The flehmen or lip-curl behavior displayed by most ungulate species is a sexually dimorphic behavior seen most frequently when males investigate the genital region of females or freshly voided urine from females. Functionally, flehmen appears to be related to the transport of nonvolatile chemosensory materials from the oral cavity to the vomeronasal organ (VNO). Three experiments were designed to further study the role of flehmen in sexual investigation and mating. In Experiment 1, involving two-choice presentation of urine samples to male goats, flehmen occurred much more frequently to urine from diestrous than estrous females. This indicated that prior to flehmen a diagnosis of estrus versus nonestrus condition had already been made, and that flehmen and the VNO are used to confirm or refine information received by regular olfaction. During mating tests conducted in Experiment 2, it was found that most flehmen responses were made after mounting or ejaculatory responses, suggesting that VNO stimulation, like regular olfactory stimulation, may function during copulatory activity to maintain sexual interest. In Experiment 3 it was found that olfactory bulbectomy virtually eliminated flehmen revealing that stimulation of the main olfactory system is responsible for evoking flehmen. Blocking the access of materials in the oral cavity to the VNO, by occluding the nasopalatine duct, did not reduce flehmen.
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