EFFECTS OF WINTER FEEDING DURING THE REARING PERIOD ON PERFORMANCE AND LONGEVITY IN DAIRY-CATTLE

Black and White dairy heifers born in autumn and programmed for early calving at approximately 2 years of age were given HIGH (H) or LOW (L) feeding treatments during each wintering period of the rearing stage according to a factorial arrangement: from birth to 6 months (H1 or L1) and between 12-18 months (H2 or L2). H1 and H2 treatments increased energetic supplies by 22 (100 UFL) and 49 (400 UFL) per cent. HIGH feeding treatments resulted in higher winter gains (H1: 826 g/d, L1: 696 g/d, H2: 88 5 g/d, L2: 639 g/d). During summer grazings, compensatory growth was moderate (50 to 55%). Feeding treatments had no effects on milk yield for each lactation. However H 1 treatment contributed to a longer productive life ( + 333 days) along with higher milk ( + 4089 kg), fat ( + 205 kg) and protein ( + 150 kg) yields. H 1 cows produced more calves ( + 0. 9) and heavier carcasses at culling ( + 20 kg). H2 heifers needed less veterinary assistance at first calving. Mastitis troubles were less frequent and mortality was lower in H 1. Hence, the live-weight of 6 month-old heifers should amount to 30% of adult cow weight. The ideal weights are judged to be 60% and 90% of mature cow weight at AI (at age 1 5 months) and before the first calving (at 24 months).