Environmental Temperature and Fertility of Southdown Rams Early in the Breeding Season

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Abstract
There was no significant difference in volume of semen produced by purebred Southdown rams kept in an air-conditioned room at 45–48° F. during the summer months when compared with rams kept at uncontrolled environmental conditions. From August 20 to September 24 the average motility rating for weekly collections was 70.3% motile cells for treated rams (air conditioned room) and 41.8% for control rams. For the same period, semen from treated rams contained 6.4% morphologically abnormal cells and the control rams 36.9%. Both of these differences were highly significant. The treated rams also had a significantly higher sperm cell concentration (3.4 vs. 2.4 million cells per mm3); their average rectal temperature and pulse rate also was significantly lower. Fifty ova were recovered from 30 ewes which were slaughtered after being bred early in the breeding season with semen from the control rams, and 26.0% of the ova were cleaved. Of 53 ova recovered from 30 ewes bred by the treated rams 64.2% were cleaved. Lambing percentages of similar groups of ewes not slaughtered were 13.3% and 50.0% for the control and treated rams, respectively. The differences between the ram groups in percent of ova fertilized and in percent of ewes lambing were both highly significant. Estimated embryonic death loss was higher (not significant) in ewes bred to control rams. Embryonic death rate was calculated to be 69.2% and 41.2% for ewes bred to control and treated rams, respectively. Estimated percentage of embryonic death loss in ewes bred to individual rams ranged from 14.3 to 100, with an over-all estimated embryonic loss of 48.0%. These results indicate that summer temperatures are partly responsible for poor conception rate of ewes bred to Southdown rams early in the breeding season. They also point out the possibility of improving conception rate early in the breeding season by keeping rams at lower environmental temperatures during the summer months.

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