Relative value of oocyst counts in evaluating anticoccidial activity

Birds medicated with roxarsone and in another experiment with zoalene in the feed produced higher oocysts counts than unmedicated control birds receiving the same oocyst dose of Eimeria tenella or a mixture of six species (E. tenella, E. necatrix, E. brunetti, E. maxima, E. acervulina, and E. mitvati). These experiments confirm the conclusion that oocyst counts constitute an unsatisfactory and unreliable parameter for judging effectiveness of an anticoccidial even though such increases are a relatively rare occurrence in anticoccidial evaluation experiments.