Productive life of the dairy cow : effect of breeding period on performances in first lactation

Abstract

Growth curves from 971 heifers born from 1963 to 1990 in 3 experimental INRA herds were analysed as well as their consequences on performances in early first lactation. These heifers from Montbéliarde, Friesian and Holstein breeds and their Holstein crossbreeds had early (2 years old, n=274) or late (3 years old, n=697) calvings. Early primiparous cows produced less milk (2 kg/d), and had more health disorders at calving than late ones. These 2 groups were analysed separately. A classification of these heifers based on their liveweight gains (birth to 6 months, 6 to 12 months, 12 months to first calving) allowed different profiles possible to be built. These profiles were analysed according to herd, breed, birth period and birth season. Post-calving live-weights varied from 470 to 490 kg for early calving heifers and from 510 to 610 kg for late calving heifers according to the profiles. The largest live-weight differences were 45 kg and 81 kg at 6 and 12 months. Early calving profiles (n=4) had no effect on milk production in early first lactation. Late calving heifers (7 profiles) produced more milk when post-calving weight increased (+1.8 kg/d from 530 kg to 590 kg). Moderate live-weight gains are suitable for late calving heifers from birth to 12 months (700 g/d) and then to post-calving age (400 g/d). These values agree with results observed in heifers in this study.