ULTRASONOGRAPHIC MONITORING OF ANTRAL FOLLICLE DEVELOPMENT IN RED DEER (CERVUS-ELAPHUS)

Ovarian follicular dynamics were monitored in 12 surgically modified r ed deer hinds (ovaries adhered to vaginal wall) by transvaginal real-t ime ultrasonography during the luteal cycle, anoestrus and induction o f superovulation. All 12 hinds showed evidence of regular luteal (plas ma progesterone) cyclicity during the breeding season, although luteal tissue was not observed on the ultrasonograms. During the normal lute al cycle (14-22 days) total numbers of follicles >3 mm did not vary si gnificantly by day (range of means: 1.8-3.4; P>0.05). A single large ( greater than or equal to 6 mm) follicle was usually present on all day s except immediately after ovulation (day 0). However, the appearance of new follicles (greater than or equal to 3 mm) was not random, and w as greatest on day 1 and day 14 (P < 0.05). Tracking of individual fol licles revealed irregular waves of emergence and disappearance of the largest follicle, with either one (n = 1), two (n = 3) or three (n = 5 ) waves observed across nine luteal cycles. New follicles (greater tha n or equal to 3 mm) emerged after regression or ovulation of a large f ollicle, suggesting a dominance effect. There were no significant diff erences in the overall mean numbers of follicles during early, mid-and late anoestrus (September, November and April, respectively) but foll icle turnover was more rapid during mid-anoestrus as evidenced by a si gnificantly greater number of new small (> 3 mm) follicles (P< 0.001). Administration of superovulatory doses of ovine FSH during the breedi ng season resulted in a marked increase in the appearance of new folli cles within 48 h of initiation of the injection regimen. By terminatio n at 96 h, the time of progesterone withdrawal, the mean number of fol licles > 3 mm was significantly higher than for control hinds (9.8 ver sus 3.0; P< 0.001). While most follicles ovulated progressively 2-7 da ys later, about 40% persisted beyond this period. The study demonstrat ed the presence of discrete patterns of antral follicle growth and reg ression during the breeding and non-breeding seasons, with the luteal cycle characterized by a variable number (1-3) of dominant follicle wa ves. Anoestrus represents a period of dynamic changes in follicular tu rnover.