Abstract Introduction: Coccidiosis is one of the most common and important diseases of the poultry industry, which is caused by Eimeria protozoa and mostly occurs in the form of enteritis. Today, due to the excessive use of coccidiostat drugs, Eimeria species have developed drug resistance to these drugs, and this has economic consequences. Methods: In the present study, litter samples were collected from broiler farms with a history of coccidiosis in Mazandaran province. Eimeria oocysts from infected samples were cultured and propagated in a 2.5% potassium dichromate solution in a humid incubator at 27 °C, and the sporulated oocysts were counted and washed for propagation in broiler chickens. Then, 60 broilers of Ross breed were divided into 3 groups. (Maduramycin group, positive control group, negative control group) From the beginning of the study, maduramycin drug was added to the diet of the maduramycin group for 30 days. On the fourteenth day, 200,000 mixed oocysts of Eimeria species were given orally to each bird. Daily litter samples were collected from the 5th day to the 14th day after infection, and the OPG of the litter of each group was determined using the McMaster method. In addition, chickens of each group were weighed daily until the end of the study. Discussion and conclusion: Based on the results of this study, the presence of drug resistance of Eimeria species to maduramycin in the broiler farms of Mazandaran province is confirmed and reported (because there was a significant difference between the OPG of the maduramycin group and the positive control group (P<0.05).) It is necessary for the health authorities of the country’s poultry industry to look for a solution to solve this health problem so that more economic damage is not caused to the industry and the country’s economy.

Keywords