Genotype x Nutritional Environment Interaction in a Composite Beef Cattle Breed

Environmental effects have been shown to influence several economically important traits in beef cattle. In this study, genetic x nutritional environment interaction was evaluated in a composite beef cattle breed (50% Red Angus, 25% Charolais, 25% Tarentaise). Cows were randomly assigned to be fed levels of harvested supplemental feed from Dec to March of each year that were expected to result in adequate (ADEQ) or marginal (MARG;~ 61% of the supplemental feed provided to ADEQ) levels of protein based on average quality and availability of winter forage. At weaning, daughters from these cows were randomly assigned to either ad libitum (CONTROL) or restricted (RESTRICTED; 80% of control at a common body weight basis) access to feeding for 140-d development post weaning. Similar nutritional treatments were applied to the male offspring.This design resulted in offspring exposed to 1 of 2 prenatal and 1 of 2 postweaning nutritional treatments resulting in four different environments: MARG-CONTROL, MARG-RESTRICTED, ADEQ-CONTROL and ADEQ-RESTRICTED. 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-RESTRICTED, MARG-CONTROL and ADEQ-RESTRICTED and ADEQ-CONTROL respectively. The genetic correlations were also estimated using a multi-trait model, ADG and IMF traits showed correlations less than 0.80 between the four different environments, providing evidence of genetic by environment intereaction. The genetic correlation for ADG of MARG-CONTROL and MARG-RESTRICTED was 0.73 and 0.65 of ADEQ-RESTRICTED and MARG-RESTRICTED. The present study demonstrated the existence of genetic by nutritional environment interaction for growth and carcass traits in beef cattle.