Milk production of Holstein heifers fed either alfalfa or corn silage diets at two rates of daily gain.

Seventy-five prepubertal heifers were fed diets based on either alfalfa silage or corn silage plus soybean meal for daily gains of either 725 or 950 g/d in a 2 x 2 factorial. Heifers were fed from 175 to 325 kg of body weight (BW). The alfalfa diet contained more digestible protein and less digestible energy than did the diet containing corn silage plus soybean meal. Actual gains were preexperimental BW gain, 633 g/d; lowest experimental BW gain, 785 g/d; highest experimental BW gain, 994 g/d; lowest postexperimental BW gain, 494 g/d; and highest postexperimental BW gain, 546 g/d. Compensatory postexperimental BW gains of heifers fed a common diet allowed the heifers to calve at 732 d of age. The postcalving BW was 508 kg, and precalving height at withers was 134 cm. A total mixed diet containing 17.1% CP and digestible energy at 3.12 Mcal/kg of dry matter was fed during lactation. Feed intake, milk and milk component production, and milk composition were not affected by either experimental diet or growth rate. As covariates, milk production was related to age at calving and was more strongly related to BW after calving, but no differences were observed among growth diets. Differences in protein and energy concentrations in experimental growth diets did not affect lactation performance. About 75% of total BW gains during the treatment period occurred before puberty, but rate of gain did not affect milk production. This lack of an effect of prepubertal growth rates on the milk production of primiparous heifers is consistent with six other similar studies that were conducted recently.