The breakdown of acquired immunity during the periparturient period in the ewe can be reduced by metabolizable protein (MP) supplementation (Houdijk et al 2001). Recent evidence suggests that the development of immune response results in reduced food intake (anorexia) in many disease models (Materase et al, 2005). However, it is not known whether an immune response following the periparturient relaxation of immunity is associated with a reduction in food intake and whether this is affected by protein supplementation in parasitized ewes. In addition, differences in nutrient partitioning between sheep breeds that differ in production potential may affect the ability of the hosts to express immunity and this may be reflected by differences in their magnitude and/or duration of anorexia. The aim of the present study was to test the hypotheses that: a) nematode infection during the periparturient period results in anorexia and protein supplementation can effect the degree of anorexia in ewes, and b) ewes of a high production potential breed show higher breakdown of acquired immunity than ewes of a low production potential breed, and exhibit higher degree of anorexia.