Effect of plane of nutrition of dairy heifers before and during gestation on milk production, reproduction, and health.

Fifty-nine heifers (1 yr of age; 320 +/- 12 kg) were assigned to one of four treatments of a 2 x 2 factorial design. Main effects were plane of nutrition (ad libitum vs. moderate feeding) during the second isometric phase (1 yr of age to 3 mo of gestation) and during the second allometric phase (3 mo of gestation to 14 d before calving) of mammary development. During the isometric phase, average daily gain were .72 and .84 kg/d for heifers fed a moderate or ad libitum diet, respectively. During the allometric phase, average daily gain was affected by previous plane of nutrition and averaged .84, .66, .95, and .73 for continuous ad libitum, ad libitum followed by moderate, moderate followed by ad libitum, and continuous moderate feeding, respectively. The BW at the end of gestation and BW after calving were increased by ad libitum feeding during the allometric phase (643 vs. 605; 588 vs. 558 kg, respectively). Milk production, protein content, and withers height were not affected by plane of nutrition. Milk fat was increased by ad libitum feeding during the isometric phase (3.9 vs. 3.6%). Cows on ad libitum feeding during the allometric phase had reduced average daily gain during lactation (.02 vs. .15 kg/d). The resumption of ovarian activity (progesterone > 1 ng/ml) was not affected by treatment, but days to first observed estrus increased with ad libitum feeding during the allometric phase. Finally, ad libitum feeding during isometric phase resulted in a higher incidence of displaced abomasum after calving, 9 versus 2.(ABSTRACT TRUNCATED AT 250 WORDS)