Lactating mammals usually exhibit a breakdown of immunity to parasites, i.e. they have larger worm burdens than their non-lactating counterparts. Here, we tested the hypothesis that a secondary infection with Nippostrongylus brasiliensis in lactating rats is sensitive to dietary protein content. We also tested whether this infection affects host food intake. Rats either remained uninfected throughout the study or were given a single infection before mating (primary infection) and re-infected on day 2 of lactation (secondary infection) with 1600 infective larvae. Infected rats were fed foods during lactation formulated to supply 100 (low protein; LP), 200 (medium protein; MP) or 300 (high protein; HP) g crude protein per kg DM; non-infected rats were fed either the LP or HP food. Litter size was standardized to ten pups between parturition (day 0) and secondary infection (day 2). Ten days after secondary infection, MP and HP rats had excreted fewer nematode eggs, and had fewer adult nematodes in their small intestine and nematode eggs in their colon than the LP rats. Primary infection increased food intake in late pregnancy, and increased maternal body weight and litter size at parturition. Secondary infection did not affect mean food intake, maternal and litter weight, although food intake was reduced for 1 d following infection. These results support the view that a secondary infection with N. brasiliensis is sensitive to dietary protein content, and that the latter infection does not impair lactational performance. Future studies may focus on elucidating the nutritional sensitivity of immune responses underlying the reduced secondary N. brasiliensis infection.