Coccidiosis in broilers: The effect of monensin and other anticoccidial drug treatments on oocyst output

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Abstract
The effect of using monensin at a concentration of 100 ppm in the food of broiler chickens for the first 6 weeks followed by zoalene at 125 ppm for the last weeks was studied over a 2.5 year period by monitoring the numbers of coccidial oocysts present in the litter. Oocyst numbers in the litter remained low after 11 successive batches of chickens had been given this treatment. In a single trial medication with clopidol or zoalene for the 2 weeks following monensin was equally effective in controlling numbers of oocysts in the litter. On two of five farms there was an indication that oocyst numbers increased 2 weeks after the end of monensin treatment. The oocysts most frequently found in the litter were E. acervulina and E. maxima and oocysts of E. maxima predominated in samples taken at 6 and 8 weeks. In a single trial in which the inclusion of monensin was limited to the time when birds were 3 to 6 weeks of age, preceded and followed by other drugs, the numbers of oocysts in litter were not increased.