Frostbite in Horses

Those of us that live in Northern climes have felt it--the chilly, tingly, numbing feeling of ears, nose, fingers, or toes exposed too long to cold. If exposure to frigid temperatures continues, frostbite can occur.

Fortunately, Mother Nature has better provided for horses than for humans against the perils of frostbite. Explained Janice Sojka, VMD, associate professor of large animal medicine, Purdue University, "Humans evolved as tropical animals. We spread out beyond a tropical environment because we've succeeded in taking our tropical environment with us: That's why we have central heating! But horses evolved as temperate animals, and are actually more comfortable in cold temperatures than in warm. One source states the horse's neutral zone--the temperature where the animal is most comfortable and is not expending any energy to keep itself cool or warm--is between 20 and 40 degrees Fahrenheit."

That's why healthy horses, when left to their own devices, don't suffer the same discomforts as humans when exposed to chilling temperatures.

Additionally, although mammals protect their vital organs against severe cold by shunting blood away from the extremities to the core, leaving the extremities vulnerable to frostbite, horses can shunt a lot of blood away from their feet and still have a very functional foot.

"We don't understand blood shunting of the horses' feet very well," says Andris J. Kaneps, DVM, PhD, Diplomate, ACVS, an assistant professor of large animal surgery, Oregon State University. "But there is some type of protective role to the feet in cold weather. It's empirical information, because we know a horse can stand all day in a snowbank and not get frozen feet, whereas if you or I stood in a snowbank, we'd have frozen feet pretty quickly. The hoof capsule helps protect the internal structures, and many of the tissues in the foot can sustain some level of decreased blood flow naturally without being damaged."

Although frostbite in healthy horses is quite uncommon, certain conditions can place horses at risk. Says Gerald E. Hackett Jr., DVM, MS, professor of animal and veterinary science, California State Polytechnic University, Pomona, "Horses out in extreme cold that are unable to find shelter from the wind, or unable to stay dry, or are unable to take in adequate calories and forage to generate normal body heat, are most likely to become victims of frostbite."

Horses kept inside metal sheds or plastic-covered wooden barns that do not have adequate ventilation are also at increased risk. Explains Hackett, "In trying to protect our horses from bitter cold and wind, we sometimes put them at great risk of exposure and severe respiratory disease by bringing them into inadequately ventilated or 'windproofed' metal sheds, old barns, or wooden sheds wrapped in plastic. As we 'tighten up' buildings to keep the wind out and the horse warm, we may be keeping in too much moisture from the horse's breath and urine. Even in the coldest weather, the horse barn needs to be designed to have several air changes an hour. Without this, it may stay somewhat warmer in the barn, but you will also get humidity, ammonia, and other air contaminants too high for good health. It also may be a false kindness to bring in a horse that has been out, and has a full winter coat, to protect it from a cold snap. The horse may sweat in the warmer, wind-free environment, then with a damp winter coat, really get cold!"

Hackett also points out that certain molds or plant toxins occasionally found in feeds can cause peripheral vasoconstriction, thus making an animal much more susceptible to frostbite and/or exposure.

"Some of the mycotoxins that may be produced by mold are vasoactive substances, and the severe vasoconstriction they may cause will result in poor peripheral circulation, hence a greater susceptibility to frostbite," he explains. "While it is a good idea to increase the amount of hay a horse is fed in cold weather, it is never a good idea to feed moldy hay or grain. Unfortunately, this practice may not completely protect your horse from mycotoxins, as some of them are so potent that the amount of mold required to produce dangerous amounts of some mycotoxins is so small as to be imperceptible to the naked eye."

When frostbite does occur, it's likely to strike the ear tips. However, a stallion or gelding who has been sedated and subsequently can't retract his penis might be in danger of frostbite of the external genitalia. Explains Kaneps, "Acepromazine and a couple of other tranquilizers have a direct effect on the relaxation of the retractor penis muscle; acepromazine is used very frequently to clean the sheath of horses because it relaxes the retractor muscle."

In addition, day-old foals, who don't have many fat stores, and ill horses suffering from conditions that cause shunting of blood away from extremities, are also more susceptible to frostbite of the limbs.

Frostbite Explained

Frostbite might be superficial, affecting only the outside layers of the skin that will show marked discoloration when healed, or it can be more serious, extending to deeper fascial layers.

Frostbite occurs when tissues become frozen and ice crystals form inside cell membranes.

Says Kaneps, "When the cell gets cold enough, its contents expand and damage the cell membrane. This results in dehydration of tissue and cells, and damage to small blood vessels in the region affected. Ischemia, or lack of good blood supply, of the affected tissues leads to necrosis of those tissues."

Frostbitten tissues don't recover with thawing: Once they're dead, they're dead.

"Ice crystals inside the cells cause those cells to rupture and die," says Hackett. "This is why frozen tissue typically turns black after it thaws. The thawing process cannot restore the integrity of the cells, so if frostbite is severe and the tissue dies, that is a permanent situation and the affected tissue will slough off and the area will scar over. If the frozen area is large enough and vital enough, euthanasia or surgical amputation/debridement may be indicated. Also, the larger the area of dead or devitalized tissue, the greater the likelihood of serious complications from bacterial invasion and toxin production in that dead tissue (gangrene, tetanus, etc.)."

Most cases of equine frostbite involve the ears. Clinical signs often are masked by hair coat or skin coloration.

"In most cases, horse owners don't discover their horses had frostbite until after the ear tips fall off," says Kaneps. "But if you have a really astute eye and you're looking very closely, you should find a sharp demarcation between normal and frostbitten tissues. If skin coloration is in your favor, the area will be very, very pale compared to the normal tissue around it. As the situation progresses, the affected area becomes swollen because of the edema of the damaged tissue, and it can redden as the small blood vessels try to continue to get blood into the area. Eventually, the tip of the ear dries up like a piece of beef jerky, shrivels, and falls off."

Aside from cosmetics, this usually doesn't pose a problem for the horse.

Far more serious, although far rarer, are frostbite cases involving the feet. One veterinarian on an E-mail list reported on an 8-hour-old Standardbred filly born in a snowbank in sub-zero temperatures. At first, the veterinarians were encouraged as the youngster only sloughed superficial skin over the fetlock during the first week. However, by the time she was 10 days old, the filly had sloughed two hooves, and she subsequently was euthanized.

Kaneps treated two horses which were presumed to have frostbitten extremities, as both had been standing in cold, wet conditions.

"One horse was in and out of boggy conditions," he says. "It sloughed most of its skin distal to the fetlock, but survived as a broodmare. The other horse sloughed skin and the hoof of the limb, and was subsequently destroyed."


Treatment, which is aimed at minimizing the damage, is based on medical experience for treating humans. Says Kaneps, "Frostbite should be treated by rapid thawing in warm (38-44° Celsius) water."

Kaneps warns against using hair dryers as there is less control over the heat. "It's better if you use a bucket of warm water, wetting a towel and putting it on the affected area."

Although we humans usually rub cold hands to warm them, frostbitten areas should never be rubbed because that can cause further tissue damage.

Non-steroidal anti-inflammatories can be administered to reduce pain and inflammation. In addition, to inhibit blood clot formation, vasodilators such as acepromazine or NSAIDs such as heparin can be administered.

The best treatment of all, though, is prevention through common sense horsekeeping. Says Hackett: "Horses that can stay dry, find shelter from the wind, have adequate energy and forage intake, and are allowed to acclimate to the cold gradually (as would normally happen with the change of seasons) can survive bitter cold (-20 to -40° F) temperatures quite nicely, even for extended periods of time."

About the Author

Marcia King

Marcia King is an award-winning freelance writer based in Ohio who specializes in equine, canine, and feline veterinary topics. She's schooled in hunt seat, dressage, and Western pleasure.

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