Long-term effects of social stress on antiviral immunity in pigs

Mixing of unfamiliar pigs is common practice in intensive pig husbandry. Si nce pigs maintain a dominance hierarchy, mixing often leads to vigorous fig hting. Apart from the negative impact that fighting has on welfare, there i s evidence that the social stress associated with fighting suppresses immun e function. In the present experiment, we investigated the impact of mixing on specific long-term immune responses and protection against challenge in fection after vaccination with pseudorabies virus (PRV). Specific pathogen- free (SPF) pigs were mixed pairwise with an unfamiliar same-gender conspeci fic or left undisturbed with a same-gender littermate at 3 days after vacci nation with PRV. Half of the pigs were females (gilts) and half were castra ted males (barrows). Mixing increased agonistic behavior to the same degree in gilts and barrows. Cortisol concentrations in saliva and catecholamine excretion in urine were increased in mixed pigs, and these effects were ind ependent of dominance status and gender. Subsequently, the effects of mixin g, gender, dominance status and interactions between these factors on immun e response parameters were studied. The main result was that mixed barrows showed suppressed immune responses after vaccination and increased clinical symptoms after challenge infection compared to control barrows. Mixed gilt s however did not differ from control gilts. It also appeared that mixed do minants were more seriously affected than mixed subordinates were. We concl ude that, in some pigs, social stress after mixing suppresses the immune re sponse to a viral vaccine and consequently impairs protection against chall enge infection. (C) 2001 Elsevier Science Inc. All rights reserved.