| dc.description.abstract | Virtually, all dairy cows have their first follicular wave within two weeks postpartum. However, only 30 - 50% ovulates within three weeks postpartum. The aim of this study was to evaluate factors affecting ovulation within 21 days in milk (DIM) in dairy cows. Cows (n = 768) from 2 herds had their ovaries scanned by ultrasonography twice a week starting at 17±3 DIM for a total of 4 ultrasound examinations (US). Ovulation was characterized by the presence of a corpus luteum (CL) ≥ 20mm in any US or when a CL <20mm appeared in two consecutive US. If a cow received GnRH on her first US, a CL of ≥22mm in the second US represented ovulation. The following information was collected (for up to 14 DIM): Parity, body condition score at enrollment (BCS), calving problems (dystocia, twins, stillbirths (dead on arrival, DOA), abortions, retained fetal membranes (RFM)), metabolic problems (ketosis or hypocalcaemia), infections (metritis or mastitis), digestive problems (indigestion or displaced abomasum (DA)), lameness, calving season (CS; summer or fall vs. winter or spring), dry period length (DPL; ≤70 or >70d), body weight loss (BWL; ≤28 or >28kg) in the first 14 DIM, and average daily milk yield in the first 14 DIM. Data were analyzed with a univariable and a multivariable analysis. For the multivariable analysis, the GLIMMIX procedure of SAS was used. Three models were constructed: 1 – excluding both DPL (not available for primiparous cows) and BWL (only available for 456 cows); 2 – including DPL; 3 – including BWL. Only variables with a P≤0.2 were included in each model. Herd was random. In model 1, cows with metabolic problems (20.7 vs. 33.9%; P=0.003), digestive problems (19.4 vs. 32.2%; P=0.05), or cows that calved in the winter or spring (23.5 vs. 33.1%; P=0.02) had a delay in ovulation within 21 DIM. Dystocia tended to decrease (24.1 vs. 32.9%; P=0.06) ovulation. In model 2, cows with metabolic problems (22.0 vs. 38.6%; P=0.02) and metritis (17.3 vs. 35.8%; P=0.05) had a delay in ovulation early postpartum. Cows with >70d DPL tended to have decreased (23.9 vs. 36.2%; P=0.07) ovulation. In model 3, cows with metritis (21.2 vs. 34.7%; P=0.03), digestive problems (20.0 vs. 33.4%; P=0.05), calved in the winter or spring (24.1 vs. 35.2%; P=0.01), or lost >28kg BW (27.7 vs. 38.5%; P=0.04) experienced a delay in the resumption of ovarian cyclicity. In conclusion, cows that had metabolic problems, digestive problems, dystocia, metritis, long DPL, calved in the winter or spring or lost > 28kg BW in the first 14 DIM had decreased ovulation within 21 DIM. | |
