Volume 72 (2022) Issue: 2022 No#1

Moxidectin: a viable alternative for the control of ivermectin-resistant gastrointestinal nematodes in beef cattle

Author(s): Dyego Gonçalves Lino Borges, Mário Henrique Conde, Cibele Cristina Tavares Cunha, Mariana Green de Freitas, Elio Moro, Fernando de Almeida Borges

Keywords:Anthelmintic, macrocyclic lactones, resistance, ruminants

The increasing prevalence of anthelmintic resistance in cattle especially for avermectins, is a challenge for controlling parasites in some herds. Thus, field studies demonstrating the increase in productivity by the use of anthelmintic formulations, even when a suboptimal treatment (efficacy below 95%), can contribute to the development of gastrointestinal nematodes control programs in beef cattle. The objective of the present study was to evaluate the anthelmintic efficacy and productive performance in pasture-raised beef calves, treated with macrocyclic lactones. A Split plot in time randomized block design was used to assess weight gain and reduction in fecal egg count (FECs) of treatments: 1% moxidectin (1% MOX), ivermectin (IVM) and abamectin (ABM) (2.25% IVM+1.25% ABM), 4% IVM, 3.15% IVM and placebo. For the evaluation of FECs and weight gain of the animals, individual samples were collected seven days before treatment and, +14, +30, +56, +91 and +118 days post-treatment (DPT). The efficacies in the 14th DPT were: 72.3% (1% MOX) , 22.1% (4% IVM) , 22% (2.25% IVM + 1.25% ABM) and 0% (3.15% ivermectin) . 1% MOX was the only treatment that resulted in a significant increase in weight gain of the animals compared to the placebo group after 118 days of treatment, with a difference of 7.6 kg. Therefore, MOX remains a viable alternative for the control of helminths resistant to avermectins and still capable of resulting in significant productive gains, even with an efficacy below 95%.