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 microsc opic lesion scoring (MLS) system to measure magnitudes of E, maxima infecti on in sections of broiler chick intestine, and to help make decisions regar ding the efficacy of an E, maxima abatement programme. Chicks with whole-bo dy pallor, elevated feed conversion ratios (10 points higher than normal) a nd reduced body sizes (0.1 kg smaller than normal) had light microscopic le sions caused by E, maxima infections. These intestine segments had high Eim eria maxima MLSs, High scores, coupled with the fact that there was no micr oscopic 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 anothe r 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 th at the MLS is suitable for use in health programmes that depend upon detect ion of E. maxima in broilers.