Growth performance and gut health of broilers fed graded inclusion levels of soyhulls in low-protein soybean meal diets and challenged with mixed Eimeria spp

The 42-d study investigated the effects of standard soybean meal (SSBM, 464 g/kg crude protein) or low-protein SBM (LPSBM) produced by adding soyhulls (SH) at 27, 55, or 86 g/kg (yielding 449, 437, and 417 g/kg crude protein, respectively; LPSBM 1-3) on growth performance and gut health in broilers challenged with mixed Eimeria spp. The aim was to investigate the impact of increasing dietary soybean fiber on growth, amino acid (AA) digestibility, and immune response in broiler chickens. 1,056 male broilers were allocated to 8 treatments in a 4 × 2 factorial arrangement, with 4 corn-based diets with or without a mixed-Eimeria challenge. All diets were balanced for ME, crude protein, and standardized digestible AA. The Eimeria-challenged birds were inoculated with a mixed-Eimeria spp. inoculum on d 14, and performance was recorded on 0, 10, 14, 17, 21, 28, and 42 d of age. During the acute phase (d 17-21), the challenge decreased body weight gain (BWG) and increased FCR (P ≤ 0.001). However, in the overall phase, Eimeria-challenged birds fed SSBM or LPSBM1 diets had higher BWG and final BW (P < 0.05). On d21, N, Tyr, and Met digestibility decreased linearly with the increasing dietary SH inclusion in the challenged birds (P < 0.05). The challenged birds had higher cecal isobutyrate levels and lower relative mRNA expression of jejunal PepT1, EAAT3, and OCLDN (P < 0.05). An interaction effect was observed for villi height: crypt depth, with non-challenged birds receiving LPSBM2 having a higher ratio than those fed the SSBM diet (P = 0.05). On d 21, challenged birds fed LPSBM1 had lower relative expression of cecal tonsils IL-1 and IFN-γ (P < 0.05). In conclusion, Eimeria challenge impaired growth performance. However, a moderate inclusion level of soybean fiber in birds fed the diet containing LPSBM1 enhanced growth performance metrics and positively modulated immune responses, whereas higher dietary SH levels (LPSBM2 and LPSBM3) negatively affected growth performance, particularly in the challenged birds.