Ivermectin should not be the drug of choice for controlling Parascaris equorum (large roundworm) in foals a recent study warns.
Dr Eva Osterman-Lind and Dr Dan Cristensson of the National Veterinary Institute, Uppsala, Sweden, investigated the occurrence of Parascaris equorum infection on nine stud farms in Sweden and assessed the efficacy of three commonly used dewormers.
They found that ivermectin had very little, or no, effect on the output of ascarid eggs.
“The most striking result from this study was that in five studs out of six, ivermectin failed to suppress the faecal output of P. equorum eggs” Osterman-Lind and Cristensson report in the journal Acta Vet Scandinavica. “Ivermectin resistance is now a widespread problem in Swedish stud farms.”