Q: When my mare sleeps, she lies flat out on her side and snores. Loudly. It’s quite funny to hear, but I worry it might be a sign of something wrong. Do horses get sleep apnea? Do I need to worry? She’s not obese but is a little on the chunky side. Should I have her lose weight? Any advice would be most appreciated. Name withheld by request

A: You’ve asked a very thought-provoking question! First off, it’s great that your mare is so comfortable with her environment that she spends a good deal of time sleeping on her side. In horses, this is the ideal position for REM (rapid eye movement or dream) sleep, an important stage in the normal sleep cycle.

Snoring that occurs only while a horse sleeps isn’t necessarily a problem as long as it is fairly regular. Respiration tends to be rhythmic during SWS (slow wave sleep) but can vary somewhat during REM sleep. Many animals (including people) do snore without experiencing a negative impact on their health—though it can be a different story for those who live with them. However, if your mare’s breathing is also noisy when she is awake, have her examined by your veterinarian.

In people with sleep apnea, breathing/snoring stops for extended periods and often resumes with a gasp or snort. This pattern repeats numerous times during the course of one night’s sleep. Sufferers aren’t generally aware of these episodes but do complain of excessive sleepiness during the day.

Sleep apnea comes in two forms, depending on the underlying cause. When the problem is caused by brain, nerve or muscle malfunction during respiration, it is referred to as central sleep apnea. The more common form is obstructive sleep apnea, which, as the name implies, is a blockage of airflow to the lungs. Obesity and certain anatomical conditions, such as an elongated soft palate, contribute to this problem.

The actual diagnosis of sleep apnea is made in a laboratory setting by documenting the occurrence of these events while recording the patients’ electroencephalogram (EEG), electrocardiogram (ECG), respiration and oxygen saturation as they sleep.

We still have a lot to learn about what constitutes normal sleep in horses, so diagnosing disorders is a challenge. At present, there are no actual reports of equine sleep apnea, but that doesn’t mean the condition (or something like it) doesn’t exist. Laryngeal hemiplegia (roaring) is associated with snoring as the result of airway obstruction and could also lead to similar sleep disturbances. Trauma and certain neuromuscular diseases also have the potential to make the rarer form of sleep apnea a possibility in animals.

If your mare’s snoring is erratic and her breathing stops and restarts as she sleeps, or she seems excessively tired during the day, make a video (including audio) of the behavior and show it to your veterinarian. He or she will help you decide whether your horse requires attention. Regardless, though, horses maintained at their ideal weight tend to be healthier overall, so I’d still address that issue. Perhaps your mare’s snoring will decrease in volume as she drops the extra pounds. She is very fortunate to have such a devoted owner.

Colette Williams, PhD
University of California–Davis
Davis, California