New study finds promising alternative to traditional fly control in Brazilian calf farms

Researchers at the Federal University of Mato Grosso do Sul test fluralaner, showing 96% protection against naval myiasis in calves, offering a new approach amid rising resistance to conventional treatments.

Newborn calves remain one of beef farming’s most vulnerable points, and naval myiasis is a persistent threat in Brazilian herds. The condition, caused by the larvae of Cochliomyia hominivorax, can progress quickly after flies are drawn to the exposed umbilical area, with larvae hatching in less than a day and feeding on living tissue. Left unchecked, the infestation can trigger secondary bacterial infection, swollen joints and, in severe cases, death.

For decades, many farms relied on doramectin as a preventive measure. But veterinarians now say that prolonged and widespread use has selected resistant fly populations. Fernando Borges, a veterinary surgeon with postgraduate qualifications in the field, says studies in Brazil and Argentina have already documented reduced efficacy, leaving producers with fewer practical options and raising the risk of over-dosing in an effort to compensate.

Against that backdrop, researchers at the Federal University of Mato Grosso do Sul, working with MSD Saúde Animal, tested fluralaner in field conditions. The company says the 5% formulation delivered 96% preventive protection in calves studied.

Daniel Rodrigues, technical manager for ruminants at MSD Saúde Animal, says early protection can reduce later corrective treatment, antibiotic use and losses in the maternity pen. The broader message, experts say, is that parasite control now depends on rotation of active ingredients, tighter neonatal management and close veterinary oversight.

Reference: de Freitas, M.D.B., Rodrigues, D.d., de Paiva, P.E.M. et al. Overcoming doramectin failure: field efficacy of pour-on 5% fluralaner and an experimental 1% oral formulation for the prevention of Cochliomyia hominivorax–associated umbilical myiasis in newborn calves. Parasites Vectors (2026). https://doi.org/10.1186/s13071-026-07455-5