What is the purpose of a mouth gag?

The purpose of a mouth gag is to keep a horse's mouth open during examination or procedures. This is essential because it allows veterinarians or technicians to effectively inspect the horse's teeth and oral cavity without obstruction. Having a clear view and access to the mouth is critical for performing thorough dental examinations, administering treatments, or performing any necessary procedures that require the horse's mouth to be held open.

In this context, the other choices address different aspects of horse health care. While breathing is an important consideration during examinations, the mouth gag specifically assists with visibility and access, not breathing. Restraint tools are also used to keep a horse still, but they operate under different principles and aren't exclusively for accessing the mouth. Regarding diet control, that falls outside the function of a mouth gag, which focuses on providing access for examination rather than influencing dietary habits.