Horses often yawn when they are drowsy, hungry, or stressed. | Photo: iStock

A: Horses often yawn when they are drowsy, hungry, or stressed. Pain is one source of stress, but anything that increases arousal—including physical discomfort, fear, excitement, or mental challenge—can induce yawning. Physiologically, yawning is a response linked to increased cortisol levels, elevated body temperature (called the “brain cooling” theory of yawning), or gastrointestinal discomfort.

Yawning is an involuntary reflex, so it’s unlikely that your horse is yawning on purpose. To avoid being bridled—which might also mean to avoid being ridden—a horse will typically learn to move its head out of reach or press its mouth closed.

Physical discomfort or emotional stress are the most likely reasons that your horse is yawning. It might be in anticipation being bridled or ridden; however, what happens before he yawns—such as being groomed, saddled, or girthed—is probably a more important clue. This is because animals tend to yawn after the stressor is taken away (for example, many horses yawn at the end of a strenuous work or when the bit is removed). You can test this by changing the order of your routine and bridling first, to see if and when your horse still yawns