The development of protective immunity against gastrointestinal nematode and lungworm infections after use of an ivermectin bolus in first-year grazing calves

Abstract

Interactions between treatment with an ivermectin bolus at turnout and immunity to bovine parasitic gastroenteritis and bronchitis were examined. Immunity related parameters, i.e. development of clinical disease, parasite development and stimulation of parasite specific antibodies were examined for two grazing seasons and compared with untreated second season cattle (immune control) and untreated parasite naive cattle (nonimmune control). With resppect to gastrointestinal nematodes, clinical condition, body weight development, faecal egg counts and pepsinogen concentrations of the bolus treated animals were not significantly different from the respective values of untreated immune cattle, showing a considerable degree of resistance in both groups compared to the parasite naive cattle. With respect to lungworms, untreated immune cattle were protected against clinical disease, but two of eight animals shed larvae again. Bolus treated animals transiently showed mild clinical symptoms and six of seven animals shed low numbers of larvae again, whereas all parasite naive cattle shed himbers of lungworm larvae and showed signs of disease during the whole grazing season. In spite of the effective treatment with an ivermectin bolus during the first year a considerable resistance to gastrointestinal nematode and lungworm infection was present in the second grazing season.