Gonadotrophin-releasing hormone and the control of ovulation rate by the FecB gene in Booroola ewes

Abstract

Booroola sheep carry a FecB gene that confers high fecundity. The aims of the present studies were to determine in homozygous carriers (BB) and non-carriers (++) of the Booroola FecB gene whether there are FecB differences in the secretory characteristics of GnRH in hypophyseal-portal blood of ovariectomized ewes (Expt 1) and whether differences in ovulation rate would occur following the administration of PMSG and pulsatile GnRH to ovary-intact Booroola ewes with hypothalamic-pituitary disconnection (HPD) (Expt 2). In Expt 1, no FecB gene-specific differences were noted for GnRH with respect to pulse frequency, pulse amplitude or overall secretion rate. Irrespective of genotype there were 1.9 +/- 0.2 GnRH pulses h-1 (n = 20 ewes; 10 BB and 10 ++ animals) and 1.9 +/- 0.1 pulses of immunoreactive (i) LH h-1. In Expt 2, ovulation was induced in the HPD ovary-intact animals on three occasions (e.g. 56, 393 and 423 days after HPD surgery) using a PMSG (200 or 400 iu)-GnRH pulse (250 ng i.v. for 96 h)-GnRH bolus (10 micrograms i.v.) regimen after pretreating the animals with GnRH pulses (250 ng i.v. for 14 days). On all occasions the ovulation rates were significantly higher (P < 0.05) in BB ewes (n = 6 or 7) than in ++ animals (n = 7). No differences between the genotypes were noted with respect to the mean concentrations of progesterone in plasma notwithstanding the differences in ovulation rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a 6-Day Treatment with Medroxyprogesterone Acetate after Prostaglandin F2α-Induced Luteolysis at Midcycle on Antral Follicular Development and Ovulation Rate in Nonprolific Western White-Faced Ewes1

“…Earlier studies failed to produce convincing evidence that differences in circulating concentrations of gonadotropic hormones were solely responsible for differences in ovulation rate in ewes [34]. It has been suggested that the high ovulation rate in prolific sheep is due to intraovarian rather than pituitary factors [34][35][36]. We propose that the difference in the pattern of follicle development and ovulation rate between breeds of sheep differing in prolificacy may be partly due to a difference in circulating concentrations of progesterone.…”

The activin receptor-like kinase 6 Booroola mutation enhances suppressive effects of bone morphogenetic protein 2 (BMP2), BMP4, BMP6 and growth and differentiation factor-9 on FSH release from ovine primary pituitary cell cultures

“…The plasma concentrations of FSH were found to be consistently higher in the homozygous Booroola ewes compared with the wild-type (WT) ewes throughout the oestrous cycle, anoestrus and after ovariectomy. They were also found to be higher in ovariectomised or ovary-intact ewes treated with gonadotrophin-releasing hormone (GnRH) following hypothalamic-pituitary disconnection (HPD; McNatty et al 1987McNatty et al , 1989McNatty et al , 1991aMcNatty et al , 1993. When HPD or Deslorelin-treated (GnRH agonist) homozygous ALK6 (BB) and WTewes were administered identical doses of FSH, the ovulation rate and plasma concentrations of FSH in those animals which ovulated was the same in both genotypes (Hudson et al 1999).…”

Plasma FSH, LH and immunoreactive inhibin concentrations in FecBB/FecBB and FecB+/FecB+ Booroola ewes and rams from birth to 12 months of age

“…In ram lambs, the effects of the FecBB gene on plasma hormone concentrations are equivocal (Seek el al, 1988;Montgomery et al, 1989;Purvis el al, 1991) and, to our (Bindon, 1984;McNatty et al, 1991aMcNatty et al, , 1992Montgomery el al, 1992 (McNatty et al, 1987a(McNatty et al, , 1989(McNatty et al, , 1993a. In rams, most studies have found no effect of the FecBB gene on plasma FSH and LH concentrations that are independent of sire effects (Bindon et al, 1985(Bindon et al, , 1989Montgomery et al, 1989;Hochereau-de Reviers and Seek, 1991;Price et al, 1991a, b, c;Isaacs et al, 1992 (1982).…”