_ZA |
| dc.subject | Environment | en_ZA |
| dc.subject | Plasticity | en_ZA |
| dc.subject | Crossbreeding | en_ZA |
| dc.subject | Beef | en_ZA |
| dc.subject | Cattle | en_ZA |
| dc.subject | Feed | en_ZA |
| dc.subject | Partial body weight | en_ZA |
| dc.subject | Serial correlation | en_ZA |
| dc.subject | Breed additive | en_ZA |
| dc.subject | Heterosis | en_ZA |
| dc.title | Breed genetic and heterosis effects on variability of growth and efficiency traits in beef cattle | en_ZA |
| dc.type | Thesis |