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Recently, the inflammation of the intestinal mucosa has been related to many diseases in humans and animals. The concept of Microscopic Enteritis (ME) used in human pathology through the Marsh classification system has no counter-part in veterinary medicine. In poultry science, the I See Inside (ISI) methodology, unlike the current linear measures of villi and crypts, generates possibilities to describe and understand the avian ME. Through specific parameters, graded from 0 to 3, the model links proliferative and/or inflammatory reactions in the intestinal layers to some loss in performance. Herein, two trials were conducted in order to describe the development of ME through the ISI methodology in chickens challenged or not with Eimeria spp. and Clostridium perfringens. In each trial, a total of 64 birds were divided in 2 treatments with 4 replicates containing 8 birds each: non-challenged (NCH) and challenged (CH) through gavage with an Eimeria spp. vaccine at 1 day of age and 108 CFU/mL of Clostridium perfringens administered at 10, 11, and 12 days of age. At 7, 14, 21, and 28 days of age birds were euthanized and samples of ileum and liver were collected for ISI evaluation, cytokines and presence of macrophages, CD4+ and CD8+ cell. The results allowed the description of the avian Microscopic Enteritis and of its two basic components: a basal enteritis (BE) in NCH broilers, over which the infectious enteritis is developed in CH birds. In addition, the chronology of ME translated by the ISI methodology parameters were associated to losses in zootechnical performance.

The maintenance of integrity of the gastrointestinal tract is an important aspect for animal productivity, since it is able to absorb nutrients more efficiently and serves as a barrier against microorganisms. To control agents detrimental to intestinal integrity, growth-promoting antibiotics (AGP) are used, which reduce the number of toxin-producing microorganisms in the intestinal lumen, acting as anti-inflammatory agents. There is a demand for restriction of use of AGP in animal feed, but there are few studies showing what parameters we should observe to search for alternative additives. The aim of this study was to establish histological parameters that explain the effect of enramycin as growth promoter on intestinal health in broilers challenged with Eimeria and Clostridium perfringens. The zootechnical performance and the histology by I See Inside (ISI) methodology were evaluated on liver and ileum samples. Chickens challenged without AGP have the worst BWG, FCR, and histological ISI score (ISI score 9) in the ileum compared to non-challenged (ISI score 5). The use of enramycin on challenged group significantly minimized the ISI score in the ileum at 21 and 28 d (ISI score 7.4 and 8.0, respectively) compared with the challenged group not fed with enramycin (ISI score 9.2 and 9.9, respectively), associated with reduced lamina propria thickness and inflammatory cell infiltration. We suggest these 2 histological parameters as a standard to compare products for gut health.

Highlights • The ISI was applied to evaluate histologic alterations specific of Eimeria infection. • The ISI histological score show high correlation with broilers performance. • The higher the ISI scores the worse are the performance results of birds challenged., The present study evaluated the effects of coccidiosis on histological parameters and performance of broilers submitted to a mild challenge with Eimeria sp. A total of 132 broilers were randomly divided into two groups with 6 replicates of 11 birds each: negative control (NC) – birds uninfected and challenge (CH) - birds infected by gavage at day-one with 10x the manufacturer recommended dose of Bio-Coccivet R® live vaccine by Biovet, with strains of E. acervulina, E. brunetti, E. maxima, E. necatrix, E. praecox, E. tenella and E. mitis. From 1 to 28 d of age, weekly the zootechnical performance was evaluated and samples of the liver, duodenum, jejunum and ileum were collected and submitted to histological analysis by the I See Inside methodology (ISI). The ISI methodology is a metric evaluation of histological alterations in the intestine and liver. Which translates macroscopic and microscopic alterations into numbers and allows their correlation with the animal zootechnical performance. Pearson’s correlation was used to demonstrates how the damages to the gut, evaluated by ISI method, could affect negatively the performance of broilers. The presence of oocysts in histological analysis of the jejunum and ileum at 7d indicate a negative effect on performance over the next 2 weeks (14d and 21d). When the ISI total score was measured in the ileum at 14d, we observed a strong negative effect on zootechnical performance from that period on 14d, 21d and 28d. The obtained data demonstrates that the higher the ISI scores, the worse are the zootechnical performance results of broilers challenged with Eimeria sp. and the I See Inside scores could be applied to evaluate coccidiosis effect on performance in future.