In this study, differences between castrated and intact male piglets in the immediate immune response to early-weaning stress were determined. Testosterone and 17-estradiol were both higher in intact males than in castrates, while cortisol was not different between gonadal groups. CBC results showed a tendency for castrates to have a greater increase in neutrophil:lymphocyte ratio over 24 hours, indicating greater inflammation. Thymuses tended to be longer in intact males than in castrates. Basal testosterone levels in intact males were strongly associated with increased total mast cell numbers in the small intestinal tissues. Basal testosterone was associated with increased 0-hour neutrophil numbers in intact males and 24-hour 17-estradiol was associated with decreased 24-hour neutrophil numbers in the villus crypts of the small intestine tissues. This study has revealed gonadal effects on the immediate immune response to early-weaning stress, but the hormonal relationships revealed need to be confirmed by hormone blockade and/or replacement studies.
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