Plasma FSH and LH in Prepubertal Booroola Ewe Lambs

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Abstract
Basal plasma concentrations (four 30-min samples) and GnRH-induced release of gonadotrophins were measured every 15 days between 30 and 90 days and at 110 days of age in Merino ewe lambs from the prolific Booroo1a ('B') flock (n = 18-23), the medium prolificacy ('T') flock (n = 14-20), and the '0' flock (n = 4-8) of low prolificacy. At ages of 30 and 45 days B ewe lambs had mean basal plasma FSH concentrations of 145 and 122 ng/ml which were significantly higher (P < 0·01) than those seen in T (45 and 53 ng/ml), and 0 (39 and 38 ng/ml) flock ewes. Between 60 and 110 days of age there were no significant differences between genotypes. The increment in FSH concentrations above basal levels induced by the subcutaneous injection of 100 ,.g synthetic GnRH was only significantly (P < 0·05) greater in B than T and 0 genotype ewe lambs at llO days of age but not at other ages. The basal plasma FSH differences between the B, T and 0 genotypes at 30 and 45 days of age were not consistently related to the size of litter in which lambs were born.