VARIATIONS OF EQUINE URINARY VOLATILE COMPOUNDS DURING THE ESTROUS-CYCLE

Equine urine was analysed by capillary gas chromatography. The volatil e profiles from oestrous and dioestrous samples were compared to estab lish any qualitative or quantitative difference that may have potentia l value in olfactory communication. Forty-five different volatile comp ounds were detected. Of these, 17 major compounds were common to all c hromatograms. The chemical profile of oestrous urine was distinguished by the presence of a unique peak that was not present in dioestrous s amples. Numerous constituents exhibited endocrine dependence: while th e concentrations of seix peaks increased at oestrus, the concentration s of another five peaks decreased at the same time. Since oestrous uri ne, but not dioestrous urine, has been shown to elicit sexual behaviou r in the stallion, the unique peak, together with the peaks that were present in increased concentrations at oestrus, may represent importan t chemical signals that stallions use to detect urinary 'oestrous odou rs'. Statistical analyses also indicated that the relative ratios (nor malized peak areas) of many peaks changed significantly across the oes trous cycle: the ratios increased in nine peaks, decreased in six peak s, and remained constant in two peaks at oestrus.