Influence of weaning age, restraint stress, and cortisol addition in vitro on immune function in swine

This research attempted to examine the influence of restraint stress in confinement housing in gilts and age of weaning on cellular immune function in the pig. Peripheral blood mononuclear cell (PBMC) blastogenic response to mitogen, neutrophil elastase degranulation, and neutrophil phagocytic ability were examined as indicators of cell mediated immunity. Traditional measures of stress including total and percent free cortisol, total leukocyte number, and leukocyte differential counts were used as another measure of stress. In vitro examinations were made to establish a culture system using cortisol concentrations that were suppressive and those that were not for PBMC blastogenic response to mitogens. Using this system the effects of vitamin C were tested to determine if coincubation of PBMC with cortisol, at suppressive levels, and vitamin C would decrease the suppressive effects seen in blastogenic response to mitogens.

The results indicated that restraint stress causes suppression of PBMC blastogenic response for at least 14 d indicating that the animal is still experiencing stress. The other measures of stress, i. e. total and percent free cortisol only indicated a stress response for 4 d. Weaning before 5 wk of age causes a suppression of PBMC blastogenic response to mitogens. However, weaning age did not appear to affect neutrophil function. Based on these results it would appear that several measures of physiological response to stressors need to be used if the effects of stress are to be reported.

Cortisol addition in vitro can cause suppression of PBMC blastogenic response at various concentrations. Vitamin C did not appear to have any stimulatory effects on PBMC response to mitogens regardless of the presence or concentration of cortisol. Cortisol can be added at various concentrations to PBMC cultures and not suppress blastogenic response to mitogens.