Evaluation of diclazuril and amprolium against Eimeria spp. in Vietnamese broilers: Implications for intestinal integrity and claudin gene expression

This study aimed to assess the resistance status of Eimeria spp. in Vietnam to diclazuril and amprolium and to evaluate their effects on intestinal recovery following infection. One hundred 12-day-old chicks were randomly allotted to four groups: a non-infected negative control (NC), an infected untreated as positive control (PC), an infected group treated with diclazuril (DI), and an infected group treated with amprolium (AM). At day 14, chicks from all groups except NC were orally challenged with 2 × 10⁴ sporulated Eimeria oocysts (E. tenella, E. maxima, E. acervulina, and E. mitis). On day 7 post-infection, chickens were euthanized to assess gross and microscopic intestinal lesions and to analyze the expression of tight-junction genes. Anticoccidial resistance was determined using four indicators: anticoccidial index, percentage of optimum anticoccidial activity, reduction of lesion score, and reduction of oocyst production. The results showed that Eimeria isolate exhibited complete resistance to diclazuril across all four indices, while remaining fully sensitive to amprolium. Chicks in the AM group demonstrated markedly reduced oocyst shedding, lower gross and microscopic lesion scores, and enhanced expression of Claudin family genes, particularly Claudin-3, which plays a key role in reinforcing epithelial barrier integrity during recovery. These findings identify amprolium as an effective therapeutic option for controlling coccidiosis under the current field conditions in Vietnam and highlight the necessity of ongoing monitoring of anticoccidial drug resistance to inform sustainable poultry health management strategies.