[Feeding, pathology and productivity of the dairy cow: interrelations during the course of lactation]

The influence of winter feeding (hay versus grass silage-based diets, supplemented with a high or low level of concentrate) and disease on the longevity of 136 Friesian or Montbeliarde dairy cows was studied in a long-term experiment spanning 6 consecutive years. Breed had no great effect on longevity. The longevity of cows given a silage diet with a low level of supplementation was lower than that of cows given any one of the other diets (2.5 lactation/cycle versus 3.2-3.5). Cows that developed frequent lameness during the 1st lactation had a shorter period of productivity (-1.1 lactation/cycle) than comparable healthy animals. Among the different pathological lactation profiles, only the profile "healthy lactation" recurs from one lactation to the next (41% of the cases). In particular, lameness (which is very recurrent during a single lactation) is not recurrent from one lactation to the next. The characteristics of the 1st lactation cycle (disease, milk production, reproduction) appeared to be determinant for the productive future of the animals. On average, milk production and live-weight increased by 352 and 24 kg respectively between the 1st and 2nd lactation and by 270 and 27 kg between the 2nd and 3rd lactation. Cows given a hay diet (with a low or high level of supplementation) or a silage diet with a high level of supplementation showed a greater increase in production between the 1st and 3rd lactation (+ 752 kg) than those given a silage diet with a low level of supplementation (+ 359 kg). Over 3 lactations, the cumulative effects of the type of winter feeding can become marked: differences in milk production can attain up to 2770 kg between a hay/high concentrate and a silage/low concentrate diet. These results question the validity of conclusions drawn from experiments conducted over 1 winter or 1 lactation cycle only.