Airways & Lungs - The Forgotten Organs
By the time a horse crosses the finish line in a five-furlong race, has completed a Grand Prix show jumping round, or gone one-sixth of the way around a 3 star cross-country course, he will have somewhere around 1,800 litres of air in and out of the lungs. If you find 1,800 litres hard to visualise, then think of six bathtubs full of air. This equates to moving two five gallon buckets of air into and out of the lungs every second.

The air inhaled during a race will consist of around 380 litres of oxygen, with the rest being made up of the gas nitrogen. The horse will take up into the blood and use about a quarter of this oxygen, i.e. 95 litres. Of the total amount of energy the racehorse needs to get from the starting gate to the finish line in the five furlong race, around 70% will come from aerobic (oxygen-based metabolism). The same can be said for the show jumping horse (70%) and a horse completing the cross-country portion of a three day event (90%).

Aerobic metabolism is essentially the process of using oxygen to get energy from glucose (carbohydrates) in structures inside the muscle cells know as mitochondria. The remainder of the energy comes from anaerobic metabolism, which also breaks down glucose to generate energy. The anaerobic system is very fast, but inefficient, and it can be used for only a short period of time due to build up of lactic acid. Aerobic metabolism is not so fast, but it is very efficient at generating the energy to run. So even in a race or jumping round lasting less than a minute, the majority of the energy generated by the muscles must come from using oxygen to “burn” carbohydrates. Even in a Quarter Horse race (involving short, intense bursts of speed) around 40% of the energy to run comes from aerobic metabolism. These examples underline the importance of the respiratory system. The harder a horse works, the more oxygen it needs and the more air it must move into and out of the lungs. In fact, these are so tightly coupled that if a horse doubles its speed, it will need twice the amount of air moved into and out of the lungs.

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