Epidemiology of Eimeria in broiler flocks and the effect of anticoccidial drugs on the economic performance.
On two farms of a poultry integration the incidence of subclinical coccidiosis was monitored by means of the indicator bird method. On one farm the anticoccidial drug Lerbek (The Dow Chemical Company) was used and performance was compared with that of the other farm, which used Zoalene (The Dow Chemical Company). Zoalene had been used on both farms for the previous 3 years. The peak oocyst score for E. acervulina occurred in the 4th to 6th week and for E. maxima in the 5th to 7th week. The introduction of the new anticoccidial drug, Lerbek, retarded the infection curve; this retardation diminished as the anticoccidial drug was used over a period. The infection increased also in severity when usage of the drug was extended. It was shown that, in the whole integration, subclinical coccidiosis was of significant influence on the economic performance (expressed in production number), specially on the farm which continued using Zoalene. The introduction of Lerbek resulted in more effective coccidiosis control and thus in a better economic performance of the flocks. E. maxima infections were correlated negatively with the production number and this appeared to coincide with the acceleration phase of the infection curve.
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