Effect of mating stimuli on LH release in bulls

Fourteen crossbred beef bulls were assigned at random to receive one of four sexual stimuli treatments. Treatments consisted of: (1) controls (four bulls), no visual or physical contact with any cows; (2) false mount (two bulls), allowed to mount an estrual cow; (3) mated (four bulls), allowed to mount an estrual cow with intromission and ejaculation; (4) electroejaculated (four bulls), no exposure to cows. Serum from blood samples taken at 15-min intervals from -15 min to 2 hr from sexual stimuli were radioimmunoassayed for luteinizing hormone (LH). Four bulls had elevated levels at the pretreatment bleeding, but none of the stimuli induced or were associated with LH releases. Basal levels of LH were consistent within bulls but varied considerably among bulls. Conclusion is that stimuli associated with mating do not cause a release of LH.