THE EFFECT OF LEVEL OF CONCENTRATE FEEDING ON THE PERFORMANCE OF DAIRY-COWS OF DIFFERENT BREEDS

We have studied 120 Holstein (25 primiparous and 27 multiparous) or Tarentaise (26 primiparous and 42 multiparous) dairy cows with a mean calving date of 15 December. In winter, the animals were fed a diet of native meadow hay ad libitum. From the 10th lactation day and for at least 16 weeks, the animals were divided into 2 groups within each breed and each lactation number (primiparous and multiparous). Animals of the H groups received concentrate amounts to best cover their requirements. Animals of the B groups received 3 kg/d less concentrate than those of the H groups, for the same projected level of production. Concentrate composition was adapted so as to ensure that nitrogen supplementation was not limiting and was similar in both groups H and B. During the first 16 lactation weeks, Holstein cows of groups B and H produced the same mean quantity of milk (23.2 and 23.5 kg/d, respectively), whereas the primiparous Tarentaise cows of the B group reduced their milk yield by almost 3 kg/d (9.9 versus 12.8 kg/d in the H group). The maximal body mass losses observed in primiparous cows of groups B and H were 68 and 52 kg in Holstein, and 34 and 33 kg in Tarentaise cows. Energy undernutrition had the same effect on milk production of multiparous cows of both breeds (-1.0 and -1.2 kg/d milk between groups B and H in Holstein and Tarentaise cows, respectively). In all B groups, undernutrition induced a significant decrease in milk protein content (from 0.8 to 1.9 g/kg), but did not affect fat content. It did not induce any marked modifications of the animals' reproduction performance. Tarentaise primiparous and multiparous cows exhibited better reproduction performance than Holstein cows. The reasons for such differences in the cows' response to energy undernutrition are discussed, in particular in relation to body reserves mobilization and energy partition between milk production and growth.