Now that winter is fast approaching, horse owners must take precautions to ensure that their horses are warm and healthy in cold weather. When temperatures drop below 45°F, the horse needs energy to stay warm. Sometimes, wind chill needs to be kept in consideration when determining how cold the weather actually is. The best way for a horse to generate body heat to maintain its temperature in cold weather is through the calories it consumes. These body heat calories are measured as digestible energy (DE). This measurement is done by using the formula: critical temperature – actual temperature = % increase in DE required. The best way to determine this formula is to look at the actual temperature outside, figure out what the wind chill temperature is, and then subtract the wind chill temperature from the actual temperature. For example, if it is 32°F outside, and the wind coming over a snow-capped mountain brings the temperature down to 27°F, the actual temperature becomes 27°F. Since it is necessary to adjust the DE at a temperature of 45°F, the critical temperature is 45°F. Therefore, the next step is to subtract the adjusted actual temperature from the critical temperature, thus: 45°F – 27°F. This comes to 18%, so there is an 18% increase in the required DE. According to the National Research Council, an average mature horse weighing 500 kilograms (1100 pounds) requires approximately 16.65 Mcal to maintain a normal DE. Therefore, the formula to determine the needed calories for an 1100 pound horse needing an increase of 18% DE is thus: 16.7 Mcal x 18% = 3 Mcal increase. So, 16.7 + 3 = 19.7 Mcal DE/day. Now, an 1100 pound horse eats 19 pounds of food a day, which includes forage, so this amounts to .90 Mcal DE/lb of feed per day. So the increase is calculated as follows: 3 Mcal ÷ .90 Mcal = 3.33 pounds of increased feed to maintain an Mcal of 19.7 DE per day. Therefore, an additional 3.33 pounds of feed added to the normal 19 pounds an 1100 pound horse eats comes to approximately 22.33 pounds of feed per day (19 + 3.33 = 22.33).
According to the Institute of Agriculture at the University of Tennessee, an increase of 5% hay should be fed when the temperature falls below 32°F. When the temperature falls between 10-20°F, 10% more hay should be given. Under 10°F, 15% more hay should be given. This should be high-quality hay. If good hay is not available, then approximately 2 pounds of whole oats can be added to the grain ration in lieu of extra hay, along with the regular ration of hay. Therefore, the extra 3.33 pounds of extra feed can be in the form of hay or oats – depending on the quality of the hay.
North Carolina State University National Research Council
National Research Council