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Pituitary Activity of Sheep in Relation to the Breeding Season

University of Illinois¹

Abstract

RECENTLY considerable interest has been shown in the possibility of increasing the prolificacy of sheep. A variety of means has been employed experimentally to cause sheep to breed out of season. Cole and Miller (1933) were the first to demonstrate that anestrus ewes may be caused to conceive by appropriate hormone treatments. These and subsequent investigators have found this technique somewhat inefficient since, in spite of a high proportion of ewes ovulating, the resulting lamb crop is low. Hart (1950) subjected ewes to a regularly maintained rhythm of light and dark and was able to cause "out of season" breeding. Yeates (1949) found that in Suffolks the breeding season started some ten to 14 weeks after the longest day, and similar results were obtained by Hafez (1951). The seasonal breeding behavior of sheep can also be modified by genetic means (Hafez, 1951), and the possibility of prolonging the breeding season by genetic selection is now being investigated in this and other laboratories.

¹ Department of Animal Science.