Author
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Stellflug, John |
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Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/2/2003 Publication Date: 9/2/2003 Citation: Stellflug, J.N. Use of naloxone challenge to predict sexual performance of young rams. Journal of Animal Science. 2003. v. 81. p. 2111-2117. Interpretive Summary: The willingness to breed ewes is highly variable among rams and can have a major impact on sheep production, especially in a single sire mating scheme. Serving capacity tests are the primary method used to identify rams as sexually active, sexually inactive, or low sexual performers. Labor and time requirements often make serving capacity tests impractical. Therefore, a hormone based blood test to predict sexual activity was developed using the response of luteinizing hormone and testosterone to naloxone. This test effectively identified sexually active and inactive mature rams during the breeding season. However, the naloxone challenge test could not discriminate between sexually active and inactive rams at 8 mo of age during the breeding season and was accurate in predicting 69% sexually active and 29% sexually inactive 17 month old rams in August just before the fall breeding season. Further research is required to fully determine the age of ram and time of year related to breeding season when this sire identification test for libido has significant accuracy. Technical Abstract: The possibility of developing a hormone-based test to predict libido was evaluated using response of LH and testosterone to naloxone. This test had effectively identified sexually active and inactive mature rams in the middle of the breeding season. The objective of this study was to determine whether the blood test could be used to detect differences in sexual performance of postpubertal (29 ± 0.1 wk) rams during the breeding season in November and again at approximately 70 wk of age before the breeding season in August. Rams were classed as sexually active and inactive using serving capacity tests after the naloxone challenges. Naloxone (0.75 mg/kg BW) was injected i.v. into 38 white-faced crossbred, 16 Polypay and 49 Targhee rams. Blood samples were collected at 15-min intervals for 1 h before and 2 h after naloxone to measure LH and testosterone. Separate mixed model analyses for repeated measures were used to analyze data for the same rams at 29 and 70 wk of age. Proc Logistics was used to model probabilities that rams were correctly predicted sexually active. The breed-type x sexual activity x time interaction for LH was significant after naloxone (P < 0.05) in 29-wk-old rams. At 70 wk of age, the breed-type x time interaction was significant (P < 0.001) for LH response to naloxone but LH did not differ by sexual activity. At 29 wk of age, the breed-type x time interaction for testosterone response after naloxone was significant (P < 0.001). At 70 wk of age, the sexual activity x time interaction was significant (p < 0.05) for testosterone after naloxone. Sexually active and inactive rams were not predicted accurately at 29 wk of age and were predicted 69 and 29% of the time for sexually active and inactive, respectively, at 70 wk of age. In conclusion, the naloxone challenge test can be influenced by breed-type at 29 and 70 wk of age, but the test cannot discriminate between sexually active and inactive 29-wk-old rams during the breeding season or at 70 wk of age immediately before the breeding season. |
