Carey Williams, Ph.D., an associate equine specialist at Rutgers, the State University of New Jersey, described the importance of antioxidants in equine nutrition, highlighting the studies she has undertaken during her tenure as a researcher.
Oxidative stress occurs in horses at all times but is accelerated during exercise, aging, and disease processes. Defense mechanisms against oxidative stress include vitamins E, C, and A as well as certain enzymes. Though oxidative stress cannot be directly measured with ease, intermediate or end products during oxidation can be measured.
The first two studies discussed by Williams involved 80-km endurance rides. In the first study, 46 horses were separated into two groups and given either vitamin E, or vitamin E and vitamin C. for three weeks prior to the race Thirty-four horses completed the race. Conclusions derived include that horses were in fact undergoing oxidative stress, though the effects of antioxidant supplementation could not be evaluated as beneficial because there was no control group used in the study.
In the second study, 40 horses were used. Two groups were created following the race: finishers and nonfinishers. Levels of vitamin E consumed prior to the races differed considerably, ranging from 1150 to 4700 IU/day. Most horses with high vitamin E intakes had greater access to pasture than horses with lower intakes. A negative correlation was found between the vitamin E intake and muscle damage, and a positive correlation was found with intake and plasma vitamin E. A negative correlation was found between finishing time and vitamin E intake for the 24 horses that finished the race. According to Williams, one hypothesis for this finding could be that the higher-placed horses were working at greater intensity and/or being trained harder, thus having more sweet feed or supplements in the diet. Their higher level of conditioning may also have allowed these horses to work harder with lower muscle enzyme activities.
In the third study, treadmill-trained Arabians were separated into three groups: vitamin E, lopoic acid, and control. A simulated endurance exercise test of three exercise bouts totaling 55 km, with 20-minute vet checks separating each. Apoptosis (programmed cell death) was measured. Results showed that apoptosis occurs in white blood cells during exercise, and it can be moderated by supplementation with vitamin E or lopoic acid. The vitamin E group had 50% lower and the lopoic acid group had 40% lower apoptosis compared to the control group. The increase in antioxidant status in the vitamin E and lipoic acid groups aided the white blood cells in scavenging the free radicals, thereby triggering the apoptosis in these cells.
The studies presented by Williams have positively shown oxidative stress during endurance, intense, and treadmill exercise, though oxidative stress and muscle-enzyme leakage was dependent on numerous factors (environmental conditions, level of exercise, conditioning of horse, for example). Supplementing with antioxidants decreases oxidative stress and muscle-enzyme leakage.