Ask a Vet: Rattlesnake Bites in Horses

Q: I have heard of several rattlesnake bites already this year, and some fatalities from them. How have you successfully treated a rattlesnake bite to an equidae? I’d especially like to hear from folks who had venomous bites, not just dry ones. We lost Josh’s mule last year to a bite and I would like to know how to reverse that outcome if it should happen to another critter. Antivenin is very expensive-do you vets keep it around…isn’t it expensive? Doesn’t it expire? Thanks in advance for any advice you can give me! ~ Lisa Wolters
 

Lisa,
This a great question and very timely as we are definetly starting to see these snakes emerge from their dens this time of year.  Rattlesnake bites are frightening and can be challenging to treat. Unfortunately there is currently no equine rattlesnake vaccine like they have for dogs.  Rattlesnakes present several unique challenges in the horse. 

The most important and most immediate is that unlike most species, horses are obligate nasal breathers, meaning that they can only breath out of their nose and not their mouth.  In addition, the majority of rattlesnake bites occur on the face or muzzle when horses are grazing and startle a snake.  When this occurs the face and muzzle can rapidly start to swell and within several hours after a snake bite nasal swelling may becomes so severe that horses are unable to breath.  If this occurs the horse often requires a procedure called a temporary tracheotomy; a surgical incision in the neck to open the trachea which allows the horse to breath.  In the event that your veterinarian is unable to get to you and your horse right away, two six inch segments of garden hose can be cut and inserted into the nostril to keep the airway open long enough for your veterinarian to reach you.  Once an open airway has been established horses should be started on antibiotics and anti-inflammatory drugs (usually NSAID, steroids or both) to decrease the swelling, pain and inflammation associated with the bite.

Horses may also need supportive treatment such as IV fluid or a liquid diet for a few days if facial swelling prevents them from being able to easily eat and drink.  In addition to the immediate life threatening facial swelling rattlesnake venom has several other slower onset complications.   The two most significant is the venom’s ability to effect blood clotting and its effect on the heart.  Horses can develop dangerous cardiac arrhythmias or they can sustain damage to the heart muscle itself causing heart attack like results. These side effects often don’t occur until several days(and in some cases up to months) after the snake bite.  Antivenin can be used to treat horses but there are several draw backs to its use.  First, in Texas where I practice we have several different types of venomous snakes in our area including the Coral snake for which rattlesnake antivenin is not effective and more often than not, the type of snake is unknown.  Second, very little research has been done looking at antivenin in the horse.  For that reason, the most effective dose is really not known.  Lastly, like you noted it is extremely expensive.  The cost for antivenin is about $2,000 per vial, the average human patient is usually given at least five vials.  For this reason most veterinary practices don’t keep it on the shelf but it can sometimes be obtained from nearby human hospitals.

Although rattle snake bites are painful and frightening, most horses survive them.  A recent study from the UC Davis School of Veterinary Medicine found that 91% of horses survived rattlesnake bites. The most important aspect of successful treatment of rattlesnake bites is rapid treatment.  My condolences for the lost of your Mule, and I hope this information helps prevent future tragedies from snake bites.
~ Rachel Wilson, DVM

Dr. Wilson is a native of Dripping Springs, Texas. She attended Texas A&M for her undergraduate studies in Biomedical Science and obtained her Doctor of Veterinary Medicine degree in the Spring of 2010. She has particular interests in lameness, internal medicine and surgery. Dr. Wilson joined Austin Equine as our first veterinary intern. She is member of the American Association of Equine Practitioners and the American Veterinary Medical Association. Dr. Wilson is thrilled to be living in the Austin area. Away from work, she is an avid rider and owns Malcolm, a twenty-one year old Thoroughbred.http://www.austinequine.com/

If you have a question you would like to ASK A VET, please email laurie@actha.us with the subject: ‘ask a vet’

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