The effects of immune system activation and diet complexity on average daily gain. Dietary treatments include feeding a complex starter diet, a medium complexity diet, and a low complexity diet. Immune activation includes control pigs fed ad libitum, LPS injected pigs fed ad libitum, and control pigs pair-fed to that of the LPS challenged pigs. Main effects of diet complexity and immune system activation are significant (P < 0.01). There was no immune system by diet complexity interactions (Adapted from Dritz et al., 1996 ).