Background: Lamb coccidiosis, caused by intestinal parasites of the Eimeria genus, has pronounced health and economic impacts throughout the world. Eimeria ovinoidalis and Eimeria crandallis are the most pathogenic species in sheep. Control of these parasites requires the use of anticoccidial drugs such as sulfonamides, diclazuril, and toltrazuril. In this study, resistance to anticoccidial drugs was suspected in two farms as clinical signs (diarrhea) persisted after treatment. Method: On each farm, 4.5-month-old rams were divided into three groups so that they were either (i) left untreated (Control group), (ii) treated with diclazuril (1 mg/kg body weight), or (iii) treated with toltrazuril (20 mg/kg body weight). Animals were treated at day 0 (D0) and fecal samples were collected at D0 and eight days later (D8) to evaluate the reduction in intensity of Eimeria oocyst excretion. Oocyst morphology and morphometry were used to identify Eimeria species at both sampling dates. Results: Reduction of oocyst shedding was incomplete in both farms (92.44% and 93.58%) after diclazuril treatment. More specifically, the efficacy was reduced in both farms for E. ovinoidalis/Eimeria marsica (92.59% and 91.87%) and E. crandallis/Eimeria weybridgensis (75.34% and 80.10%). The general efficacy of toltrazuril was high in both farms (97.6% and 97.96%). However, a slightly reduced efficacy was noted in farm 1 for E. crandallis/E. weybridgensis (93.26%) while this efficacy was high in farm 2 (98.88%). Conclusions: We suggest a simple protocol to investigate the efficacy of anticoccidial treatments in sheep and to rapidly identify potentially resistant species. In these two farms, treating animals with diclazuril will select pathogenic species, and toltrazuril could favor resistant E. crandallis/E. weybridgensis in one of them.

Background: Lamb coccidiosis, caused by intestinal parasites of the Eimeria genus, has pronounced health and economic impacts throughout the world. Eimeria ovinoidalis and Eimeria crandallis are the most pathogenic species in sheep. Control of these parasites requires the use of anticoccidial drugs such as sulfonamides, diclazuril, and toltrazuril. In this study, resistance to anticoccidial drugs was suspected in two farms as clinical signs (diarrhea) persisted after treatment. Method: On each farm, 4.5-month-old rams were divided into three groups so that they were either (i) left untreated (Control group), (ii) treated with diclazuril (1 mg/kg body weight), or (iii) treated with toltrazuril (20 mg/kg body weight). Animals were treated at day 0 (D0) and fecal samples were collected at D0 and eight days later (D8) to evaluate the reduction in intensity of Eimeria oocyst excretion. Oocyst morphology and morphometry were used to identify Eimeria species at both sampling dates. Results: Reduction of oocyst shedding was incomplete in both farms (92.44% and 93.58%) after diclazuril treatment. More specifically, the efficacy was reduced in both farms for E. ovinoidalis/Eimeria marsica (92.59% and 91.87%) and E. crandallis/Eimeria weybridgensis (75.34% and 80.10%). The general efficacy of toltrazuril was high in both farms (97.6% and 97.96%). However, a slightly reduced efficacy was noted in farm 1 for E. crandallis/E. weybridgensis (93.26%) while this efficacy was high in farm 2 (98.88%). Conclusions: We suggest a simple protocol to investigate the efficacy of anticoccidial treatments in sheep and to rapidly identify potentially resistant species. In these two farms, treating animals with diclazuril will select pathogenic species, and toltrazuril could favor resistant E. crandallis/E. weybridgensis in one of them.