Abstract

Patterns of secretion of FSH, LH and prolactin were investigated in the luteal and follicular phases of the cycle prior to mating in Cheviot ewes on high and low intakes (approximately 3.0 and 0.8 kg DM per head per day) during the weeks before mating. Ewes on the high intake had a higher mean ovulation rate (1.95 vs 1.40; P < 0.01) and higher mean potential litter size (1.75 vs 1.00; P < 0.001) as determined at slaughter 3 weeks after mating. No significant differences associated with intake were observed in the endocrine profiles during the luteal phase of the cycle before mating, indicating that differences in reproductive performance were not mediated by changes in endocrine profiles in this period. However, during periods of the subsequent follicular phase, ewes on a high intake had a higher LH pulse frequency, higher mean prolactin levels and non-significantly higher FSH levels. The preovulatory peaks of these hormones were not altered by the level of intake but the mean peak values for prolactin and LH were significantly higher in ewes with multiple ovulations than in those with single ovulations. Differences in endocrine status prior to mating were not associated with differences in luteal function after mating, as measured by circulating progesterone levels. However, mean progesterone levels were higher in ewes on a low intake after mating compared with those on a high intake.

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