Some degree of exercise-induced inflammation is necessary during training for tissue repair and to help horses adapt to exercise. Too much, however, can cause inflammatory-related muscle damage and hinder performance ability.
Previous study results have shown that dietary omega-3 polyunsaturated fatty acids, specifically docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA), might reduce inflammation in conjunction with eicosapentaenoic acid (EPA); however, the ideal dose in the diet has yet to be determined. In a recent study, Tanja Hess, DVM, PhD, and colleagues from Colorado State University aimed find out the ideal dose of DHA to reduce inflammation in exercising horses.
Hess and her team tested three doses of a DHA supplement on post-exercise inflammatory responses in 20 trained and conditioned polo ponies. They first assessed body condition score and body weight, then sorted each horse into one of four groups that received:
- A control diet of concentrate and free-choice hay;
- The control diet with 10 grams of DHA per day;
- The control diet with 20 grams of DHA per day; and
- The control diet with 50 grams of DHA per day.
Before starting the study and 30 and 60 days after beginning dietary treatments, the team conducted lactate threshold tests (LT, designed to trigger inflammatory reactions) on each horse. These tests included a warm-up phase, trot phase, and incremental 2-minute gallop phases at increasing speeds depending on the horse’s threshold (determined when blood lactate concentrations exceeded 5 mmol/liter). The team took blood samples and measured lactate levels before and two minutes after each gallop phase and sampled blood before and after each LT test to identify markers of inflammation and other parameters.
As the researchers expected, blood plasma DHA was highest in horses consuming the DHA-supplemented diets, and plasma DHA increased in all treatment groups over time. At Days 30 and 60 of the treatment diets, vitamin E concentrations dropped below the baseline sample (that taken prior to starting treatments) in horses receiving the 20 g and 50 g DHA doses, indicating that supplements containing higher doses of DHA did not contain sufficient antioxidant levels.
Exercise normally increases inflammatory cytokine (a protein secreted by certain immune system cells) concentrations and subsequent inflammation. Study horses consuming 10 grams of DHA per day had the lowest interferon gamma and IL-10 (two pro-inflammatory cytokines) changes post-exercise, compared to horses consuming 20 or 50 grams DHA per day.
“Probably due to the lack of antioxidants, the anti-inflammatory effect was absent” in the 20- and 50-gram horses, said Hess.
Based on these results, the team determined that the DHA supplement did not contain enough antioxidants to prevent more than 20 grams of DHA from oxidizing (undergoing a chemical reaction with oxygen that rendered the DHA ineffective) prior to being fed.
Supplementing exercising horses’ diets with 20 or 50 grams of DHA does not alter exercise-induced inflammatory markers, Hess’s team concluded. They believe that with higher levels of DHA, the long-chain fatty acids get oxidized prior to being fed. Even so, horses receiving 10 grams of DHA a day showed signs of lower inflammation, warranting further research in this area.