The breakdown of immunity to parasites during the periparturient period plays an important role in parasite epidemiology and it is believed that it has a nutritional basis. A lactating rat model has been used to address this issue, as their nutritional status can be easily manipulated through altering greatly supply and demand and they exhibit a breakdown of immunity to the gastrointestinal nematode, Nippostrongylus brasiliensis. Previous experiments have shown that an increasing protein supply and reducing protein demand improves resistance (Houdijk et al., 2005; Normanton et al., 2005). However, in these studies, an increase in protein contents was associated with an increase in feed intake per se. Therefore, effects of protein supply could be confounded with effects of any nutrient or energy intake. The objective of the current experiment was to test the effect of increased protein supply or reduced protein demand on the resistance to parasites in lactating rats whilst energy intake was kept constant.