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

We have studied 120 Holstein (25 primiparous and 27 multiparous) or Ta rentaise (26 primiparous and 42 multiparous) dairy cows with a mean ca lving date of 15 December. In winter, the animals were fed a diet of n ative meadow hay ad libitum. From the 10th lactation day and for at le ast 16 weeks, the animals were divided into 2 groups within each breed and each lactation number (primiparous and multiparous). Animals of t he H groups received concentrate amounts to best cover their requireme nts. Animals of the B groups received 3 kg/d less concentrate than tho se of the H groups, for the same projected level of production. Concen trate composition was adapted so as to ensure that nitrogen supplement ation 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), wh ereas the primiparous Tarentaise cows of the B group reduced their mil k yield by almost 3 kg/d (9.9 versus 12.8 kg/d in the H group). The ma ximal 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. En ergy undernutrition had the same effect on milk production of multipar ous 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, und ernutrition induced a significant decrease in milk protein content (fr om 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. Ta rentaise primiparous and multiparous cows exhibited better reproductio n performance than Holstein cows. The reasons for such differences in the cows' response to energy undernutrition are discussed, in particul ar in relation to body reserves mobilization and energy partition betw een milk production and growth.