What is the primary function of the spleen in horses during exercise?

The primary function of the spleen in horses during exercise is to store red blood cells, which contributes to increased endurance. When a horse engages in physical activity, the body requires more oxygen to be delivered to the muscles, and the spleen helps meet this demand by releasing stored red blood cells into circulation. This release enhances the blood's oxygen-carrying capacity, allowing the horse to sustain performance over longer periods.

While the spleen does have roles in filtering impurities from the blood and can be involved in various immune responses, its critical role during exercise is related to the storage and release of red blood cells. Other choices regarding hormone production and nutrient absorption do not accurately reflect the spleen's function in relation to exercise in horses. Thus, the emphasis on the storage and release of red blood cells underscores the spleen's importance in a horse's endurance and overall performance during exertion.