This study was conducted to evaluate graded Eimeria challenge on growth performance, apparent ileal digestibility, gastrointestinal permeability, intestinal morphology, gene expression of tight junction protein, and intestinal lesion scores in broiler chickens. There were 5 groups in this study, including a control and 4 different Eimeria treatment doses. A mixed Eimeria spp . solution with 50,000 Eimeria maxima , 50,000 Eimeria tenella , and 250,000 Eimeria acervulina per milliliter was prepared for the high-dose challenge treatment. The 2-fold serial dilution was used to make the medium-high (25,000 E. maxima ; 25,000 E. tenella ; 125,000 E. acervulina ), the medium-low (12,500 E. maxima ; 12,500 E. tenella ; 62,500 E. acervulina ), and the low challenge dose (6,250 E. maxima ; 6,250 E. tenella ; 31,250 E. acervulina ). A total of three hundred sixty 13-day-old male broiler chickens were randomly allocated into 5 treatments with 6 replicated cages. Growth performance was calculated from 0 to 6 D postinfection (DPI) . Intestine lesion was scored on 6 DPI. Gastrointestinal permeability was measured on 3, 5, 6, 7, and 9 DPI. The results indicated significant linear reduction in growth performance, intestinal villi height, and ileal nutrient digestibility in response to the increase of Eimeria challenge dose. Furthermore, gene expression of tight junction protein was linearly upregulated by the increasing challenge doses. Significant linear increases of gastrointestinal permeability were found on 5, 6, and 7 DPI ( P < 0.01). On 9 DPI, the gastrointestinal permeability was recovered back to normal level in the challenge groups. In conclusion, the higher Eimeria doses birds received, the more severe intestine damage was observed in several gastrointestinal health parameters. The medium-low or medium-high levels of mixed Eimeria oocysts is suggested as an optimum Eimeria -challenge dose to establish a subclinical challenge model for future studies evaluating nutritional strategies. Moreover, it is recommended to measure gastrointestinal permeability on 5 DPI with higher oocysts doses and 6 DPI when using the lower oocysts doses.

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Amino acids such as arginine, methionine, and cysteine are the precursors of essential molecules that regulate growth and health, being classified as functional amino acids. This review describes the metabolism of arginine and the sulfur amino acids and how they modulate, directly or indirectly, different tissues. Emphasis is placed on their effects in supporting health during challenging conditions, such as heat stress and Eimeria infection. The use of arginine has been shown to reduce abdominal fat pad in ducks and increase lean tissue and bone mineral density in broilers. Additionally, the sulfur amino acids have been shown to improve bone development and are beneficial during heat stress. The use of L-methionine increased the cortical and trabecular bone mineral densities, in laying hens. Moreover, the dietary inclusion of these amino acids could reduce the damage caused by Eimeria spp. infection by regulating the antioxidant system and cell repair. Understanding how these amino acids can mitigate stressful conditions may provide us novel insights of their use as nutritional strategies to modulate the health status of chickens.

This study evaluated the effects of varying levels of L-arginine ( Arg ) on performance and intestinal health of broilers challenged with Eimeria. Cobb 500 male chicks ( n = 720) were randomly distributed in a 5 × 2 factorial arrangement (6 replicates/12 birds). The main factors were Arg levels (1.04, 1.14, 1.24, 1.34, 1.44%) and challenge or non-challenge with Eimeria. At day 12, in the challenge group, each bird received orally 12,500 Eimeria maxima , 12,500 Eimeria tenella , and 62,500 Eimeria acervulina sporulated oocysts. At 5 d postinfection ( dpi ), intestinal permeability was measured. At 6 and 14 dpi, performance, intestinal histomorphology, nutrient digestibility, tight junction protein ( TJP ) gene expression, and antioxidant markers were evaluated. Few interactions were found, and when significant, the supplementation of Arg did not counteract the negative effects of Eimeria challenge. Challenge, regardless of Arg level, increased intestinal permeability, although the expression of Claudin-1, a TJP, was upregulated. At 6 dpi, the antioxidant system was impaired by the challenge. Moreover, growth performance, intestinal histomorphology, and nutrient digestibility were negatively affected by challenge at 6 and 14 dpi. Regardless of challenge, from 0 to 14 dpi, birds fed 1.44% showed higher weight gain than 1.04% of Arg, and birds fed 1.34% showed lower feed conversion than 1.04% of Arg. At 5 dpi, intestinal permeability was improved in birds fed 1.34% than 1.04% of Arg. Moreover, 1.34% of Arg upregulated the expression of the TJP Zonula occludens-1 ( ZO-1 ) as compared with 1.24 and 1.44% of Arg at 6 dpi. At 14 dpi, 1.44% of Arg upregulated the expression of ZO-1 and ZO-2 compared with 1.24 and 1.34% of Arg. The nutrient digestibility was quadratically influenced by Arg, whereas the antioxidant markers were unaffected. Thus, the challenge with Eimeria had a negative impact on growth and intestinal health. The dietary supplementation of levels ranging from 1.24 to 1.44% of Arg showed promising results, improving overall growth, intestinal integrity, and morphology in broilers subjected or not to Eimeria challenge.

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