Heritability and repeatability of sexual performance scores of rams

Abstract

Sexual performance has been subjectively measured with a libido test during screening of rams before public sale and breeding at the U.S. Sheep Experiment Station from 1990 to 2000. The objective of this study was to determine whether 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. Variance components were estimated using a REML algorithm. Fixed effects were breed of ram, selection line within breed, and year by breed. A permanent environmental effect for ram was included to account for repeated observations on individual animals. Age and weight of the rams at time of the libido test were linear covariates and were breed-specific. Adjusted means for sexual performance scores did not differ among breeds (P > 0.05). Age was a significant effect (P < 0.01), with sexual performance score increasing 0.05 units for each month of age. 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 screening for sexual performance provides a reliable measure of sexual performance and that favorable response to selection for ram serving capacity may be expected.

Libido and serving capacity of mature hair rams under tropical environmental conditions

“…Consequently, more oestrous ewes could be mated in shorter time, improving the flock fertility when breeding intensity would be required. This was demonstrated with the use of higher performing rams that increased the pregnancy rate, supporting studies by Barwick et al (1989), Perkins and Fitzgerald (1994) and Snowder et al (2002). However, further experiments should be conducted to clarify this breed effect on serving capacity of hair rams.…”

“…It is very important to evaluate the sexual behaviour; therefore, several procedures to measure sexual performance in rams have been developed (Álvarez-Córdoba et al 1999, Ibarra et al 1999, Snowder et al 2002, Stellflug and Berardinelli 2002, Kridli et al 2007, Stellflug et al 2008. However, these procedures are difficult to conduct due to required labour, time and significant number of synchronized females (Katz 2008, Alexander et al 2010.…”

Relationships between physiological and behavioral responses of goat bucks in mating season

“…However, Imwalle and Katz (2004) suggested that additional opportunities are useful to learn important cues from does to improve sexual experience. Similar findings were indicated by other researchers for rams (Snowder et al, 2002;Stellflug and Berardinelli, 2002). Various factors were reported to affect the findings of sexual performance tests such as sexual motivation, experience, separation anxiety, sexual attractiveness of partner, length of testing period, etc.…”

“…In addition, three of the IA young bucks never mounted does. Similar findings reported that 28-40% of yearlings that had no previous sexual experience were sexually inactive during the first test with estrus females (Price et al, 1994;Snowder et al, 2002).…”

“…Various factors were reported to affect the findings of sexual performance tests such as sexual motivation, experience, separation anxiety, sexual attractiveness of partner, length of testing period, etc. (Snowder et al, 2002;Imwalle and Katz, 2004). In the present study, it was observed that some of the IA young bucks displayed separation anxiety when removed from pen mates to the test site.…”