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According to some researchers, milk thistle (Silybum marianum) confers health benefits to horses, including anti-inflammatory and antioxidant properties. When the benefits of milk thistle were evaluated recently in exercising horses, the stress hormone cortisol was lower in those supplemented compared to the control group, suggesting that supplemented horses were better able to manage the rigors of athletic training.*

In a study of 12 fit Czech Warmblood driving horses, a wide variety of blood parameters were assessed after supplementing horses with milk thistle for 56 days. Horses in the experimental group were given 19.4 g of milk thistle per day in a barley-based extruded feed, while the control horses received the same extruded feed without milk thistle. All horses were otherwise cared for under identical conditions.

On the day of experimentation, all horses were driven for two hours, a usual bout of exercise for them. Horses worked in pairs, with one horse pulled from the control group and the other from the milk thistle group. Blood samples were collected prior to exercise and again 15 and 60 minutes after intense exercise. The blood samples were evaluated for liver and kidney health, energy metabolism, and stress (via cortisol levels). Antioxidant capacity and muscle function were also evaluated.

“The most notable observation in this study involved lower post-exercise cortisol levels in horses supplemented with milk thistle,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

The data showed that cortisol levels increased in both supplemented and unsupplemented horses during exercise. Specifically, cortisol values were higher in blood samples taken 15 minutes after exercise than in samples collected 60 minutes following exercise when levels were returning to pre-exercise values.

“Studies show that exercise increases cortisol with peak levels observed at 15-30 minutes after exercise. In this study, horses supplemented with milk thistle had significantly lower increases in cortisol 15 minutes after exercise,” Whitehouse said.

“The authors noted large individual variation in cortisol response to exercise and suggested that, when using cortisol values to assess stress, they should be approached according to individual pre-and post-exercise levels,” Whitehouse added. “Nonetheless, the potential benefits of milk thistle supplementation on modulating exercise-induced stress response are interesting and warrant additional investigation.”

This study also found that milk thistle supplementation did not have any effect on liver or kidney function.

“Nutritional strategies and tailored training programs can help reduce stress related to exercise and competition. For more information on feeding performance horses, access Kentucky Equine Research’s 90-page guide titled Nutrition of the Performance Horse,” advised Whitehouse.

For optimal antioxidant protection, choose a traditional antioxidant supplement such as Nano-Q10, researched and formulated by Kentucky Equine Research. This unique antioxidant uses nanotechnology to create a rapidly available and absorbed source of coenzyme Q10 that is three times more bioavailable than powdered crystalline ubiquinone. Coenzyme Q10 helps protect cells from free radical damage and improves the antioxidant potential of other antioxidants in the body, like vitamins C and E.

*Dockalova, H., D. Baholet, A. Batik, L. Zeman, and P. Horky. 2022. Effect of milk thistle (Silybum marianum) seed cakes by horses subjected to physical exertion. Journal of Equine Veterinary Science 113:103937.

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