Genetic parameters, heterosis, and breed effects for body condition score and mature cow weight in beef cattle

Understanding the genetic relationship between mature cow weight (MWT) and body condition score (BCS) is useful to implement selection programs focused on cow efficiency. The objectives of this study were to estimate genetic parameters, heterosis, and breed effects for MWT and BCS. In total, 25,035 and 24,522 overlapping records were available for MWT and BCS on 6,138 and 6,131 cows, respectively, from the Germplasm Evaluation program, a crossbred beef population at the U.S. Meat Animal Research Center. Pedigree was available for 48,013 individuals. Univariate animal models were used to estimate heritabilities for each trait by parity. Bivariate animal models were used to estimate genetic correlations between parities within a trait and between traits within parities. Bivariate repeatability animal models were used to estimate genetic correlations between traits across parities. Estimates of heritability for different parities ranged from 0.43 +/- 0.05 to 0.55 +/- 0.07 for MWT and from 0.12 +/- 0.03 to 0.25 +/- 0.04 for BCS and were lower with the repeatability model at 0.40 +/- 0.02 and 0.11 +/- 0.01 for MWT and BCS, respectively. Estimates of repeatability were high for MWT (0.67 +/- 0.005) and low for BCS (0.22 +/- 0.006). Estimates of genetic correlation for MWT and BCS between parities were, in general, high, especially between consecutive parities. Estimates of genetic correlation between MWT and BCS were positive and moderate, ranging from 0.32 +/- 0.09 to 0.68 +/- 0.14. The direct heterosis estimates were 21.56 +/- 3.53 kg (P <= 0.001) for MWT and 0.095 +/- 0.034 (P <= 0.001) for BCS. Ordered by decreasing MWT, the breeds ranked Brahman, Charolais, Angus, Simmental, Salers, Hereford, Santa Gertrudis, Chiangus, Brangus, Red Angus, Shorthorn, Maine-Anjou, Gelbvieh, Beefmaster, Limousin, and Braunvieh. Ordered by decreasing BCS, the breeds ranked Brahman, Red Angus, Charolais, Angus, Hereford, Brangus, Beefmaster, Chiangus, Salers, Simmental, Maine-Anjou, Limousin, Santa Gertrudis, Shorthorn, Gelbvieh, and Braunvieh. Estimates of breed differences for MWT were also adjusted for BCS (AMWT), and in general, AMWT depicted smaller differences between breeds with some degree of re-ranking (r = 0.59). These results suggest that MWT and BCS are at least moderately genetically correlated and that they would respond favorably to selection. Estimates of breed differences and heterotic effects could be used to parameterize multibreed genetic evaluations for indicators of cow maintenance energy requirements. Lay Summary The current study estimated the genetic relationship between mature cow weight (MWT) and body condition score (BCS), heterosis, and breed effects for these traits in a crossbred beef population. In total, 25,035 and 24,522 overlapping records were available for MWT and BCS, respectively. Pedigree was available for 48,013 individuals. Heritability and genetic correlations were estimated within a trait between parities, between traits within parities, and between traits across parities. Estimates of heritability ranged from 0.40 +/- 0.02 to 0.55 +/- 0.07 for MWT and from 0.11 +/- 0.01 to 0.25 +/- 0.04 for BCS. Genetic correlations within a trait and between parities were, in general, high. Estimates of genetic correlation between MWT and BCS were positive and moderate, ranging from 0.32 +/- 0.09 to 0.68 +/- 0.14. Heterosis effects were 21.56 +/- 3.53 kg for MWT and 0.095 +/- 0.034 for BCS. For both traits, Brahman and Braunvieh were associated with the highest and lowest breed effects, respectively. These results suggest that MWT and BCS would respond favorably to selection and are moderately genetically correlated. Breed differences and heterotic effects could be used to parameterize multibreed genetic evaluations for indicators of cow maintenance energy requirements. Mature cow weight and body condition score are heritable and moderately genetically correlated and could be used as indicators of cow maintenance energy requirements. Breed differences and heterotic effects are useful to parameterize multibreed genetic evaluations.

Automated summary

This study analyzed a crossbred beef population to estimate the genetic relationship, heterosis, and breed effects between mature cow weight (MWT) and body condition score (BCS). The results showed that MWT and BCS are moderately genetically correlated and would respond favorably to selection. Breed differences and heterotic effects can be used in multibreed genetic evaluations for cow maintenance energy requirements.