Association of postpartum milk fat, protein and fat-to-protein ratio with 120 days pregnancy risk in Holstein dairy cows

Induced lipolysis by negative energy balance causes an increase in milk fat, a decrease in milk protein, and also as a consequence an increase in milk fat to protein ratio (FPR). The objective of this study was to evaluate available data in each milk record such as fat, protein and their ratio, somatic cell count (SCC) and the history of dairy cows in order to determine pregnancy risk (PR) till 120 days in milk (DIM). Therefore, the information of 1,279 primiparous and multiparous Holstein dairy cows was collected on days 30 and 60 of DIM and near the first artificial insemination (AI) postpartum. The results illustrated the amount of milk fat, protein and FPR on day 30 of DIM in non-pregnant and pregnant groups were (2.67±1.2, 2.62±1.04 and 1.01±0.4) and (2.87±1.16, 2.76±0.95 and 1.03±0.36), on day 60 of DIM were (2.87±1.06, 2.7±0.86 and 1.06±0.35) and (2.97±1.15, 2.73±0.9 and 1.08±0.36), and near the first AI were (2.62±1.2, 2.53±1.04 and 1.03±0.4) and (2.8±1.24, 2.63±1.01 and 1.06±0.5), respectively, in which their effects on PR till 120 DIM were significant at two sampling times (pp=0.023); but none of the milk constituents and SCC had constant effect when analyzed by Logistic regression. Seasons of calving (p=0.02) and AI (p=0.00), previous DIM (p=0.001) and milk production (p=0.016) were analyzed by COX model and it was demonstrated that only previous DIM (p=0.021, Odds ratio=0.985) and season of AI (p=0.040, Odds ratio= 7.5) had significant effect on pregnancy till 120 DIM. The result of the present study shows that the effect of previous DIM and season of AI are significant on pregnancy till 120 DIM, but milk constituents had no effect on it.