Oral vitamin E supplementation on oxidative stress, vitamin and antioxidant status in intensely exercised horses.

This study investigates the effects of various levels of vitamin E supplementation on the oxidative stress and antioxidant health of vigorously exercised horses. The main finding is that excessively high vitamin E supplementation, nearly 10 times the recommended level, doesn’t reduce horses’ oxidative stress and could potentially inhibit beneficial processes involving beta-carotene.

Research Context and Objective

• Vitamin E is the most frequently provided antioxidant supplement for horses. However, there is no definitive consensus on the optimal level of this vitamin for horses that undergo intensive exercise.
• This research aimed to analyze the impacts of three different levels of oral vitamin E supplementation on both oxidative stress and vitamin/antioxidant status in strenuously exercised horses. The ultimate goal was to ascertain the best level of vitamin E supplementation.

Methodology

• Twelve unfit Standardbred horses were divided into three groups. They received either no supplementation (CON group), moderate supplementation (MOD group, 5000 iu/day), or high supplementation (HI group, 10,000 iu/day) of DL-alpha-tocopheryl acetate–a form of Vitamin E.
• The study was structured using a 3×3 Latin square design, which comprised three separate four-week supplementation periods followed by four-week ‘wash-out’ periods.
• After each supplementation period, horses underwent treadmill interval exercise tests. Blood samples were taken, and heart rates were measured before, during, and post-exercise.
• The collected data were analysed using the ANOVA testing method with repeated measures in SAS.

Results

• The study found that the CON group had a lower heart rate throughout the exercise test compared to the MOD and HI groups.
• Exercise led to an increase in plasma retinol, beta-carotene, red blood cell total glutathione, and glutathione peroxidase across all groups. However, all these levels returned to their baseline status after 24 hours.
• Exercise also led to increased levels of plasma alpha-tocopherol in all groups, with noticeable variations in treatment after 24 hours.
• It was found that the HI and CON groups had lower beta-carotene levels compared to the MOD group.

Conclusions

• The research concluded that horses, when given vitamin E supplements at a level nearly 10 times higher than the NRC-recommended level, did not show lower levels of oxidative stress compared to the control group horses.
• The HI group horses showed lower plasma beta-carotene levels, suggesting that high doses of vitamin E could inhibit beta-carotene metabolism.
• The study found that supplementation exceeding control levels is not more beneficial and can be potentially detrimental to the oxidative stress and antioxidant status in intensely exercised horses. Accordingly, extremely high vitamin E supplementation, especially those more than 10 times the control levels, should be avoided.