Gastrointestinal parasite infections represent a major welfare problem in small ruminants reared in extensive systems, which may be exacerbated by anthelmintic resistance. Therefore, we aimed to study the efficacy of albendazole and ivermectin in sheep. Eighty-six animals were selected from commercial farms in the temperate area of the State of Mexico at the age of seven months. These animals were randomly distributed into three groups: Group A, treated with albendazole, Group I, treated with ivermectin and Group C, left untreated. Faecal samples were collected before the anthelmintic was administered and 15 days post-treatment. Both Group A and Group I displayed a significant decrease of faecal egg counts when pre- and post-treatment values were compared (p = 0.003 and p = 0.049, respectively), and a significantly lower faecal egg count when compared with Group C after the treatment (p < 0.05). However, the faecal egg count reduction test showed that gastrointestinal nematodes (GIN) developed anthelmintic resistance to both albendazole and ivermectin. The results of the polymerase chain reaction (PCR) allowed the identification of Cooperia spp., and Trichostrongylus colubriformis. The allele-specific PCR results confirmed that T. colubriformis was resistant to albendazole. In conclusion, this study showed the presence of resistant GIN to albendazole and ivermectin in sheep reared in Mexican temperate zones. Therefore, nematode infections should be systematically monitored in order to implement integrated management strategies to prevent the spread of anthelmintic resistance.
Keywords: anthelminthic resistance; benzimidazole; gastrointestinal nematodes; ivermectin; sheep.