In-feed Salmonella-specific phages alter the physiology, intestinal histomorphology, and carcass and meat quality parameters in broiler chickens

Abstract

The use of antibiotic growth promoters (AGP) in broiler production leads to the emergence of antibiotic-resistant bacterial pathogens. To mitigate this challenge, biocontrol agents such as phages are being investigated as sustainable alternatives to AGP in commercial broiler production systems. This study aims to investigate the effect of different levels of an in-feed encapsulated Salmonella-specific phage cocktail (SPC) on various parameters, including growth performance, blood indices, carcass characteristics, intestinal histomorphology, and meat quality traits in broiler chickens. A total of 400-day-old Ross 308 male chicks (49.84 ± 1.03 g live weight) were reared on five experimental diets. The diets were formulated as follows: 1) a negative control diet without zinc bacitracin and SPC (NC), 2) a positive control diet with 0.5 g/kg zinc bacitracin but without SPC (PC), and 3) NC with 0.075 (SP75), 0.1 (SP100), and 0.175 g/kg SPC (SP175). During the feeding trial, phages were added on days 1 – 2; 11 – 12; 21 – 22; and 29 – 30 for the SPC treatments. Feed intake, bird weight, and blood parameters were determined during the feeding trial. Birds were slaughtered at the end of the feeding trial (5 weeks) to evaluate carcass characteristics, intestinal histomorphology, and meat quality traits. Five-week-old birds reared on SP100 had lower weight gains (555.7 g/bird) than those reared in the other treatment groups (p < 0.05). The inclusion of SPC in diets induced positive quadratic effects on overall feed intake (R2 = 0.169; p = 0.048) and meat chroma (R2 = 0.184; p = 0.024) but resulted in negative quadratic effects for breast weight (R2 = 0.418; p = 0.046) and linear effects for meat pH 1-h post-mortem (R2 = 0.161; p = 0.040) and proventriculus weight (R2 = 0.195; p = 0.024). A positive quadratic effect was noted for duodenal villus height (R2 = 0.935; p = 0.003), width (R2 = 0.882; p = 0.009), and area (R2 = 0.929; p = 0.001); jejunal villus height (R2 = 0.914; p = 0.001), width (R2 = 0.917; p = 0.002), area (R2 = 0.903; p = 0.001), and muscle thickness (R2 = 0.970; p = 0.001); ileal villus width (R2 = 0.747; p = 0.006), and crypt depth (R2 = 0.916; p = 0.001). Compared to the negative control, SPC induced positive changes in the jejunal and ileal villus height and VH:CD, however, this did not improve growth performance of broiler chickens. It can be concluded that periodic SPC inclusion has the potential to replace subtherapeutic antibiotic use in poultry production.