OVARIAN RESPONSE TO GONADOTROPIN TREATMENT INITIATED RELATIVE TO WAVEEMERGENCE IN ULTRASONOGRAPHICALLY MONITORED EWES

Follicular recruitment and luteal response to superovulatory treatment initiated relative to the status of the first wave of the ovine estro us cycle (Wave 1) were studied. All ewes (n=25) received an intravagin al progestagen sponge to synchronize estrous cycles, and ewes were mon itored daily by transrectal ultrasonography. Multiple-dose FSH treatme nt (total dose=100 mg NIH-FSH-PI) was initiated on the day of ovulatio n (Day 0 group) in 16 ewes. In the remaining 9 ewes, FSH treatment was started 3 d after emergence of the largest follicle of Wave 1 (Day 3 group). Ewes received PGF(2 alpha) with the last 2 FSH treatments to i nduce luteolysis. Daily blood samples were taken to determine progeste rone profiles and to evaluate the luteal response subsequent to supero vulation. The ovulation rate was determined by ultrasonography and cor related with direct observation of the ovaries during laparotomy 5 to 6 d after superovulatory estrus when the uterus was flushed to collect embryos. Results confirmed that follicular recruitment was suppressed by the presence of a large, growing follicle. In the Day 0 and Day 3 groups, respectively, mean numbers (+/-SEM) of large follicles (greate r than or equal to 4 mm) recruited were 6.4 +/- 0.6 and 2.7 +/- 0.7 (P <0.01) at 48 h after the onset of treatment, and 6.7 +/- 0.5 and 5.1 /- 0.6 (P=0.08) at 72 h after the onset of treatment. Ovulation rates were 5.6 +/- 0.8 and 3.3 +/- 0.8 in the respective groups (P<0.05). Th e number of transferable embryos was 1.8 +/- 0.5 and 0.3 +/- 0.2 in th e respective groups (P<0.05). Short luteal phases (less than or equal to 3 d) associated with low serum progesterone (maximum of less than o r equal to 1.4 ng/ml) were detected after superovulation in 1/16 and 6 /9 ewes in the Day 0 and Day 3 groups, respectively (P<0.001). In conc lusion, gonadotropin treatment initiated at the time of emergence of W ave 1 induced a superovulatory response in ewes. Response was influenc ed by the status of the follicular wave. The presence of a large growi ng follicle at time of superstimulatory treatment was associated with lower follicle recruitment, fewer ovulations, fewer transferable embry os, and the development of functionally subnormal corpora lutea (CL). The results demonstrate that follicle dominance is operative during th e early luteal phase of the ovine estrous cycle. (C) 1997 by Elsevier Science Inc.