AbstractSixty Holstein heifers supplied by private farms were stratified by liveweight into 15 quartets upon reaching breeding age, and used in a randomized block design with four treatments, based on grazing with or without supplementation, until shortly after parturition. Treatments were: 1) stocking rate of 3.125 animals/ha, fertilization with 2.25 t/ha of a 15-5-10 analysis annually, without supplemental feeding; 2) same stocking rate, 1.65 t of fertilizer, supplementation with 3 kg per head daily of bulky concentrates, beginning at 3 months pregnant; 3) 5 animals/ha, fertilization with 2.25 t/ha, 1.8 kg daily of conventional concentrates continuously; 4) as in treatment 3, except for supplementation at 4 kg daily from the 5th month of pregnancy onward. In 270 days mean liveweights increased from 347 kg initially to values ranging from 502 kg to 517 kg for treatments 4 and 1, respectively. Daily gains of .63, .57, .61, and .58 kg in the four respective treatments were not significantly different. Treatments affected growth in body dimensions minimally. Mean age at first calving ranged from 30.8 to 32.2 months for treatments 4 and 2, respectively. Mean first lactation milk yields (305-day mature-equivalent DHIA records) by heifers formerly in the four respective treatments were 4,210, 4,253, 4,762, and 4,683 kg, not differing significantly. Under excellent grazing conditions, as in this experiment, concentrate feeding prepartum was not shown to be necessary for satisfactory growth, reproduction and milk yield, but it did result in a lower postpartum attrition rate than grazing only during rearing.
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