Q. My pony yawns (sometimes several times in a row) after I stop to give him a treat or when he comes out for a walk. I have heard this means a horse is stressed, but it always seems to happen along with pleasant things that he likes. What’s the truth about yawning?

Heather, via e-mail

A. Yawning in horses is much like yawning in people; it occurs in a few different contexts. The most common situation in which horses yawn is in association with the state we know as drowsiness. This is sometimes before a period of standing sleep, but most often occurs as they are waking or rousing from a period of recumbent or standing rest or sleep, often when they are stretching and walking off after a long rest. A second common situation in which people and horses yawn is when something in the environment has caused a sudden fright or has aroused the individual, then things quiet down again. In some circumstances, this could be a stressful arousal, but it can also be a pleasant arousal.

Physiologically, yawning is associated with a variety of neurochemical substances that are secreted in the brain in association with changes in state of arousal, and research is just beginning to evaluate the relationships. If you do a Google search on "yawning" on the Internet, you will find some science articles about current research. Sometimes excessive yawning (much more than your pony does) is associated with medications that affect the brain chemistry. For example, some of the common antidepressant drugs given to people cause excessive yawning