Heed the snake's oath: "Don't tread on me"

Oct 8, 2010

”Autumn, with its cooler temperatures and shorter days, is a busy season for ranch horses. Fall works are underway and horses are a vital part of ranching operations. Autumn is also a busy time for rattlesnakes, too. The fall marks the beginning of hibernation for rattlesnakes as they begin to travel and return to their dens. So, if the leaves are fallin’, the snakes are crawlin’. They are returning to the dens they leave in late spring when they initiate the start of the next breeding season. Snakes are most active from April through October when the temperature is between 70-95 degrees and their activity decreases with temperature drops in the fall. Whenever the movement and activity of rattlesnakes increases, be it spring or fall, the incidence of horses bitten by rattlesnakes likewise increases.

Of the 28 species of rattlesnakes in the U.S., 21 live in the western U.S. Arizona and Texas take top honors for having the most species taking up residence. Within these states, the Western Diamondback Rattlesnake is the most numerous rattlesnake while the smaller Prairie Rattlesnake is the most widely distributed. Approximately 85 percent of the rattlesnake bites to horses occur in the western states and an overwhelming majority of these bites occur on the face, primarily on the nose when horses are grazing. Horses can also receive nose bites when they become curious to the sound, sight and smell of rattlesnakes. The second most common bite site, an estimated 15-20 percent, occurs on the lower limbs. There also are the unusual cases when horses receive rattlesnake bites to the chest, abdomen, upper legs or other uncommon locations when they are lying down.

Rattlesnake venom contains many toxins: myotoxins, which are muscle and tissue destroying enzymes, and hemotoxins, which are enzymes affecting the vascular system. These toxins cause primarily swelling and tissue damage, doing a veritable war dance on a horse’s muzzle. Signs of rattlesnake bites include significant to severe swelling, pain, and bleeding at the bite site.

Factors related to the horse’s outcome from a rattlesnake bite include whether the bite is an offensive bite or defensive bite used for immobilizing its prey. A rattlesnake can regulate the volume of the venom it injects and some species of rattlesnakes are more aggressive than others, but they can all look pretty aggressive and “on the prod” when they are buzzing, coiled up and ready to extend two thirds of their body’s length to bite someone or something. As well as venom quality, quantity and concentration factor into the local and systemic symptoms. For example, a Prairie Rattler’s venom is estimated to be about three times more concentrated than a Diamondback’s venom, but Diamondbacks can get much larger, allowing them to deliver more venom. Depletion of toxin stores after a recent meal can lessen the severity of a bite or produce a “dry” bite in which no venom is injected.

Size, species, health, age of the snake and conditions of its fangs can additionally affect the severity of the bite. Worst-case scenario for a rattlesnake bite to a horse (or anyone for that matter): Healthy eight-foot Western Diamondback, that has good fangs, is really mad and hasn’t eaten since his last rabbit two weeks ago. Bestcase scenario for same horse et al: Sickly one-foot Western Diamondback with broken fangs that doesn’t get too excited when he bites and has just depleted what venom stores he had left only minutes ago when he bit a slow-moving rabbit.

When a horse gets a snake bite to the nose, one or both nostrils can become partially or completely shut. Because horses are obligate nose breathers, unable to breathe through their mouths, there is a characteristic difficulty seen in their respiration. Breathing rates are elevated, and their nostrils can flare a bunch ... sometimes a whole bunch, the equine version of “gasping for air.” Lethargy is normally present. Ranch work suddenly becomes a lesser priority to a horse.

The capacity for a horse’s ability to breathe through its swollen nose can be estimated by placing a hand in front of each nostril to feel the air movement, and these horses can have trouble eating and drinking due to the swelling and pain. Luckily, most facial bites resolve within a week’s time with early treatment. Not so with leg bites, however.

Rattlesnake bites to horses’ legs can behave a bit different. These horses with lower leg bites are usually lame with moderate swelling, pain and bite-site drainage, and may have to receive more lengthy and extensive treatment. Plus, rattlesnake bites to a horse’s legs aren’t always quite as forgiving as they are to a horse’s face. Approximately 20 percent of lower leg bites result in chronic problems such as lameness, infection, arthritis, tissue sloughing, scarring, dysfunction and laminitis.

Although it is uncommon for a horse to have to deal with systemic problems such as dehydration, fever, shock and irregularities in heart function, these symptoms, when present, do develop fairly quickly. Chronic problems such as liver and heart damage can be a consequence of rattlesnake bites. They may lose some of their stamina—“ain’t got no bottom to him anymore.” But it is rare for horses to die from snakebites and, when this occurs, it is usually from asphyxiation when both nostrils are completely swollen shut.

When a horse receives a rattlesnake bite, minimizing the horse’s movement or excitement prevents further absorption and circulation of the venom. A calm horse is less likely to further increase its respiratory rate through already restricted air passages. A calm owner is helpful likewise. Halters may not fit over the bridge of a swollen nose, so ropes, with a noseband looped through it, can be used.

Initial emergency treatment is aimed at ensuring that the horse can move air through its swollen nasal passages. Useful tools such as cut-off garden hoses or plastic syringe barrels and cases can be placed a distance, about 4” – 6”, up the lower portion of the horse’s nostrils to open up the airways. Vet lube or oily Vit A and D on the end of tubes makes passage easier. Although this is a handy procedure, some horses won’t tolerate it because their nose hurts too much to touch and/ or they are frightened. Tubes and human hands may be the last thing that horse wants near his painful, swollen muzzle. In lifethreatening situations, veterinarians may have to perform temporary tracheotomies.

Medical treatment used by veterinarians to decrease swelling around the bite site and minimize some of the other effects of rattlesnake venom includes steroids and non-steroidal anti-inflammatory drugs. Tetanus prophylaxis is necessary in cases of rattlesnake bites and antibiotics are used systemically and locally in wound therapy on leg bites. Hydrotherapy, running water over the swollen legs, is very helpful, and some bite wounds may eventually need to be bandaged. Draining or puncturing the bite site with hypodermic needles should never be done and these procedures can cause further damage to the bite site (as well as damage to the person poking 14-gauge needles repeatedly into a horse’s nose.) Wetting the hay and feed can make it easier for some horses with swollen, painful facial bites to eat.

In general, rattlesnake bites to horses are fairly easy to recognize when they occur on the face due to the characteristic swelling and fang bites. A quick corralside diagnosis of a typical rattlesnake bite to the nose of a horse can use the following thought process: If it looks like a duck, and quacks like a duck, it’s probably a duck, (looks like a snake-bit horse, breathes like a snakebit horse ...).

But lower limb bites occasionally stir the pot and can be confused with other syndromes such as infection from other causes. All in all, horses that have been bitten by rattlesnakes generally have a good prognosis with treatment, however, leg bites can result in more extensive treatments with a higher rate of longterm problems than face bites.

So a good herd health suggestion to the remuda:

“Watch where you step.” — Ginger Elliott, WLJ