PSXII-5 - Genetic parameters for dry matter intake in beef cattle as a function of water restriction: insights into environmental sensitivity and genetic-by-environment interactions

Abstract: Genetic selection for animals more tolerant or less sensitive to inadequate water availability may become critical to beef production, particularly as water resources become scarce or represent a meaningful cost to producers. The objectives of this study were 1) to explore the genetic component and environmental sensitivity (ES) of dry matter intake (DMI) to water restriction (WR) and 2) to evaluate genetic-by-environment interactions (G×E) with respect to WR using a reaction norm. A group of 788 crossbred steers arranged across seven cohorts were provided feed and water whereby daily water intake (WI) and DMI values were recorded automatically on an individual basis. After an initial acclimation period, data was collected for 70 days in which ad libitum water was provided and baseline WI was determined on each steer. Next, steers were restricted by approximately 10% of their baseline WI every seven days until 50% WR was achieved and subsequently maintained for 42 days. The reaction norm was modeled with a linear random regression allowing for additive genetic animal-specific intercepts and slope parameters as a function of the WR environmental covariate. The relationship covariance matrix for the additive genetic animal parameters was estimated using genotypes. The model was fit using the THR3GIBBSf90 program in the BLUPf90 software. The additive genetic variances for animal-specific intercepts and WR-driven slopes, as well as their covariance, were estimated. The estimated (posterior median and 95% highest posterior density) ES to WR, represented by the regression coefficient on the WR covariate, was -0.410 (-0.422, -0.399) kg daily DMI per 10% WR, indicating evidence for population-level DMI sensitivity to WR. The estimated additive genetic correlation between animal-specific intercept (i.e., ad libitum WI) and animal-specific slope (i.e., sensitivity to WR) was -0.75 (-0.88, -0.59), supporting an association between selection for increased DMI at ad libitum WI and ES. The additive genetic correlation between DMI at 0% and 25% WR was estimated at 0.96 (0.94, 0.99) and at 0% and 50% WR was 0.78 (0.65, 0.91), thereby indicating G×E had limited influence on the overall EBV ranking of animals as WR increased. The results of this study do not indicate major G×E concerns in DMI with respect to WR in the overall population; however, ES to WR may be important to producers as selection on DMI at ad libitum WI could increase ES.