Relationship of coccidial lesion scores and weight gain in infections of Eimeria acervulina, E. maxima and E. tenella in broilers.

A relationship was estimated between weight gains and coccidial lesion scores measured on individual male broiler chicks experimentally infected with different field isolates of Eimeria acervulina (seven tests), E. maxima (five tests) or E. tenella (eight tests). There was a small decrease in weight gain as lesion scores increased in E. acervulina infections, and a modest reduction in weight gain with increasing lesion scores in E. maxima and E. tenella infections. This relationship was observed in both nonmedicated birds and birds fed on diets containing 60 mg salinomycin/kg. The weight gains for birds fed 60 mg/kg with lesion scores of 2, 3 and 4 for E. acervulina. 1,2,3 and 4 for E. maxima and 2 and 3 for E. tenella were significantly greater than the weight gains of nonmedicated birds with the same lesion scores. The results demonstrated that lesion scoring does not fully reflect the degree of disease severity in induced infection. High lesion scores caused by the three species studied were associated with small changes in weight gain in medicated birds when compared with nonmedicated birds.