Veterinary session

The most significant internal parasites of foals under one year of age are ascarids, which can lead to mortality in cases of severe infection. Therefore, the appropriate treatment of ascarid infections in young horses is of critical importance. In recent years, resistance of ascarids to multiple anthelmintics has been documented on several occasions. The objective of our study was to examine the efficacy of fenbendazole and ivermectin, and to evaluate the ascarid treatment protocols of 12 Hungarian stud farms.

The subjects of the experiments were 3–7-month-old Thoroughbred foals from the Dióspuszta Stud of the Bábolna National Stud Farm. First, we tested the efficacy of the stud's own deworming protocol using two active ingredients on 23 foals. In the first trial, the foals received a single dose of fenbendazole at 6.6 mg/kg body weight (Fenbendanin 50 mg/g oral powder, Vim Spectrum Srl., Corunca, Romania). In another experiment, 23 foals were treated with ivermectin (Noromectin paste, Norbrook Laboratories Ltd) at a dose of 0.2 mg/kg body weight. In the third trial, 19 foals were treated with the previously tested fenbendazole product at the manufacturer’s recommended dose of 10 mg/kg body weight. In all three trials, individual fecal samples were collected immediately before treatment and on the 14th day post-deworming. The ascarid egg counts per gram were determined using the Mini-FLOTAC method. The efficacy of the two active ingredients was assessed according to the guidelines published by the World Association for the Advancement of Veterinary Parasitology in 2023. The domestic practice of foal ascarid treatment was examined in 12 stud farms using a questionnaire we developed.

When fenbendazole was administered, the reduction in fecal egg count ranged between 82.7%-90.2% (90% CI) at a dose of 6.6 mg/kg, and between 89%-99.9% (90% CI) at a dose of 10 mg/kg. For ivermectin administered at a dose of 0.2 mg/kg, the reduction in egg count ranged between -378.6% and 83.2% (90% CI).

Fenbendanin powder, when applied at a low dose (6.6 mg/kg), was not effective. At a dose of 10 mg/kg, its efficacy improved significantly, but based on the confidence interval, this value was classified as inconclusive, meaning that neither resistance nor efficacy could be determined. According to our survey, fenbendazole-based products are not administered at the recommended dosage in several stud farms. To our knowledge, we were the first to confirm resistance to ivermectin in ascarids in Hungary. This is particularly important because, in half of the surveyed stud farms, foals are treated against ascarids with ivermectin.

Our results highlight the importance of selecting the appropriate drug and dosage for effective control of ascarid infections in foals. We plan to conduct further studies on the efficacy of fenbendazole and recommend its routine testing for all practicing equine veterinarians.