Q. My 3-year-old gelding seems to be a very sound sleeper. I often find him flat out in his stall, snoring. Sometimes, I even catch him dreaming—or at least I think he’s dreaming—while he’s lying down sound asleep: He’ll moan and kick out a little or move his legs like he’s trying to run. I’ve received distressed phone calls from boarders at the barn who see my horse doing this and they think he is sick. Should I be concerned about these deep sleeps (my horse seems really healthy), and do you know whether horses really do dream?

A. Just like dogs, cats and humans, horses have sleep cycles, which are necessary to their health. The average duration of a sleep cycle in a horse is about 15 minutes, and a period of drowsiness usually precedes falling into a deep sleep. This may be an evolutionary mechanism once necessary to affirm that the environment is safe before falling into a deep, restorative slumber.

Most horses sleep between three to five hours per day. Usually, a horse will sleep in 30 to 40 minute bouts, about five to seven times during the night. “Paradoxical sleep,” more commonly known as REM sleep, is the time dreaming occurs. Horses usually reach this deep sleep for a total of approximately 45 minutes each day. A horse must lie flat in lateral recumbency to attain paradoxical sleep.

If your horse is relaxed in his environment and not disturbed by the goings-on in the barn,he is probably comfortable lying down and sleeping during periods when people are milling about. He also probably sleeps during the night hours, especially between midnight and 4 a.m. Horses are able to also rest and sleep on their feet, but in this standing state they won’t dream or go into the deep slumber of REM. A horse that rests in sternal recumbency (legs tucked under, head and neck upright) only reaches slow-wave sleep, without full relaxation. It is thought that while slow-wave sleep rests the brain, paradoxical sleep rests the body due to almost complete muscle relaxation.

To achieve a full sleep cycle, a horse must enter paradoxical sleep, and it sounds like your horse does commonly, or at least more often during the day than most horses. This does not mean he is sick, but rather that he is extremely comfortable with his surroundings. As your horse gets older, he will probably achieve his rest in more frequent periods of snoozing on his feet rather than lying flat out in the stall, where you currently find him galloping in the pastures of his dreams.

Expert: Nancy S. Loving, DVM, is a performance horse veterinarian based in Boulder, Colo. She is also the author of All Horse Systems Go.