Performance and longevity of dairy heifers born during winter 1 (W1) and reared according to three growth profiles during winter 2 (W2) in a strategy based on first calving at 36Â months of age

An experiment was performed to test the hypothesis that restricted growth patterns during winter 2 (W2) would affect subsequent performance of dairy heifers born during winter 1 (W1) and going through first calving at 36 mo of age. The study used simultaneously two INRA experimental herds in two different parts of France (Le Pin-au-Haras and Mirecourt), totalling 158 heifers born during three successive winters (1994-1997). All animals were followed from birth until the day of culling. Animal breeds were Holstein (Ho) and Normande (No) at Le Pin-au-Haras, and Holstein (Ho) and Montbeliarde (Mo) at Mirecourt. At the beginning of W2, heifers were 332 (± 19) and 365 (± 27) d old at Le Pin-au-Haras and Mirecourt, respectively. The animals were then housed and subjected to a restricted feeding strategy to achieve an average daily gain (ADG) of 600, 400 or 200 g/d at Le Pin-au-Haras, and 500, 200 and −200 g/d at Mirecourt, respectively. Duration of W2 varied from 114 to 167 days depending on birth year and herd. At the end of W2, animals were 453 (± 19) and 514 (± 33) d old at Le Pin-au-Haras and Mirecourt, respectively. During pasture grazing seasons, management and feeding were similar for all animals. As expected, body weight differed between treatments at the end of W2 (p < 0.05), but not at first calving. In both herds, performance during the first lactation was generally unaffected by feeding treatments. On overall lactations, the 600 g/d group of heifers at Le Pin-au-Haras showed lower milk performance calculated on a 4% basis and a poorer milk composition (p < 0.05). However, when expressed per productive day of life, milk production on a 305-day basis (p < 0.05) was the highest for these animals. Of the 158 animals that started the experiment, 41% were culled due to reproductive disorders, probably a result of the seasonal calving system. These results indicate that a strategy based on first calving at 36 mo of age makes it possible to voluntarily reduce ADG during a short growth period without any major effects on short- or long-term performance.