EFFECTS OF FIGHTING AFTER GROUPING ON PLASMA-CORTISOL CONCENTRATION AND LYMPHOCYTE BLASTOGENESIS OF PERIPHERAL-BLOOD MONONUCLEAR-CELLS INDUCED BY MITOGENS IN PIGLETS

One litter (Group A) of three unacquainted groups of littermates (4 pi glets/litter), 64.0 +/- 0.8 days old, was moved to the pen of another litter (Group B) and they were housed together for 19 days after group ing (phase 1). The pigs in Group B violently attacked all the pigs in Group A for 9 hr after grouping. The remaining group was not grouped a nd used as controls. The plasma cortisol concentrations 1 hr after gro uping were significantly higher than those 1 hr before and 24 hr after grouping, and the suppression of lymphocyte blastogenesis of peripher al blood mononuclear cells (PBMC) induced by mitogens was observed on 3, 8 and 19 days after grouping. After phase 1 ended, the pigs in Grou p A were returned to their own pen for 7 days, and then they were regr ouped with the pigs in Group B and reared together for a further 14 da ys. Neither agonistic behavior nor change of plasma cortisol after reg rouping was seen. Though the lymphocyte blastogenesis of PBMC induced by the mitogens on day 9 after regrouping was significantly lower in t he pigs of Groups A and B compared to those in control pigs, a signifi cant difference in lymphocyte blastogenesis among three groups was not seen on 7 and 14 days after regrouping. These findings indicate that fighting after grouping unacquainted litters increases plasma cortisol , and suppresses lymphocyte blastogenesis for 26 days after grouping.