CHANGES IN MORPHOLOGICAL APPEARANCE AND FUNCTIONAL-CAPACITY OF RECRUITED FOLLICLES IN COWS TREATED WITH FSH IN THE PRESENCE OR ABSENCE OF ADOMINANT FOLLICLE

This study was designed to determine the effect of the presence of a d ominant follicle at the beginning of FSH stimulation on the morphologi cal appearance and functional capacity of recruited follicles during F SH stimulation in cattle. Synchronized nonlactating dairy cows were as signed to 1 of 2 groups and treated with FSH in the presence (n = 5) o r absence (n = 6) of a dominant follicle between Days 7 and 12 of the estrous cycle (Day 0 = estrus) to stimulate follicular growth. Dominan t follicles were identified by daily ultrasonographic observations, be ginning on Day 3 of the estrous cycle. Dominant follicle had an ultras onographic diameter greater than or equal to 10 mm and were in a growi ng phase, or maintaining a constant diameter (greater than or equal to 10 mm) for less than 4 d. Ovaries were collected at daughter on the m orning of the third day following initiation of the FSH stimulation. A ll follicles > 2 mm were dissected, classified according to diameter ( Class 1: 2 to 4.4 mm; Class 2: 4.5 to 7.9 mm; Class 3: > 8 mm), and in cubated individually for 90 min in medium M-199 (37 degrees C, 5% CO2) . Following incubation, integrity of each follicle was evaluated histo logically to assess the level of atresia and biochemically to determin e the in vitro release of estradiol (E2) and androstenedione in cultur e media On Day 3 of the FSH treatment, mean number of follicles in eac h class was similar (P > 0.1) between the 2 groups. The percentage of atretic follicles in Classes 1 and 3 on Day 3 of the FSH stimulation d id nor differ (P > 0.1) between the 2 groups. However, the percentage of atretic follicles in Class 2 was higher (P < 0.005) in cows treated with FSH in presence than in absence of a dominant follicle (60.8 vs 38.2%). The release of E2 in culture media by small Class 1 atretic or healthy follicles, by Class 2 atretic and by Class 3 healthy follicle s was not affected (P > 0.1) by the ovarian status. However(P < 0.001) , the release of E2 in culture media of Class 2 healthy and Class 3 at retic follicles was less for follicles harvested from cows bearing tha n from those not bearing a dominant follicle. Within each follicular c lass, concentrations of androstenedione in the culture media did not d iffer between the 2 groups (P > 0.1). These results suggest that the p resence of a dominant follicle at the beginning of FSH stimulation alt ers the population of follicles recruited FSH stimulation. This may be associated with the reported decrease of the superovulatory response in cows superovulated in presence of a dominant follicle.