Increasing dietary indigestible protein may exacerbate coccidiosis in broiler chickens.

The objective was to determine whether increasing dietary indigestible protein concentration exacerbates detrimental effects of coccidiosis in broiler chickens. A total of 192 male broiler chickens (Cobb 500, initial body weight = 310 ± 30 g) on d 11 post hatching were allotted to 4 treatments in a randomized complete block design. Each dietary treatment contained 8 replicate cages with 6 birds per cage. The treatments were based on a 2 (control vs. coccidia challenge) × 2 (standard diet vs. high-indigestible protein diet) factorial treatment arrangement. Non-autoclaved poultry meal was used in the standard diet, whereas autoclaved poultry meal was included in the high-indigestible protein diet to induce a difference in the intestinal indigestible protein concentration between the 2 diets. On d 12 post hatching, birds were orally gavaged with either 1 mL of saline or 1 mL of a solution containing 25,000 oocysts of , 25,000 oocysts of , and 125,000 oocysts of , depending on their respective treatment. On d 18, birds were euthanized for ileal digesta collection. Jejunal tissue and cecal mucosa were collected from the bird with median weight in each cage. Body weight gain loss was greater when birds were fed the high-indigestible protein diet, but the degree of the decrease was greater in the coccidia-challenged group compared with the non-challenged group (interaction; < 0.05). There was a tendency for an interaction between coccidia challenge and diet ( = 0.052) for feed intake with a greater intake of the high-indigestible protein compared with the standard diet in non-challenged birds, whereas a difference in feed intake was not observed between the two diets in the challenged birds. Coccidia challenge or increasing dietary indigestible protein concentration decreased ileal nitrogen digestibility, which increased ileal indigestible nitrogen concentration ( < 0.05). Coccidia challenge did not affect goblet cell count per jejunal villus when birds were fed the standard diet, but the count decreased under the high-indigestible protein diet (interaction, < 0.05). Coccidia challenge increased ( < 0.05) the mRNA expression of tumor necrosis factor-α and interleukin-1β, whereas feeding the high-indigestible protein diet decreased ( < 0.05) occludin mRNA expression in cecal mucosa. In conclusion, increasing dietary indigestible protein has the potential to exacerbate detrimental effects, and decrease the gene expression of cecal tight junction protein during coccidia challenge.