Sources of variation in response intervals after prostaglandin treatment in mares with functional corpora lutea.

This research investigated the variations in response time to prostaglandin treatment in mares with functional corpora lutea, focusing on the size of the mare’s follicles at the time of treatment and the subsequent ovulation times. A significant finding is that ovulation time is less predictable in mares with larger follicles due to their occasional regression and later ovulation of a succeeding follicle.

Methodology and Participants

• This study used 62 non-cycling mares who were classified based on the size of their largest follicles at the time of treatment with Prostalene, a prostaglandin analogue.
• Additionally, the study included 90 foaling mares that were given Prostalene at various days following the first postpartum ovulation.

Results and Findings

• Though oestrus was observed in only 77.4% of the mares, a high percentage (98.4%) ovulated, with an average ovulation happening 6.8 days post-treatment.
• There was a high variance in the interval to ovulation for mares with follicles of 40mm or larger at treatment time. This was caused by the regression of large follicles about one-third of the time and the subsequent later ovulation of another follicle.
• As a result, predicting ovulation time based on ovarian palpation was found to be most uncertain in mares with larger follicles.
• In the case of the 90 foaling mares, ovulation occurring less than 6 days post-treatment was strongly associated with the presence of a large follicle on the treatment day. For the majority (72%), ovulation occurred between 6 to 10 days after treatment.
• There was a difference in the distribution of interovulatory periods when Prostalene was given on Day 6 post-ovulation compared to Day 8 treatment.

Conclusion

• This study revealed that the response interval to prostaglandin treatment in mares with functional corpora lutea varies significantly, especially in those with larger follicles. As such, predicting ovulation times can be challenging particularly in these cases.