Multispecies resistance of cattle gastrointestinal nematodes to long-acting avermectin formulations in Mato Grosso do Sul
2015
Borges, Fernando de Almeida | Borges, Dyego Gonçalves Lino | Heckler, Rafael Pereira | Neves, Juliana Paniago Lordello | Lopes, Fernando Gonçalves | Onizuka, Marcel Kenzo Vilalba
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 The prohibition; however, was rescinded in 2015, but a scientific discussion of the pros and cons of the use of these formulations is necessary.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.
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