IMPLICATIONS OF NUTRITION FOR THE ABILITY OF RUMINANTS TO WITHSTAND GASTROINTESTINAL NEMATODE INFECTIONS

Resistance and resilience of the ruminant host to gastrointestinal (GI ) parasitic nematode infections are influenced by many factors, includ ing nutrition. This review examines the effects of host nutrition on t he ability of ruminants to withstand GI nematode infections. Firstly t he effects of infection an host metabolism are summarised briefly. An important factor in the pathogenesis is a reduction in feed intake by the host. Gut nematodes also increase endogenous protein losses, which result in net loss of amino acids to the parasitised host, though ene rgy and mineral metabolism are also perturbed. The indications are tha t the major nutritional change is in protein metabolism. Resilience(th e ability of an animal to withstand the effects of infection) can be e nhanced markedly by increasing metabolisable protein supply and to a l esser extent metabolisable energy supply. Resistance to GI nematodes ( ability of host to prevent establishment and/or development of infecti on) is also influenced by diet, particularly metabolisable protein sup ply. While there do not appear to be any effects of host nutrition on establishment of infective larvae, the rate of rejection of adult warm s can be enhanced by improved nutrition. The exact nutritional require ments or the mechanisms involved are not known. It appears that the ef fects of improving nutritional status on host resilience are more dear ly defined than effects on host resistance. The implication of changes in host resistance with nutritional state for host productivity need to be better described. Understanding the role of nutrition in improvi ng both resistance and resilience of the host to GI parasites will be important if producers are to make better use of host acquired immunit y and reduce dependence on pesticides far prophylaxis. Copyright (C) 1 996 Australian Society for Parasitology. Published by Elsevier Science Ltd.