Using genetic evaluations for growth and maternal gain from birth to weaning to predict energy requirements of Line 1 Hereford beef cows.

The maintenance energy required to sustain the cow herd is a major cost of beef production. This work proposes modifying parameter estimates for a population-specific lactation curve with genetic evaluations for the maternal genetic effect on calf gain from birth to weaning to provide inputs for a commonly used prediction of energy requirement. Daily milk production (y) was modeled as a function of stage of lactation (T, d) using the function y = AT(B)exp(-CT) modified to incorporate effects of genetic evaluation for the maternal effect on calf gain from birth to weaning and age of dam. A 1-kg increase in predicted maternal breeding value for calf gain from birth to weaning from within-herd genetic evaluation increased the lactation curve parameter A by 10.3+/-4.6% and reduced the B parameter by 1.0+/-0.6%. Similarly, a 1-kg increase in maternal breeding value for gain from birth to weaning from national cattle evaluation increased the A parameter by 1.7+/-0.2%. Corresponding estimates of peak milk yield and time of peak lactation were derived for individual animals from their genetic evaluation. Additional inputs for predicting maintenance energy requirements were derived from genetic evaluations for birth weight and mature size. The methodology is demonstrated using genetic evaluations of sires from the Miles City Line 1 Hereford population. Further refinement and application of this methodology may facilitate characterization of beef cattle seedstock for their potential genetic contributions to profitability.