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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #127189
Title: USE OF NALOXONE CHALLENGE TO PREDICT SEXUAL PERFORMANCE OF RAMS BEFORE THE FALL BREEDING SEASON

Author
item Stellflug, John

Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2002
Publication Date: 6/6/2002
Citation: Stellflug, J.N. Use of naloxone challenge to predict sexual performance of rams before the fall breeding season. Theriogenology. 2002. v. 58. p. 123-134.

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 rams during the breeding season. However, just before the breeding season in late July and August, the naloxone challenge test could not discriminate between sexually active and inactive rams. Further research is required to fully determine the different times of year when this sire identification test for libido has significant accuracy.

Technical Abstract: Serving capacity tests (SCT) identify rams as sexually active (SA), sexually inactive (SIA), or low sexual performers. Labor and time requirements often make SCT impractical. Therefore, a hormone based test for libido was developed using the response of LH and testosterone (T) to naloxone. This test effectively identified SA and SIA rams during the breeding season. Data reported herein evaluate the effectiveness of this method at a different time of the year. Objectives were 1) to determine if the blood test can detect differences in libido during late July and August, and 2) to elucidate more fully the time course of response of LH and T to naloxone. Naloxone (0.75 mg/kg BW) was used to test rams of several breeds (n = 34; Expt. 1) with known sexual performance and Suffolk white face rams with unknown performance (n = 72; Expt. 2) in July and August. Rams were classed as SA and SIA directly using SCT. Mixed model analyses for repeated measures with repeated factors (month and sample time) and a covariant for mean LH or T before naloxone were used for LH and T data. Proc Logistics modeled probabilities that rams were sexually active. The LH response to naloxone increased but did not differ (P > 0.09) by ram class (SA or SIA) or month. The T response peaked 75 to 90 min after naloxone and was still elevated at 120 min. Testosterone differed (P < 0.03) for ram class by month by time in Expt. 1 and differed (P < 0.01) between months in Expt. 2. Proc Logistics, incorrectly indicated that SA and SIA rams were all sexually active. This study indicates that the naloxone challenge test cannot discriminate between SA and SIA rams during July and August. Further research is required to fully determine the time of year when this identification test for libido has significant accuracy.