Evaluation of three Pakistani sheep breeds for their natural resistance to artificial infection of Haemonchus contortus.

This study was carried out to evaluate three Pakistani sheep breeds (Kachhi, Lohi and Thalli) for their natural resistance against artificial infection of Haemonchus contortus. Lambs were weaned at 3 months of age, housed in separate pens and treated with Avermectin to eliminate gastrointestinal nematode infection. Each lamb was infected orally with approximately 10,000 third stage larvae of H. contortus. Selected breeds were compared on the basis of parasitological, haematological, biochemical and histopathological parameters over a period of 9 weeks. Faecal egg counts were measured weekly while packed cell volume, total serum protein, serum albumin and live weight were determined fortnightly. At 9th-week post-infection, 10 animals of each breed were randomly selected and slaughtered for worm, eosinophil and mast cell counts from the abomasum of each animal. Faecal egg counts and worm burden were significantly lower (P < 0.05) in Lohi sheep than Kachhi and Thalli breeds. Furthermore, the Lohi breed also exhibited the highest levels of packed cell volume, total serum protein, albumin as well as eosinophils and mast cell counts. Breed × week interaction also remained significant (P < 0.05) in most of the parameters for Lohi breed. The results suggested that Lohi breed expressed a significant innate resistance to artificial infection of H. contortus.