Association between milk production and treatment response of ovarian cysts in lactating dairy cows using the Ovsynch protocol.

The objective of this study was to evaluate the association between the level of milk production on the day of diagnosis of ovarian cysts and treatment response using the Ovsynch protocol. On the day of cyst diagnosis (Day 0), 260 lactating dairy cows with ovarian cysts were treated with gonadotropin-releasing hormone (GnRH), PGF2alpha on Day 7, GnRH on Day 9, and timed inseminated 16-20 h later (Ovsynch protocol). Pregnancy was determined (by transrectal palpation) between 42 and 49 days after insemination. On Day 0, data for milk production (kg/day), parity, days in milk (DIM), and body condition score (BCS) were recorded. Using the median value for milk production on the day of diagnosis, cows were classified as high producers (>28.5 kg) and low producers (<or=28.5 kg). Cows were classified as primiparous (first lactation) or multiparous (second or more lactations). Data for conception rate (CR) were analyzed using logistic regression accounting for milk production on the day of diagnosis, parity, DIM, and BCS. The CR for low and high producers was 6 and 16%, respectively. There was no association between DIM and BCS with the other variables (P>or=0.05). Primiparous cows were more likely (adjusted odds ratio: AOR=3.63; 95% CI: 95% confidence intervals=1.28-10.30; P<or=0.01) to become pregnant than multiparous cows, and low producers were less likely (AOR=0.31; 95% CI=0.11-0.85; P<or=0.02) to become pregnant than high producers. It was concluded that cows with high milk production on the day of cyst diagnosis were more likely to become pregnant following treatment than cows with low milk production. It appears paradoxical that high milk production predisposes to the occurrence of ovarian cysts, but that high-producing cows respond better to treatment compared to low-producing cows. It is hypothesized that the level of milk production on the day of cyst diagnosis could be an additional potential predictor of success to treatment of lactating cows with ovarian cysts using the Ovsynch protocol.