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Estrous-marker and sexual-pheromone volatiles from bovine body fluids
We evaluated various body fluids with a bull behavioral assay (BBA) in the absence of a female. It specified 15 behaviors involving attraction to the body fluids, detection of the stimulus, and subsequent sexual preparation behaviors. These behaviors were stereotyped and occurred in a specific sequence. Positive responses could be produced by serum taken at estrus and by vulval skin gland secretions (VSGS). VSGS may be a specialized site for the production or concentration of the pheromone. Light microscopy demonstrated that the onset of estrus is characterized by histomorphic changes in vulval sweat glands. Also, the ovarian follicle might be a source of estrous-marker and sexual-pheromone volatiles. In culture granulosa cells only the culture media from pre-ovulatory follicle and the FSH-treated cells elicited the three sets of stereotyped sexual behaviors. In the BBA, licking was an important effect of pheromonal stimulation. To test the importance of direct contact by licking or touching the sample, we exposed unrestrained bulls to female estrous serum that was presented in either a flat dish or a deep bowl in which direct contact was not possible. Cues from the non-volatile portion of the liquid sample were necessary for the complete expression of male sexual behavior. However, the volatile cues alone enabled the bulls to recognize sexual-pheromone from cows in pro-estrus. We developed a headspace gas chromatographic analysis procedure for monitoring metabolic profiles during the estrous cycle. Comparison of the most volatile fraction of blood from estrous and non-estrous samples revealed a chromatographic profile that correlated with pro-estrous. One peak of the characteristic profile appeared the day [plus or minus]1 before a rise in estrogen, and its peak abundance increased until the day of estrus [plus or minus]1, then dropped to low or no value. The blood-volatile profile agreed with profile of pre-ovulatory follicular fluid. The ratio of volatiles from vulval skin gland secretion changed just before the day of estrus. Such profiles have the potential to predict and diagnose pro-estrus.