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The Effect of Low Environmental Temperature on Initiation of the Breeding Season and Fertility in Sheep¹

Kentucky Agricultural Experiment Station, University of Kentucky

Abstract

Two groups of 20 ewes and three rams each were used to study the effect of low environmental temperature during the summer season on the time of onset of the breeding season and level of fertility. One group was placed in an air-conditioned room with natural light conditions and where the temperature was kept at 45° to 48° F. on May 26, and the other group was placed in a control room of similar size. Both groups remained in their respective rooms until October 8. Availability of feed was the same for both groups. Average date of first estrus was nearly eight weeks earlier for the treated ewes than for the control ewes (July 10 vs. September 2). Regular recurrence of estrus for the ewes which came into estrus early but did not conceive indicates that normal sexual activity had been initiated in ewes kept in the air-conditioned room. Fertility of the ewes in which estrus was initiated early was apparently normal as shown by the breeding data. Treated ewes bred to treated rams required 1.9 services per conception, compared to 2.0 services per conception required to settle control ewes.

Semen from treated rams did not show the marked decrease in motility of cells or increase in percent of abnormal cells which was found for the control rams. Treated rams bred to treated ewes required an average of 1.9 services per conception, while control rams required 5.3 services per conception. The average date of lambing for treated ewes bred to the two groups of rams was December 10 and February 15, respectively.

Rectal body temperature of control ewes averaged 1.4° F. above those of treated ewes on days when the outside temperature was 88° F. or higher. The respiration rate (breaths per minute) averaged 150 for control ewes and 28 for ewes in the air-conditioned room. No difference in the pulse rate (heart beats per minute) between the two groups of ewes was found under conditions of the experiment.

¹ The investigation reported in this paper is in connection with a project of the Kentucky Agricultural Experiment Station and is published by permission of the Director.

² Animal Husbandry Department, South Dakota State College, Brookings.

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