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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #124927

Title: HERITABILITY AND REPEATABILITY OF SEXUAL PERFORMANCE

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

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2001
Publication Date: 3/1/2001
Citation: Snowder, G.D., Stellflug, J.N., Van Vleck, L.D. 2001. Heritability and repeatability of sexual performance. Proc. Western Section, American Society of Animal Science 52:118-120.

Interpretive Summary: Differences in sexual behavior among rams has been recognized for many years. Consequently, various procedures to measure sexual behaviour in rams were developed. Positive associations between rams with high scores for sexual performance and ewe fertility have been reported. It was suggested that differences among rams for sexual performance may be genetically influenced. Although some research results have suggested sexual performance of rams is influenced by genetic effects, there have been no reliable estimates of heritability. Therefore, the objective of this study was to determine if sexual behavior as measured with a performance test has a genetic basis. Testing of rams for sexual performance has occurred at the U.s. Sheep Experiment Station for over 10 years. This study investigated a very large data set on over 3,500 rams. It was found that the heritability estimate for sexual performance score is moderate. This suggests that selection can be used to improve sexual performance. It was also found that the test for sexual performance of rams at the U.S. Sheep Experiment Station is a reliable test based on the large repeatability of sexual performance scores.. The test can identify rams with high sexual performance at an early age (14 months). Selection indices for overall merit will need to consider including sexual performance scores. Rams with highly desirable production traits and high sexual performance will leave more offspring for future generations.

Technical Abstract: Sexual performance has been subjectively measured in a libido test for screening 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 estrus ewes. Overall average sexual performance score was 3.5 +/ 0.02. Records from four breeds (Columbia, 807; Polypay, 1,668; Rambouillet, 1,208; and Targhee, 1,002) were combined into a multiple breed analyses because breeds had similar phenotypic variances. Total numbers of records were 4,685 and included a second sexual performance test on 1,212 rams in the subsequent year. Variance component estimation was accomplished using REML analyses. Fixed effects were breed of ram, genetic selection line within breed, year by breed code, and season born by breed code. A permanent environmental effect for ram was included to account for repeated measures. Age and weight of the rams at time of the libido test were considered as linear covariates and were breed specific. The additive genetic variance was estimated as 0.54. The variance due to repeated measures was 1.19; and the residual variance was estimated as 0.67. The heritability estimate was moderate (0.22 +/ 0.04). The repeatability of the score was high (0.72). The residual variance accounted for only 28% of the total phenotypic variance. These results imply that the sexual performance test is reliably measured and also that response to selection for ram serving capacity will be favorable.