Evaluating a Salmonella Typhimurium, Eimeria maxima, and Clostridium perfringens coinfection necrotic enteritis model in broiler chickens: repeatability, dosing, and immune outcomes

Coccidiosis and necrotic enteritis negatively impact poultry production, making challenge model repeatability important for evaluating mitigation strategies. Study objectives were: 1) evaluate Salmonella Typhimurium-Eimeria maxima-Clostridium perfringens necrotic enteritis coinfection model repeatability and 2) investigate E. maxima dose and early S. Typhimurium challenge on immune responses. Three trials using Ross 308 chicks assigned to 12 cages/trial (7 chicks/cage) in wire -floor brooders were completed. Tri-als 1 and 2 determined E. maxima dose for necrotic enteritis challenge in trial 3. Chicks in trials 1 and 2 were inoculated with 0 (control), 5, 15, or 25,000 sporulated E. maxima M6 oocysts on d 14 and jejunal lesion scores evaluated on d 20. In trial 3, chicks were assigned to control or necrotic enteritis challenge (42 chicks/ group). Necrotic enteritis challenge chicks were inoculated with 1 x 10(5) colony forming units (CFU) S. Typhimurium on d 1, 15,000 E. maxima oocysts on d 14, and 1 x 10(8) CFU C. perfringens on d 19 and 20 with lesion scoring on d 22. Bird and feeder weights were recorded throughout each trial. Peripheral blood mono-nuclear cells (PBMC) were isolated from 1 chick/cage at baseline (all trials), 4 chicks/dose (trials 1 and 2) or 8 chicks/challenge (trial 3) 24 h post-inoculation (pi) with E. maxima for immunometabolic assays and immune cell profiling. Data were analyzed by mixed procedure (SAS 9.4) with challenge and timepoint fixed effects (P <= 0.05, trends 0.05 <= P <= 0.01). Inoculating chicks with 15,000 E. maxima oocysts increased d 14 to 20 FCR 79 points (trials 1 and 2; P = 0.009) vs. unchallenged chicks and achieved a target lesion score of 2. While C. perfringens challenge reduced trial 3 performance, average lesion scores were <1. Salmonella inoculation on d 1 tended to increase PBMC ATP production 41.6% 24 hpi with E. maxima vs. chicks challenged with E. maxima only (P = 0.06). These results provide insight for future model optimization and considerations regarding S. Typhimurium's effect on E. maxima immune response timelines.