Form of Vitamin E Supplementation Affects Oxidative and Inflammatory Response in Exercising Horses

Vitamin E is an essential antioxidant that may benefit athletes by reducing oxidative stress and influencing cytokine expression. Supplements can be derived from natural or manufactured synthetic sources. This study aimed to determine (1) if supplemental vitamin E is beneficial to exercising horses and (2) if there is a benefit of natural versus synthetic vitamin E. After 2 weeks on the control diet (vitamin E-deficient grain and hay), 18 horses were divided into three groups and fed the control diet plus (1) 1000 IU/d synthetic α-tocopherol (SYN-L), (2) 4000 IU/d synthetic α-tocopherol (SYN-H), or (3) 4000 IU/d RRR-α-tocopherol (natural source [NAT]). On day 7, horses began a 6-week training protocol, with standard exercise tests (SETs) performed before and after the 6-week protocol. Venous blood samples were collected on days 0, 7, 29, and 49. Horses fed NAT had higher α-tocopherol (P < .05) at post-SET1 through post-SET2. Plasma thiobarbituric acid-reactive substance levels were lower in NAT versus SYN-L horses after SET2 (P = .02). Serum aspartate aminotransferase was lower after exercise in NAT horses versus SYN-L and SYN-H (P = .02), and less reduction in stride duration was seen after exercise in NAT as compared with SYN-L and SYN-H (P = .02). Gene expression of tumor necrosis factor α was lower in NAT compared with SYN-H (P = .01) but not SYN-L. In conclusion, feeding higher levels of natural vitamin E source resulted in higher serum α-tocopherol levels as well as some improvement in oxidative and inflammatory response and improved functional outcomes in response to an exercise test.