As the country rapidly slips into winter, questions on cold weather feeding increase. People want to know what to feed and how much more in winter. The short answer is, it depends.
If you have done any reading on this you have come across the term “critical temperature”. This is the environmental temperature below which the horse’s body has to work to maintain normal body temperature. For horses with a summer coat, it is 40 degrees F (4.4 C) and with a thick winter coat it is 18 F (- 7.7 C). For coats that are in between slick and full, the temperature will also be in between but it’s important to realize that length per se does not predict the warmth of the coat. Most important is the presence of a dense undercoat.
For every drop of 1 degree F, the horse needs 1% more calories. For example, a 500 lb pony eating 10 lbs of hay/day needs an extra 0.1 lbs = 1.6 ounces of hay. This is a very small amount and it’s perfectly reasonable not to make adjustments until you reach a more easily measurable amount such as at least half a pound (8 oz) so in this case you would adjust by adding half a pound for every 5 F drop below critical temperature. If you had a 1000 lb horse eating 20 lbs/day you could adjust sooner because every 2.5 F drop would = an 8 oz change in hay.
You could also make more frequent adjustments using something more easy to measure than hay – pellets or cubes. Keep a scale in your feed room to measure ounces accurately and just add the pellets or cubes to your feed bucket. A fish scale works well.
If your horse is eating both grain and hay, you can either increase both by the same % or convert the increase in grain to extra hay instead. This will keep you from overfeeding grain. It is also of benefit because the fermentation of hay in your horse’s intestinal tract generates heat. To convert from grain to hay, multiply the amount of extra grain by 2 if plain grains, 2.5 if sweet feed and 3 if high fat feed. In other words, to go from 1/2 lb of extra grain to hay, it would be equivalent to 1 lb of hay for plain grain, 1.25 pounds of hay for sweet feed and 1.5 pounds of hay for high fat feed. These are approximate. You may need slightly more or less.
Several things can influence your horse’s critical temperature and how much you need to feed. Young or small horses have a higher ratio of body surface area to weight so lose heat faster. Thin animals have less fat insulation. Horses without good shelter lose more heat (use the wind chill corrected temperature in this scenario). Heavy blanketing or obesity reduce the extra calorie requirement. The individual’s metabolism will also play a role.
Remember that more food can’t guarantee the horse stays warm and horses don’t always hold weight as predicted by equations. Any horse that is shivering is cold. Palpate deeply through the coat to feel for ribs on a regular basis and increase calories if needed.
As mentioned, hay is the best thing to feed because heat will be generated in the intestine in the process of fermenting it. The same is true of high fiber feeds such as beet pulp and soy hulls. Horses that don’t drink well won’t eat well either so feed salt and provide water at a comfortable temperature. Finally, if you have increased hay or feed it free choice but are still detecting weight loss, don’t hesitate to feed a more dense calorie source of grain, fat or high soluble fiber from flax, beet pulp or soy hulls.
Note: If your horse is overweight consider not increasing his winter feeding unless you can feel his ribs. The calories he needs to stay warm can come from his stored fat rather than more food. In the cold, the horse also produces internal heat by making energy generation in the mitochondria less efficient, a process known as uncoupling. The fat calories that don’t go to making ATP are converted to heat.
Eleanor Kellon, VMD