Effects of dosage of FSH, vehicle and time of treatment on ovulation rate and prolificacy in ewes during the anestrous season

The effects of dosage of follicle stimulating hormone (FSH), vehicle and time of injection on ovulation rate and prolificacy were evaluated during the anestrous season. Ewes on four farms (n=445) were treated with a CIDR-G® device for 5 days and exposed to rams upon removal of the insert (CRRI, day 0). A 3×2×2 factorial arrangement tested effects of dosage of FSH (Folltropin®; 0, 42 or 68 mg NIH-FSH-P1), vehicle (saline:propylene glycol 1:4, v/v [PGL], or 50% polyvinylpyrrolidone K 29-32 [PVP]) and time of injection (12 or 36 h before CRRI). Follicular growth was monitored by ultrasonography in four ewes per treatment at injection of FSH, at CRRI, and on days 1-3 post-CRRI. All ewes were examined by ultrasonography on days 10-14 for ovulation rate, and on days 26-31 and 46-51 for pregnancy and number of embryos. The largest follicle (F1) increased in diameter (mm) between FSH injection (5.3+/-0.1) and day 1 (6.1+/-0.1; P<0.01). The F1 was larger at CRRI (P≤0.05) in ewes receiving 42 than 0 mg FSH, and 68 than 42 mg FSH. The F2 increased in diameter (P<0.05) from FSH injection (4.7+/-0.2) to CRRI (5.2+/-0.2) and to day 1 (5.8+/-0.2), but was not affected by treatment. Number of small follicles (≤4 mm) did not differ with time or treatment. Number of medium follicles (5 mm) declined (P<0.05) between FSH (1.5+/-0.2) and days 1 (0.8+/-0.2), 2 (0.9+/-0.2), and 3 (0.5+/-0.2). Number of large follicles (≥6 mm) increased from FSH (0.6+/-0.3) to CRRI (1.4+/-0.3; P<0.05), and day 1 (2.3+/-0.3; P<0.05), then declined by day 3 (0.6+/-0.3; P<0.05). There were more large follicles at CRRI (P<0.05) with 68 mg (2.1+/-0.3) or 42 mg (1.6+/-0.2) than 0 mg (0.5+/-0.4) FSH. Ovulation rate (mean 2.12+/-0.05) increased with FSH given 12 h, but not 36 h before CRRI (dosage × time, P<0.05). Estrous response, conception rate, percentage of ewes lambing or prolificacy did not differ. However, number of corpora lutea not represented by embryos increased with dosage of FSH (P<0.01; 0.25+/-0.14, 0.55+/-0.09, 0.71+/-0.09 for ewes treated with 0, 42, and 68 mg FSH, respectively).