SUPEROVULATORY RESPONSE OF CHIOS AND FRIESIAN EWES TO 2 FSH-P DOSE LEVELS

Superovulatory response of Chios and Friesian ewes to follicle stimula ting hormone (FSH-P) was studied in this experiment. Thirty-four Chios and 23 Friesian ewes were superovulated during the breeding season wi th two FSH-P regimens (12 mg and 16 mg, in six decreasing doses, at 12 h intervals). Oestrus cycles were synchronized using medroxyprogester one acetate (MAP) impregnated intravaginal sponges for 14 days; FSH-P injections were begun 60 h before sponge withdrawal. Six days after th e onset of oestrus, midventral laparotomy was performed and the ova we re flushed from the uterine horns, identified and evaluated for fertil ization 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 corp ora lutea, p < 0.001 and 4.3 +/- 0.8 vs. 2.4 +/- 0.4 ova, p < 0.05) br eeds. 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 lu tea, p < 0.001 and 8.7 +/- 1.0 vs. 4.3 +/- 0.8 ova, p < 0.01). Althoug h 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 embr yos, respectively), this difference was not significant because of the lower fertilization rate observed in Chios than in Friesian ewes afte r 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 recip ient ewes immediately after collection resulted in the birth of 18 (51 .4%) lambs.