Hay is just dried grass and grass is the horse’s natural food so it shouldn’t need any supplementation – right? Wrong.
Variety is a major difference between the diet of feral horses and that of domesticated horses fed hay. The feral horse consumes many different plants grown on a variety of soils while the domesticated horse eats the same thing 24/7 for prolonged periods. The variety gives the feral horse a wide range of mineral intakes which tend to balance themselves out. No single hay is ever nutritionally complete and balanced.
Hay is also deficient in the most important nutrient – water. Hay is like grass jerky. A constant supply of fresh, clean, palatable water is essential for digestion, normal gut motility and hydration. Snow is not good enough! Very cold water may also not be consumed in sufficient amounts. Horses prefer water at body temperature.
Compared to fresh grass, hay is lacking in omega-3 fatty acids, vitamin E and vitamin C. These nutrients are rapidly destroyed in the drying process and are key to balanced immune function. The horse can manufacture vitamin C in sufficient amounts to prevent full blown scurvy but studies have shown that levels drop precipitously in horses not on pasture.
As hay ages, levels of the vitamin A precursor carotene drop off to the point most hays fail to meet requirements by the time they are 12 months old. Hays that are yellowed rather than green also have low levels.
Finally, both hays and fresh grasses of all types are deficient in sodium/salt. Feral horses make periodic pilgrimages to areas of salt deposits in their range. The domestic horse should have constant access to free choice salt and if they don’t consume enough either add it to bucket feeds or dissolve and spray on hay. “Enough” is 1 oz/day for the average full size horse in winter and 2 to 4 oz in hot weather.
Supplements based on flaxseed are ideal for omega-3 fatty acid supplementation. Feed 4 to 6 oz/day. Vitamin E requirement is 1000 to 2000 IU/day. Start vitamin A supplementation at 20,000 IU/day when hay is 6 months old; increasing to 40,000 to 60,000 IU after it reaches 12 months old. Vitamin C should be used judiciously since large doses will increase iron absorption which most horses don’t need. If supplementation is thought to be desirable for tendon, ligament, joint or lung support keep it at 5000 mg per dose or less.
Mineral requirements for your hay will vary depending on the type, where it was grown, age at cutting, soil treatments used and even the weather. The most accurate way to balance hay is based on a hay analysis. Your local agricultural extension agent can direct you to a laboratory.
If analysis isn’t possible because the supply changes too frequently, the Ag agent can help get you information on typical profiles for the area where the hay was grown. It’s not ideal, but better than blindly buying a supplement without considering the levels of minerals in it. If you own a metabolically challenged horse the analysis is critical to safety. Include tests for starch and ESC (ethanol soluble carbohydrates = simple sugars).
Like anything else new, correctly supplementing hay will seem like a lot of work when you first do it but the obvious benefits to the horse in terms of coat, skin, hoof, energy and immune system health are usually so obvious you will never go back.
Eleanor Kellon, VMD