Vaccination of calves against Cooperia oncophora with a double-domain activation-associated secreted protein reduces parasite egg output and pasture contamination.

•A double-domain activation-associated secreted protein (ASP) purified from Cooperia oncophora is a potent vaccine antigen.•Vaccination of calves reduces worm egg output and pasture infection levels.•Vaccinated animals had 81% less worms at the end of the grazing season.