Relationships Of Milk Production Of Beef Cows To Postweaning Gain Of Their Calves

Milk yield from Brangus cows sired by 6 breeds (Bonsmara, Brangus, Charolais, Gelbvieh, Romosinuano) was measured over a 3-yr period with a single-cow milking machine to estimate the relationship of actual milk yield of cows and their calves'postweaning average daily gain on two postweaning management systems (drylot or wheat pasture). Milk yield was measured monthly six times per year and averaged over month. Calf postweaning average daily gain was calculated for seven periods of time: weaning to initiation of postweaning management treatments; first three weeks after initiation of postweaning management treatments in the fall; initiation of postweaning management treatments to end of fall/winter grazing; initiation of spring grazing period in March for the first three weeks; initiation of spring grazing period in March to the end of spring grazing in April; initiation of postweaning management treatments in fall to end of spring grazing in April; and weaning to end of spring grazing in April of the subsequent year. Calf ADG for the different periods was regressed on dam 24-h milk yield and interactions of linear and quadratic regression coefficients with either sire breed of calf or postweaning treatment-sex of calf were evaluated. The combination of postweaning treatment-sex of calf was used because drylot heifers were rotated from drylot to wheat pasture at the initiation of spring grazing to evaluate adaptation to wheat pasture. Generally, regression analyses indicated that calf postweaning ADG was related to dam milk yield but the relationships depended on either sire of calf or the postweaning treatment-sex of calf combination. The results showed that there was small relationship of dam milk to calf postweaning ADG which depended on postweaning calf management and sire breed of calf and the determinant coefficients were R2=0.12 and R2=0.09 ,respectively. Dam milk yield had positive effects on drylot steers and heifers,and the regression equations of calf postweaning ADG on dam 24h milk...