The thermometer showed 42°F this morning - chilly for those of us used to the sunny warmth of Southern Arizona but just right for our horses.
Horses thrive in “thermo neutral” temperatures ranging from 40 or 45°F to 65°F. Above 65, they begin to rely on sweating, with water and salt loss, for cooling. Under 45 they use energy to maintain their body temperature.
According to Dr. Robert A. Mowrey, Extension Horse Specialist at North Carolina State University, the standard “critical temperature” is 45°F, with 10 degrees subtracted for wind and another 10 degrees subtracted for rain/wet coats becoming the “actual” temperature.
On a 45 degree day, if the horse is wet and unprotected from wind the “actual” temperature is 25 degrees - which is cold. For each degree below the critical temperature the horse requires a 1% increase in calories to maintain a constant temperature.
At 25°F a horse needs 20% more calories than when the temperature is a neutral 45 degrees. That’s 20% more calories, not 20% more forage - how that translates to hay or beet pulp depends on the DE (digestible energy in Mcal per pound) of the forage. For grass hay with a DE of 0.8 Mcal/lb that would mean an additional 1.2 pounds of hay, with alfalfa hay or beet pulp at about 1.2 Mcal/lb, he would need less than a pound of additional forage.
The calorie increase should come from forage - preferably long stem grass or alfalfa hay, but cubes, pellets or beet pulp also work. This is because the greatest amount of immediate heat maintaining energy is produced by the fermentation of forage in the hind gut. While additional calories from grain will help retain body weight, grain doesn’t provide the heat-producing fermentation that forage does.
The Cold Weather Feeding Chart and Calculator on my web site can help you determine how much additional forage is needed for your winter temperatures. The Chart in the pdf file is set for a 1000 lb horse; you can use a percentage of the recommendation if your horse weighs more or less. Or, if you’re comfortable with spreadsheets, you can download the Excel version (opens with Excel, Numbers or Open Office Calc) and plug in your horse’s weight and the DE of your hay.
These are starting points - your easy keeper may need less and your hard keeper may need the more concentrated calories from alfalfa or beet pulp. And if your horse is a senior or is IR/PPID and prone to laminitis in the winter, don’t forget the boots and leg warmers. Do use a cooler until your horse is dry after work but think twice about blanketing a horse with a full winter coat - no matter how cold it feels to us your horse can easily become overheated and start sweating under a winter blanket.
Patti in sunny but chilly Vail, AZ
Cold Weather Feeding Chart (pdf and Excel) http://www.desertequinebalance.com/Files/handy-calculators
Cold Weather Feeding Practices for Horses
Nutritional content averages for feeds - Dairy One Feed Composition Library