Pituitary response to GnRH and ovariectomy in Booroola-Awassi and Awassi ewe lambs

Summary. Booroola-Awassi ewe lambs were heterozygous (F +) for a major gene F, influencing their ovulation rate, while Awassi lambs were non-carriers (++). Basal plasma FSH concentration (mean \m=+-\s.e.m.) in Booroola\p=n-\Awassiewe lambs at 4 weeks of age was significantly higher than in Awassi lambs of the same age (5\m=.\06\m=+-\0\m=.\60and 2\m=.\04\m=+-\0\m=.\32ng/ml respectively; P < 0\m=.\001).After GnRH administration, FSH increased from 3\m=.\89\m=+-\1\m=.\10to 10\m=.\58\m=+-\1\m=.\30ng/ml in Booroola\p=n-\Awassi(N = 6) and from 1\m=.\87\m=+-\0\m=.\29to 4\m=.\64\m=+-\0\m=.\33ng/ml in Awassi (N = 6) ewe lambs (P < 0\m=.\05).Ovari-ectomy caused an increase in plasma FSH in Booroola\p=n-\Awassi(N = 4) and Awassi (N = 4) ewe lambs. At 1 week after ovariectomy plasma FSH increased from 5\m=.\96\m=+-\1\m=.\02to 7\m=.\06\m=+-\1\m=.\05ng/ml in F+ and from 1\m=.\67\m=+-\1\m=.\06to 5\m=.\21\m=+-\0\m=.\66ng/ml in ++ ewe lambs, suggesting a stronger negative feed-back effect exerted by the ovaries of Awassi lambs. At 15 weeks after ovariectomy FSH values were similar in Booroola\x=req-\ Awassi (18\m=.\28\m=+-\1\m=.\96ng/ml) and Awassi (16\m=.\07\m=+-\0\m=.\70ng/ml) lambs. Although the overall pattern of pituitary response to ovariectomy was similar in the F + and ++ ewe lambs, Booroola\p=n-\Awassilambs had small ovaries (132\m=.\5\m=+-\24\m=.\9mg) and follicula