Exploiting Nutrition-Parasite Interaction for Sustainable Control of Gastrointestinal Nematodosis in Sheep

Abstract

Parasites are a major constraint on animal productivity throughout the world.  Gastrointestinal nematodes are ubiquitous parasites of grazing ruminants and cause decreases in survival, live-weight gain, wool and milk production and reproduction performance.  These losses can be particularly severe in developing countries where control measures are less readily available. This overview focuses on  the interaction between nutritional status and  gastrointestinal nematode infection in ruminants  and considers: (i) the influence of the parasite on  host metabolism; and (ii) the effect of host  nutrition on the establishment and survival of  parasite populations, the development of the host immune  response and the pathophysiology of  infection (Petkevičius, 2007). Gastrointestinal nematodes reduce voluntary feed intake and efficiency of feed utilisation, a key feature being an increased endogenous loss of protein into the gastrointestinal tract. Overall, there is movement of protein from productive processes into repair of the gastrointestinal tract, synthesis of plasma proteins and mucoprotein production. Although reduction in feed intake is a major factor contributing to the reduced performance of parasitized ruminants, the underlying mechanisms of the anorexia are poorly understood (Coop and Kyriazakis, 1999). Supplementation of the diet with additional protein does not appear to affect initial establishment of nematode infections but the pathophysiological consequences are generally more severe on lower planes of protein nutrition. The main effect of protein supplementation is to increase the rate of acquisition of immunity and increase resistance to reinfection and this has been associated with an enhanced cellular immune response in the gastrointestinal mucosa. The unresponsiveness of the young lamb can be improved by dietary protein supplementation. Recent trials have  shown that growing sheep offered a free choice  between a low and a high protein ration  (Swarnkar and Singh, 2005) or non-protein  nitrogen supplementation through urea molasses  mineral blocks (Roy, 2007), are able to modify  their diet selection in order to alleviate the  increase in protein requirements which result  from gastrointestinal nematode infection.  Implications of these findings are discussed for the formulation of strategy for sustainable control of parasitic gastroenteritis in small ruminants using nutritional management technology as alternative control option.