Genetic parameters for growth and cow productivity traits in Angus, Hereford and crossbred cattle

Abstract

Reproductive and growth performance are major factors affecting the efficiency of beef production. The objectives of this study were to estimate genetic parameters for five cow fertility and productivity traits (pre-weaning average daily gain (PWG), weaning-to-first calving average daily gain (WFCG), age at first calving (AFC), cow weight at weaning (CWW) and cow average annual productivity (CAAP) in an experimental herd of Angus, Hereford, and reciprocal Hereford-Angus crossbred cattle. (Co)variance components were estimated by Bayesian inference using ten bivariate animal models representing all possible pairwise combinations of the five traits. Fixed environmental effects were contemporary group (all traits), class of age of dam at calving (PWG only), age of heifer at first calving (WFCG only), and cow age at weaning, age of calf at weaning and sex of calf (CWW only). Fixed genetic effects for all traits were breed group of cow and heterosis of the cow as a function of expected heterozygosity. Random effects were direct additive genetic (PWGd and WFCGd; d = direct), maternal additive genetic effects (PWGm and WFCGm; m = maternal), maternal permanent environmental effect (PWG only), direct permanent environmental effect (CWW only), and residual (all traits). Direct heritability estimates ± standard deviations for PWG and WFCG were 0.15 ± 0.04 and 0.44 ± 0.18, respectively. Heritability for maternal additive genetic effects was lower for WFCG (0.08 ± 0.05) than for PWG (0.17 ± 0.13). Direct-maternal genetic correlations were -0.38 ± 0.35 for WFCG and -0.26 ± 0.17 for PWG. Heritabilities were low for AFC (0.08 ± 0.05) and CAAP (0.17 ± 0.06). Conversely, CWW had high heritability (0.64 ± 0.13) and repeatability estimates (0.74 ± 0.03). AFC showed a high positive genetic correlation with PWGd (0.98 ± 0.01) and a negative correlation with PWGm (-0.51 ± 0.13). CWW was positively and highly associated genetically with PWGd and WFCGd, while genetic correlations were moderate and positive between CAAP and CWW (0.46 ± 0.13) and high and positive between CAAP and PWGm (0.93 ± 0.03). The estimated genetic variation for CAAP makes it a good selection objective. However, unrestricted selection for CAAP could increase mature weight. Thus, monitoring female mature weight under grazing conditions is essential to avoid large and heavy replacement cows with high nutritional requirements. Therefore, beef selection programs in Argentina should be aimed at increasing CAAP while maintaining mature weight, by imposing restrictions on CWW or other traits measured earlier in life. Outcomes of this study will contribute to the development of optimized bioeconomic models for commercial beef cattle herds under the extensive production conditions in Argentina.