Abstract
We investigated the effects of arginine and methionine supplementation in reduced protein diets on performance of broilers under concurrent heat stress (HS) and coccidia challenge. From d9 to 28, the experimental grower diets: positive control (PC) with 20.0 % crude protein (CP); negative control (NC) with 17.5 % CP; NC + 50 % arginine or methionine (ARG/MET) were fed to the chickens. From d14, chickens in the thermoneutral (NT) groups were raised under recommended temperature, and chickens in HS group were exposed to cyclic HS at 35°C for 8h/day. All chickens were oral-challenged with mixed Eimeria spp. on d 14. From d4 to 7-day post inoculation (DPI), the HS group had decreased BWG compared to the NT group, and the ARG group had higher BWG compared to the PC and MET group (P < 0.05). From d0 to 7 DPI, the PC group in HS had decreased BWG and FI compared to the PC group in NT (P < 0.05). On 7 DPI, the NC group in HS had higher AA digestibility compared to the PC group in NT (P < 0.05). On 7 and 14 DPI, HS increased the expression of AA transporters and tight junction protein genes (P < 0.05). The ARG group had the highest OCLN and ZO1 gene expression levels among the groups in 7 and 14 DPI (P < 0.05). On 14 DPI, the ARG group in HS increased the expression of protein metabolism genes in the breast muscle compared to the ARG group in NT (P < 0.05). On 7 DPI, the NC group in HS had higher CD8(+) cell percentage and CD8(+):CD4(+) ratio compared to the NC group in NT (P < 0.05). In conclusion, our study revealed the intricate interactions between HS and the dietary treatments in broilers challenged with Eimeria on growth performance, intestinal health, and immune responses, with overall performance improvement observed with arginine supplementation due to its positive effects on immune responses and intestinal health.