There is some evidence that surgically castrated piglets may be more prone to disease than gilts or entire male pigs (EFSA, 2004). Tielen (1974) reported that the prevalence of pneumonia is higher in castrates than in gilts, which was confirmed by an investigation of 18,000 pigs at a Dutch abattoir (de Kruijf and Welling, 1988).
The influence of castration on the immune system was demonstrated in a study by Lessard et al. (2002). They observed lower antibody responses in piglets castrated at 10 or 17 days of age and challenged twice with an antigen. Immunosuppressive effects of castration could be related to the stress reaction, inducing cortisol and catecholamine release, or to the lack of testicular androgens since these hormones are known to promote immunocompetence (the ability of the body to produce a normal immune response) (De Kruijf and Welling, 1988; da Silva, 1999).