Vitamin E Testing and Understanding Results

When should I test my horse’s vitamin E levels?

If you are seeing any of the following signs of vitamin E deficiency, talk to your vet about testing.

• Lack of energy or sour attitude
• Stiff before and sore after exercise
• Anxiety when being trained or ridden
• Poorly developed topline
• Abnormal neurological exam
• Evidence of muscle myopathy
• Poor immune response

What is a normal level of vitamin E found in the blood?

There are several ways to measure a horse’s vitamin E levels, including testing via blood plasma or serum or muscle. Depending on the lab your veterinarian uses to have your horse’s blood sample analyzed, your results can be recorded using different units.

Testing units:

• ug/mL (micrograms per milliliter). The range for ug/mL is 1 to 10.

• ug/dL (micrograms per deciliter). The range for ug/dL is 100 to 1,000.

Understanding the results:

• Adequate is above 2 ug/mL (200 ug/dL). The preferred range is 3 ug/mL to 6 ug/mL (300 ug/dL to 600 ug/dL).
• Marginal is 1.5-2 ug/mL (150-200 ug/dL).
• Deficient is less than 1.5 ug/mL (150 ug/dL).
• The recommended range for the average performance horse is 3 ug/mL to 5 ug/mL (300 ug/dL to 500 ug/dL).

As noted above, labs report differently. Most use micrograms/milliliter. But Cornell University uses micrograms/deciliter, so its reported numbers run 100 times larger (with “adequate” between 200 and 600). To convert Cornell’s measurements to the more typical micrograms/milliliter, move the decimal point two places to the left. In 2025, Michigan State University changed the method it uses to measure vitamin E, and there is no way to convert that measurement to other lab results because of the different methodology. That method reports adequate levels between 3 to 9. To avoid discrepancies, pick one lab and stay with it.

It is best to keep blood levels below 10 ug/mL (1,000 ug/dL). There has been no toxic level of vitamin E established in horses, but researchers at the University of California, Davis, are studying whether over-supplementation can cause issues in horses.

When should I retest vitamin E levels?

Work with your veterinarian to determine when retesting is needed. If you supplement with a water-soluble natural vitamin E liquid that can double blood levels in two to three days, then you can test sooner than if you are using a natural powder or pellet, which takes about eight weeks to raise levels.

Should I test my horses annually?

You can test annually as part of your wellness exam, but if your horse is adequately supplemented and isn’t show any symptoms of vitamin E deficiency, it isn’t necessary.

What type of vitamin E should I give my horse?

Both natural and synthetic vitamin E products are on the market. Knowing the difference is important. Product ingredients that include dl-alpha tocopheryl acetate are synthetic—the “dl” in the compound is the giveaway. Natural powder or pellets list d-alpha-tocopheryl acetate. Natural liquid lists d-alpha-tocopherol. Regarding which to give, if you supplement with synthetic, you must give a lot, and it takes a long time to raise levels.

Whether your horse needs powder/pellet or liquid depends on how fast you need to raise his vitamin E level. Natural powder or pellet is convenient to add to feed but takes eight to 10 weeks to raise levels. That’s fine in a horse who has no clinical signs of disease. By contrast, water-soluble natural vitamin E liquid can double blood levels in two to three days, which is better for horses with clinical signs or under acute stress.

When deciding what level of vitamin E supplementation to give your horse, consider other sources of natural vitamin E that may be part of his diet, such as fortified grains, balancer pellets or vitamin/mineral supplements. If you can’t tell if the vitamin E in a feed or supplement is natural, contact the manufacturer and ask.

What levels of vitamin E supplementation should I give my horse?

Below are recommended supplementation levels of natural vitamin E per day. But different horses doing different jobs and in different grazing situations need different amounts of vitamin E. Your veterinarian may recommend more or less, depending on your horse’s individual needs.

• Horses on full-time, good quality pasture in no work to light work: 1,000 IU in the winter only.
• Horses on full-time, good quality pasture in medium to heavy work: 1,000 IU to 2,000 IU depending on workload.
• Horses without access to pasture or on limited turnout, at maintenance or in light work: 1,000 IU to 2,000 IU.
• Horses without access to pasture or on limited turnout in medium to heavy work: 2,000 IU to 5,000 IU.
• Pregnant or nursing mares, regardless of turnout status: 3,000 IU.
• Foals: 3,000 IU.
• Horses with muscle myopathy or neurological disease may require 6,000 IU to 10,000 IU per day. Please consult with the treating veterinarian before supplementing at these levels. Severity of symptoms and current vitamin E status will inform supplementation levels.

Finally, remember to treat your individual horse. Horses can each respond differently to vitamin E supplementation even if they’re all taking the same supplement at the same dose.