Evaluation of the Effects of Thyme (Thymus vulgaris) on Intestinal Lesions Caused by Eimeria spp. in Broiler Chickens: A Controlled Study Assessing Efficacy, Safety, and Economic Impact

Background: Coccidiosis, caused by multiple species of Eimeria, remains one of the most economically detrimental enteric diseases in modern broiler production. The disease negatively affects intestinal integrity, nutrient absorption, growth efficiency, and survivability, leading to increased reliance on anticoccidial drugs. With the emergence of drug-resistant Eimeria strains and growing demand for antibiotic-free poultry products, phytogenic feed additives-especially thyme (Thymus vulgaris) rich in thymol and carvacrol have gained considerable attention as natural anticoccidial alternatives. Objective: This study investigated the dose-response effects of graded dietary thyme powder levels on intestinal lesions, oocyst shedding (OPG), growth performance, European Production Index (EPI), survivability, intestinal morphology, antioxidant status, and the expression of key tight-junction and inflammatory genes in broiler chickens experimentally challenged with a mixed Eimeria infection. Methods: A total of ۳۶۰ male Ross ۳۰۸ broilers were assigned to six dietary treatments using a completely randomized design: non-infected negative control, infected positive control, and thyme inclusion at ۰.۲۵%, ۰.۵%, ۱.۰%, and ۱.۵% of the diet. Each treatment consisted of five replicates with twelve birds. On day ۱۴, all infected groups received an oral challenge of a mixed suspension of E. tenella, E. acervulina, and E. maxima totaling ۵×۱۰^۴ sporulated oocysts per bird. Growth performance indices (BW, FI, FCR), EPI, and mortality were recorded throughout the ۴۲-day trial. Lesion scoring (Johnson and Reid, ۰-۴ scale), oocyst enumeration (McMaster technique), villus height and crypt depth measurements, and mucosal antioxidant indices (SOD, GPX, T-AOC, MDA) were assessed. Gene expression of ZO-۱, claudin-۱, IL-۱ẞ, and TNF-α was quantified by qPCR on days ۲۱ and ۲۸ using the AACt method. Statistical analyses were performed using one-way ANOVA and Tukey's post hoc test (a=۰.۰۵), supplemented with Emax dose-response modeling to estimate ED۵۰ values. Results: Thyme supplementation exerted significant dose-dependent anticoccidial and growth-promoting effects. The ۱.۰% thyme level demonstrated the most balanced efficacy, reducing mean intestinal lesion scores from ۳.۳ to ۱.۳, while decreasing OPG by approximately ۵۸% compared with the infected control. Although ۱.۵% thyme achieved a slightly greater reduction in oocyst shedding (~۶۴%), mild feed intake suppression and reduced weight gain were observed. Birds fed ۱.۰% thyme exhibited a ۱۰.۳% increase in final body weight, an improved FCR (۱.۶۶ vs. ۱.۸۲), and achieved the highest EPI (~۳۵۶). Histomorphological analysis showed notable improvements in villus height and villus-to-crypt ratio (from ۲.۰ to ۳.۱). Thyme enhanced intestinal barrier integrity by upregulating ZO-۱ and claudin-۱, while markedly downregulating inflammatory cytokines IL-۱ẞ and TNF-α (p < ۰.۰۵). Antioxidant enzyme activities increased significantly, accompanied by reduced MDA levels, indicating lower oxidative stress. No adverse effects were detected at ≤۱.۰% inclusion, whereas ۱.۵% thyme caused mild appetite reduction. Dose-response modeling estimated the ED۵۰ for lesion and OPG reduction at ~۰.۶% thyme. Economic assessment suggested an added net profit of ۷۸-۱۱۲ USD per ۱۰۰۰ birds with ۱.۰% thyme supplementation. Conclusion: Dietary inclusion of ۱.۰% thyme powder offers a safe, natural, and effective strategy for improving intestinal health, mitigating coccidial pathology, and enhancing performance in broiler chickens challenged with Eimeria spp. The benefits are mediated through antiparasitic, anti-inflammatory, antioxidant, and tight-junction-modulating mechanisms. Incorporation of thyme is recommended as part of an integrated coccidiosis management program alongside appropriate biosecurity and vaccination practices.

کلیدواژه ها:

thyme ، Thymus vulgaris ، coccidiosis ، Eimeria spp. ، broiler chickens ، oocyst shedding ، intestinal lesions ، thymol ، carvacrol ، tight junctions ، antioxidant activity ، growth performance