How does intense exercise affect a horse's need for oxygen?

Intense exercise significantly increases a horse's need for oxygen due to the heightened demand for energy during physical activity. When a horse is engaged in strenuous work, its muscles require more oxygen to support the increased metabolic processes necessary for endurance and strength. This demand arises because muscles use oxygen to convert stored energy (from sources such as glycogen and fat) into usable energy in the form of ATP (adenosine triphosphate).

As the intensity of the exercise rises, the horse's respiratory rate increases to improve the intake of oxygen, and its heart rate accelerates to pump oxygen-rich blood more effectively to the working muscles. This physiological response ensures that the horse can maintain performance and avoid fatigue during intense periods of exertion. Therefore, the correct answer emphasizes the essential relationship between intense physical activity and the elevated requirement for oxygen to optimize performance and sustain activity levels.