Vaccination of young Dorset lambs against haemonchosis.

Six Dorset Horn lambs were each vaccinated at age 7 weeks and 9 weeks with 50 micrograms of glycosylated integral membrane proteins, particularly enriched in the protein H11 from the intestinal brush border of adult Haemonchus. At 11 weeks of age the lambs were infected with 10,000 infective third stage Haemonchus larvae. Compared with the average for the control group the vaccinated group of lambs had a 78% reduction in parasite egg output over the patent period, with four of the six better than 93% protected. At autopsy 35 days post-infection the mean total worm burden of the vaccinated lambs was 83% reduced compared with the controls. The serum antibody titres to H11 correlated with the degree of protection.