Oxidative Stress and Antioxidant Status in Horses Competing
in the Jersey Fresh CCI** and CCI*** (Short Format)
 

Carey A. Williams, Ph.D.
Departments of Extension Specialists1 and Animal Science,
Rutgers University, New Brunswick, NJ

ABSTRACT: Oxidative stress occurs in horses undergoing endurance exercise as well as maximally intense exercise. To minimize the stress of event horses we first need to quantify the current nutritional management practices of the horses and take a series of blood samples during an intense 3-day event competition. The competition will be located in Allentown, New Jersey at the Jersey Fresh CCI** and CCI*** short format version without steeplechase. Horses will have blood taken before, immediately after and the day after cross-country. Blood will be analyzed for various oxidative stress and antioxidant status measures to determine the level of stress these horses undergo during competition. From these results we might be able to more definitively recommend nutrition and management strategies to increase the health and well being of performance horses during competition.
 

Problem and Significance

     Losses of top equine athletes at the 1992 Olympic Games in Barcelona and the 2002 World Equestrian Games in Jerez have provoked public interest in the performance and welfare of competitive horses. Oxidative stress is now recognized as one of the possible dangers. Oxidative stress occurs when the antioxidant defense system in the body is overwhelmed with reactive oxygen species (ROS). An increase in ROS may occur due to increased exposure to oxidants from the environment, increased production within the body from an increase in oxygen metabolism during exercise, or an imbalance in antioxidants. Useful properties of ROS include targeting of bacteria and viruses by the immune cells and serving as special messengers within nerve cells. However, if ROS accumulation becomes too great it can be damaging to the DNA, protein and fats in cells. Oxidative stress has been suspected to cause certain diseases (e.g. cancer, AIDS, and Alzheimer’s disease) and has been linked with the aging process and exercise.

     Reactive oxygen species are oxygen-containing molecules that are more active than the oxygen contained in the air we breathe. They are normally produced during the metabolism of oxygen. During oxygen metabolism, about 98 % of the oxygen consumed forms water and carbon dioxide; however, about 1 to 2 % of the oxygen is not completely consumed and instead becomes ROS.

     Antioxidants are substances that may prevent oxidant damage in several ways: getting rid of ROS; making ROS less reactive; helping repair damage caused by ROS; and providing an environment favorable for activity of other antioxidants.

     Vitamin E is the most commonly supplemented antioxidant in horses. In one study, vitamin E was supplemented above and below NRC (1989) recommendations, and they found that oxidative stress did increase after intense exercise. Results have also shown that horses conditioned for several weeks or subjected to repeated bouts of exercise may require higher levels of vitamin E than recommended.
Evidence of possible oxidative stress in horses has been described in reports dealing with maximally intense exercise and long distance endurance exercise. Oxidative stress occurs in conjunction with muscle membrane leakage of enzymes in endurance horses. Survey results from endurance horses have correlated with measures of oxidative stress and antioxidant status during an endurance ride.

Results from a study performed on Thoroughbreds immediately post-race showed an increase in the breakdown of fats that make up the membranes around cells (cold lead to destruction of the cell) compared to pre-race levels. In another study, immediately after and eighteen hours after intense exercise there was a 25 % increase in this fat breakdown, and an increase in total glutathione was also found immediately after exercise. A further study in horses demonstrated an increase in fat breakdown 5 and 30 min after maximal exercise, which returned to resting levels by two hours post-race.

     These are examples that oxidative stress does exist in the intensely exercising horse; however, there has never been an attempt to determine the oxidative stress of competitive event horses or develop feeding management practices that could reduce the levels of oxidative stress in these horses.

Objective

The objective of this study is to measure the amount of oxidative stress a seasoned event horse undergoes during a three-day event competition. We will also determine the level of antioxidants in the horses’ systems and hope to evaluate the need for additional supplementation during exercise and/or competition.
 

Study Details

     Horses from the Jersey Fresh CCI** and CCI*** will participate in the study pending the rider’s signature on the Research Authorization Form (enclosed). Horses will have blood samples collected by the principal investigator (Dr. Carey Williams) immediately after their first inspection on Wednesday, May 31st, 2006. Another blood sample will be collected immediately after horses enter the veterinary check box after the Cross-Country phase on Saturday, June 3rd. A final blood sample will be collected on Sunday morning, June 4th, immediately after the second horse inspection. Also collected during this study will be weights and body condition scores on Wednesday and Sunday. Heart rate, temperature, respiration and the respective recovery data will be taken from the veterinary box information after cross-country on Saturday.

     Blood samples will be collected via a venous jugular needle puncture. The blood will be immediately placed on ice, and processed into red blood cell and plasma aliquots. The samples will then be frozen at -80°C for storage until further analysis. Red blood cells will be analyzed for glutathione peroxidase (GPx), and glutathione (GSH), and blood plasma for creatine kinase (CK), lipid hydroperoxides (LPO), albumin (ALB), -tocopherol (TOC), and ascorbate (ASC).

Possible Results

Results from this study will help determine the level of stress horses are under during a three-day event competition. From these results we might be able to more definitively recommend nutrition and management strategies to increase the health and well being of performance horses during competition.