Rattlesnake Bites in Horses

As an equine veterinarian, I'm often asked about rattlesnake bites this time of year. Rattlesnake bites usually occur in the spring and summer. The most common sites are on the nose, head, neck, and legs. Rattlesnake bites may or may not involve actual envenomation. Bites in which no venom is injected (dry bites) will cause some pain and minimal swelling. When envenomation occurs (wet bites) rapid swelling and pain follow, usually within 60 minutes of the bite. Fang marks are often difficult to find because of the amount of swelling.

Horses react differently to rattlesnake bites than dogs do. Unlike dogs, horses are less likely to suffer organ dysfunction from rattlesnake bites. It is the localized swelling and tissue damage around the bite that affects horses the most. Rattlesnake bites involving the muzzle are the most concerning. Because horses can only breathe through their nostrils (not through their mouths) swelling in the muzzle can cause respiratory difficulty. Severe swelling in the muzzle may require a tracheostomy. Some owners keep short lengths of hose on hand to place in their horse’s nasal passages to prevent airway obstruction in case of severe muzzle swelling.

Many horses that are bitten on the muzzle don’t require a tracheostomy if they are treated by a veterinarian with (non-steroidal and steroidal) anti-inflammatories soon after envenomation. Because rattlesnake bites tend to cause substantial tissue damage in the area of the bite they are often treated with broad-spectrum antibiotics. The wounds which develop days after the bite sometime need to be surgically debrided. 

There is now a very effective hyperimmune plasma available to treat rattlesnake bites in horses. This plasma greatly reduces the suffering horses experience if it is given promptly. 

The over-all prognosis for rattlesnake bites is usually good as long as they are treated promptly and the airway is protected. There is rattlesnake vaccine available for horses, but it important to note that it has so far only received a conditional license by the USDA. This means that it has been shown to be safe to give to horses, but its efficacy has not yet been proven.