Superovulatory response of chios and Friesian ewes to two FSH-P dose levels

Superovulatory response of Chios and Friesian ewes to follicle stimulating hormone (FSH-P) was studied in this experiment. Thirty-four Chios and 23 Friesian ewes were superovulated during the breeding season with two FSH-P regimens (12 mg and 16 mg, in six decreasing doses, at 12 h intervals). Oestrus cycles were synchronized using medroxyprogesterone acetate (MAP) impregnated intravaginal sponges for 14 days; FSH-P injections were begun 60 h before sponge withdrawal. Six days after the onset of oestrus, midventral laparotomy was performed and the ova were flushed from the uterine horns, identified and evaluated for fertilization and degeneration according to morphological criteria. Animals treated with 16 mg FSH-P had a higher ovulation rate and yielded more ova per ewe than those treated with 12 mg FSH-P in both Chios (12.4 +/- 0.9 vs. 5.5 +/- 0.7 corpora lutea, p < 0.001 and 8.7 +/- 1.0 vs. 4.4 +/- 0.7 ova, p < 0.01) and Friesian (7.0 +/- 0.6 vs. 3.6 +/- 0.4 corpora lutea, p < 0.001 and 4.3 +/- 0.8 vs. 2.4 +/- 0.4 ova, p < 0.05) breeds. Chios ewes had a higher ovulation rate and yielded more ova per ewe than Friesian ewes after the injection of either 12(5.5 +/- 0.7 vs. 3.6 +/- 0.4 corpora lutea, p < 0.05 and 4.4 +/- 0.7 vs. 2.4 +/- 0.4 ova, p < 0.05) or 16 mg FSH-P (12.4 +/- 0.9 vs. 7.0 +/- 0.6 corpora lutea, p < 0.001 and 8.7 +/- 1.0 vs. 4.3 +/- 0.8 ova, p < 0.01). Although freezable embryo yield was higher in Chios than in Friesian ewes (1.9 +/- 0.6 and 4.1 +/- 0.8 embryos vs. 1.5 +/- 0.5 and 3.2 +/- 0.7 embryos, respectively), this difference was not significant because of the lower fertilization rate observed in Chios than in Friesian ewes after the injection of either 12 mg(65.4 +/- 10.3% vs. 95.6 +/- 3.0%, p < 0.01) or 16 mg FSH-P (67.8 +/- 9.3% vs. 90.8 +/- 4.1%, p < 0.05). The transfer of 35 embryos (20 freezable and 15 non-freezable) to 15 recipient ewes immediately after collection resulted in the birth of 18 (51.4%) lambs.