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Observations on Sexually Inhibited Rams

U. S. Department of Agriculture¹

Abstract

Over an 8-year period 29.6% of 2,175 rams observed were inhibited (failed to mate during several short interval exposures to ewes). Of 23 inhibited rams placed in continuous company with ewes, only 35% began mating within 24 hr. as compared to 100% of a normal group. Seventy percent started breeding within 48 hr. Four rams (17%) were removed at 8 or 9 days for failure to breed. After inhibited rams began mating activity their libido appeared normal.

The average lambing date of 1,378 ewes mated to 90 inhibited rams was 1.4 days later than the average of a comparable group of 1,356 ewes mated to 90 normal rams. Ten inhibited rams were removed from breeding because of failure to breed and three had zero fertility.

The average fertility for the normal and inhibited rams was 93 and 76%, respectively. Failure to breed, delayed breeding and less accurate selection for fertility on the basis of semen quality probably account for most of this difference.

There were no important differences in the quality of electroejaculated semen samples obtained from 97 normal and 43 inhibited rams. However, the semen traits of the normal rams were more highly correlated with fertility than those of the inhibited rams (R=0.65 vs. 0.30).

Significantly fewer mature rams (18.5%) and ram lambs (22.9%) were inhibited than yearling rams (36.2%). Year had a significant effect on the percent of sexually inhibited rams.

¹ From the U. S. Sheep Experiment Station and Western Sheep Breeding Laboratory, Sheep and Fur Animal Research Branch, Animal Husbandry Research Division, ARS, Dubios, Idaho, in cooperation with the University of Idaho. Published with the approval of the Director of the Idaho Agricultural Experiment Station, Moscow, as Research Paper No. 621.

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