Superovulation and embryo recovery in ewes treated with gonadotrophin-releasing hormone agonist and purified follicle-stimulating hormone.

Chronic treatment with gonadotrophin-releasing hormone (GnRH) agonist eliminates luteinizing hormone (LH) pulses and inhibits maturation of Graafian follicles in sheep. Since the presence of 'dominant' follicles may inhibit superovulatory responses, an experiment was conducted to determine whether a GnRH agonist could be used in conjunction with follicle-stimulating hormone (FSH) to induce a superovulatory response with production of normal embryos. Twenty-four Welsh Mountain ewes were chronically treated with GnRH agonist by means of a subcutaneous minipump. Twelve of the ewes were given 12 mg progesterone intramuscularly (i.m.) twice daily for four days; all ewes were then given 672 micrograms (total) of highly purified FSH continually infused intravenously for either 72 h (Group A) or 96 h (Group B) in a 2 x 2 experimental design (n = 6). Ovulation was then induced with 750 I.U. human chorionic gonadotrophin injected i.m. (Day 0) and all ewes were inseminated into the uterus with > 100 x 10(6) fresh sperm on Day 0. Embryos were flushed from the uterus, and ovaries were inspected at laparotomy on Day 5. Pretreatment with progesterone did not affect any of the parameters measured and data were pooled accordingly. There were no differences between Groups A and B in the number of ovulations or the number of embryos recovered, although there were more large unruptured follicles in Group A animals (8.8 +/- 0.8 v. 3.1 +/- 0.7, P < 0.001). The embryo recovery rate was higher in Group A ewes (52.5 v. 26.4, P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)