Parasitism is the most expensive disease in the sheep industry if one considers the cost of deworming and the decreased performance that is caused by parasites. Due to variation in climatic conditions, location and sheep density, no single recommendation can be made that will be effective across the country. However, there are a few things to keep in mind when developing an internal parasite control program.
Roundworms attach to the intestinal surface and suck blood or serum from the animal.
The most serious of these parasites is Haemonchus contortus. These worms will drain enough blood that the sheep will become anemic, very unthrifty and may die from blood loss. Other parasites in this group are Ostertagia, Nematodirus and lungworms. Haemonchus is the most efficient at developing resistance to dewormers. Generally if the deworming program can control Haemochus the other roundworm will be controlled as well.