MILK-PRODUCTION OF HOLSTEIN HEIFERS FED EITHER ALFALFA OR CORN-SILAGEDIETS AT 2 RATES OF DAILY GAIN

Seventy-five prepubertal heifers mere fed diets based on either alfalf a silage or corn silage plus soybean meal for daily gains of either 72 5 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 prote in 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 postexp erimental 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 a t 3.12 Mcal/kg of dry matter was fed during lactation. Feed intake, mi lk and milk component production, and milk composition were not affect ed by either experimental diet or growth rate. As covariates, milk pro duction 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 gro wth 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 prepub ertal growth rates on the milk production of primiparous heifers is co nsistent with six other similar studies that were conducted recently.