Sometime back I was giving a lecture and the question about natural compared to synthetic vitamin came up.  There is quite a bit of information in the literature concerning each of these sources of vitamin E.  If you use “natural source vitamin E” in the search box, you will get something like 31 million hits.  Doing the same with “synthetic source vitamin E” results in about 1/3 that amount.

The question I had was “which is better”.  I love open-ended questions.  What are the major differences between the two?  One difference is the chemical structure.  Natural vitamin E is called d-alpha-tocopherol and contains only one isomer or form.  Synthetic vitamin E is referred to as d,l-alpha-tocopherol or d,l-alpha-tocopheryl acetate and may contain as many as eight isomers, one of which is identical to the natural isomer.  So what?  The body will preferentially transport and incorporate the natural isomer making the bioavailability greater than that of the synthetic.  The natural source E will cross the blood-brain barrier much more efficiently than synthetic E.  For horses with neurologic issues that is very important.

Green forages are the primary source of naturally occurring vitamin E with as much as 50 IU of activity per pound of dry matter.  Grains have lesser concentrations.  The concentration of naturally occurring vitamin E decrease over time in stored feeds and may result in a wide variation in vitamin E intake in the horse.  Vitamin E activity is given in international units (IU) per milligram of vitamin E.  Natural source E contains 1.36 IU activity/mg while synthetic E provides 1.00 IU activity/mg.  Reports in the scientific literature suggest the natural source E is more efficient in raising the serum or plasma concentration of vitamin E compared to synthetic.

Should I be adding vitamin E to my horse’s diet and if so, which to use?  If your horse is on good green pasture is in good health and is not subjected to a great deal of external stress, then the odds of needing supplementation is very small.  On the other hand, if your horse has very limited access to good green pasture then supplementation may be warranted.  If he is receiving a good quality feed that has been fortified with vitamins and fed at the recommended intake, additional supplementation may not be required.  Horses even with some access to green grass that are in stressful situations may benefit from supplementation.  These include pregnant and lactating mares.  There is at least one report where natural source E was more effective in stimulating maternal IgG and IgM production in colostrum and enhanced vitamin E and IgM status in foals.  If you choose to supplement broodmares with E, I suggest only supplementing for the last 60 days of gestation and the first 30 days of lactation.  Work also increases the need for antioxidants, and you may consider increasing the E intake.  Horses that are being exposed to other horses, e.g. shows, I suggest using natural source E.  I think this is important given the amount of neurological issues we see occurring at many of the equine shows/competitions.

In summary:

• Vitamin E can be either natural or synthetic. Natural E is more potent and crosses the blood-brain barrier more efficiently than synthetic.  Natural E is more expensive.
• For horses diagnosed with neurological issues, natural E should be the preferred source.
• For horses with low serum or plasma E, natural E has been shown to be more efficient in raising the levels of E.

Horses exposed to stress may benefit from E supplementation regardless of form.  Vitamin E may be fed as a liquid or powder.

Natural Vitamin E Label

Synthetic Vitamin E Label