What is true about horses’ hormone levels?

Horses' hormone levels are primarily controlled by the pituitary gland, which is a critical part of the endocrine system. This gland produces hormones that regulate various bodily functions, including growth, metabolism, and stress responses. For example, the pituitary gland secretes adrenocorticotropic hormone (ACTH) which influences cortisol levels and can affect a horse's stamina and performance in competitive environments, such as rodeos. Understanding the role of this gland is essential for managing a horse's health and optimizing its performance in competitive settings.

Other options may touch on different aspects of horse physiology, but they do not accurately reflect the primary regulatory mechanism of hormone levels. While weight can be a factor in overall health and metabolic function, it does not determine hormone levels in a direct way. Similarly, external factors like weather can influence a horse's behavior and condition, but the primary regulation of hormones is achieved through the actions of the pituitary gland. Lastly, hormone levels are indeed significant to rodeo performance, as they can impact energy levels, stress responses, and overall health, which are crucial for an animal competing in high-stakes environments.