Testosterone and luteinizing hormone responses to naloxone help predict sexual performance in rams.

The first objective of this study was to determine whether LH and testosterone respond differently to a naloxone injection in relation to varying sexual performance in rams. If differences occurred, the second objective was to determine whether differences would predict variation in sexual performance. From a group of 1.5- to 3-yr-old rams, 20 sexually active and 39 sexually inactive rams were selected based on previously observed sexual behavior with estrual ewes. Each ram was exposed to three estrual ewes for 18 30-min sexual performance tests, and those found to be inactive were given two 30-min sexual partner preference tests. The final distribution was 28 sexually active, 22 inactive, and nine male-oriented rams. Rams were treated with 1.5 mg of naloxone/kg BW in December of Year 1 and again with either 0.75 or 1.5 mg of naloxone/kg BW in November of Year 2. Plasma concentrations of LH and testosterone were evaluated with mixed model analyses for repeated measures separately for each year to coincide with logistic procedures for modeling the probability that rams were sexually active. For Year 1, a sexual activity x age x time interaction for LH after naloxone was observed (P < 0.03). For testosterone, there was a sexual activity x time interaction (P < 0.03), with a similar, early increase for sexually active female-and male-oriented rams compared with a delayed, minimal increase for inactive rams. For Year 2, when all rams were over 2.5 yr of age, a sexual activity x time interaction for both LH and testosterone (P < 0.02) seemed more related to an earlier increase of both hormones for sexually active rams than the increase observed for inactive rams. In addition, sexually active rams had a greater increase in testosterone than inactive rams. No significant difference was observed between 0.75 and 1.50 mg of naloxone/kg BW. Testosterone and LH were used as explanatory variables and sexual activity was used as the response variable in logistic procedures. In Year 1, greatest prediction accuracy was 73.5% using testosterone at 60 min after naloxone injection. In Year 2, the greatest prediction accuracy was 85% using LH at 15 min multiplied by testosterone at 60 min after naloxone. Test repeatability for both years on the same rams was 76%. In conclusion, pattern and magnitude of naloxone-induced changes in endocrine function may facilitate identification of sexually active and inactive rams during the breeding season. Prediction accuracy of the naloxone-based test was 69 to 85%.

Influence of simulated photoperiod alteration and induced estrus on reproductive performance of spring-born Columbia and Targhee ewe lambs.

The objective of this study was to test the hypothesis that a combination of induced estrus (IE) and melatonin (MEL) would increase reproductive performance in breeds characterized by late maturity more than either IE or MEL alone. Spring-born Columbia (C; n = 161; 188 to 222 d range of age at breeding; 49 to 80 kg range of BW at breeding) and Targhee (T; n = 166; 183 to 210 d range of age at breeding; 40 to 68 kg range of BW at breeding) ewe lambs were stratified randomly by breed to treatments: ambient controls (AC); IE; MEL; and MEL+IE. Melatonin (18 mg of Regulin) was implanted on September 7. Estrus induction included medroxyprogesterone acetate (MAP) pessaries inserted for 12 d and pregnant mare's serum gonadotropin (PMSG; 500 IU i.m.) at time of MAP removal. Ewe lambs were placed into two pens with five rams per pen by breed. Targhee ewes lambed at an increased rate with IE vs no IE (84.5 vs 67.9%; P < .01) and tended to lamb at an increased rate with MEL vs no MEL (82.5 vs 70.6%; P = .07). The 92.7% lambing rate observed in the Targhee ewe lambs for the combined treatment (MEL+IE) was slightly higher than an additive effect but the interaction between IE and MEL was not significant (P = .24). By contrast, none of the treatments altered (P = .5) lambing rate, number of lambs born, or number born alive for Columbia ewe lambs.(ABSTRACT TRUNCATED AT 250 WORDS)