Oral vitamin E supplementation on oxidative stress, vitamin and antioxidant status in intensely exercised horses.
BACKGROUND
Vitamin E is the most commonly supplemented antioxidant in horses; however, previous research is not conclusive as to the recommended level for exercising horses.


OBJECTIVE
To evaluate the effects of 3 levels of vitamin E supplementation on oxidative stress and vitamin/antioxidant status in intensely exercised horses to determine the optimal level of vitamin E supplementation.


METHODS
Twelve unfit Standardbreds were divided into 3 groups, supplemented orally with 0 (CON), 5000 (MOD), or 10,000 (HI) iu/day of DL-alpha-tocopheryl acetate. The 3 x 3 Latin square design consisted of three 4 week supplementation periods with 4 week wash out periods between. After each period, horses underwent a treadmill interval exercise test. Blood samples were collected and heart rate (HR) measured before, during and after exercise. Data were analysed using ANOVA with repeated measures in SAS.


RESULTS
The CON group had lower HR throughout the test compared to the MOD and HI groups (P<0.05). There was an increase in plasma retinol (RET), beta-carotene (BC), red blood cell total glutathione and glutathione peroxidase with exercise (P<0.05), but all groups returned to baseline after 24 h. Plasma alpha-tocopherol (TOC) increased from baseline with exercise (P<0.0001) in all groups; treatment differences were observed at 24 h (P<0.05). The HI and CON groups had lower BC compared to the MOD group (P = 0.05).


CONCLUSIONS
Horses supplemented with vitamin E, at nearly 10-times the 1989 NRC recommended level, did not experience lower oxidative stress compared to control horses. Additionally, lower plasma BC levels observed in the HI group, which may indicate that vitamin E has an inhibitory effect on BC metabolism.


CONCLUSIONS
Supplementation above control levels is not more beneficial to oxidative stress and antioxidant status in intensely exercising horses; indeed, levels 10 times in excess may be detrimental to BC and should be avoided.
Williams
C A
CA
Rutgers, the State University of New Jersey, Cook Campus, Department of Animal Science, 84 Lipman Drive, New Brunswick, New Jersey 08901, USA.
Carlucci
S A
SA
D000284:Administration, Oral; D000704:Analysis of Variance; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000975:Antioxidants / Q000008:administration & dosage* / Q000378:metabolism; D018592:Cross-Over Studies; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006736:Horses; D009752:Nutritional Status; D018384:Oxidative Stress / Q000187:drug effects*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D014810:Vitamin E / Q000008:administration & dosage* / Q000097:blood; D019207:beta Carotene / Q000037:antagonists & inhibitors* / Q000097:blood / Q000378:metabolism
D000975:Antioxidants; D019207:beta Carotene; D014810:Vitamin E