Immunisation against coccidiosis in chickens: Tests under simulated field conditions

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Abstract
Two trials designed to examine the effect of a vaccine against coccidiosis were carried out with commercial replacement layers. The effect of vaccination was evaluated by challenging vaccinated and non‐vaccinated chickens. In the first trial chickens vaccinated at 14 days of age were compared with non‐vaccinated, medicated chickens fed robenidine at 66 ppm throughout and with unmedicated chickens kept in the same house. In the second trial birds were vaccinated at 7 days of age and compared with non‐vaccinated birds on a ‘Pancoxin’ stepdown programme and with chickens maintained coccidia‐free by feeding robenidine at 66 ppm throughout. The vaccine was composed of two attenuated strains of E. mivati and E. tenella, and virulent laboratory strains of three or four other species of Eimeria. Resistance of the chickens to E. acervulina, E. brunetii and E. maxima and partial resistance to the other species developed within 3 weeks. In general, immunity increased and was high against all species, although less complete in the case of E. mivati and, when judged by lesion scores, E. tenella. Vaccination against coccidiosis was more effective, judged by resistance to challenge infection and performance, in terms of food conversion ratio, than the commercially accepted ‘Pancoxin’ regimen.