Vitamin E is particularly well known as an important nutrient for the normal function of muscles, the nervous system and cells. In equine nutrition, its importance increases especially when the amount of fresh pasture grass decreases or when a horse has no access to pasture at all.
A study published in 2025 provided interesting new information on the subject from a real-world horse population. The study, conducted at the University of Pennsylvania’s New Bolton Center, investigated blood vitamin E concentrations in horses presented to the hospital. The results showed that vitamin E deficiency was not an uncommon finding.
Around one in six adult horses was vitamin E deficient
The study included adult horses and foals presented to the hospital. Serum alpha-tocopherol concentrations were measured to assess vitamin E status.
Of all horses studied, 12.7% were vitamin E deficient on arrival at the hospital.
When adult horses were examined separately, the proportion was even higher:
16.5% of adult horses were vitamin E deficient.
In other words, approximately one in six adult horses had blood vitamin E concentrations within the deficient range. Among foals, the corresponding figure was 5.5%.
The researchers concluded that vitamin E deficiency occurs frequently enough in horses that measuring blood vitamin E concentrations should be considered, particularly when there are factors that may predispose a horse to deficiency or when vitamin E status may be relevant to the horse’s condition.
However, the study does not mean that one in six healthy horses is deficient
This distinction is important.
The horses included in the 2025 study were not a randomly selected group of healthy horses. They had been brought to an equine hospital either as patients or as companions to another horse. Therefore, the results cannot be directly generalised to the entire horse population.
Nevertheless, the study highlights an important practical point: inadequate vitamin E concentrations do occur in real-world horse populations, and vitamin E status should not automatically be assumed to be sufficient simply because a horse appears healthy and in good condition.
Pasture is an important natural source of vitamin E for horses
An earlier large field study supports the findings of the 2025 study.
The study investigated blood concentrations of vitamin E, selenium and beta-carotene in horses, as well as how feeding and management practices were associated with the risk of deficiency.
Among the horses studied, 15.4% had vitamin E concentrations within the deficient range and nearly 20% had marginally low concentrations. In total, more than one third of the horses therefore had concentrations that were either deficient or borderline.
One particularly interesting finding concerned access to pasture.
Horses that had access to pasture for more than six hours per day had higher blood alpha-tocopherol concentrations. Horses receiving at least 500 IU of supplemental vitamin E per day also had higher concentrations on average.
This is consistent with the basic principles of equine nutrition: fresh green forage is an important natural source of vitamin E.
When the grazing season ends and the diet becomes based mainly on conserved forage, vitamin E intake may change considerably.
Vitamin E is not preserved in forage in the same way as in fresh plants
Vitamin E is sensitive to oxidation. Once plants are harvested, dried and stored, their vitamin E content decreases over time.
For this reason, even very green hay does not automatically provide the same amount of vitamin E as fresh pasture grass.
In practice, this means that the end of the grazing season is a good time to reassess a horse’s vitamin E intake.
This is particularly important for horses that:
- have little or no access to pasture
- mainly eat conserved forage
- are in active work
- receive large amounts of added fat in the diet
- are growing, recovering or otherwise have increased nutritional demands.
Why do horses need vitamin E?
Vitamin E is a fat-soluble vitamin and one of the body’s important antioxidants.
One of its key functions is to help protect the fatty acids in cell membranes against oxidation. This is important in all tissues, but particularly in muscle and nervous tissue, where normal cell function is sensitive to oxidative damage.
During physical exercise, oxygen consumption and energy metabolism increase. At the same time, the body produces more reactive oxygen species.
This does not mean that exercise is harmful – oxidative processes are a normal part of metabolism. However, the body needs an effective antioxidant system to keep these processes in balance.
Vitamin E is one of the key nutrients involved in this system.
Natural or synthetic vitamin E?
The form of vitamin E may also matter.
A study published in 2020 compared natural and synthetic vitamin E in exercising horses. Horses receiving natural vitamin E achieved higher blood alpha-tocopherol concentrations than horses receiving the synthetic form. In addition, some markers associated with oxidative stress and inflammatory responses showed differences favouring the natural vitamin E group.
The study does not mean that synthetic vitamin E is ineffective. However, it supports previous evidence showing that natural RRR-alpha-tocopherol is utilised by the body considerably more efficiently.
This is one reason why it is worth checking not only the IU content of a vitamin E supplement, but also the form of vitamin E it contains.
More is not always better
When it comes to antioxidants, it is easy to assume that more must always be better.
Research does not support such a simple conclusion.
In a study involving intensely exercised horses, very high doses of vitamin E did not reduce markers of oxidative stress compared with the control diet. The researchers concluded that very large doses did not provide additional benefit and that excessive supplementation should be avoided.
The aim of vitamin E supplementation is therefore not to provide the highest possible dose, but rather to ensure adequate intake in relation to the horse’s diet and individual needs.
If there is uncertainty about a horse’s vitamin E status, blood alpha-tocopherol concentrations can be measured by a veterinarian.
What does this mean in practice for equine feeding?
Research highlights the importance of assessing the need for vitamin E supplementation in horses, particularly outside the grazing season in Nordic conditions.
It also reminds us of several important points:
- studies have shown that vitamin E deficiency does occur in horses
- pasture access is associated with higher blood vitamin E concentrations
- conserved forage does not provide vitamin E in the same way as fresh green forage
- the source and form of vitamin E affect how efficiently it is utilised
- unnecessarily high doses have not been shown to provide automatic additional benefits.
As the grazing season comes to an end in autumn, it is therefore a good time to check where your horse is getting its vitamin E from.
Natural vitamin E for targeted supplementation
CdGE is a 100% natural vitamin E supplement containing natural RRR-alpha-tocopheryl acetate.
The product provides 500 IU of vitamin E per gram, allowing vitamin E intake to be increased without adding large amounts of other feed. One 2.5 ml scoop corresponds to approximately 1.5 grams and provides 750 IU of vitamin E.
The product is intended to supplement a horse’s diet when vitamin E intake from the basic ration is insufficient.
However, a vitamin E supplement does not replace good-quality forage or the need to assess the diet as a whole. The appropriate amount depends on factors including pasture intake, forage, other complementary feeds, the horse’s workload and individual needs.
Perhaps the most important message from the 2025 study is simple:
Adequate vitamin E intake should not be taken for granted.
Especially as the grazing season comes to an end, it is a good time to check where your horse is getting its vitamin E from – and whether supplementation may be needed.
References
Palmisano MG, Colmer SF, Saw YL, Xu X, Stefanovski D, Murphy L, Johnson AL. Vitamin E concentrations in hospitalized adult horses and foals. Journal of the American Veterinary Medical Association. 2025;263(5):604–611. doi:10.2460/javma.24.09.0590.
Finno CJ et al. Influence of specific management practices on blood selenium, vitamin E, and beta-carotene concentrations in horses and risk of nutritional deficiency. Journal of Veterinary Internal Medicine. 2020.
Fagan MM et al. Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses. Journal of Equine Veterinary Science. 2020.
Williams CA et al. Oral vitamin E supplementation on oxidative stress, vitamin and antioxidant status in intensely exercised horses. Equine Veterinary Journal. 2007.
