Understanding Iron Homeostasis in Sport Horses

The essential mineral iron is a component of hemoglobin and myoglobin, a cofactor for metabolic enzymes, and a regulator of immune function and development. With these physiologic roles, iron is important for horses’ performance. Iron homeostasis in equine athletes might be impacted by exercise-induced inflammation’s effect on hepcidin, a liver-derived hormone that is a key regulator of iron balance in mammals. In a recent paper, researchers in Poland discussed our current understanding of iron homeostasis in sport horses.

Iron Loss in Sport Horses

Horses can lose iron through sweat, gastrointestinal bleeding (e.g., gastric ulcer syndrome), exercise-induced hemolysis or pulmonary hemorrhage, and increased iron utilization associated with increased levels of red blood cell production. In an endurance horse study, high hemolysis markers were associated with horses that were eliminated for metabolic reasons (versus horses eliminated for lameness or that finished the event).

Hepcidin elevates with inflammation and infection as a host defense strategy to reduce iron availability to pathogens. Chronic increases in hepcidin triggered by post-exercise inflammatory cytokines can lead to iron deficiency. High-intensity exercise that increases lactic acid accumulation stimulates hepcidin production, which reduces iron availability. The degree of exercise-induced inflammation depends on the type of physical activity, its intensity and duration, and the horse’s conditioning level.

Exercise also affects other hormones, including prolactin, testosterone, estradiol, progesterone, and growth hormone. These hormones might influence hepcidin regulation and iron metabolism in horses, but more research is required to understand the mechanisms.

Monitoring Horses’ Iron Levels

Veterinarians do not routinely test horses’ iron levels, but this information could be useful given iron’s impact on physical performance. The authors noted that hematological values from before and after exercise not only “reflect the dynamics of iron metabolism but also reveal the mobilization of the splenic red blood cell reserve” with exertion. They stressed that hematocrit, red blood cell, and hemoglobin values may decrease during training but might not reflect a true anemia due to exercise-related physiologic changes.

In humans, iron deficiency can impact aerobic performance, as it leads to mitochondrial dysfunction that causes decreased energy production and diminished muscle contractility. The authors suggested similar underlying physiological mechanisms might exist for horses.

Risks of Supplementation and Training Adaptations

Veterinarians should exercise caution when considering iron supplementation, as iron overload can cause oxidative stress, immune dysregulation, and liver lesions and fibrosis. Administration of erythropoietin can improve performance, but it can also increase red cell mass and blood viscosity with potential thrombotic events.

Altitude training improves blood volume and elevates 2,3-diphophoglycerate, which improves the horse’s aerobic capacity when returned to lower altitudes. Because of horses’ large splenic reserve, it is difficult to assess actual erythropoietin responses; there might be increased vascular risk from elevated pulmonary artery pressures.

Take-Home Message

Iron deficiency is rare in sport horses. In general, excessive iron levels are believed to be more detrimental than insufficient levels due to the risk of oxidative stress, damaged erythrocyte membranes, and secondary copper deficiencies that impair red blood cell production. “It is important to monitor iron parameters alongside inflammatory markers and hepcidin concentrations,” the authors wrote.

Reference

Kie.bik P, Witkowska-Pi.aszewicz O. Iron Status in Sport Horses: Is It Important for Equine Athletes? International Journal of Molecular Sciences. 2025, vol. 26; DOI:10.3390/ijms26125653

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• Research Spotlight: Preventing Heat Stress in Athletic Horses
• Does Carnitine Facilitate Rapid Exercise Recovery in Horses?
• Exercise’s Effects on Respiratory Pathogen Detection in Healthy Horses

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