Postpartum ovarian activity in primiparous Holstein dairy cows

Postpartum anestrus is a major problem in primiparous dairy cows. The objective of this study was to investigate postpartum ovarian activity in primiparous Holstein dairy cows. Seven primiparous Holstein dairy cows were monitored for ovarian activity using a combination of ultrasound examination and alteration in progesterone concentrations. Daily blood sampling and ultrasound examination were conducted starting from day 6 until the third ovulation postpartum. First wave dominant follicles (>10 mm in diameter) were detected on day 11.5±1.48 postpartum. This follicle did not ovulate in any of the experimental cows. Moreover, none of the cows ovulated within 20 days postpartum. There was no difference in the follicular growth rate and the diameter of ovulatory follicles between the first, the second and the third ovulations postpartum (p>0.05). Interval from calving to the first postpartum ovulation was 48.1±6.89 days. Mean diameter of corpus luteum and progesterone concentrations of the first cycle (18.8±0.94 mm and 2.0±0.24 ng/mL) were significantly less than those of the second cycle (24.0±0.89 mm and 3.6±0.36 ng/mL; p<0.05). In conclusion, increased interval from parturition to the first ovulation is not due to the delayed or lack of the first wave dominant follicle formation after parturition; but is due to the regression of this follicle.