Rattlesnake Bites in Horses: A Retrospective Review

Rattlesnake Bites in Horses: A Retrospective Review

The overall mortality rate of horses bitten by rattlesnakes, like the one seen here, was 9% in the current study, a lower percentage than reported in previous studies

Photo: Eileen Hackett, DVM, MS, Dipl. ACVS, Dipl. ACVECC

Rattlesnakes can pose a serious threat not only to humans and small animals, but also to horses. Horses bitten by rattlesnakes have historically had a higher mortality rate compared to other species, but according to the results of a recent study, their chances for a recovery might be better than originally thought.

Because rattlesnake venom contains a mixture of natural products, a bite can cause numerous problems in horses including extensive tissue damage, coagulopathy (clotting abnormalities) and/or thrombocytopenia (low platelet counts) leading to bleeding disorders, cardiovascular toxicity (heart damage), and neurotoxicity (nerve damage).

A recent retrospective study led by Langdon Fielding, DVM, Dipl. ACVECC, of Loomis Basin Equine Medical Center (LBEMC) in Loomis, Calif., reviewed records of 58 equids that had received treatment for rattlesnake bites at either LBEMC or the Veterinary Medical Teaching Hospital at the University of California, Davis, between 1992 and 2009. Fielding hoped to evaluate treatment and outcome in horses with rattlesnake envenomation.

Fielding applied a ten point scoring system, known as rattlesnake bite severity score (RBSS) in which a score of 10 is the worst possible scenario, to each case for comparison purposes,

Key findings in the study included:

  • The overall mortality rate of equids in this study was 9%, a lower percentage than reported in previous studies;
  • All horses with an RBSS of eight or less survived;
  • The study's most successful treatment was an equine-derived antivenom (made by "administering low doses of venom to horses and then harvesting the plasma," explained Fielding), and all nine horses that received the antivenom survived, had no complications in treatment, and recovered completely;
  • Other treatments identified in the study included antimicrobials for fighting infection, non-steroidal anti-inflammatory drugs (NSAIDs) for pain, corticosteroids to reduce inflammation and control immune response, and isotonic crystalloids to keep the animal hydrated; and
  • More than half of the horses in the study required a tracheotomy to maintain respiratory function.

"Most horses in the study had a good prognosis after being bitten by rattlesnakes," Fielding reported. "But more research is needed to evaluate the importance of specific treatments as some of them such as corticosteroids and antimicrobials may not be necessary."

In the event a horse is bitten by a rattlesnake, owners are advised to call a veterinarian immediately and immobilize the animal to reduce the amount of toxin spread throughout the system. As with most ailments, the quicker the horse receives veterinary attention, the better prognosis they have.

The study, "Rattlesnake envenomation in horses: 58 cases (1992-2009)," was published in March 2011 in the Journal of American Veterinary Medical Association. The abstract is available online.

About the Author

Casie Bazay, NBCAAM

Casie Bazay holds a bachelor of science degree in education from Oklahoma State University. She taught middle school for ten years, but now is a nationally certified equine acupressure practitioner and freelance writer. She has owned Quarter Horses nearly her entire life and has participated in a variety of horse events including Western and English pleasure, trail riding, and speed events. She was a competitive barrel racer for many years and hopes to pursue the sport again soon.

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