Lack of correlation between microscopic lesion scores and gross lesion scores in commercially grown broilers examined for small intestinal Eimeria spp. coccidiosis.

Comparisons were made between microscopic lesion scores (MLSs) and gross lesion scores (GLSs) in sections from small intestine of broilers during three routine coccidiosis screenings. The duodenal and jejunal GLS were determined and recorded by different evaluators. During each screening, 2-cm sections of duodenum and jejunum were collected, and sections of intestine were then scored using a microscopic lesion scoring system. No correlation between MLS and GLS was observed in duodenum in two out of three coccidiosis screenings, and no correlation was observed between MLS and GLS in jejunum in three out of three screenings. Our findings demonstrate that, if used alone in coccidiosis screening, GLSs can underestimate infections and may not provide a true representation of the magnitude of Eimeria maxima infection within broiler flocks.

Quantitative pathology of small intestinal coccidiosis caused by Eimeria maxima in young broilers.

The objective of this study was to apply a microscopic lesion scoring system for assessing the severity of experimental coccidiosis. To accomplish this objective, we examined the effects of varying doses of E. maxima in chicks by comparisons of gross and microscopic lesion scores, body weight gains, feed conversion ratios and faecal oocyst counts. In the battery trial, 3-day-old chicks inoculated with 2.5 x 10(3) or more oocysts had significantly lower growth rate than the controls. The mean feed conversion ratio for days 0 to 36 were significantly greater than those of 0 to 10 and 0 to 17 p.i. The intestinal gross lesion scores and microscopic lesion scores were significantly affected by days p.i. and oocyst dosage. In the floor pen trials, the mean adjusted body weights of 3- and 14-day-old chicks inoculated with 2.5 X 10(4) oocysts of the same strain of E. maxima were significantly lower than the controls. Gross and microscopic lesion scores regressed with significant (P<0.05) linearity on body weight gains. Under experimental conditions, both duodenal and jejunal microscopic lesion scores regressed with significant linearity on gross lesion scores.