Some dog breeds (especially the Rough Collie, the Smooth Collie, the Shetland Sheepdog, and the Australian Shepherd), though, have a high incidence of a certain mutation within the MDR1 gene; affected animals are particularly sensitive to the toxic effects of ivermectin.
According to Dr. Stanley Coren, an expert on animal intelligence, the Shetland sheepdog is one of the brightest dogs, ranking 6th out of 132 breeds tested.
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