Direct comparison of host resistance status and Barbervax vaccination to control parasitism in sheep subjected to a mixed parasite field challenge

Integrated parasite management strategies including paddock rotations, pasture management, vaccination and parasite resistance genetics, may be used to control sheep parasitism whilst minimising anthelmintic treatment. However, the efficacy of host parasite resistance traits and/or vaccination to reduce reliance on anthelmintics to control haemonchosis from a mixed parasite field trial remains unknown. Animals from three flocks with different genetic backgrounds received a standard Barbervax vaccination schedule (5 vaccinations) and were grazed as a single mob, ensuring each cohort received the same parasite exposure during the field trial. Lambs received rescue treatments if their haemoglobin concentration was less than 85 g/dL and/or had worm egg count above 15,000 eggs/g. After three vaccinations, lambs from all lines produced significant H-gal-GP antibody titres which, for parasite-susceptible and parasite-unselected lines provided protection against haemonchosis (reduced anaemia and low Haemonchus contortus egg counts) compared to unvaccinated lambs. Barbervax also reduced the need to rescue treat lambs in the parasite-unselected and parasite-susceptible flocks by 73 % and 93 %, respectively, compared to unvaccinated lambs from the same lines. After three Barbervax vaccinations lambs from a parasite-unselected flock were protected from haemonchosis but not from scouring caused by Trichostrongylus spp., whereas parasite-resistant line lambs were protected from haemonchosis and scouring, did not require rescue drenching and did not substantially benefit from Barbervax vaccination.