Clinical application of a light microscopic scoring method to make decisions regarding the pharmacotherapy of an Eimeria maxima abatement programme.

The purpose of the present study was to use an Eimeria maxima light microscopic lesion scoring (MLS) system to measure magnitudes of E. maxima infection in sections of broiler chick intestine, and to help make decisions regarding the efficacy of an E. maxima abatement programme. Chicks with whole-body pallor, elevated feed conversion ratios (10 points higher than normal) and reduced body sizes (0.1 kg smaller than normal) had light microscopic lesions caused by E. maxima infections. These intestine segments had high Eimeria maxima MLSs. High scores, coupled with the fact that there was no microscopic evidence for the presence of gastrointestinal pathogens other than E. maxima, allowed us to conclude that E. maxima was the cause of the signs observed. When changes in the pharmacotherapy of the coccidiosis abatement programme were made (substitution of one ionophore coccidiostat for another ionophore coccidiostat), the MLSs were significantly (P < 0.01) reduced, and chicks returned to their normal colour (yellow) and normal target body size (2.091 kg) on a normal feed conversion ratio (2.06). It was decided that the MLS is suitable for use in health programmes that depend upon detection of E. maxima in broilers.