Genotype x nutritional environment interaction in a composite beef cattle breed for growth and carcass traits

Environmental conditions have been shown to impact several economically important traits in beef cattle. In this study, genetic x nutritional environment interaction has been evaluated in a composite beef cattle breed (50% Red Angus, 25% Charolais, 25% Tarentaise). Four nutritional environments (MARG-RES, MARG-CTRL, ADEQ-RES and ADEQ-CTRL) were created based on 2 levels of winter supplement provided to dams grazing winter range during gestation (MARG and ADEQ) and 2 levels of input to offspring during post-weaning development (RES and CTRL). Genetic parameters of average daily gain during the 140-d post wean trial (ADG), yearling weight (YW), and ultrasound measurement of fat depth over the rib (FAT) and intramuscular fat (IMF) of 3,020 individuals in the four environments were estimated. The heritabilities estimated using a single trait mixed linear model were: ADG: 0.21, 0.23, 0.19 and 0.21; YW: 0.27, 0.33, 0.20 and 0.26; FAT: 0.30, 0.29, 0.29, 0.55; IMF: 0.45, 0.51, 0.33, 0.53 for MARG-RES, MARG-CTRL and ADEQ-RES and ADEQ-CTRL respectively. To evaluate the extent of genotype x environment interaction reaction norms was implemented. The correlations between the intercept and the slope were -0.19, -0.34, 0.98, and 0.05 for ADG, YW, FAT and IMF respectively. High correlations between intercept and slope indicate that animals with high genetic merit respond better to improvement of the environment. Low correlations between intercept and slope could potentially mean re-ranking of animals. The heritabilities were higher in high feed inputs during post weaning period (ADEQ-MARG, ADEQ-CTRL) for ADG, YW and FAT. Furthermore, the reaction norm model results showed that genotype by environment interaction had a higher effect on traits with a lower heritability.