Agonistic behavior, plasma stress hormones, and metabolites in response to dyadic encounters in domestic pigs: Interrelationships and effect of dominance status

Abstract

Agonistic behavior, neuroendocrine, and plasma metabolite changes were studied in 16 domestic Large White pigs (100 ± 5 kg) submitted to dyadic encounters (30 min) in a neutral environment. The animals had been housed individually for 2 months prior to the experiment. Aggressive and submissive behaviors were recorded for each animal during the encounter. Surgically implanted catheters allowed collection of blood samples at selected times. Plasma levels of cortisol, catecholamines, and metabolites were determined and compared with data obtained on eight control pigs kept under resting conditions. Resting plasma cortisol levels tended to be higher in subordinate compared to dominant subjects, suggesting a relationship between baseline adrenocortical activity and submissive behavior during aggressive encounters in domestic pigs. Plasma norepinephrine and epinephrine levels did not differ between dominants and subordinates, but they were linearly correlated with aggressive behaviors. Metabolic state changed in reponse to the encounters, as evidenced by increased plasma levels of free fatty acids, glucose, and lactate at the end of the dyads. Dominance status did not significantly affect plasma metabolite levels. Plasma lactate and glucose levels were linearly correlated with both aggressive behaviors and plasma catecholamines. The present results provide evidence suggesting that stimulation of the sympathetic nervous system and physical activity are both involved in the control of the mobilization of body energy sources in response to aggressive encounters in domestic pigs.