Does variable weather cause colic?

Can wide-ranging weather conditions affect your horse? A top vet weighs in on this hot topic.

A recent study of horses that suffered colic after a snowstorm indicates the bad weather likely wasn’t the reason. The probable cause: a decrease in exercise—the horses stayed in their stalls longer than usual—with no reduction in their daily grain ration. © Lisa Dijk/

Question: On the East Coast last winter, we had a lot of wide-ranging weather conditions. One day it was sunny and almost 60 degrees, the next it was 20 degrees and sleeting, with everything in between. I’ve heard of horses having a lot of trouble health-wise, especially colic, because of this variation. Is this true and, if so, is there anything I can do to protect my horse when the weather changes so drastically in a short period of time?

Answer: This subject has intrigued many people over the years, including experts who have studied it scientifically. So far, there is no evidence of any direct causal link between variable weather and an increased incidence of colic. However, there are several related factors that might explain this common observation. For example, broodmares experience a higher risk of colic immediately before and after they foal. A secondary effect of pregnancy, this is sometimes mistakenly blamed on the changing weather since most mares foal in the spring.

Another seasonally-related factor is parasites, specifically strongyles, which typically increase their egg production in the spring or early fall. The greater intake of larvae can sometimes cause colic in horses with heavy parasite loads.

In a recent study of weather and colic conducted by Virginia Tech researchers, the only observed correlation was one spike in colic cases coinciding with a major snowstorm. The researchers determined that this spike wasn’t caused by the weather itself, but rather by changes in the horses’ management. Those horses who suffered from colic had been stabled for a longer period of time than usual because of the storm. At the same time, though, they were still fed their usual grain meals. This disrupted the very important balance between exercise and energy. Horses expend a markedly decreased amount of energy when they’re kept in stalls versus when they’re turned out. Unless an indoor arena is available for maintaining their normal activity levels while stabled, their caloric needs drop significantly.

When a horse eats more grain than required to satisfy his immediate energy needs, it sometimes lingers in his digestive tract, causing uncomfortable gas. Furthermore, exercise stimulates digestive motility. In other words, it helps to move food through your horse’s system. So whenever he is stalled more than usual, it’s important to reduce his grain portions—or eliminate them altogether. (If he gets really fussy at mealtime, it’s OK to give him a handful of grain to keep him happy.) At the same time, provide plenty of good-quality hay. Forage doesn’t cause the same problems that grain does in these situations; in fact, it helps to keep your horse’s digestive system running smoothly.

There are two other problems that can be caused indirectly by extreme, rather than variable, weather. When temperatures drop near or below freezing, horses can become dehydrated, either because their water is frozen and inaccessible or because they don’t like to drink extremely cold water. Dehydration can lead to impaction colic, so find a safe way to heat your horse’s water to an acceptable temperature and monitor his water intake carefully during the winter.

On the other extreme, hot weather can contribute to potentially harmful electrolyte losses if your horse sweats excessively, for example, while competing in an endurance race or exercising with a heavy winter coat. Electrolyte imbalances affect the motility of the digestive tract so this, too, can increase the risk of colic. If you plan to compete in strenuous endurance events, ask your veterinarian how to design the right electrolyte-supplement plan for your horse. In most other cases, so long as you provide adequate water and a mineral salt lick, he should be able to maintain his electrolyte balance just fine.

Other than these examples, horses are generally very tolerant of weather changes—even severe ones—so long as no additional changes are made to their management routines. For example, horses turned out to pasture 24/7 are usually perfectly comfortable through all types of weather swings—from hot sun to cold rain to wind and snow—so long as they have decent shelter.

Studies do show that sudden changes in diet can increase the risk of colic, regardless of weather conditions. Switching the type of hay or grain that you feed your horse or turning him out into a lush pasture after months of keeping him in a drylot can disrupt the natural flora, or bacteria, in his gut. As a result, just like us, when horses eat a lot of something they’re not accustomed to, they get a stomachache. To give their digestive flora time to adjust to new food sources, a good rule of thumb is to introduce them in very small amounts and gradually transition to them over seven to 10 days.

Dr. Nathaniel White is a veterinary surgeon, author, professor and speaker widely recognized for his expertise on the topic of colic. He taught at Kansas State University and the University of Georgia before taking a position at Virginia Tech’s Marion duPont Scott Equine Medical Center in 1985. There, he served as the Theodora Ayer Randolph Professor of Surgery from 1987 to 2003 and the Jean Ellen Shehan Professor and Director from 2003 to 2012. He was named Professor Emeritus in Equine Surgery in 2013. Dr. White is also a former president and director-at-large of the American Association of Equine Practitioners and a past president of both the American College of Veterinary Surgeons and the ACVS Research and Education Foundation.

This article originally appeared in the August 2017 issue of Practical Horseman. 

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