Body reserves can be regarded as sources of nutrients at times of scarce nutrient intake. It has been suggested that the latter is responsible for the periparturient breakdown in immunity to parasites (BIP), since most scarce nutrients are expected to be allocated to the prioritised reproductive effort (Coop and Kyriazakis, 1999). Nutrient supply from body reserves may partly overcome scarce nutrient intake and, as a consequence, can be expected to affect BIP. It has been shown that an increased supply of dietary metabolizable protein (MP), but not of metabolizable energy (ME), reduces periparturient BIP (Donaldson et al., 1998). Therefore, we tested the hypotheses that body protein reserves, but not body fat reserves, affect BIP and its relationship with dietary MP supply in periparturient ewes.