With increasing incidence in anthelmintic drench resistance, it is appropriate that more sustainable approaches to controlling nematode infections in livestock should be investigated. It is believed that larval contamination of pasture originates from the mature breeding ewe during the periparturient breakdown of immunity. Donaldson et al. (1998) reported that increasing the metabolisable protein (MP) supply of the ewe in late pregnancy may moderate the periparturient relaxation of immunity. The most pronounced results to date are those involving the supplementation of diets with fishmeal, believed to be related to the ‘protected’ protein content of the ration. Fishmeal increases both MP and polyunsaturated fatty acid content of the diet but as yet it is unclear which of these components of the diet may affect immunity to parasites. This study investigated the role of MP supply in maintaining immunity to parasitic infection in pedigree Friesland dairy ewes.