Cardiovascular Health Is Essential for Exercising Horses

The exercising horse depends on a number of different physiological systems to supply fuel to the muscles and remove waste products during exercise. Any one of these systems may limit the horse’s ability to work. The horse’s well-developed cardiovascular system is among the most important for supporting performance.

Once oxygen has entered the bloodstream from the lungs, it must be transported to working muscles, and waste products must also be removed. Cardiac output (CO) is a measure of how much blood the heart can move per minute. CO is the product of heart rate (HR) multiplied by stroke volume (SV). HR in healthy resting horses varies from 25-45 beats per minute and averages around 32-35. Horses have a maximal HR of 220-250 beats per minute. SV is around 0.8 – 1.2 liters per beat. Therefore, at maximal exercise, CO can reach over 250 liters per minute. This is comparable to pumping a 55-gallon drum of blood through the heart each minute. This massive CO is one reason horses are such good natural athletes.

As a horse becomes more fit, SV tends to increase and HR at a particular speed decreases. Measuring the speed at which a horse can exercise at a specific HR (i.e., 180 or 200) gives a good indication of its relative fitness. Low-cost HR monitors are available that enable horsemen to monitor their horse’s training progress in the field.

Oxygen is carried through the blood stream in red blood cells, so the number of these cells can affect performance. Horses have the ability to store as many as half of their red blood cells in the spleen when they are not exercising. When strenuous exercise begins, these cells are mobilized into the bloodstream where they can quickly double the blood’s oxygen-carrying capacity. A deficiency of red blood cells (anemia) could possibly limit performance, but this usually only happens when the horse has suffered some type of blood loss, infection, or illness. Nutritional anemia (iron or vitamin deficiency) is rare in horses.