Effects of season, GnRH administration and lupin supplementation on the ovarian and endocrine responses of merino ewes treated with PMSG and FSH-P to induce superovulation.

Administration of gonadotrophin releasing hormone (GnRH) 24 h after sponge withdrawal did not affect the numbers of corpora lutea (CL) or persistent large follicles (LF) in ewes superovulated with 400 I.U. pregnant mare serum gonadotrophin and 12 mg follicle stimulating hormone in spring (11.6 +/- 0.9 v. 13.0 +/- 0.9 CL and 0.8 +/- 0.9 v. 0.9 +/- 0.3 LF, for +GnRH and -GnRH ewes, respectively). However, it did increase the ovulatory response of ewes superovulated in autumn (15.8 +/- 1.2 v. 11.8 +/- 1.1 CL). The incidence of ewes with prematurely regressed CL was also greater in autumn than in spring (21/89 v. 5/88). Supplementary feeding with lupin grain in autumn had no effect on numbers of CL but did increase the incidence of ewes with LF (18/48 v. 7/46) and caused a marked reduction in the incidence of ewes with regressed CL (1/44 v. 20/45). For ewes treated in autumn, there were no effects of lupin supplementation or GnRH administration on peak oestradiol-17 beta (E2) or peak luteinizing hormone (LH) levels. However, when peak E2 concentrations in the plasma were adjusted for numbers of preovulatory follicles, higher concentrations were observed for ewes in the +lupin/-GnRH group (12.4 +/- 2.9 pg mL-1) than in other treatment groups (range 4.3 +/- 0.4 to 5.7 +/- 0.3 pg mL-1). Moreover, the time of the LH peak was advanced by both lupin supplementation and GnRH treatment.(ABSTRACT TRUNCATED AT 250 WORDS)