Hormonal and behavioral correlates of emotional states in sexually trained boars.

Physiological and behavioral traits of sexually mature boars were compared between episodes of copulation and sexual frustration in order to determine reliable indicators of the differences in emotional states. Ten boars, approximately 6 mo of age, were trained to mount a stationary artificial sow (ArtSow) and to ejaculate when digital pressure was applied to the extended penis. This method of semen collection is the typical procedure of the industry. All 10 boars used in this study were fully trained to this procedure before the onset of the study. Each boar was subjected to trials in which one of the following two treatments was applied. In the control (CTRL) treatment, boars were treated the same as during their training (i.e., allowed to complete ejaculation). In the frustration (FRUS) treatment, boars were allowed to mount the ArtSow, but because no manual pressure was applied to the extended penis, ejaculation never occurred. Blood was collected via indwelling catheters before onset of the trial, during exposure to the ArtSow, and after returning to their home pen. Concentrations of testosterone, cortisol, and β-endorphin were quantified. Behavior of the boars was recorded during exposure to the ArtSow and for 30 min after return to their home pen. Relative to preexposure levels, serum cortisol increased (P <.05) during CTRL exposure and after exposure to both treatments (CTRL; P <.04 and FRUS; P <.06). Serum testosterone did not change during and after either treatment. Serum concentrations of β-endorphin did not change during or after CTRL trials, but serum β-endorphin was greater (P <.05) during FRUS than during CTRL trials. Behavioral analysis revealed that boars spent less time lying down and more time moving about their home pen (P <.05) after a FRUS than after a CTRL trial. In summary, serum cortisol did not allow us to distinguish between the excitement of copulation and the negative affect associated with sexual frustration, whereas increases in serum β-endorphin and motor activity seemed to be indicators of the negative emotional state of sexual frustration in trained boars.