Horse Nutrients in Tandem
- Feb 1, 2010
If you've visited your doctor recently, you might have received the vitamin D speech. Vitamin D is one of the latest vitamins that doctors have determined are essential and often lacking in the human diet.
The reason isn't simply that you need vitamin D. The nutrient works in tandem with calcium, helping your body absorb the calcium you need for strong bones.
Equine nutrients often perform the same way. Yes, your horse needs certain items in his diet, but they don't work unilaterally on his body. Instead, they help each other to help your horse.
If you understand how these nutrients support each other, you can make better feeding choices. Instead of simply throwing your horse some hay, a little grain, and a generic blend of vitamins and minerals, you can determine how everything works together and adjust where necessary.
Equine nutritionists often list six categories of nutrients that your horse requires: water, protein, carbohydrates, fat, vitamins, and minerals. (In fact, human nutritionists will tell you that your body requires those same six.) Of course, you provide your horse access to water, and he can often get many of the other nutrients from his forage.
Therefore, anytime you examine a horse's diet, you should start with forage, which consists of hay or pasture. Does he get his forage from grazing, or does all or part of it come from hay? What he gets nutritionally from his hay or pasture will determine what type of concentrate, if any, you should add.
"Forage always forms the basis of the feeding program," says Dennis H. Sigler, PhD, a professor, extension horse specialist, and horse section leader at Texas A&M University in College Station. "The concentrate portion of the total diet is selected based on the type and quality of the forage program. The level of protein, calcium, and phosphorus in the forage are the main determining factors in deciding what concentrate to select."
Sigler noted that nutritional requirements vary widely, depending on a horse's age, exercise level, and whether he or she is being used as a breeding animal. In this article we will discuss mature, nonbreeding horses that do light to moderate exercise-- in short, the average riding horse.
What Does My Horse Need?
"Hay should be fed at no less than 50% of the horse's diet and no less than 1% of the horse's body weight," says Anne Rodiek, PhD, of the Center for Food Science and Nutrition Research at California State University, Fresno. "Hay should be fed at a constant rate at a level that is as high (relative to grain) as possible to meet the horse's energy (or other) needs. On the other hand, grain should not comprise more than 50% of the diet."
Having your hay analyzed will help you decide what type of concentrate to use, says Tanja M. Hess, DVM, PhD, a professor in the Equine Science Department at Colorado State University in Fort Collins. Knowing what type of hay it is and what it provides will show you what is lacking.
If your horse grazes on pasture for part of the year and you supplement with more hay during the colder months, you might have to rebalance your ration seasonally.
"Pasture offers a lot of good nutrition when available and needs to be accounted for in the ration," says Amy M. Gill, PhD, an equine nutritionist based in Central Kentucky. She has worked as a consultant for several feed companies, as well as for Tho-roughbred racing stables and breeding farms (www.amymgillphd.com). "Likewise, when pasture is gone, forage needs to be supplemented to replace the nutrients not coming from grass."
Gill noted that in addition to seasonal changes affecting a horse's diet, changes in a horse's activity level and age should also be considered.
"No diet is adequate forever," she reminds us.
The Calcium/Phosphorus Ratio
One of the most important dietary balances is the ratio of the minerals calcium and phosphorus, which should be between 1:1 and 2:1. Calcium and phosphorus work together in many parts of the body, but particularly in bone. While the calcium ratio can be higher without ill effects in a mature horse, you should avoid allowing the phosphorus level to creep up relative to cal-cium.
"Excessive phosphorus will decrease calcium balance," says Hess. "The body will try to compensate using calcium from the bones."
That can cause the body to substitute fibrous tissue for calcium, primarily in the face bones, and the horse could develop into a condition known as "big head," says Hess. It can also weaken the bones, leading to lameness.
Alfalfa is high in calcium and is often fed in part for this reason.
"Today, many horse nutritionists believe that if phosphorus levels are met, calcium levels can be much higher than the minimum requirements," says Rodiek. "Excess calcium is not thought to interfere with either absorption or metabolism of phosphorus. Inverse calcium to phosphorus ratios are uncommon in horses fed alfalfa hay, but can be found in horses fed grass hays and grains."
Other Vitamins and Minerals
Just like we do, horses need a variety of vitamins and minerals in their diet to thrive. Specifics on how many, in what amounts, and why could fill a book. Yet knowledge of a few of the basics can help you select the proper supplement to your horse's forage. Often that is in the form of a concentrate that also includes vitamins and minerals.
Sigler and Gill advise spending your money on a good-quality concentrate instead of supplements. Gill likened some supplements to "kitchen sink" mixtures.
"They contain a lot of ingredients, but very little of each, making them essentially ineffective and a waste of money," she says. "The best way to ensure a balanced ration is to choose the correct type of hay for the horse, then complement with a prepared, balanced ration designed for the type of horse being fed. Save your money--buy the best quality forage and feeds and drop the vitamin and mineral supplements."
Some trace minerals, instead of working together, can act against each other if the ratios are incorrect.
"Too much iron in the diet can interfere with zinc absorption," says Sigler, "and can actually induce a zinc deficiency, even though the actual level of zinc in the total diet appears to be adequate. The main point here is to leave ration balancing to the experts who study this every day. Don't attempt to balance your own rations at home by adding a little of this supplement and a little of that."
Hess pointed out that zinc can sometimes be a culprit in copper deficiency and that you should consider the ratio between the two minerals. Because zinc and copper actually compete with each other by using the same mechanisms to travel to the body's cells, too much zinc could cause a copper deficiency.
In some cases, a vitamin and a mineral work in tandem. Vitamin E and selenium together protect body tissues, says Hess. Gill adds that vitamin E and selenium help to prevent free radical damage to cells resulting from normal metabolism. (Free radicals are unstable oxygen molecules that have an unpaired electron that makes them quicker to react with other molecules, stealing electrons from their outer orbits. This damages the other molecules and can damage cell walls.) She says the two can also help the horse recover from muscle problems, such as tying-up, or neurologic disorders, such as EPM.
"Selenium also has a function in controlling thyroid hormone metabolism," says Hess. "Selenium deficiency occurs in about 46 states in the USA. Deficiency can lead to muscle diseases."
But selenium is also a perfect example of the fallacy in thinking that if some is good, more is better.
Hess tells us selenium can be toxic if ingested at levels beyond what is needed by the horse. Selenium toxicity can develop over time.
Perhaps the most tragic example of acute selenium toxicity occurred in the spring of 2009, when 21 polo ponies died in Florida. The culprit was determined to be an overdose of selenium due to incorrect compounding (see TheHorse.com/14068 for more information on this case).
Amino acids work together in that they are the building blocks of protein. Horses need protein in their diet so that their bodies can use the amino acid chains to build the particular proteins they need.
"Amino acids are required in a certain amount by every living creature in order to build proteins in their body, such as muscle, bone, hair, eyeballs, etc.," says Gill. "Amino acids are linked together in specific orders to make the different types of proteins."
Hess explained that proteins differ not only in the length of amino acid chains, but in the types of amino acids within the protein. The amino acids work together so well that if one is missing, a horse's health can suffer.
"If one amino acid is present in insufficient amounts, it is referred to as a limiting amino acid because it will limit protein synthesis," explains Hess.
Gill likened it to making a cake. "If you put in all the ingredients, but you leave out the sugar, you get a cake, but it's not a very good one," she says.
Researchers are working to determine the ideal ratios of amino acids. Rodiek says that swine and poultry nutritionists are ahead of equine nutritionists in such research. "Ratios of amino acids are not usually considered in formulating horse rations," she says.
One of the amino acids on which equine research has been performed is lysine. It can be lacking in the common equine diet, says Rodiek, and it is needed for growth. "Therefore, it is the first one that can limit the rate of growth," she explains.
Because of this, lysine is particularly important for a broodmare during gestation and during a horse's early years. Chuck Bowlan, DVM, of Bowlan Farms in Tecumseh, Okla., recommends a young horse's diet contain at least 1% lysine. Bowlan Farms raises high-performance animals, primarily Quarter Horse and Paint racehorses and barrel horses.
Bowlan says that alfalfa is high in lysine. That characteristic and alfalfa's high calcium content are two of the reasons he feeds that type of hay. Lysine is also an ingredient in the custom concentrate he feeds.
"When feeding horses, we must provide adequate amounts of protein that allows for sufficient amino acids to circulate in the body," says Hess. "Protein quality is a consequence of amino acid profile and digestibility of the protein source."
Of the 20 amino acids, 10 must come from the diet, explains Gill. Many feeds today are now fortified with lysine, methionine, and threonine because these are considered the first three limiting amino acids.
Hess recommends horse owners not stint in the quality of the protein contained in what they feed. She says soy or alfalfa pro-tein are often a good-quality source in concentrates.
You know your horse needs nutrients, but remember those nutrients can work together and, in some cases, against each other. Have your forage analyzed so you know what nutrients your horse is receiving, then supplement what is missing. If that supplement comes from a concentrate, choose one that has been formulated by experts and that will complement your horse's forage.
About the Author
Tracy Gantz is a freelance writer based in Southern California. She is the Southern California correspondent for The Blood-Horse and a regular contributor to Paint Horse Journal, Paint Racing News, and Appaloosa Journal.
POLL: University Equine Hospitals