When a horse's diaphragm works correctly during breathing, what is its primary function?

The diaphragm plays a crucial role in breathing mechanics, and its primary function is to facilitate lung expansion. When the diaphragm contracts, it moves downward, creating more space in the thoracic cavity. This decrease in pressure allows the lungs to expand, drawing air in through the nostrils and down into the airways. As the lungs fill with air, oxygen is transferred into the bloodstream, which is vital for the horse's overall health and performance.

The effectiveness of this process is essential for a horse, particularly during exercise, as it enables efficient respiration and helps maintain optimal oxygen levels in the body. Thus, the correct choice emphasizes the diaphragm's role in promoting effective breathing and supporting vital biological functions related to respiration.