Effects of first postpartum progesterone rise, metabolites, milk yield, and body condition score on the subsequent ovarian activity and fertility in lactating Holstein dairy cows.

Seventy multiparous healthy lactating Holstein cows (fat-corrected milk yield = 7,561.8 kg) were monitored from 14 days before to 70 days after calving. Transrectal ultrasound scanning was performed twice weekly from 7 to 65 days postpartum. Blood samples were also collected twice weekly to measure serum P(4) and biweekly to detect serum beta-hydroxybutyrate (betaHB) and nonesterified fatty acid (NEFA) concentrations. Body condition score (BCS) was taken biweekly after calving. Based on the serum P(4) profile of 59 cows (11 cows were excluded due to the occurrence of postpartum diseases) studied, 27 (45.8%) had normal ovarian activity, while 21 (35.6%), six (10.1%), three (5.1%), and two (3.4%) had delayed ovulation (DOV), prolonged luteal phase (PLP), short luteal phase (SLP), and cessation of ovarian activity, respectively. Cows with PLP had an earlier ovulation compared to that of cows with normal ovarian activity (23.16 +/- 4.02 vs 31.9 +/- 8.35 days; P < 0.05). PLP cows also had a greater mean +/- standard deviation peak milk yield (44.2 +/- 5.8 vs 37.2 +/- 5.7 kg/day, 75 days postpartum; P < 0.05) than cows with normal postpartum ovarian activity. The PLP group also had greater milk production in the previous lactation period. Logistic regression analysis indicated that cows with P(4) concentration > or =1 ng/ml on day 24 after calving were more at risk for PLP by 1.1 for each 1 kg increase in mean peak milk yield during 75 days after calving. BCS was lower in cows with DOV compared to that of cows with normal ovarian activity at any time after calving (P < 0.05). Serum betaHB concentrations in DOV cows were significantly higher than that of normal cows on day 42 after calving (0.69 +/- 0.29 vs 0.54 +/- 0.12 mmol/L, P < 0.05). No significant difference was found in the mean concentrations of NEFA between cows in different groups at any time after calving (P > 0.05). The concentrations of P(4) on days 28 and 31 were negatively correlated with betaHB concentration on day 42 after calving in cows with normal ovarian activity (R = -0.44, P = 0.02). In conclusion, these findings suggest that early ovulation and hence early postpartum P(4) rise in addition to the high milk production could partly be responsible for the occurrence of PLP in dairy cows.