Environmental Factors in the Induction of Estrus in Sheep

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Abstract
Four experiments involving 158 ewes were conducted. With the exception of 10 Southdown and 5 Hampshire ewes, the sheep were western ewes of mixed Rambouillet, Hampshire and Suffolk breeding. The reduction of day length to 10 hours during the nonbreeding season from approximately March 15 to July 15 was effective in the induction of estrus. None of 28 ewes in a normal environment came in heat in comparison with 27 of 39 receiving 10 hours of light. However, only 13 of 27 ewes which came in heat during the 10-hr. light treatment produced lambs. It may be concluded that a reduction in day length during anestrum is highly effective in the induction of estrus, but that fertility as measured by actual lambing is low. The reduction of day length during the early part of the normal breeding season from approximately July 15 to September 17 appeared to hasten the onset of estrus, but satisfactory fertility was not obtained. Of 30 western ewes maintained in a normal environment, 17 came in heat prior to September 17. Thirty-three of 40 ewes subjected to a reduced lighting regime came in estrus, but only 5 of these conceived on the first induced period. Thus, there was little advantage in terms of early lamb production. The role of the ram and the incidence of early embryonic mortality were not investigated. The administration of progesterone in conjunction with a reduction in day length did not hasten the onset of estrus or improve fertility. Copyright © . .