Risk factors and effects of postpartum anovulation in dairy cows

The objectives were to identify risk factors for and to quantify the effect of postpartum anovulation on reproductive performance in dairy cows. Data from 2,178 Holstein cows in 6 commercial herds enrolled in a randomized clinical trial were used. Data on periparturient disease incidence, calving history, and body condition score were collected. Cows were examined at wk 5 postpartum for reproductive tract disease; cytological endometritis was defined as >= 6% polymorphonuclear cells in endometrial cytology, and purulent vaginal discharge was defined as the presence of mucopurulent or purulent vaginal discharge. Cows were followed until 300 d in milk (DIM) for reproductive performance. Serum nonesterified fatty acids (NEFA) concentration was measured once during the week before expected calving. Serum beta-hydroxybutyrate, NEFA, and haptoglobin were measured at wk 1, 2, and 3 postpartum. Serum progesterone (P4) was measured at wk 3, 5, 7, and 9 postpartum. The end of the postpartum anovulation period was defined as the first sampling time at which P4 was >1 ng/mL. Statistical analyses were performed using logistic regression models and Cox proportional hazard models. The prevalence of anovulation was 72, 44, 26, and 17% at wk 3, 5, 7, and 9, respectively. Cows were classified according to their ovulatory status as having luteal function at 21 DIM (Cyc21), as having low P4 at 21 DIM but having luteal function at least once at 35 or 49 or 63 DIM (Cyc63), or being anovulatory at 63 DIM (Anov63; no samples with P4 >1 ng/mL). Factors associated with early ovulation (Cyc21) included season, parity, decreased haptoglobinemia, and decreased serum NEFA concentration before and after parturition. Risk factors for prolonged anovulation (Anov63) included cytological endometritis, increased haptoglobinemia, and greater serum NEFA concentrations before and after parturition. Cows classified as Anov63 had an increased median time to first breeding compared with Cyc63 (74.1 vs. 73.2 d). The effect of prolonged postpartum anovulation on median time to pregnancy was conditional on parity group; a detrimental effect was present in cows of parity >= 3 (129 d for Cyc21, 151 d for Cyc63, and 180 d for Anov63), but no effect was observed in cows of parity <= 2. Overall, these findings suggest that postpartum anovulation was associated with indicators of energy balance and uterine inflammation, and with detrimental effects on reproductive performance.