Ovulation rate and distribution in the thoroughbred mare, as determined by ultrasonic scanning: the effect of age.

The research studies the ovulation patterns of thoroughbred brood mares using ultrasonic scanning. The study identified that there is almost equal distribution of ovulation between the left and right ovaries, the likelihood of multiple ovulations increases with age, and that ovulation patterns can be somewhat predictable from one cycle to the next.

Methodology

• The study monitored ovarian activity in 2181 oestrous cycles from 1136 thoroughbred brood mares in order to determine their ovulation rate and the distribution of ovulation between the left and right ovaries.
• The researchers used ultrasonic scanning to monitor the mares, as it has been shown to have a higher accuracy rate than rectal palpation and slaughterhouse material.

Findings

• The study found that there was a roughly equal distribution of ovulation occurring on the right (49.5% of all ovulations) or left ovary (50.5%).
• Multiple ovulations were found to occur in 22.4% of oestrous cycles.
• Importantly, the study found that there was a significant association between age and the incidence of multiple ovulations. The younger age group (3-5 years) had a 15% incidence of multiple ovulations, this increased steadily with age, reaching 35.1% in the oldest age group (18-22 years).

Ovulation Pattern Consistency

• The study also looked at whether the ovulation pattern in one cycle affected the pattern within the next.
• It found that if a mare exhibited multiple ovulations in one cycle, there was an increased probability of multiple ovulations occurring in the next cycle.
• The study also revealed that single ovulations in one ovary were more likely to be followed by a single ovulation on the alternate ovary during the next cycle.

Conclusions

• Based on their findings, the researchers concluded that mares are symmetrical ovulators – meaning they are equally likely to ovulate from the left or right ovary.
• They also concluded that the incidence of multiple ovulations increases with age, and the exhibition of multiple ovulations in one cycle is linked to an increased probability of a multiple ovulations occurring in the next one.
• Lastly, they concluded that single ovulations in one ovary are more likely to be followed by a single ovulation on the alternate ovary during the next cycle.