Rattlesnake Bite Recourse in Horses

“A snake bit Mac on the nose!” says the alarmed horse owner who has just called the clinic. My technician and I head out to the owner’s farm immediately because quick treatment is crucial with these cases. As we arrive, we see a rattlesnake slithering away into the deep grass, confirming our fears.

Mac’s muzzle has already started to swell; soon the swelling will obscure the serum-­oozing fang marks. We ­immediately start ­treatment, which includes administering non-steroidal anti-­inflammatories (NSAIDs) and antibiotics and moving Mac under shelter to protect him from the sun. Rattlesnake venom can damage the liver, and the sun’s rays only increase this risk. The owner makes arrangements to transport Mac to our hospital.

By the time Mac arrives, the swelling has spread to his eyes. We administer fluids intravenously (IV) along with one vial of antivenom. The swelling continues, closing Mac’s eyelids partially and limiting his vision. Mucoid (mucousy), blood-tinged fluid accumulates in his nostrils, which have swollen to the point that his air passages are dangerously obstructed. To maintain air flow, we insert open syringe cases into both nares. If this isn’t sufficient, we have a tracheostomy tube (which veterinarians can use to assist breathing during airway surgery) ready stallside.

After two hours Mac’s facial swelling stops, and within five hours the nostril swelling subsides to the point that the syringe case tubes fall out. Three days later Mac returns home. Although he still has some minor swelling, he’s no longer likely to die. Mac is one of the lucky ones; the reported death rate from rattlesnake bites is 9-25% in horses.

We schedule an exam to assess his heart rhythm and rate six months later, because that’s when snakebite-caused heart damage generally manifests.

Rattlesnakes live in all but the most upper of the United States. They hibernate in the winter, are active in the summer, and breed around August. Bites occur most often on the muzzle, but also on the limbs. In my experience, bites are more common in curious, naive, or young horses, although last year we had two client horses bitten during a trail ride. Both horses moved off the cleared path into the long grass, where horse and rider couldn’t see the snake.

A bite’s severity depends on its location, the amount of venom introduced, the horse’s immune response, the size of the snake, and other factors. Venom causes profuse bleeding and, therefore, swelling in the tissues, followed by necrosis, or tissue death. The toxins move through the circulation and cause necrosis of the heart muscle, often resulting in ­permanent damage.

The most important thing to remember about rattlesnake bites is that successful outcomes are more likely when you get veterinary treatment right away. This consists of relieving clinical signs as we did with Mac, using pain control, antibiotics, IV fluids, and maintaining the airways. Some veterinarians also administer corticosteroids and/or antihistamines. We administer IV antivenom, which is a product prepared from the serum of horses exposed to venoms. It provides an antidote to the venom, decreasing its toxic effects. Reports in veterinary literature show fatality rates in horses decreased from 10% to 0% with antivenom, and fatality rates in dogs decreased 50%. In our practice, we have seen a reduction in the amount of swelling and number of days horses remain hospitalized, as well as a lower death rate using antivenom.

There are ways to help prevent snake bites. First, stay on trail paths if ­possible—this goes for your dogs, too. Before heading into a grassy area, throw some rocks or sand to scare off any unseen predators. If you spot a rattler on the trail, stay at least 8 to 10 feet away, and it will usually leave you alone. Examine horses living in snake-infested areas daily for swellings characteristic of bites. A preventive vaccine, Crotalus Atrox Toxoid, is available, with anecdotal reports of less severe clinical signs in bitten vaccinated horses. It can also reduce the pain associated with rattlesnake bites in horses. If you suspect a bite, call your veterinarian immediately, and keep your horse out of the sun.