Effect of Dietary Benzoic Acid and Oregano Essential Oil as a Substitute for an Anti-Coccidial Agent on Growth Performance and Physiological and Immunological Responses in Broiler Chickens Challenged with Eimeria Species

To overcome the antimicrobial residues in food, benzoic acid (BA) and oregano essential oil (OEO) are used in the broiler chicken industry. Independently, both exerted anticoccidial and antimicrobial actions and improved growth performance in broiler chickens. Their effect may be multiplied when they are used in combination. This present study was carried out to evaluate the efficacy of dietary BA and OEO alone or in combination as a substitute for a commercial coccidiostatic drug on growth performance and physiological and immunological responses in broiler chickens challenged with <i>Eimeria</i> species. A total of 252 unsexed 1-day-old broiler chicks were equally allotted to 36 pens, each pen containing seven chicks. The pens were randomly assigned to six treatments with six pens (replicates) for each treatment (<i>n</i> = 6)-(i) negative control, (ii) positive control, <i>coccidia</i>-challenged and non-treated, (iii) supplemented with salinomycin (an anti-coccidial drug) at 60 mg/kg of feed and <i>coccidia</i>-challenged, (iv) supplemented with BA at 500 mg/kg of feed and <i>coccidia</i>-challenged, (v) supplemented with OEOat 500 mg/kg of feed and <i>coccidia</i>-challenged (OEO), and (vi) supplemented with BA at 500 mg/kg of feed and OEO at 500 mg/kg of feed and <i>coccidia</i>-challenged (B&O). The liver enzymes and thyroxine and creatinine levels were not affected (<i>p</i> > 0.05) both in coccidia-challenged and supplemented chickens. The BA and OEO applied separately or in combination (B&O) significantly (<i>p</i> < 0.05) reduced gut pathogenic bacteria (<i>Salmonella</i> and <i>Escherichia coli</i>) and <i>Eimeria</i> spp., and concurrently enhanced (<i>p</i> > 0.05) the <i>Lactobacillus</i> population with better body weight gain, improved feed utilization, and superior hematological values. It also up-regulated (<i>p</i> > 0.05) the interferon-γ gene expression and down-regulated (<i>p</i> < 0.05) the interleukin-10 and Toll-like receptor-4 gene expression to protect the chickens from inflammatory reactions, which were not demonstrated in salinomycin-treated birds. The B&O supplementation increased (<i>p</i> < 0.05) the immune system by enhancing <i>Eimeria</i>-specific immunoglobulin Y titer and lymphocyte proliferation response. This study suggests that the combined application of OEO and BA can substitute for a commercial anti-coccidial agent (salinomycin) in controlling coccidiosis as well as improving growth performance, gut health, and immune responses in broiler chickens with a means of antimicrobial-resistant free food products.