Behavior and endocrine changes in high-performing, low-performing, and male-oriented domestic rams following exposure to rams and ewes in estrus whencopulation is precluded

High-performing, low-performing, and male-oriented rams were used to invest igate behavior and neuroendocrine correlates of sexual interest and discrim ination. Treatment consisted of visual and olfactory contact with stimulus animals through a woven wire fence, which inhibited copulation (either ewes in estrus or other rams), for 4 h on each of three consecutive days. Befor e exposure to stimulus animals on d 1 and during the final 1 h of exposure on d 2, blood samples were collected every 15 min for Ih to determine conce ntrations of LH and testosterone. During exposure to stimulus animals, rams were continuously observed and investigatory behaviors were recorded. Ther e was no day effect for ally behavior. Groups of rams differed (P < .05) in amounts of behaviors exhibited, but behaviors were not influenced by sex o f stimulus animals. High-performing rams exhibited more (P < .05) investiga tory behaviors toward stimulus animals than low-performing or male-oriented rams. Plasma concentrations of LH increased (P < .05) in high-performing r ams following exposure to estrous ewes, but not following exposure to rams. In low-performing and male-orientated rams, concentrations of LH were unch anged regardless of sex of the stimulus animal. Change in plasma concentrat ions of testosterone from pre- to posttreatment did not differ between high -performing, low-performing, and male-oriented rams. However, low-performin g rams exhibited an increase (P < .05) in plasma concentrations of testoste rone following exposure to rams. In conclusion, high-performing rams exhibi t a high degree of investigatory behaviors toward estrous ewes and other ra ms. High-performing rams seem to discriminate sex of stimulus animals and e xhibit a neuroendocrine response (i.e., increased plasma LH) only when expo sed to ewes in estrus. The sensory signals provided by estrous females are either not detected by low-performing or male-oriented rams or are not suff iciently provocative to elicit further investigation by these rams.