The Shetland Sheepdog, often known as the Sheltie, is a breed of herding dog that originated in the Shetland Islands of Scotland. Dogs carrying Mdr1-1 share a common ancestor that experienced remarkable evolutionary success, having contributed genetically to at least nine distinct breeds of dog. Due to this genetic mutation, affected dogs may exhibit sensitivity or adverse reactions to many drugs, including acepromazine, butorphanol, doxorubicin, erythromycin, ivermectin, loperamide, milbemycin, moxidectin, rifampin, selamectin, vinblastine, and vincristine. Shelties can also be great therapy dogs for those who need comfort during hard times such as natural disasters or severe illness. Due to this genetic mutation, affected dogs may exhibit sensitivity or adverse reactions to many drugs, including acepromazine, butorphanol, doxorubicin, erythromycin, ivermectin, loperamide, milbemycin, moxidectin, rifampin, selamectin, vinblastine, and vincristine. Shelties can also be great therapy dogs for those who need comfort during hard times such as natural disasters or severe illness. 