Equine Health Update Issue 2 Volume 19 - Page 29

EQUINE | Equine Disease Update phores formulated for cattle or through a feed-mixing error. Acute ionophore intoxication causes anorexia, muscle tremors, rapid heart rate, and respiratory distress due to heart failure. Chronic expo sure results in unthrift- iness, poor performance, exercise intolerance, rapid breathing, and sudden death from cardiac damage. Blister beetles can be found in alfalfa hay, and are toxic to horses because they contain a highly irritating sub- stance called cantharidin. Small amounts of canthari- din cause irritation to the gastrointestinal and urinary tracts. Moderate amounts cause cardiac muscle dam- age, low calcium, and synchronous diaphragmatic flut- ter (“thumps”). Large amounts cause shock and death within hours. Taxus is a common cause of poisoning of horses in Cen- tral Kentucky. Taxus, or yew, is a popular evergreen orna- mental shrub. Almost all parts of the plant, including the seeds, contain highly toxic compounds called taxines. In the winter, the concentration of taxines is at its high- est within the plant. Even a small amount of plant ma- terial can cause rapid heart failure. Because taxines act so quickly, horses ingesting yew are often found dead without signs. When present, signs include weakness, incoordination, slow heart rate, and difficulty breathing. White snakeroot is a perennial woodlands plant com- mon throughout the Eastern United States. White snake- root contains a mixture of compounds called “tremetol.” Intoxication is sporadic because the concentration of tremetol in the plant varies depending on location and prevailing growing conditions. Tremetol causes conges- tive heart failure and cardiac degeneration in horses. Tremetol can pass into the milk, poisoning nursing foals. Rhododendrons, azaleas, laurels, mountain pieris, and fetterbush all contain grayanotoxins. Grayanotoxins cause either slow or rapid heart rate, abnormal rhythm, weak pulse, and cardiac arrest. These plants are particu- larly attractive in winter because their leaves remain green. Milkweeds, or butterfly weeds, are wildflowers as well as cultivated ornamentals. Some milkweeds contain car- diotoxins called “cardenolides.” Signs can begin within hours of plant ingestion and include slow or rapid heart rate, low blood pressure, and arrhythmias. Fresh cardio- toxic plants are generally unpalatable. They are more edible as clippings or baled with hay, but are no less toxic than fresh material. Venomous snakes native to North America include the pit vipers—rattlesnakes, water moccasins, and cop- perheads. In Central Kentucky, timber rattlesnakes and copperheads are the most common. Most pit-viper ven- oms comprise dozens of different components, some of them as yet unidentified. Snakebites in horses most of- ten occur on or near the muzzle and can result in severe swelling and edema. If the nasal passages become so swollen that labored breathing ensues, a tracheostomy may be necessary. Bleeding, tissue necrosis, and second- ary bacterial infection around the bite wound are com- mon sequelae. Some venoms contain cardiotoxins that damage the heart. Antivenins are available but must be administered in a timely manner, as they cannot reverse tissue damage that has already occurred. Many other substances can be cardiotoxic, including a number of additional plants, medications (e.g. xylazine and theophylline), and illicit drugs (e.g. amphetamines and cocaine). Contact: Megan Romano, DVM Veterinary toxicology resident Megan.romano@uky.edu (859) 257-6777 Uni- versity of Kentucky Veterinary Diagnostic Laboratory Lexington, KY. • Volume 19 no 2 • June 2017 • 29