Anyone who has managed animals in cold weather understands that cold stress affects nutritional needs. Horses will use extra energy stored in the body to maintain body temperature when temperatures are cold. The long-term affect is loss of body weight, which can be quick and dramatic if adequate nutrition is not supplied.
The first question is how cold is cold? Temperatures that are low enough to make us respond to cold by seeking shelter, shivering and bundling up with clothes may not be cold enough to affect the horse. Physiologically, the temperature below which animals start to spend a significant amount of additional energy to maintain body warmth is the ‘lower critical temperature’. Hair thickness, fat cover, how well the horse has previously adjusted to cold weather (acclimatization), and exposure to wind and moisture will affect the lower critical temperature for horses. This temperature for a horse that is thin with a short hair coat, not use to cold, and exposed to wet, windy weather may be as high as 40 to degrees F. A horse that is acclimatized to cold weather, with a thick hair coat and fat cover may not use appreciably more energy until the temperature drops below 30 degrees F. Nonetheless, as a general rule, the lower end of the comfort zone for horses is lower than ours; so don’t make the mistake of heating barns at similar temperatures as you would your house. Not only is this wasteful, because of ventilation problems in barns closed up in the winter, high temperatures may increase respiratory irritants that cause the horse to cough and congest the respiratory system.
As a general rule, a little over 1% increase in the energy requirements is needed to replace energy loss from the cold weather for each degree the temperature falls below the horse's lower critical temperature. If a horse is in good body condition, has a thick hair coat and is well acclimatized to cold weather, its lower critical temperature may be around 32F. Exposure to a period of time that weather drops to an average of 20F means energy requirements would increase about 12%. For an 1100-pound horse, energy requirements are estimated at 16 Megacalories of digestible energy per day to replace the normal energy expended to maintain the body. The increase in energy needs to replace losses in cold weather would increase this amount to 18 Megacalories per day.
How to best meet increased nutritional needs will depend on your feed supplies, what the horse is used to eating and how large an adjustment you have to make. In terms of supplying energy, grains have much more energy per pound than hays so increasing grain amount may be most efficient. The additional 2 Megacalories per day could be met by increasing the grain allotment about 1 and ˝ pounds as a typical grain formulation for horses will have between 1.2 and 1.5 Megacalories of Digestible Energy per pound. You have to be cautious when adjusting grain levels, so immediately increasing grain allotments to offset energy losses is not as safe as preconditioning the horses by gradually feeding more energy prior to weather extremes. The horse may consume a little extra in the weeks before cold weather is expected, and put on a small amount of fat cover. When exposed to cold weather for several days to weeks, they will most likely lose the small increases in fat cover and enter into the spring in adequate body condition for their intended needs.
Many managers meet the increased energy needs by increasing the supply of hay. Hay provides large amounts of fiber. Fiber is less energy dense than the energetic compounds in grains, so more hay would have to be consumed. With the expected energy value in alfalfa, the same example that needed an additional 1-˝ pounds of grain might need 2 to 2-˝ pounds of alfalfa. As the energy content of grass hay is less, the amount of grass hay to meet additional energy would be more, in this example maybe 3 to 3-˝ pounds additional hay per day.
Meeting increased energy needs by supplying free-choice hay has some advantages. A continual supply of hay may help keep the body warm by maintaining a fuller digestive tract. The way that horses digest fiber generates significant amount of heat. This heat production in the digestive tract is thought to help keep the horse’s internal temperature warmer. As such, it is recommended to maintain access to long stem forage in the winter, which means you will have to feed hay because most pasture forage is limited in the winter. As long as wastage of hay is not large, many owners find that free choice access to grass hays is an effective way to meet much of the nutrient requirement. The down side to free choice hay is hay supply may not be available and wastage may make it uneconomical.
Regardless of how much hay you supply, most winters in Oklahoma will be harsh and long enough to require graining horses to meet energy needs. Again, because feeding too much grain at one time or making large changes in amounts of hay and grain too quickly can lead to colic, horses should be preconditioned for cold weather. Fat cover insulates the horse’s body from cold. Horses exposed to long periods of cold can be expected to lose body condition. Preconditioning horses by increasing their fat cover before the onset of long-term cold weather will partially offset the negative effects of losing condition during cold weather.
There are several ways horse owners can lessen the nutritional stress resulting from exposure to cold weather. The most obvious is to provide some form of shelter from wind, rain and cold. Blankets provide insulation for horses with short hair coats, such as those housed in barns under lighting programs to maintain a short hair coat for showing. Blanketing outside horses has the disadvantage of increasing the risk of injury if the blanket hangs on an object. Also, horses exercising in blankets are more prone to becoming entangled if the blanket doesn’t keep its position. Blanketing horses housed outside is also a problem in wet weather, as a wet blanket can have an adverse affect on keeping the horse warm.
Many pastures may provide enough natural protection without need for man-made shelters. However, those owners housing horses in areas unprotected from wet, windy weather should provide windbreaks or covered sheds. The cost of windbreaks and sheds will be partially offset by savings from feed costs. Owners have to consider herding instincts and herd pecking orders when deciding on windbreak or shed design. Those areas housing one or two horses that are compatible to one another will allow for an enclosed shed with three or four sides. However, larger groups or those with dominant pecking orders may necessitate a one-sided structure so access is greater for more horses.