In India parasitic nematodes are a major constraint on sheep production and worm control programme mainly relies on the use of anthelmintics. The suppressive use of anthelmintics had increased the cost of production and more importantly leads to selection of anthelmintic resistant strains of parasites (Yadav 1990, Yadav et al. 1993, Singh et al. 1995, 1996, Gill 1996). Moreover, increased public awareness for the" presence of chemical residues in livestock products and their impact on environment has stimulated interest in worm control methods which are sustainable, less reliant on chemotherapy, cost-effective and ecofriendly. Exploitation of host genetic resistance and breeding for disease resistance, seems to be a suitable alternative strategy for control of parasitic nematodes (Le Jambre 1978).

The feasibility of breeding for disease resistance within a flock can be successful only when the trait used to assess the resistance to parasitic nematodes is heritable (Gray 1991). In practical terms ante mortem assessment of resistance to nematodes can only be undertaken by measuring the nematode egg output in faeces. Faecal egg count (FEC) is a simple and most widely used trait and proven as effective selection criteria for improving within flock resistance to nematodes (Bisset et