23 Sep 2021

What’s the deal with antioxidants in horses?

Eventing is a rigorous exercise challenge, similar to the human triathlon, that tests the physical ability and skill of both horse and rider during three separate phases:

  • In dressage, a standard set of movements is performed and awarded a subjective score.
  • Cross-country jumping requires horses to jump over 35 to 40 obstacles covering 5 to 7 km of terrain within a limited time.
  • For stadium, jumping horses are jumped over 10 to 12 obstacles arranged in a course set in an enclosed arena at four levels of difficulty.

Eventing is particularly demanding on the equine body. That said, it has been reported that although physical activity is beneficial to health, all forms of exercise cause oxidative stress (partly due to increased oxygen consumption) and the formation of reactive oxygen species (RPS) that could deplete antioxidant defences1.

When retraining and crossing from one discipline to another, unaccustomed, unconventional, or exhaustive exercise may also induce inflammatory reactions that contribute to exercise-induced muscle damage and subsequent muscle soreness2.  The same way a tennis player would feel the strain differently after 18 holes at St Andrews.

Dietary antioxidants may counteract oxidative stress however, by reducing the free radicals and reactive oxygen species associated with exercise induced cell damage.

The Study:  Antioxidant Status in Elite Three-Day Event Horses during Competition3

This study was done in 2012 to ascertain the effects of a demanding exercise activity, like a three-day event, on the antioxidant status of horses.

According to this study, equine athletes competing at the top levels of their disciplines, experience physiological stress that may compromise health and performance. During exercise, horses inhale more oxygen than usual to meet the oxygen demand of their muscles. Along with supporting the muscular oxygen needs, free radicals are produced, and horses suffer “oxidative stress.”

The Study Parameters

Horses and riders participating in this study were competing in either the CCI2* or CCI3* division. Competitors rode the 2005 FEI CCI2* or CCI3* event dressage test B for their respective divisions.

The event consisted of

  • a post arrival veterinary horse inspection on day 1,
  • dressage on day 2 or 3,
  • cross-country jumping followed by the second veterinary horse inspection on day 4,
  • and then a third veterinary horse inspection followed by stadium jumping on day 5.

Trial participants:

  • For both divisions, the majority of horses were male.
  • The majority of the horses were Thoroughbreds.
  • The average age of the horses was roughly 11yrs.
  • Horses competing in the CCI2* had been competing at that level for 0 to 1 yr (50.0%), 1 to 2 yr (30.0%), or 3 to 5 yr (20.0%)
  • Horses in the CCI3* had been competing at that level for 0 to 1 yr (52.2%), 1 to 2 yr (26.1%), or 3 to 5 yr (21.7%).


The following conclusions could be made from the study results:

  • The cross-country jumping phase of a three-day event is a challenge to the horse’s antioxidant systems.
  • In dressage, CCI3* competitions proved more demanding than the CCI2*
  • An increase in antioxidant response is potentially due to increased scavenging of oxygen radicals that are created by oxidative stress during intense exercise.
  • The oxygen radicals could also increase the likelihood of dehydration.

Horses that are fitter may be better able to handle the stress of a CCI3* three-day competition, but the increased intensity also places a great deal of stress on the muscle cells more than in lower levels of competition.

Antioxidants in horse diet

“Recovery start as soon as you mount up.”

But it may be even sooner than that.

With regards to antioxidants in horses, the study concluded that

  • it is likely that levels of antioxidants in the diet could enhance the horse’s ability to cope with the physical demands of the cross-country jumping phase of a three-day event,
  • could support cells and
  • act against the effects of rigorous exercise.

1  Powers SK, Jackson MJ. Exercise-induced oxidative stress: cellular mechanisms and impact on muscle force production. Physiological Reviews 2008;88(4):1243–76. [PUBMED: 18923182]

Tsai K, Hsu TG, Hsu KM, Cheng H, Liu TY, Hsu CF, et al. Oxidative DNA damage in human peripheral leukocytes induced by massive aerobic exercise. Free Radical Biology & Medicine 2001;31(11):1465–72. [PUBMED: 11728819]

Carey A. Williams, Amy O. Burk, “Antioxidant Status in Elite Three-Day Event Horses during Competition”, Oxidative Medicine and Cellular Longevity, vol. 2012, Article ID 572090, 8 pages, 2012. https://doi.org/10.1155/2012/572090


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