Genetic evaluation of growth and reproductive performance of the Afrikaner Cattle Breed

Abstract

The objective of the current study was to estimate genetic parameters for growth and reproductive traits of the South African Afrikaner cattle population, using different genetic models after accounting for known systematic non-genetic effects. The data originated from records collected between 1966 and 2017, from a population of 260 789 animals. For final analysis, the available data were substantially reduced after removing data with missing information on pedigree or performance records. Performance records available after editing were 27 633 for birth weight (BWT), 70 504 for weaning weight (WWT), 21 624 for yearling weight (YWT) and 23 248 for eighteen months? weight (EWT). A total of 6 502 contemporary groups (herd, year and season of birth) were identified from weight records. Reproduction records available after editing were 45 819 for age at first calving (AFC), 21 695 for calving interval (CI) and 15 157 for accumulated productivity (ACP). Data were analysed using linear univariate and bivariate models, fitting the animal (AM) and sire-maternal grandsire (S-MGS) models. The S-MGS model was used to analyse data of BWT and WWT which are traits that are expected to be highly influenced by maternal effects. Estimates of (co)variance components were obtained with the commonly used ASREML package. Using the AM, direct heritability estimates of BWT, WWT, YWT and EWT were 0.28, 0.27, 0.24 and 0.35, respectively. The corresponding maternal heritability estimates were 0.05, 0.12, 0.10 and 0.08, respectively. Similarly, the corresponding total heritability estimates were 0.19, 0.20, 0.24 and 0.32, respectively. From the S-MGS model, direct heritability estimates were the same (0.23) for BWT and WWT, while maternal heritability estimates were 0.18 and 0.19, respectively. The permanent maternal environmental component contributed 4 to 13 % of the total phenotypic variance for the growth traits under consideration. A negative association was found between direct and maternal effects with a genetic correlation of -0.64, -0.49, -0.22 and -0.26 for BWT, WWT, YWT and EWT, respectively. Using the S-MGS model, estimates of the correlation between direct- and maternal genetic effects improved to -0.28 for BWT and to -0.29 for WWT. Estimates of direct genetic correlations between BWT and weights at later ages ranged from 0.27 to 0.35. The corresponding estimates of phenotypic correlations ranged from 0.14 to 0.17, indicating a weak observable relationship between BWT and weights at later ages. Estimates of direct genetic correlations for WWT with YWT and EWT were 0.89 and 0.85, respectively while the correlation between YWT and EWT was 0.88. For reproductive traits, additive genetic variance accounted for the least variation for AFC and CI, resulting in low heritability estimates. Heritability estimates for AFC and CI were 0.093 and 0.096, respectively. The heritability estimate for ACP was of a moderate magnitude (0.39), suggesting that selection on this trait will yield moderate genetic gains. For growth traits, the estimates of direct and maternal heritability revealed that the genotype of the calf was more important than that of the dam in determining the weight of the calf at all ages.