U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska
Date of this Version
1965
Abstract
The widespread existence of biological clocks among animals is documented by a considerable body of evidence. Recently Farner (13) has reviewed this subject covering information on a large variety of animals. In this paper an attempt will be made to restrict most of the discussion to sheep. Experimental data from other species, however, will be cited when it can be usefully related to an understanding of the mechanisms controlling seasonal breeding activity in this species. As far as present knowledge is concerned, the factors regulating or at least monitoring annual physiologic cycles appear to depend greatly upon the influence of changes in environment and experimental evidence supports the idea that the amount of daily light to which the animals are exposed is responsible for the initiation of the breeding season (Sykes and Cole, 23; Hafez, 16; Hart, 18; Yeates, 29).
Comments
Published in Proceedings: Conference on Estrous Cycle Control in Domestic Animals, July 9-10, 1964. Published by the Cooperative State Research Service and Agricultural Research Service, U. S. Department of Agriculture, in Cooperation with University of Nebraska. Miscellaneous Publication 1005 (1965).