It’s the time of year when even last year’s hay isn’t so new anymore and hay is getting hard to find, leading many people to settle for hay that is actually 2 years old. Properly cured hay stores well in terms of the major calorie sources (fermentable fiber and other carbohydrates) but it does incur some important nutrient losses.
Freshly harvested hay is rich in a pigment called beta-carotene which is the major precursor of vitamin A. As hay ages, light and air take their toll on the beta-carotene. As levels drop, hay begins to lose its nice green color. This is a sure sign vitamin A value has dropped. Skin, eyes, coat, thyroid and ovaries are among the tissues most affected by insufficient vitamin A. Start supplementing with 20,000 IU of vitamin A when hay is 6+ months old, increasing to 40,000 IU when over a year old.
Vitamin E activity also drops with storage and is lost even more quickly than vitamin A. All horses eating hay rather than fresh green pasture should be supplemented with 1 to 2 IU/lb of body weight daily. Alpha-tocopherol is the major biologically active form of vitamin E. If you use mixed tocopherols you will not be supplying enough alpha-tocopherol.
Both vitamin A and vitamin E are fat soluble vitamins and require adequate fat for absorption and transport. Fat is also required for the conversion of beta-carotene to active vitamin A. Curing and storage reduce the natural fat content of hay to 50% or less of the value in fresh pasture, primarily by loss of the fragile omega-3 fatty acids. High omega-3 fatty acid supplements, based on Flax and Chia, help replace these losses. Actual requirements of the horse are unknown at this time but daily supplementation of at least 2 to 4 ounces of these seeds is generally recommended.
Like vitamin E, vitamin C is rich in fresh pastures and very rapidly declines when hay is cured. The horse is capable of synthesizing his own vitamin C but this may not be enough for optimal levels. It has been documented that blood levels of vitamin C drop sharply over winter and horses may benefit from supplementation of 1 to 5 grams of vitamin C/day. Vitamin C is an important cofactor for the production and maintenance of strong immune responses and healthy skin, lung and tendon/ligament tissues.
Finally, excessive loss of moisture over time often leads to crumbling of the leaf portion of the hay, visible as a layer of “fines” when the hay is handled. The more stemmy portions left behind are lower in protein, B vitamins and fermentable fiber. A higher percentage of minerals bound to the nonfermentable fiber can also reduce mineral nutrition. Use of a full spectrum vitamin and mineral supplement formulated to complement the most common hay mineral profiles (e.g. low to no iron, low manganese) is good insurance.
Poor nutrition over winter is a common occurrence for the feral horse but there is no reason for the well managed domestic horse to have these challenges. Maintain optimal nutrition by understanding the deficiencies in older hay.
Eleanor Kellon, VMD