Copper, zinc and selenium:Copper and zinc play an important role in growth, bone and joint development, nerve function, and other vital processes. Selenium works in conjunction with vitamin E to support the immune and reproductive systems.
All of these trace minerals are also found in forages, but vary among crops, so small amounts are commonly added to commercial feeds. The recommended quantities for the average horse are 10 parts per million (ppm) copper, 40 ppm zinc and 0.1 ppm selenium. Feeds for broodmares have much higher amounts of copper and zinc to aid the development of the fetal skeleton.
Pay particular attention to the selenium content of a feed. Some commercial feeds provide much higher amounts of this mineral for those such as elite athletes or growing youngsters who may need more, and for horses living in parts of the United States with selenium-deficient soil. Keep in mind, however, that a relatively small overdose of selenium can be lethal. Do not give your horse high-selenium feed unless you are certain he needs it. Check with your veterinarian if you are unsure.
Salt is a crucial component of the equine diet and its elements--sodium and chloride--are electrolytes that play critical roles in many life functions, such as nerve function and maintaining internal fluid balances. Sodium and chloride are lost in high quantities when a horse sweats, and they are also the only electrolytes that are not naturally present in grains and grasses, so they must be replenished with supplemental salt. Fortunately, horses have a natural appetite for salt and will typically consume one to three ounces daily when it's offered as a free-choice supplement. Salt is also typically added in concentrate mixes at the rate of 0.5 percent for horses in light work and 1.0 percent for those who are more active.
Vitamin A, in international units (IU) per pound: Horses require a tremendous amount of vitamin A, which is needed to aid in vision, gene expression, immunity and many other functions. Vitamin A is abundant in alfalfa and green pasture, but levels of that nutrient drop rapidly after hay is cut--more than 50 percent is gone after about six months. Horses whose forage consists primarily of dried grass hay may benefit from feeds fortified with vitamin A. The average horse needs between 1,000 and 3,000 IU/lb. daily, but horses in rigorous work may require much more. The concentrations in commercial feeds typically range from 1,000 to 4,000 IU/lb.
Feeding Directions
Pay close attention to the feeding instructions when selecting a feed for your horse. Here you'll find a statement regarding the type of hay--grass or alfalfa--the feed is meant to accompany, as well as the suggested daily serving.
It's important to choose a feed whose suggested serving closely matches your horse's needs. All of the percentages and quantities listed under the guaranteed analysis pertain to that portion, and changing the serving size too much from the recommendation will also alter the other nutrient balances you are offering. In other words, if your horse needs fewer calories, and you scale his serving size in half, you are also offering him only half as much of the protein, calcium, Vitamin A and other crucial elements. It would be better to switch to a feed in which a single serving offers the right nutrient balances in a formula with less energy and more fiber. Another alternative would be to feed the lesser amount, but then provide a supplement that makes up the difference in lost nutrition.
Also, do not attempt to save money by diluting a balanced concentrate mix with a cheaper product. This practice will also alter the nutrient content of the total ration, and you may create deficiencies and detrimental interactions.
Equine nutrition may seem complicated, but feed companies invest a lot in research to develop formulations that meet the specific demands of a broad range of horses. All you need to do is read the feed labels and select the product best suited for your horse's age, level of work and special needs.
Kathy P. Anderson, PhD, is the horse extension specialist at the University of Nebraska-Lincoln. In addition to overseeing the horse extension program, she teaches undergraduate courses in equine management, reproduction and nutrition.
This article originally appeared in EQUUS 369, June 2008.
