Vitamin E

It’s interesting how feed/supplement companies have made horse owners think that they need to supplement all the vitamins. Research has shown that it’s generally unnecessary to supplement vitamins for horses on high forage diets. Of course, there may be exceptions but they are literally exceptions to the rule. Many of the vitamins are manufactured by the horse (via gut microbial fermentation) or are in the pasture and hay that horses eat. The main exception is vitamin E, especially for horses that are fed significant quantities of processed feed/hay or are in work.

Like selenium, vitamin E is an important antioxidant, especially in the neuromuscular and immune systems. Antioxidants protect the body against damage from reactive molecules, known as oxygen free radicals. These are generated in the body as a result of metabolism and cause cell membrane damage. It’s like the chemical reaction that creates rust on a bicycle or turns the surface of a cut apple brown – oxidation.

For horses in work, a vitamin E dietary shortfall can cause muscular problems such as poor performance, poor recovery, muscle weakness and soreness. It can even resemble ‘tying up’. Horses working at high levels produce large amounts of reactive molecules resulting in cell damage. Sufficient levels of vitamin E has a positive effect on muscle integrity in hard working horses, helping to neutralise free radicals which damage and weaken muscle tissue.

A number of specific conditions are associated with vitamin E deficiency including Equine Motor Neuron Disease (EMND), Neuroaxonal Dystrophy (equine NAD)/Degenerative Equine Myeloencephalopathy (EDM) and Vitamin E Deficient Myopathy.

Many studies have shown that the highest levels of vitamin E is in fresh grass. Ohio State University found that levels varied from 25-190 IU/kg (average, 110 IU/kg). IU = International units, the number of IU is a measure of potency. Schingoethe et al found levels ranging from 106 to 309 IU/kg (average, 219 IU/kg). Ballet et al found an average of 240 IU/kg and the older or more mature the stand of grass, the lower the vitamin E level. For some situations, this could mean up to 2000 IU or more per day, exceeding the NRC recommendations. From this we know that generally horses in no work where the intake is entirely or mainly fresh grass, especially actively growing grass don’t require additional vitamin E supplementation. For horses on mature stands of grass, there is no harm in feeding supplementary natural vitamin E, a reasonable amount is 500 IU/day.

Vitamin E content is lowest in hay with declining concentrations due to processing and storage.

If  your horse is in work, or doesn’t have the luxury of a high intake of fresh grass, then yes, vitamin E supplementation is beneficial. Many studies have shown horses benefit from vitamin E supplementation – some examples are below in the further reading section.