Influence of follicular status on twinning rate in mares.

The research investigated how the status of a mare’s follicles affects the rate of twin conception, using a variety of factors such as age, mare status, ovarian cycle, treatments received, and pregnancy status. The study found that the status of the mare and her follicles play a significant role in the outcome of the pregnancy.

Study Overview and Methodology

• The study was conducted between 1982 and 1985 on 1015 mares.
• The mares were evaluated based on numerous parameters including age, status (maiden, barren, lactating), ovarian cycle, ovarian and follicular size, treatments received, number of ovulations after mating, number of conceptuses present, and pregnancy status 45 days after mating.
• The mares were also examined ultrasonographically between Days 12 and 25 to detect the presence of embryonic vesicles and measure their dimensions.
• The collected data were then analyzed using a stepwise logistic regression method.

Results of the Study

• The study revealed that both the mare’s and the follicular status were significant predictors of the pregnancy outcome.
• The results from 2949 mare cycles showed different twin conception rates based on the mares’ status: 15.3% for maiden mares, 8.8% for lactating mares, and 14.0% for barren mares.
• When based on follicle status, twin rates with a single palpable follicle greater than 25mm were 11% in maiden, 11% in barren, and 5.3% in lactating mares.
• In 23.7% of cycles with 2 palpable follicles greater than 25mm, the twin conception rates were 30% for maiden, 23.3% for barren, and 22% for lactating mares.
• Overall, mares with a single follicle larger than 25mm had a twin conceptus rate of 7.6%, and with 2 follicles larger than 25mm, the rate was 23.6%.

Findings on Large Follicles and Double Ovulations

• When it came to mares with 2 large follicles (greater than 40mm) at mating, the twin conception rate was even higher at 38.2%.
• For mares with known synchronous double ovulations, the twin conception rate was a high 40%.
• A co-variance analysis was used to calculate the daily embryonic growth rate between Days 10 and 16 of gestation for 11 Standardbred mares. However, the abstract did not present the results of this analysis.