Vitamin E in Horses: Testing and Interpreting Results

The importance of vitamin E in a horse’s diet cannot be overstated, especially for breeding stallions, broodmares, performance horses, and all horses and ponies without access to fresh pasture. Adequate levels of vitamin E in the body maximize antioxidant defenses that in turn optimize health and performance.

Signs of vitamin E deficiency vary. If your horse shows one or more of these clinical signs, discuss vitamin E testing with your veterinarian:

• Demonstrates lack of work ethic, including low energy or sour disposition
• Recovers slowly from routine exercise, especially if it worsens gradually over time
• Displays loss of muscle mass, particularly over the topline
• Performs abnormally on neurologic examination
• Shows evidence of poor immune response, particularly to challenges handled well in the past

Horses will show low blood levels before they ever show these clinical signs. Further, and often more frustrating, not all horses show clinical signs, no matter their blood level.

Interpreting Vitamin E Test Results

Once testing is complete, your veterinarian will receive a report from the laboratory. A copy of this report may also be sent to the horse owner.

Vitamin E levels are reported as a number with a specific unit, either µg/mL (micrograms per milliliter) or µg/dL (micrograms per deciliter). The range for µg/mL is 1 to 10, while the range for µg/dL is 100 to 1,000.

The following reference ranges are clinically appropriate for concentrations of vitamin E in serum (the amber-colored, protein-rich liquid that separates out when blood changes to a semisolid or solid state).

• Adequate vitamin E: above 2 µg/mL (200 µg/dL)
• Marginal vitamin E: 1.5-2 µg/mL (150 µg/dL)
• Deficient vitamin E: 1 µg/mL (100 µg/dL) or below

Blood levels should not exceed 10 ug/mL (1,000 ug/dL).

Follow-up Testing

Follow-up testing should occur after routine supplementation with a natural-source, water-soluble vitamin E supplement, such as Nano-E. Because Nano-E acts faster than any other supplemental source of vitamin E, retesting can be done in a matter of weeks. Other vitamin E products, especially synthetic versions, take much longer to incorporate into the bloodstream and tissues, and are less potent.

Seek the advice of your veterinarian about a reasonable retesting schedule, including the option for annual testing as part of a thorough wellness exam. This may be especially informative for performance and breeding horses, as they have elevated vitamin E requirements.

Finno, C.J., and S.J. Valberg. 2012. A comparative review of vitamin E and associated equine disorders. Journal of Veterinary Internal Medicine 26:1251-1266.