With warm weather comes the increased risk of snakebite. The major venomous snakes in the United States are the pit vipers, including rattlesnakes, water moccasins, and copperheads. Pit vipers are named after the heat-detecting holes, or pits, on each side of the head that help the snake locate prey. Pit vipers can be differentiated from other snakes by their triangle-shaped heads, narrowed necks, and tail rattles (rattlesnakes only). Coral snakes, another type of poisonous snake in the United States, do not pose much risk to horses because of their small mouth size.
Venom components vary tremendously by snake species, but most venoms contain substances that cause breakdown of tissues and blood vessels, impair blood clotting, and damage the heart. Venoms from some species of snake also contain neurotoxins. Snakebite severity depends on multiple factors such as snake species, size, recent feeding, and number of bites. Some bites are “dry bites,” where little venom is injected. Other bites, such as when a snake is stepped on and releases all of its venom agonally, can be very severe. Victim factors such as horse size, age, disease conditions, medications, and bite location also influence bite severity.
Clinical signs of snakebite in horses vary widely but generally include pain and swelling at the bite site, and often sloughing of tissues near the bite. Bite wounds might not be readily apparent. Dry bites with little venom injected or bites from copperhead snakes often cause only mild signs. Bites from dangerous species of snakes and large doses of venom can cause marked pain and swelling, coagulopathy (the blood’s ability to clot is impaired), hemorrhage, cardiac arrhythmias, shock, collapse, and even death. With neurotoxic venoms, paralysis can occur. Horses bitten on the nose can develop nasal swelling and respiratory distress. Signs of envenomation can occur within minutes or be delayed for many hours.
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