On the relation between milk production and fertility in Kibbutz dairy cattle herds

Abstract

SUMMARY Milk production (305 day lactations, 3·5% fat-corrected milk), and lengths of time between calving and conception for 541 heifers and 1127 older cows were examined. These data were collected from 11 herds in collective farms in Israel during two successive years. Herd lactation means ranged from 5046 to 8570 kg for cows and from 5021 to 7250 for heifers; the ranges of time between calving and conception were 89–123 days and 99–141 days, respectively. A significant correlation was found between the weight of milk given per lactation and the length of the interval between calving and the next conception, with coefficients of 0·298 (cows) and 0·333 (heifers). There was a positive non-linear regression of length of calving to conception interval on production of milk, the regression line becoming steeper, both for cows and heifers, as yield rose. All herds practised first insemination at the first heat exhibited after 60 days from calving. The results indicate that, when this is done, cows yielding 8000 kg or over per lactation, and heifers yielding 6750 kg or over, will show calving to conception intervals exceeding a mean length of 110 days.