Winterize Your HorseCritical temperature is the temperature below which the animal must produce additional heat to maintain normal body temperature. Mature horses in good condition have a critical temperature around 30 degrees Fahrenheit during early winter. Horses will require an estimated 15 – 20% more calories for each 10 degrees Fahrenheit the ambient temperature falls below critical temperature. However, thin horses or horses with short hair may need even greater increases in dietary intake to maintain normal body temperature.