Author
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Stellflug, John |
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Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings Publication Acceptance Date: 3/6/2002 Publication Date: 6/5/2002 Citation: Stellflug, J.N. Use of naloxone challenge to predict sexual performance of rams at eight and seventeen months of age. Proceedings of the Western Section of the American Society of Animal Science. 2002. v. 53. p. 99-103. 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 for libido 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 and was accurate in predicting 69% sexually active and 29% sexually inactive 17 month old rams in November. 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 usual method of evaluating male mating behavior is a series of serving capacity tests (SCT). Labor and time requirements make SCT expensive and impractical. Therefore, a hormone based test for libido was developed using response of LH and testosterone (T) to naloxone. This test effectively identified sexually active (SA) and sexually inactive (SIA)mature rams during November and December. Objectives of this study were to determine if the blood test can detect differences in sexual performance in post-pubertal (8 mo-old) ram lambs and at 17 mo of age during late August before fall breeding season. Rams were classed as SA and SIA using SCT. Naloxone (0.75 mg/kg BW) was injected iv to rams of several breeds (n = 38 white face crossbred, 16 Polypay and 49 Targhee). Blood samples were collected at 15 min intervals for 1 h before and 2 h after naloxone. LH and T were measured by RIA. Mixed model analyses for repeated measures with repeated factor (sample time) were used for LH and T data. Main plot included ram class, breed and class by breed. Subplot included terms for sample time and two- and three-way interactions. Main plot terms were tested by rams nested within breed and class. Residual was used to test the subplot. Proc Logistics modeled probabilities that rams were SA. LH response to naloxone differed by breed (P < 0.01) but did not differ (P> 0.67) by ram class for ram lambs. At 17 mo of age, LH response to naloxone differed by breed (P < 0.01), and for breed by time interaction (P < 0.01),but not by ram class (P > 0.31). The T response after naloxone differed (P < 0.01) by breed for ram lambs and at 17 mo of age, and differed (P < 0.01) for breed by time interaction for ram lambs. With Proc Logistics, SA and SIA rams were not predicted accurately as ram lambs and were predicted 69% and 29% of the time, respectively, at 17 mo of age in late August. This study indicates that the naloxone test cannot discriminate between SA and SIA ram lambs in November or at 17 mo of age during late August. |
