Follicular Dynamics in Pubertal Arab Mares during Spontaneous Estrus

This study aims to study the follicular changes during the estrous phase of 2 years pubertal mares showed previously signs of estrous and corpora lutae were detected on their ovaries. Five fillies of 2 years old were subjected to daily ultrasonographic examination for 18 days. Follicular dynamics were studied during estrus from day 6 before ovulation (-6) till day of ovulation (day 0). Follicles were classified into small ( 10-15mm), medium ( 15- 20) and large ( 20). Number and diameter of each follicle was measured. Data was subjected to simple one way ANOVA to study the effect of day on number and growth rate of each follicle class. Results revealed that no significant variation was observed in number of all follicle classes. The dominant follicle after deviation to dominance starts to grow from 26mm in diameter to reach a maximum diameter of 42.3 mm on day of ovulation. At least one large follicle is dominant and the other large follicle is subordinate three days before ovulation. Compared to the day 6 before ovulation, the day before ovulation has significantly low large follicle number. There was a decrease of number and diameter of medium follicles on day 2 before ovulation. This study indicated that after ovulation fillies became much similar to mature and older mares. High genetic value fillies could be subjected to oocyte collection programs before enrolling her to either breeding program or performance.