Q. I live in an area in which winter is extremely cold and snowy. Keeping unfrozen water available for my horses is a challenge, especially in their pasture. I have noticed my horses eating snow when they’re turned out, even though water is available. Do I need to give them water, or can they get enough water from the snow during turnout?

—Via e-mail

A. As a rule, horses need continuous or frequent access to clean water at all times. This certainly poses a challenge when temperatures fall below freezing. Tactics such as floating tennis balls in troughs will prevent water from freezing when temperatures are at or very slightly below freezing. However, when temperatures fall well below freezing, as we have seen across much of the United States in the past week, these tactics don’t work.

Horses kept on snowy pasture will lick and eat snow, and this certainly provides a source of water. The question is, however, is it enough to meet the horse’s needs and prevent dehydration?

What One Study Found

There appears to be limited research on this topic, but a group of Norwegian researchers studied a group of Icelandic horses on pasture for more than a year to observe how extreme weather conditions affected the horses’ shelter use. As part of that study, they drew blood at intervals throughout the year, which allowed them to compare hydration parameters.

Due to some unexpected extreme weather conditions, the horse’s only natural water source froze for nine days during the second December of the trial. There was approximately 20 centimeters (nearly 8 inches) of snow on the ground during this period of time. The researchers drew blood on the horses at the end of the nine-day period to osmotic concentration to samples collected in other seasons, including samples taken the previous December. An increase in the osmotic pressure of the fluid surrounding cells stimulates receptors in the brain, which in turn promote the excretion of a hormone called vasopressin. Vasopressin is an antidiuretic hormone that reduces the amount of fluid lost in urine to help maintain bodily fluid levels. Additionally, studies have shown thirst in other species results after a 3% increase in osmotic concentration occurs.

The horses showed no physical change in appearance after relying on snow as their sole water source for nine days, and the researchers didn’t observe any change in the herd’s feed intake or feeding behavior—their feeders were filled with grass silage at the same frequency whether the horses had water available or not. A veterinarian examined the horses and found no clinical signs of ill health, including response to skin turgor testing (elasticity when pulled, or the “pinch test,” an indicator of hydration).

Also at the end of the nine-day period, the researchers gave the horses access to water from their commonly used drinking bowls and reported that they showed very little interest in drinking—some did not drink, and those that did only drank for a few seconds.

Bloodwork showed no significant differences in osmotic concentration between the samples taken after nine days without free water and the one taken the previous December, when the horses had access to water. With the lack of free access to water in this case, the researchers expected an increase in osmotic concentration; however that did not appear to occur.

The horses appeared unaffected by having only access to snow as a water source for the nine-day period.

Horses Still Need Access to Water

The researchers concluded that horses eating grass silage and adapted to consuming snow can manage for several days with snow as a substitute for liquid water. However, there are some important points to understand about these conclusions when applying them to horses kept in similar, but not identical, conditions.

First, the grass silage had a dry matter content of more than 30%, while a typical grass hay would likely have a dry matter content of more than 80%. Silage is typically quite moist and, therefore, provides greater source of moisture to the horse than dry hay. And, people with experience feeding silage note that in more typical conditions, horses still consume 15 to 30 liters (roughly 4 to 8 gallons) of water a day. This would suggest that consuming silage alone is not an adequate source of moisture, and the snow must have provided a fairly significant hydration source. Also, the amount of water needed from snow would likely be less for silage-fed horses than hay-fed ones, and it’s possible that snow alone might not be able to meet the latter group’s water needs.

Another important consideration: Horses in this study were used to living in snowy conditions and eating snow, and the Icelandic breed is hardy and developed in a country that has cold winters. A horse that’s not as well-adapted to such conditions and isn’t accustomed to eating snow might not consume enough to fully meet its water requirement.

Finally, snow consumed by horses could be contaminated with grit and dirt that might contribute to sand colic.

Take-Home Message

The recommendation remains to always provide horses with a source of fresh, clean, and unfrozen water. Still, this research suggests that it might be possible, in severe conditions, for certain horses adapted to winter conditions to rely on snow as a water source.