Impact of estrous synchronization methods on cellular proportions in cervical mucus and serum hormone concentrations

The objective of this study was to examine cytological changes of cervical mucus following the induction of estrus with intra-vaginal drug release (CIDR) devices in dairy cows. Sixty healthy Holstein Frisian cows, averaging 80 (±10) days post-partum, were selected from a commercial dairy farm around Shiraz. Cows in the control group were synchronized by the Ovsynch protocol. Cows in the second group (OV + CIDR) were subjected to the same Ovsynch protocol but in addition were administered a progesterone-releasing CIDR. Cows in the third group (OV + S-CIDR) were subjected to Ovsynch procedures but received the skeleton of a CIDR device, which did not release progesterone. Cows in the fourth group (E2 + CIDR) received a progesterone releasing CIDR but were injected with estradiol benzoate. Cows in group 5 (E2 + S-CIDR) received a CIDR skeleton and estrodial benzoate. CIDR devices were removed from cows in groups 2–4 and all cows were injected with PGF2α on day −3. Blood samples and cervical mucus discharges were collected from all cows on days −10, −3, 0 and 12 relative to AI. On the day of AI, the mean ± S.D. percentage of neutrophils was significantly higher (p < 0.05) in the S-CIDR + OV and S-CIDR + E2 groups than in Ovsynch group. Comparing the percentage of neutrophils in cervical mucus of Ovsynch group (less than 1%) with that of other treatment groups on the day of AI (from 5 to 39%) revealed the influential effect of a CIDR device on the reproductive tract. Results of the current study did not reveal hormonal effects but did identify mechanical effects of CIDRs on cell percentages in cervical mucus. The hormonal effects were probably masked by mechanical effects. Therefore, we were not able to confirm hormonal effects on proportions of different cells in cervical mucus. Consequently, additional research on hormonal effects and the mechanical effects of CIDR on the uterus is required.