We aimed to identify the biological factors during the voluntary waiting period (VWP) that are associated with subsequent reproductive performance in dairy cows. Two hundred and one pregnant dairy cows had their body condition score (BCS) evaluated and blood samples taken 4 weeks before calving, at calving, and 1, 2, 4, 6, and 8 weeks after calving, to measure serum metabolite and progesterone concentrations. In addition, any peri- and postpartum disorders within 4 weeks of calving, and the mean milk yields 4 and 8 weeks postpartum, were recorded. The cows were allocated to two groups according to whether they had become pregnant or not by 120 days after calving: a pregnant group (n = 50) and a non-pregnant group (n = 151). Analyses of serum metabolite concentrations showed that the aspartate aminotransferase and γ-glutamyltransferase activities 2 weeks (p < 0.05) and the non-esterified fatty acid concentration 6 weeks (p < 0.01) postpartum were higher in the non-pregnant than in the pregnant group. However, the albumin concentrations between 2 and 8 weeks and the total cholesterol and magnesium concentrations between 4 and 8 weeks postpartum were lower in the non-pregnant group (p < 0.05). The BCS (p < 0.05) and percentages of cows that had resumed cyclicity (p < 0.001) by 6 and 8 weeks postpartum were higher in the pregnant than in the non-pregnant group, whereas the incidence of peri- and postpartum disorders was higher in the non-pregnant group (p < 0.05). In conclusion, high serum enzyme activities, which imply liver damage, imbalances in energy metabolites and magnesium, and a higher incidence of peri- and postpartum disorders, are associated with poorer reproductive performance, whereas high BCS and early resumption of cyclicity during the VWP are associated with superior reproductive performance in dairy cows.

Keywords: dairy cow, voluntary waiting period, reproductive performance