Relationships of Milk Production of Beef Cows to Postweaning Gain of the Calves12

Milk yield from 158 Brangus cows bred to 6 sire breeds (Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, Romosinuano) was measured for 3 yr to estimate relationships of milk yield of cows and postweaning ADG of their calves on 2 postweaning systems (dry lot or wheat pasture). Milk yield was measured monthly 6 times per year and averaged over 1 mo. Calf postweaning ADG was calculated from the initiation of postweaning management treatments in the fall to the end of spring grazing in April. Calf ADG was regressed on dam 24-h milk yield, and interactions of linear and quadratic regression coefficients with calf sire breed and postweaning treatment of calf were evaluated. In general, regression analyses indicated that calf postweaning ADG was linearly related to dam milk yield, but the relationships depended on the calf sire breed and postweaning treatment (P < 0.01). On dry-lot management, greater cow milk production was associated with lesser postweaning ADG in Gelbvieh- (P < 0.05) and Bonsmara-sired (P < 0.01) calves, whereas greater cow milk production was associated with greater postweaning ADG in Brangus-sired calves (P < 0.01), and a similar trend was observed in Charolais-sired (P < 0.19) calves. On wheat pasture management, greater cow milk production was associated with greater postweaning ADG in Gelbvieh-sired calves (P < 0.11), with a trend for greater cow milk production to be associated with lower postweaning ADG in Romosinuano-sired calves (P < 0.25). Results indicate that accurate determination of the relationship of dam milk production and calf postweaning ADG will require consideration of both calf postweaning management and calf sire breed.