J. Anim Sci.
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J. Anim Sci. 1970. 30:214-218.
© 1970 American Society of Animal Science
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Effects of Season and Progesterone Synchronization on Ovulation Rate in Mature Western Range Ewes1

W. C. Dermody2, Warren C. Foote and C. V. Hulet3

Utah State University and U. S. Department of Agriculture

Abstract

Environmental factors associated with season of year have been shown to influence many reproductive processes including the occurrence of both estrus and ovulation.

McKenzie and Terrill (1937) found the breeding season in Hampshire and grade ewes to begin in late August and early September and end in late December or January. The ovulation rate for mature Hampshire ewes increased from 1.50 at the beginning of the breeding season to 1.76 during the period from September 16 to November 15. Ovulation rate then declined to 1.21 for the period from January 16 to February 15. Radford (1959) in Australia measured ovulation rate at 10- to 12-week intervals in Merino ewes kept at constant body weight and found the highest ovulation rate in late autumn (May to June) and the lowest in the spring (October to December).

Information does not appear to be available on changes in ovulation rate during the breeding season when measured at estrous cycle length intervals.

Footnotes

1 From Utah State University and the U. S. Sheep Experiment Station, Sheep and Fur Animal Research Branch, Animal Husbandry Research Division, A.R.S. Dubois, Idaho. Published with the approval of the Director of the Utah Agricultural Experiment Station, Logan, as Research Paper No. 588.

2 Postdoctoral Fellow, Poultry Science Department, Cornell University, Ithaca, New York.

3 U. S. Sheep Experiment Station, A.R.S., Dubois, Idaho.






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