Equine cardiac disease is an uncommon but potentially serious condition. Clinical signs range from poor performance to sudden death, and causes in horses include congenital malformation, chronic valvular degeneration, cardiomyopathy, inflammatory or infectious disease, ruptured chordae tendineae, and cardiotoxins. Here’s we’ll review some common cardiotoxins that have been implicated in affecting horses in Central Kentucky.

Ionophores (e.g. monensin and lasalocid) are common feed additives and supplements intended for cattle, pigs, or chickens. Exposure occurs when horses have access to concentrated mineral premixes containing ionophores 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 exposure results in unthriftiness, 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 substance called cantharidin. Small amounts of cantharidin cause irritation to the gastrointestinal and urinary tracts. Moderate amounts cause cardiac muscle damage, low blood calcium concentrations, and synchronous diaphragmatic flutter (“thumps”). Large amounts cause shock and death within hours.

Taxus is a common cause of poisoning of horses in Central Kentucky. Taxus, or yew, is a popular evergreen ornamental 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 highest within the plant. Even a small amount of plant material 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