Use and Safety of Injectable Vitamin E-Selenium in Equine Practice 

At the 2025 American Association of Equine Practitioners (AAEP) Convention, held Dec. 6-10 in Denver, Colorado, John Madigan, DVM, MS, DACVIM, ACAW, and Carrie J. Finno, DVM, PhD, DACVIM, presented the results of a survey about practitioner use of intravenous or intramuscular vitamin E-selenium supplements. At the initiation of the survey, it was unknown how often equine veterinarians administered vitamin E-selenium. The findings showed it’s widely used, with newer practitioners administering it more frequently.  

Breaking Down the Survey Results 

Of 285 veterinarian responses, including 17% international reach, 40% administer vitamin E-selenium 3-10 times a year and 34% administer it more than 10 times a year. Over half (52%) use injectable forms of the supplement. The primary practice areas for vitamin E-selenium use are sport horse (65%), pleasure (50%), and racing (21%). 

The survey respondents justified its use for suspected deficiencies (54.5%) and performance support (28.7%). Neonatal foals comprised 61% of injectable vitamin E-selenium supplement recipients. Of the practitioners surveyed, 74.6% gave it IM and 16% IV. 

Concerningly, 31% of practitioners reported adverse reactions following administration, with 65% of those being anaphylaxis. Of the anaphylactic cases, 62% recovered and 35% were fatal. Other adverse reactions included injection site swelling and pain (48%), respiratory distress (16%), and diarrhea (6%). 

Despite the high incidence of adverse reactions, only 31% of veterinarians administering vitamin E-selenium injectable products discussed the risks with owners. Thirty-eight percent reported having risk mitigation protocols at the ready when giving the injection. That said, 90% of the surveyed veterinarians indicated they’d heard about adverse reactions from colleagues or through the literature. 

One-third of respondents said they believed the risks of using this supplement outweigh the benefits; one-third felt the risks do not outweigh the benefits, and 28% were unsure. Finno suggested this reflects a lack of consensus in equine practice about the use of injectable vitamin E-selenium. 

Considerations for Supplementation 

Finno said veterinarians have safer oral alternatives than injectable vitamin E-selenium for most indications. She also noted that the vitamin E in the injectable supplement is a synthetic form and, therefore, is not absorbable by the horse, making it essentially a nonuseful “medication.” She recommended evaluating a horse’s baseline selenium and vitamin E status before using an injectable product. If there is a significant medical need to use it for a time-sensitive issue (e.g., in a pregnant mare), a veterinarian should first advise the owner of the risks, then give it IM rather than IV while having emergency protocols on hand to reverse a serious adverse reaction such as anaphylaxis. She referred practitioners to the 2024 AAEP Proceedings for oral vitamin E supplements (liquid, powder, or pellets) that can achieve results in 2-3 days (liquid) to 8-10 weeks (powder or pellets), depending on the formulation. 

Citing the immediate death of an FEI Jumping horse in 2024 after receiving an IV injection of a vitamin E-selenium product along with other joint support medications, Finno said there is no reason to use vitamin E-selenium injectable products for “performance support,” because of their serious safety risks. 

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• Disease Du Jour: Noninfectious Neurologic Diseases in Horses
• Differentiating Noninfectious Neurologic Diseases in Horses
• Demystifying Equine Muscle Disease

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