This thesis investigated the use of low-complexity, corn- and soybean meal-based diets in the nursery and as-sessed the effects of deoxynivalenol (DON) contamination and the effects of supplementation with immunomodulatory feed additives, such as a commercial anti-mycotoxin feed additive or fish oil on pig growth performance, gastrointestinal tract morphology, and immune system robustness. In the first week after weaning, both low and high DON-contaminated low-complexity diets resulted in reduced average daily gain and feed intake compared to pigs fed a high-complexity diet. When DON contamination was above 3 ppm throughout the nursery period, feed intake was reduced, resulting in lower body weight gain. Pigs fed low-complexity diets without DON contamination had growth performance not different from pigs fed the high-complexity diet and pigs fed low-complexity diets with no or low DON contamination reached the same bodyweight by the end of the nursery period as pigs fed high-complexity diets. The immunomodulatory feed additive re-stored humoral immunity when pigs were fed low-complexity diets, regardless of DON contamination and improved certain immune parameters during an acute phase challenge when feeding high DON-contaminated diets. Therefore, it is possible to feed low-complexity diets to nursery pigs without impairing growth performance so long as DON-contamination is below 1.5 ppm, and the immunomodulatory feed additive may improve immune status.