Pituitary gonadotrophins in Booroola and control Merino sheep

Abstract

Pituitary content of FSH and LH [luteinizing hormone], using radioreceptor assay methods, was determined in control and Booroola Merino ewes on the 3rd day of the estrous cycle and in adult rams slaughtered in winter. Significantly more pituitary FSH (as per gland or per g wet wt) was found in the Booroola than in the control ewe. No significant differences were found in LH content although the difference in FSH/LH ratio between Booroola and control ewes was significant (P < 0.001). Pituitary FSH content was similar in the rams of the 2 genotypes. A good correspondence between FSH values by the radioreceptor assay and by radioimmunoassays using anti-ovine and anti-human serum was observed for the Booroola ewes. Radioimmunological estimates of FSH activity were significantly higher than radioreceptor estimates in control ewes and in Booroola and control rams in which the pituitary FSH values were 5-6% of that of the ewe. This overestimation is attributed to differences in specificity between methods. Fractionation of pituitary extracts by electrofocusing indicated a similar pI [isoelectric point] profile of FSH for ewes and rams of both genotypes. Evidently, quantitative rather than qualitative differences in pituitary FSH occur in Booroola and control Merino ewes. Increased FSH levels apparently contribute to the hormonal basis for the increased ovulation rate of the Booroola Merino.