Dynamics of Anaplasma marginale in splenectomised calves treated with either imidocarb or oxytetracycline

Neither imidocarb dipropionate (at 5 mg/kg body weight intramuscularly once or twice at a seven-day interval) nor oxytetracycline hydrochloride (at 20 mg/kg body weight intramuscularly once or twice at a seven-day interval) given to animals in the prepatent period of anaplasmosis, prevented the eventual onset of infection. Both compounds delayed the onset of detectable parasitaemia but this action was more noticeable with oxytetracycline. Oxytetracycline given twice significantly reduced the severity of the primary infection but the secondary infection was more severe. Neither compound showed prophylactic properties even though both are effective in extending the prepatent period and, in the case of oxytetracycline, reducing the severity of infection.