Rattlesnake envenomation in horses: 58 cases (1992-2009).

Objective: To characterize signalment, clinical and laboratory findings, treatment, and outcome in horses with rattlesnake envenomation in northern California.

Design: Retrospective case series.

Animals: 58 client-owned horses evaluated for rattlesnake envenomation at 2 referral hospitals from 1992 to 2009.

Procedures: Records of horses with rattlesnake envenomation were reviewed, and data concerning signalment, clinical and laboratory findings, treatment, and outcome were collected. In addition, a rattlesnake-bite severity score (RBSS) was assigned to each horse. Variables were compared between horses that survived and those that did not.

Results: The overall mortality rate was 9%. Nine horses received antivenin; no complications were reported and none of the 9 died. The most common laboratory findings associated with severity of envenomation were thrombocytopenia, hypoproteinemia, hyperlactatemia, and a high RBSS.

Conclusions And Clinical Relevance: Most horses in this study had a good prognosis after being bitten by rattlesnakes. Laboratory and clinical examination findings may be useful for identifying horses with a poorer prognosis. Treatment with antivenin may be beneficial and warrants further evaluation.