In an effort to evaluate the effects of prepartum energy balance and postpartum fat supplementation on perfor-mance, University of Wyoming researchers managed 3-year-old crossbred cows to achieve a body-condition score of either 4 or 6 at parturition. At 3 days postpartum, cows within each BCS group were fed either hay plus a low-fat control supplement or hay plus high-fat safflower seed supplements. Diets were equivalent in energy and protein.
BCS had no significant effect on first-service conception rate, but overall pregnancy rate was greater in BCS 6 cows (88.9 percent vs. 63.9 percent). BCS did not influence calf birth weight or calf average daily gain. Dietary fat supplementation did not affect cow weight change, BCS change, rib-fat thickness, milk yield, milk composition, cow reproduction or calf performance.
BCS had no effect on milk yield or composition, except for protein percentage, which was lower for BCS 4 cows.
The authors concluded that although BCS 4 cows seemed capable of maintaining BCS during lactation, the overall decrease in pregnancy rate indicates that cows should be managed to achieve a BCS greater than 4 before parturition to achieve satisfactory reproduction.