Many people are confused about how to figure out how much they should feed. Horses are designed to eat grass. Period. Their digestive tract is designed to handle this type of diet.
The rule of thumb is to feed hay at a rate of 1.5% to 2% of the bodyweight per day, adding grain only if needed to hold weight. This 1.5 to 2% is ”dry matter,” the solid portion of the food after all water is removed. Properly cured hay is less than 10% water anyway so the percentage as a rule of thumb works fine. This simple rule explains why the vast majority of horses with weight problems are too thin or too fat.
To get a good estimate of what your horse weighs, use the equation:
W = HG2 x BL/330
Where W = weight in pounds, HG2 = heart girth squared, in inches (weight tape measurement), BL = body length from point of shoulder back to rump, in inches. Always do this calculation as a double check against the weight tape reading.
So, a horse that weighs 1,100 pounds and is relatively inactive will usually hold that weight on between 16.5 and 22 pounds of hay a day. If you don’t know the weight of hay you are feeding, weigh it. You can bring your bathroom scale out to the barn and weigh yourself with and without your horse’s daily hay ration, or buy an inexpensive fish scale from somewhere like Walmart to weigh your flakes.
How much grain do you need to feed along with that hay' None. Grain is a concentrated source of calories that should only be fed if you can’t hold a normal weight on hay alone.
The horse on a hay-based diet only needs:
• Vitamin E supplement ??? 1500 to 2000 IU/day
• Adequate essential fatty acids ??? 4 to 6 oz of flaxseed or ground stabilized flax
• Mineral supplement to complement/balance the hay
• White salt or iodized salt.
Your inactive horse does not ”need” grain. If you insist on feeding it, you will need to decrease the amount of hay fed to avoid weight gain.
Use these conversions:
• 1 lb commercial grain mix = 2.5 to 3 pounds of hay
• 1 pound of plain oats = 1.5 to 1.75 pounds of hay
• 1 pound of beet pulp = 1.5 to 1.75 pounds of hay
• 1 pound of rice bran = 1.75 pounds of hay
• 1 lb of complete or senior feed = 1.25 pounds of hay.
Note: Senior and complete feeds vary considerably in their calorie levels.
To get a more exact estimate, compare the recommended feeding rate for your horse’s weight to how much hay he would be expected to need.
For example, if your horse would need 22 pounds of hay and the feed says to use 15 pounds as a complete feed, divide 22 by 15 = 1.46. One pound of the feed = 1.46 pounds of the hay.
Horses in light work need about 25% more calories than inactive horses. This is usually easily met by increasing the hay by that amount on days they work.
Horses in moderate work need about 50% more on days they work, which you may or may not be able to meet with hay alone. Be realistic about your horse’s level of work. A half-hour long walk a few days a week does not mean the horse is in moderate work. Talk with your vet, if you’re not sure.
For heavier work loads, a more concentrated calorie source is almost always needed, but as you can see from the calorie equivalents above, it’s easy to do.
For example, if your horse at maintenance needs 22 pounds of hay and you start back training at a moderate work load (say 1 hour per day of trotting/cantering) you’ll need about 33 pounds of hay/day.
If your horse won’t eat more than 25 pounds, you have an 8 ”hay pound” deficit that you can meet with around 3 pounds per day of a commercial grain mix.
These recommendations are ”averages.” They actually work quite well for most horses, but individual animals may require either less or more depending on their metabolism. Hays also vary widely in their calorie content and what constitutes light versus moderate work for one horse may be different for another (e.g. if it’s out of shape).
Horses also vary in how much moving around and playing they do on turnout. This is where the art of feeding comes in. Adjust feeding to the individual.
Horses that are having a lot of trouble either holding weight or keeping it off compared to other horses in the group being fed by the same bodyweight guidelines should be evaluated by your veterinarian for an underlying medical reason.