University Park, Pa. -- Seeing horses and other livestock outdoors during frigid winter weather may trigger concerns from the public about the welfare of these animals. What most people don't understand is that most livestock can remain comfortable in low temperatures, say experts in Penn State's College of Agricultural Sciences.
Unlike humans, horses acclimate to cold weather by developing fatty tissue that "winterizes" them, according to Ann Swinker, associate professor of equine science.
"Even in cold weather, horses prefer to be outdoors," said Swinker. "The last thing you want to do is put an animal that is acclimated to the cold weather in a heated environment. If the horse is in good physical condition with a good body-fat ratio, it will be fine."
When horses exhibit cold stress, typical comfort-seeking behavior is expressed, such as huddling together and seeking shelter from wind. Foals will curl up to minimize body surface area. Shivering is also a sign of cold sensitivity. This happens when a horse might not have enough body fat or energy to keep warm.
"People need to watch body condition score during winter to make sure the diet is meeting the energy needs of the horse," said Robert Van Saun, extension veterinarian and professor of veterinary science. "The energy requirement to maintain a horse on a daily basis is going to increase. Depending on temperatures, there are some calculations for horses as well as other species in which, for every degree below the lower critical threshold temperature, you increase energy requirements by about 10 percent. We usually talk about 25 percent increase during these winter months. Adding a half-amount more of grain or fat sources to the diet is very important to accommodate the cold."
Horses also increase body metabolism through various physiological mechanisms. Bacterial fermentation of forage in the hind gut of the horse can generate a tremendous amount of heat. As a result, horses can tolerate much colder weather than humans. Adding fiber to the diet will increase heat of fermentation.
Endocrine systems perform other essential physiological functions a horse needs to stay warm. To conserve central body core temperatures, the thyroid gland produces the hormone thyroxin to increase metabolic rate and provide warmth.
Swinker noted that horses have another innate defense against cold weather. "A long winter hair coat serves as insulation by reducing the loss of body heat and provides the first line of defense against the cold," she said. "Its insulating value is reduced when the horse becomes wet and/or is covered with mud. This is why it is important to provide regular grooming and windbreaks -- whether man-made or natural, such as tree lines or shrubs."
Horses have guard hairs which serve as an external hair coat in winter that protects the animal from excessive moisture. However, Swinker pointed out, not all horses have guard hairs.
"Show horses with hair coats that are artificially short should not be turned outside in bitter winter cold without a blanket or windbreak," Swinker explained. "If you do have a show horse that is housed in a barn during most of the winter, the barn should be adequately ventilated to reduce the risk of respiratory disease. Proper ventilation eliminates excess moisture and condensation buildup. Care also should be taken to prevent a direct draft on the horse; this will cause stress and additional problems."
Although animals may adapt to cold weather, Van Saun said they may need a little extra daily attention. "Ready access to water is extremely important," he said. "Water needs to be replaced once it becomes frozen. If horses don't drink water, they can't eat dry food to get the energy needed to produce body heat. Water deprivation can cause colic or abdominal distress in horses."
For more information about equine management during the winter season, contact the Equine Science Program in Penn State's Dairy and Animal Science Department at AskDAS@psu.edu. Additional information on horse care can be found online in Swinker's "Penn State Horse" newsletter at http://www.das.psu.edu/equine-science/penn-state-horse-newsletter.