THE INFLUENCE OF FOETAL GENOTYPE ON EQUINE GONADOTROPHIN SECRETION

Abstract
SUMMARY: The serum concentration of gonadotrophin during several stages of pregnancy was determined in seven mares bred to a stallion and in four mares bred to a jack. To eliminate individual differences, two mares were bred successively to a stallion and to a jack. When the mare is carrying a mule foetus the hormone concentration is approximately one-tenth that associated with a horse foetus. One mare carrying a mule foetus was killed on the 69th day of pregnancy. Though the endometrial cups appeared normal histologically, the endometrial cup secretion was scanty and low in potency. The amount of hormone in the cups themselves was also low. The genotype of the foetus, we conclude, influences the secretory activity of the endometrial cups.

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