The phytohaemagglutinin (PHA) skin test as an indicator of stress-induced changes in immune reactivity in pigs

The present study describes two experiments to standardize the phytohaemagglutinin (PHA) skin test as an indicator of lymphocyte reactivity in pigs after exposure to stressful situations in practical pig husbandry. The first experiment was a dose-response experiment. No time dose interaction was found, so the pattern of the reaction was the same for all doses used, although the magnitude of the reaction differed. The second experiment was carried out to determine stress-induced changes in lymphocyte reactivity. One half of a group of 48 pigs was exposed to stress (mixing, moving, and an increased stocking density). The immune reactivity to intradermally injected PHA of stressed animals differed significantly (P < 0.01) from that of unstressed controls. The reaction of stressed animals can be characterized by a delayed reaction with a lower peak. It can be concluded that frequent measurements are preferable to single measurements when the effects of stress on immunological processes are studied.