Consistent magnitude of postpartum body weight loss within cows across lactations and the relation to reproductive...

Great variation exists among cows in the magnitude of tissue mobilization during early lactation; however, it is not known whether this is an intrinsic trait. Our aims were (1) to test whether the degree of body weight (BW) loss is consistent within cows across lactations by examining daily BW records of 4 to 5 consecutive lactations and their relation to milk yield, health disorders, and reproductive performance; and (2) to examine, in an intensive study, the possible underlying physiological mechanism. Data from 416 first to fifth consecutive lactations obtained from 92 Israeli high-yielding Holstein dairy cows were analyzed. Cows were divided according to percentage of BW loss from wk 1 to 5 postpartum in their last lactation, into groups of (1) low weight loss (LWL; -3 to 6%; n = 37) and (2) high weight loss (HWL; 7 to 17%; n = 55). The average percentage of BW loss was 7.6% in the HWL group and 5.3% in the LWL group, and the pattern was consistent between groups across lactations. Milk and 4% fat-corrected milk yields during the first 30 d in milk across lactations were higher in HWL than in LWL groups, but 305-d yields were similar. The number of open days and the interval between lactations were consistent across lactations, 17 and 20 d longer, respectively, in HWL versus LWL cows. Across lactations, the conception rates from first, second, and third artificial inseminations were 9.6% higher in LWL than in HWL cows. No differences in the incidence of health disorders were observed between groups. The intensive study was conducted with 12 randomly selected peripartum cows divided into c-HWL and c-LWL groups according to the same criteria. Similar dry matter intake and efficiency calculations were observed between groups postpartum, implying that the differences may not be related to these factors. In response to a glucose-tolerance test, c-HWL cows had higher insulin secretion pre- and postpartum than c-LWL cows, suggesting the former had lower sensitivity to insulin. This is the first study demonstrating that the magnitude of BW loss postpartum within cows is consistent across lactations, and this trait is associated with reproductive performance. The degree of BW loss postpartum, regardless of genetic merit for milk production, seems to be an intrinsic trait that represents the variation in trade-off toward tissue mobilization between cows.