SHIPPING STRESS AND SOCIAL-STATUS EFFECTS ON PIG PERFORMANCE, PLASMA-CORTISOL, NATURAL-KILLER-CELL ACTIVITY, AND LEUKOCYTE NUMBERS

Crossbred pigs were used to evaluate the effects of shipping stress on natural killer (NK) cell activity, leukocyte numbers, plasma cortisol, and BW changes. In the first study, pigs were bled at a commercial farm and, after shipping, resident and shipped pigs were bled again. Plasma cortisol concentrations were not different (P > .10) because of large variation in cortisol concentrations. Furthermore, NK cytotoxicity was nondetectable among all pigs. A second study showed that plasma cortisol concentration rose by approximately 2.6 ng/mL (P = .018) for each minute after pigs were aroused. In the third, more controlled study, pigs were housed in pens of three pigs each. Video recordings were made during the first 24 h pigs were grouped to identify socially dominant, intermediate, and submissive pigs. At time zero (before shipping), resident pigs and those to be shipped had similar plasma cortisol concentrations. However, after the 4-h shipping experience, shipped pigs had elevated (P < .05) plasma cortisol compared with resident control pigs. Shipped pigs lost 5.1% of their BW (P < .05) compared with resident pigs, which gained .02% of their BW. Body weight change during shipping and plasma cortisol were negatively correlated (r = -.34, P = .04), indicating pigs that had greater adrenal response to shipping also lost more weight during shipping. Shipping reduced (P < .05) NK cytotoxicity among pigs of intermediate and submissive social status compared with shipped, dominant pigs. At the end of shipping or control treatments, the correlation between NK cytotoxicity and plasma cortisol was positive (r = .35, P = .036), indicating that pigs with greater cortisol response had greater NK cytotoxicity. In both shipping studies, numbers of blood neutrophils increased (P < .01), lymphocytes decreased (P < .01), and neutrophil: lymphocyte ratio increased (P < .01) after shipping. These data suggest that 1) social status and shipping stress interact in NK cytotoxicity response, 2) shipping has defined effects on numbers of circulating leukocytes, 3) controlling or measuring social status and handling procedures allow interpretation of certain shipping stress data, and 4) socially intermediate and submissive pigs are probably more likely to succumb to viral infections after shipping than are socially dominant pigs because their immune systems are suppressed.