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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #124309
Title: HERITABILITY AND REPEATABILITY OF SEXUAL PERFORMANCE SCORES OF RAMS

Author
item Snowder, Gary
item Stellflug, John
item Van Vleck, Lloyd

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 2/6/2000
Publication Date: 3/1/2001
Citation: Snowder, G.D., Stellflug, J.N., Van Vleck, L.d. 2001. Heritability and repeatability of sexual performance scores of rams. Western Section Proceedings Journal of Animal Science 79(Suppl. 2):112.

Interpretive Summary: Mating behavior of rams can be an economically important character especially if rams do not successfully mate the ewes they are exposed to at breeding. Differences in sexual behavior among rams as measured in behavior studies have been long known. However, the influence of genetic effects on sexual behavior in rams has never been described. The objective of this study was to determine if ram sexual behavior when exposed to ewes was genetically influence. The study considered sexual behavior scores on 4,685 rams of four different breeds. There were small but significant breed differences for sexual behavior. The Polypay breed had the highest average libido score. The other breeds, Columbia, Rambouillet, and Targhee, did not differ in libido scores. The most important finding was that ram behavior at mating is genetically influenced. The estimated heritability of the libido score was .22 which suggests that rams can be successfully selected for improved sexual behavior. To the American sheep industry this implies that rams with high scores for sexual performance can be bred to more ewes.

Technical Abstract: Sexual performance has been subjectively measured with a libido test during screening of rams prior to public sale and breeding at the U.S. Sheep Experiment Station from 1990 to 2000. The objective of this study was to determine if sexual performance was genetically influenced. Sexual performance scores ranged from 1 to 6 with scores increasing from sexually inactive to highly sexually active in the presence of estrous ewes. The overall average score was 3.5 +/ 0.02. Records from four breeds (Columbia, n = 807; Polypay, n = 1,668; Rambouillet, n = 1,208; and Targhee, n = 1,002) were combined into one analysis because breeds had similar phenotypic variances. Total number of records was 4,685 which included a second sexual performance test on 1,212 rams in the following year. Estimation of variance component was accomplished using a REML algorithm. Fixed effects were breed of ram, selection line within breed, year by breed, and season born by breed. A permanent environmental effect for ram was included to account for the repeated measure. Age and weight of the rams at time of the libido test were linear covariates and were breed specific. The additive genetic variance was estimated as 0.54. The estimate of variance due to ram permanent environmental effects was 1.19. The residual variance was estimated to be 0.67. The heritability estimate was moderate (0.22 +/ 0.04) and repeatability was high (0.72). These results imply that one test provides a reliable measure of sexual performance and that favorable response to selection for ram serving capacity would be expected.