Oxygen as Fuel
Dr. Melissa Mazan
Did you know that your horse – even if he is a lazy pasture potato – is considered an elite athlete? What is it about a horse that enables him at birth to have the physiological makeup of a supreme athlete? The answer is oxygen and the horse's unique ability to use it as fuel.
Without oxygen, your horse's body would slow and quit within a matter of seconds, and the ability to consume available oxygen is an indicator of how well your horse's body can use fuel when he is working aerobically. Aerobic metabolism refers to a mode where the body relies on oxygen, which encompasses all but sprint work. A horse that is less fit, or who is a poorer athlete, will have a diminished capacity to use oxygen. The superior athlete is the one who can use the available oxygen much more efficiently.
By determining the amount of oxygen a horse burns during maximum exercise, you can determine his athletic ability and how efficiently he uses oxygen. The results of the test are expressed in milliliters of oxygen used per kilogram of body weight per minute. This will determine the amount of oxygen a specific horse consumes when he is at maximum aerobic exercise. Horses with high numbers are considered more elite athletes.
There are many factors that go into the making of an elite athlete. Coordination, the will to win, and muscle strength are just a few of these factors. However, if we look at oxygen use, we must consider the portions of the horse's body that serve merely to transfer oxygen, before it is ever used as fuel. First your horse must have good airways, so that each breath delivers the maximum amount of air, with its accompanying oxygen, to the lungs. Examples of airway problems that impede the delivery of oxygen to the lungs include laryngeal paralysis and small airway inflammatory disease.
Once the oxygen is in your horse's lungs, the blood vessels in the lungs must absorb the oxygen and bring this oxygenated blood to the heart, where the hard-working heart sends the oxygenated blood to the rest of the body. A well-trained heart increases in size and weight, and, ultimately, in strength of contraction. When your horse is at maximal exercise, the muscles of motion receive the majority of available blood, whereas the blood supply to internal organs, such as the intestines and the kidney, is at a minimum.
Your horse needs high capacity airways and healthy lungs, a large, powerful heart and a plentiful blood supply. In comparison to less athletic species, even when we adjust for size, the horse has a greater lung capacity, a larger, more powerful heart, and more power within the muscles. When comparing horses to humans, the best human athlete will be able to consume 80 mls of oxygen per kilogram of body weight per minute. A thoroughbred racehorse consumes 180 mls of oxygen per kilogram of body weight per minute. This means that horses are able to utilize twice the amount of oxygen that the best human athlete can. It is truly an amazing difference.
You will probably never need to know your horse's ability to consume oxygen, but this value becomes important in the lucrative field of horseracing. By determining and improving a horse's ability to consume oxygen, the horse may be a better athlete and may become a more successful equine. To determine a horse's ability to consume oxygen, we need to know two things: the concentration of oxygen in the air that the horse inhales and the concentration of oxygen in the air exhaled. The difference between the two is the amount that the horse has had to consume in order to produce energy for the body.
An open respirometry system and a high-speed treadmill are used to determine oxygen use. The horse wears a mask that is attached by a series of tubes to an oxygen sensor. After the horse has been trained to the treadmill – this takes anywhere from a half hour to an hour – he begins an incremental exercise test (IET), otherwise known as a stress test. The horse begins at a walk, and at the end of each minute, the speed of the treadmill is increased until the horse is going at his fastest pace. The test is ended when the horse can no longer keep his position at the front of the treadmill. The amount of oxygen consumed is measured at the end of each step.
Improving Oxygen Consumption
By using oxygen more efficiently, a horse becomes a better athlete. Fortunately, there are ways to improve your horse's oxygen consumption through routine training. But don't expect your Morgan mare to turn into Cigar. In a study done at the Large Animal Hospital at Tufts University, the fitness level in Standardbred mares, who had been deemed too slow to race successfully, were monitored. A typical starting oxygen consumption value was 90 - 110 mls/kg/min. By the end of the study, their values ranged from 130 to 160 mls/kg/min – not the level of the top racehorse, but an impressive improvement nonetheless.
Interestingly, the lungs are the one link in the chain that do not have the capacity to improve, unless they were diseased in the first place. The major improvements are made in the capacity of the heart to pump blood, the density and size of the blood vessels in the muscles, red blood cell mass and the size of the muscles themselves. Thoroughbred racehorses are born with more of these attributes than are, for instance, Shetland ponies, and they will always be faster, no matter how hard the pony trains.