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How to deal with snakebite in livestock, horses

Barney Nelson snakebit - Barney Nelson photo.jpg
A veterinarian prepares to administer a drug to help relieve the swelling after a horse suffered a snakebite.
The danger or potency of a bite depends on the amount of venom injected by the snake and the type of toxin.

Rattlesnakes are the most common poisonous snakes in the U.S.--especially in the West.   The danger or potency of a bite depends on the amount of venom injected by the snake and the type of toxin—which can vary depending on the snake.   It also makes a difference where the bite is located.  A bite on the leg is usually not as dangerous as a bite on the face.  Swelling from a bite on the nose may cause suffocation if it shuts off the air passages.

Rob Callan, Colorado State University, says most cattle don’t get too “nosy” with rattlesnakes, but horses might.  “Most bites are on the lower legs, unless it’s a curious calf.  A bite on the leg causes swelling, and you might see some local bleeding.  The biggest problem would be infection in those tissues,” he said.

If you see the animal bitten, or suspect it was bitten, it is important to administer an antibiotic.  “There are bacteria in the snake’s mouth, and bacteria that proliferate in the damaged, dying tissue.  Most of the common antibiotics will work to prevent/combat these infections, and can be used in cattle—just about any broad spectrum antibiotic,” said Callan.  Some animals develop fever/and or septicemia from the infection, so antibiotics are helpful.

The bite is painful, so treatment with non-steroidal anti-inflammatory medications like flunixin meglumine (Banamine or generic versions) can also help the animal.  “Monitor the infection.   Some cases may require surgical removal of necrotic tissue, or draining and treating an abscess that forms,” he said.

Swelling may be severe.  “One of my first snakebite cases was a bull with a hind leg swollen all the way to the stifle.  We didn’t know what caused such horrendous swelling so we put the bull onto the examination table and looked at the leg more closely.  We clipped away the hair, and saw multiple double fang marks all the way up the leg.  I don’t know if the bull stepped into a nest of snakes or stepped on the tail of a snake and it just kept biting.  We treated the bite wounds, put the bull on antibiotics, and he recovered,” said Callan.

Toxins’ impacts

Usually the toxins don’t have negative long-term effects on large animals like adult cattle or horses but could have serious consequences for a small animal like a dog or young calf.  “The toxins can sometimes be a problem for horses, however, affecting the heart—causing irregular rhythm, or damage that can be fatal.  I have not seen that affect reported in cattle,” he said.

Bites in the face can be serious because swelling blocks the air passages.  These situations can be an emergency, and you need to provide an alternate way for the animal to breathe.  “One method is to place a piece of hose up each nostril, all the way through the nasal passages to maintain an open airway, before they swell shut.”  You can lubricate a short section of garden hose and pass it into the nostril. This will keep the airway open.

“If we can’t get an airway through the nostrils, we put in a tracheostomy insert,” Callan explains.  This involves cutting through the skin and into the windpipe, inserting a small hollow tube to keep it open until the swelling goes down.

Some people use DMSO topically on the bite area to reduce swelling, but this is not recommended for food animals like cattle.  Veterinarians generally recommend other anti-inflammatory medications like dexamethasone or NSAIDs instead.  These not only reduce swelling and fever, but also provide some pain relief.  In a dog or horse, however, DMSO can be given, and works very well.

Dr. Robert Cope, veterinarian in Salmon, Idaho, has treated many snakebites in livestock and pets.  He says the first priority in treating an animal with snakebite is to prevent/reduce the resultant swelling and inflammation, and dexamethasone is usually the best way to go, in cattle.

“With a snake bite, the venom is not the only concern.  Infection is sometimes the worst danger.  The bacterial population in that snake’s mouth is huge, and the bite victim often ends up with a nasty infection at the site of the bite,” Cope explains.

“The animal will definitely need antibiotics.  Any broad-spectrum antibiotic will usually work.  For cattle I usually choose tetracyclines rather than penicillin because penicillin doesn’t do a very good job on gram negative bacteria.  There are a number of antibiotics such as Baytril, Nuflor, Draxxin, etc. that work well in cattle.  In horses you don’t want to give those, however, and tetracycline is not advised for horses because it burns the tissues.  In cattle, however, there really isn’t any best or worst antibiotic; just give one as soon as possible,” he said.  Your veterinarian can prescribe one.

“If an animal is bitten by a venous snake, I think a rattlesnake is better than some of the others because what it injects into a large animal or a person is usually a cytotoxin (which is toxic to cells).  There is no neurotoxin involved unless the snake is biting its prey (small animals like mice or birds).”

Cytotoxin is what gets injected if the snake is startled and simply striking in self-defense at something it perceives as dangerous.  “The cytotoxin damages the tissue at the bite site, but not the nervous system.  Bites from some of the other snakes like water moccasins, coral snakes, copperheads, etc. are more dangerous in terms of being life-threatening,” Cope explains.

“There are some anti-venom preparations but I’ve never used these in cattle,” said Callan.  “These are expensive, and for commercial cattle considered cost prohibitive, but with horses and dogs, some owners request that treatment,” said Callan.  Snakebite can be a more life-threatening emergency in a dog, cat or small child.

Vaccine

Some ranchers (in regions with many snakes) vaccinate horses and ranch dogs.  This is cheaper than using antivenin after an animal is bitten and more likely to be beneficial if horses are on pasture and not observed closely (and you might not find one in time to save it) or a dog is bitten when you are moving cattle, a long ways from home.

A rattlesnake vaccine for dogs has been available for many years, and one for horses has been on the market 6 years—a conditionally-licensed inactivated Crotalus atrox Toxoid for use in healthy horses 6 months of age or older.  The equine rattlesnake vaccine is made with venom from the Western Diamondback Rattlesnake, and in vitro studies showed it to be effective in neutralizing this snake’s venom.

The label says it may also provide protection against venoms of the Prairie, Great Basin, Northern and Southern Pacific varieties, Sidewinder, Timber Rattlesnake, Massasauga and Copperhead.  It may provide partial protection against Eastern Diamondback Rattlesnake venom but does not provide protection against venom from the Water Moccasin (Cottonmouth), Mojave Rattlesnake or Coral Snake.

The vaccine requires a primary series of three doses at one month intervals.  Boosters are recommended at 6 month intervals.  Manufacturer information claims the product is safe for use in pregnant mares, however this information does not appear on the product label.  There is no specific information available regarding vaccination of foals less than 6 months of age.

Lyndi Gilliam, DVM (who did early studies with the vaccine) says rattlesnake venoms, while different in many ways, are also similar in many ways and contain many similar toxins. “This leads us to believe that antibodies made against one rattlesnake venom may be partially effective at neutralizing other rattlesnake venoms,” she says.

“I participated in the safety trial for the vaccine, and we only had a couple horses develop injection site reactions. These were mild and resolved without treatment.  The timing of this vaccine should be such that the horse will have the highest antibody titer during the peak rattlesnake season, which may vary depending on the geographic area. This means horses should receive all three initial vaccines prior to the beginning of rattlesnake season, with the last one at least 10 days prior to rattlesnake season,” she explains.  Subsequent years require just one booster unless the snake season is long.

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