The multi-drug resistance (mdr-1) gene mutation is a phenomenon well known to current
veterinary practitioners. The mutation causes a predisposition for, amongst other phenomena,
macrocyclic lactone-induced neurotoxicosis in affected canines, a condition that can be fatal.
Various herding dog breeds can be heterozygous or homozygous for the mutation, and
prevalence differs only slightly in dog populations between geographical regions. This report
provides prevalence data of the canine mdr-1 mutation in 306 South African dogs.