Very high doses of vitamin E appear to benefit older horses' immune systems and could be an inexpensive means of battling "immunosenescence"–the decline in immune function because of the aging process.

"Horses have an increased susceptibility to infection because of a decline in immune function with advancing age," said Katherine Petersson, PhD, animal scientist and assistant professor at The University of Rhode Island.

Since vitamin E is known to play a key role in immune system function, Petersson's research team evaluated the effect of vitamin E on horses' immune function and response to vaccination against West Nile virus.

Sixteen older horses with an average age of 18.9 years were studied. Horses in the treatment group were supplemented once daily with 15 IU vitamin E/kg body weight–15 times the amount recommended in the NRC (2007 Nutrient Requirements of Horses). Blood was collected every two weeks for 16 weeks and all horses were vaccinated with a recombinant West Nile virus (WNV) vaccine at weeks seven and 14