Multispecies resistance of cattle gastrointestinal nematodes to long-acting avermectin formulations in Mato Grosso do Sul

•Long-acting avermectins were evaluated by an anthelmintic controlled test in cattle.•Multiple nematode species resistance to avermectins was detected.•The increase of avermectin concentration did not result in higher efficacy.

The use of long-acting avermectins (AVMs) in cattle to treat infections with gastrointestinal nematodes was common in Brazil until its prohibition by state authorities. The prohibition; however, was rescinded in 2015, but a scientific discussion of the pros and cons of the use of these formulations is necessary. We evaluated the levels of resistance to 1.0 and 3.5% doramectin and to 3.15% ivermectin in cattle. The worms in animals treated with 3.5% doramectin were characterized by the suppression of oviposition and by a higher proportion of adult females carrying no eggs. Haemonchus placei, Cooperia punctata, C. pectinata, C. spatulata, and Oesophagostomum radiatum were resistant to the above compositions. The administration of long-acting AVM formulations did not result in a higher efficacy against these helminth populations.