Cultural prejudices, lack of knowledge vilify snakes; clients should understand basics when bites occur
May 01, 2003

The rattlesnake's triangular-shaped head is one way to distinguish between a poisonous and non-poisonous snake.
Most people have a strong opinion about snakes-and it is usually bad.

We have been told that they are non-aggressive and that they do their part in the ecological scheme of things. Many rodents are kept out of feed rooms and kept from creating burrows in horse pastures by the presence of snakes on our farms.

Reptile experts are always reminding us that snakes would simply like to be left alone and that they are rarely a threat but, to the vast majority of humans, a good snake is a dead snake.

Culture casualtyThis attitude may be cultural since the snake has been associated with evil since the beginning of time.

The snake is the tempter and the original "bad guy" in biblical stories and snakes are almost always represented as cold, sneaky and untrustworthy.

Some of that attitude may come from the fact that most of us simply do not understand much about these unique creatures.

But when horses and snakes mix it is a good idea to have a bit of knowledge about these reptiles and to know how to treat snakebites.

Knowledge is powerIt is important that equine veterinarians learn a bit about the nature of snakes and the conditions that can result in snakebites in horses, as well as review the treatment of those injuries.

There's some good news and some bad news regarding snakebites. The bad news is that each year more than 8,000 people are bitten by poisonous snakes in the United States. The good news is that fewer than 10 deaths are reported yearly. That means that more people die from bee and wasp stings than from snakebites.

The exact statistics for the number of animal snakebites, and specifically for bites in horses, is unknown because many bites are unreported or unconfirmed. But because snakebites generally cause severe pain, long lasting edema, tissue damage and lameness, even non-fatal bites are to be taken seriously. Since the summer brings good weather for trail riding and other horse-related activities in the woods and pastures, it is more likely that horses and snakes will interact. Most bites occur in the southern and southwestern states between April and October.

Displaced reptilesMassive forest fires last year destroyed large tracts of forest and natural habitats. We tend to look at these natural disasters and sympathize (rightly so) with the people who lose their homes and neighborhoods. Often forgotten is the fact that countless animals also lose their homes and that they flee the fires into surrounding safer territory-often into more heavily populated areas that wild animals would never venture into if given a choice.

Equine sensitivityHorses are extremely sensitive to snake venom. They are followed, in order, by sheep, cows, goats, dogs, pigs, and cats. Humans are moderately sensitive and fall somewhere between dogs and pigs.

Horses and cattle, though very sensitive, seldom die as a result of snakebites. A lethal dose of venom is based on body weight and fortunately most horses and cows are simply too large for snakes to kill.

Important factorsOther factors that affect the severity of the bite should enter into a veterinarian's decision-making process when dealing with a snakebite. The type of snake is important. Some snakes are deadlier than others. The location of the bite is also important. Snake venom enters the circulatory system and is carried throughout the body causing damage. Bites closer to major arteries and areas of large blood supply are potentially far more serious than bites to the limbs and body. Fatalities in horses and cattle have been reported when the snakebite was on the face, head and neck.

Size and species of the victim and its age and general health and condition are also important determinants in the severity of snakebites. Generally larger, older horses in good nutritional condition without other medical problems seem to recover from snakebites easier and more quickly. Young foals and weak or sick horses are at a much greater risk of possible death or prolonged difficult recovery and these victims should be treated aggressively from the outset.

Know your adversaryBecause the type of snake is important in determining a treatment plan for a snakebitten horse, it becomes important to know your adversary. Not all snakes are poisonous. Every year countless harmless and potentially beneficial snakes are destroyed by overzealous animal owners. Non-poisonous snakes can still bite and their bites may need to be treated, but the snake may not need to be destroyed.

Venomous or poisonous snakes fall into two categories: the elipine snakes which include the cobra, mamba and coral snakes; and the viperine snakes which include the adders, pit vipers, rattlesnakes, cottonmouths, copperheads and moccasins. Elapine snakes have short fangs and tend to chew their victims. In this chewing motion they release a neurotoxic venom into the damaged tissue and vascular structures that eventually paralyzes the respiratory system and thus kills its prey.

RecoveryRecovery from bites by elapine snakes, if one is large enough, and not sensitive enough to be within the lethal dose of the snake's venom, rarely leaves any lasting effects. The best way to avoid being bitten by these snakes is to avoid travel to exotic locations. They are not generally found in the United States.

Viperine snakes are located throughout the Americas, however, and they have hinged fangs that strike, penetrate and withdraw. The motion is not unlike that of an intramuscular injection. The venom of these snakes is mainly hemotoxic consisting of potent enzymes and peptides. A vasculitis quickly occurs and massive edema, local bleeding and eventual tissue necrosis can occur. These problems can lead to tissue damage and skin necrosis even if the victim recovers and some local neurotoxins can lead to persistent lameness in some cases.

DifferentiationPoisonous snakes can be differentiated from non-poisonous snakes in some generally easy-to-remember ways that do not require close contact.

Poisonous snakes have an elliptical pupil while the pupil of non-poisonous snakes is round. Poisonous snakes have a triangular shaped-head that is generally larger than their body. Non-poisonous snakes taper to a head that is normally the same size as their body.

There are other distinguishing features such as the presence, in poisonous snakes, of single scales under their tails and a pit or hole under the nose and above the mouth but these are not practically identified in live snakes in the field. Noting the shape of the head and possibly the shape of the pupils can be done however and this information from a client will be helpful to you as you decide on treatment.

Common to U.S.The most common snakes encountered in the U.S. are the copperhead and various types of rattlers.

Rattlesnakes are relatively docile and give birth to live poisonous young. There can be many variations in color and markings between adults and their young and even variations noted in different locations within a country.

It's important to be aware of the colors and patterns in your practice area. The eastern diamondback rattler, the most dangerous American snake, can grow up to 8 feet long and weigh as much as 15 pounds. The fangs of this snake can penetrate thick hides. The western diamondback is a similar cousin but is smaller. It is responsible for the majority of recorded deaths in the United States.

The prairie rattler and the sidewinder (named for its unusual method of locomotion) are found in the western states, and the timber or banded rattlesnake is a northwestern snake often camouflaged in forested areas.

On the attackRattlers usually attack when they are startled as when a horse steps over a log in the trail to find a snake dozing in the shade on the other side.

Rattlers coil before striking, with a strike distance of one third to one half of their overall length. The sound a rattler makes is caused by the clicking together of special segments when its tail is vibrated. A wet rattler makes no noise and this can be important when your clients are riding among wet leaves or grasses.

Perhaps the most interesting fact about snakes is that the decision to inject venom during a bite is a voluntary action on the part of the snake and is totally under the reptile's control. Current theories state that the snake makes a decision as to whether the bite is protective (startled and trying to get away or to simply warn off a large predator that is too big to kill) or whether the bite is aggressive and designed to kill its victim.