- Sep 12, 2001
You don't need to be a novice to be confused about the subject of equine nutrition. Many long-time horse owners have never dabbled in the mysteries of feeding because their horses always were kept at boarding stables or managed by someone else. With all the confusing advertisements and conflicting information available on feed, it's no wonder so many owners avoid the subject of nutrition, trusting that someone else's recommendations will supply their horses with the necessary dietary ingredients for good health and performance.
But suppose you decide to buy a farm and bring your horses home. Suddenly you're the one who has to make that trip to the feed store and bring home, well, something. You always took hay for granted; now you find yourself worrying about the relative virtues of Bermuda grass, timothy, alfalfa, and endophyte-free fescue. And those feed tags, with their apocryphal percentages and parts-per-million; they're indecipherable!
At first glance, all of this might be true. But basic horse feeding isn't rocket science. To help you delve into the murky world of equine nutrition, here's what you really need to know about three key ingredients in your horse's diet--fiber, protein, and carbohydrates.
Like all true herbivores, horses may satisfy their daily energy requirements by eating plant fibers. The tough, stringy stems and leaves of pasture grasses (or hay, the dried version) are their natural diet, and they're superbly adapted to extract nutrients from those fibers. This is done with the help of a population of beneficial bacteria in the horse's cecum (part of the large colon, or hindgut, which acts as a fermentation vat for plant tissue).
In his natural state, a horse wanders and grazes for 12 to 16 hours a day. His digestive system is designed to process small amounts of feed constantly as it comes along. Without adequate fiber, the digestive system can't function properly. It loses the ability to move food particles efficiently through the gut, and its ability to conserve water and electrolytes also is compromised. The result is a horse at risk for dehydration, colic, and laminitis (not to mention stable vices like cribbing and wood-chewing, which often develop when a horse's fundamental urge to chew is not satisfied).
Fiber is so important to equine digestive health that it always should make up at least 50% (by weight) of your horse's daily diet. For the vast majority of adult horses, that percentage can be pushed up considerably higher--even to 100% if the horse is an easy keeper or is not being asked to do much work.
The fiber content of pasture and hay can fluctuate according to the environment, time of year, soil, and stage of growth of the plants. Early spring pasture, with its tender young grass shoots, tends to contain more digestible fiber. Later in the summer, the grasses become tougher and stringier, and extracting nutrients is more difficult. Likewise, hay cut early in its growth cycle, before it has developed seed heads, tends to be more digestible than hay cut late in the growth cycle. Once the plants have gone to seed, their stems tend to become tough and fibrous, and the palatability (taste appeal) and diges-tibility plummet. So, your horse might have to consume more to extract the nutrition he needs.
Hay and pasture grasses aren't the only fiber sources available to horses. One popular alternative is sugar beet pulp, a feed made from the fibrous portion of the sugar beet after the sugar has been extracted. Available in a dehydrated format (either shredded or in pellet form), beet pulp can be re-hydrated by soaking it in water for a few hours before feeding. Once soaked, it's a soft-textured, easy-to-chew, digestible fiber source. It's a useful supplement to hay or pasture if you have older horses, animals with dental problems, "hard keepers," or horses recovering from illness, injury, or surgery.
Bran, another traditional way of supplementing fiber, is a less-suitable choice. Bran is the outer layer of the wheat grain kernel. It is removed in the process of milling. A fluffy, low-density feed, bran is well-liked by horses, but it's not that digestible, meaning that it takes a lot of bran to provide sufficient fiber for the average adult horse. Additionally, bran is very high in phosphorus and low in calcium and might result in a calcuim-phosphorus imbalance in the diet. An occasional small bran mash probably does no harm, but as a fiber supplement, there are better choices. If you must feed it, make bran no more than 10% of your horse's total ration.
Hay cubes, roughage chunks or pellets, and haylage (fermented hay in airtight packaging) are three other ways you can deliver fiber to your horse. They have the advantage of being compact and easy to store, and depending on the type of forage they are made from they deliver more concentrated nutrition--pound for pound--than baled hay. But because the plant fibers in these products are chopped or ground up, they might not provide the same "chew time" as long-stemmed forage--and that can lead to a horse which feels compelled to "graze" on the walls of his stall or the fencing in his pasture.
Feeding small amounts, often, helps mimic the horse's natural grazing style and is healthier than feeding large amounts of feed in one or two big meals a day. If you can, try to keep some sort of fiber source in front of your horse for most of the day (and night); the result will be better digestive health, a lower risk of colic and ulcers, and a higher contentment quotient.
Of all the components of your horse's diet, protein is probably the most misunderstood. Protein's real role is not to act as an energy source for performance, but to provide amino acids, the building blocks for growth and repair of bones, muscles, and soft tissues.
Amino acids are involved in virtually all of the horse's vital processes. They are essential to the synthesis and the release of hormones, the synthesis of neurotransmitters and enzymes, and the regulation of sleep, appetite, and blood pressure, to name just a few functions. But primarily, amino acids are needed for the formation and repair of muscle tissue, bone, and other soft tissues throughout the body.
Growing horses which are "building" new tissues as they mature, and horses being used for breeding, have a higher protein requirement than do mature horses being used for pleasure or performance. Whether working or idle, the protein needs of most mature horses are surprisingly small (between 8% and 11% crude protein in the overall diet, as opposed to 12% to 16% for a young, growing horse or lactating broodmare).
Proteins are "chains" made up of various combinations of the 22 amino acids that exist in nature. The position and number of the amino acids in a single protein make up its "amino acid profile." When a horse ingests protein, the chain of amino acids is broken up in the digestive tract by enzymes and acids, and the individual amino acids are absorbed through the wall of the small intestine and into the bloodstream via the liver. From there, they travel to the sites where they are most needed.
Although amino acids are absorbed from the small intestine in a format relatively unchanged from their original chemical composition, the horse's body does have the ability to change some amino acids into different formats as the need exists, a process that occurs in the liver. You must remember, however, that the horse's body does not have the ability to create all the amino acids it needs. Some amino acids only can be synthesized by microorganisms or green plants; these are called the "essential" amino acids, and they must be obtained by the horse from his environment. ("Non-essential" amino acids are those the horse can synthesize himself.)
A good-quality protein source is a food that provides a sufficient amount of essential amino acids, particularly the amino acids lysine and methionine. Lysine is often called the "first limiting" amino acid, meaning that if insufficient quantities of lysine are present, then the horse's body will have difficulty utilizing any of the other amino acids. Methionine is second in line. The best source of high-lysine protein for foals is milk protein; for adult horses, a plant source such as soybean meal is the best way to go. (Cottonseed meal and linseed meal, two other common protein sources used in horse feeds, have far less lysine and thus aren't considered to be as high in quality as soybean meal.)
That said, the amino acid profile of a feed is more important to a young, growing horse than to a mature one; adult horses are far less sensitive to differences in protein quality. Lysine and methionine often are deficient in the ingredients that make up normal horse feeds, but since they can be synthesized inexpensively, it's routine for feed companies to add these to improve the overall amino acid profile. (Not all amino acids can be easily synthesized, however.)
Can protein serve as an energy source? Yes, but metabolically, it's an expensive process, producing three to six times more body heat than the breakdown of carbohydrates or fats, and yielding considerably less energy. The heating factor might be beneficial in a cold environment, but it can contribute to excessive sweating and possible heat exhaustion during hard work, especially in a warmer climate. Since protein is one of the more expensive ingredients in a feed, it's impractical to feed higher levels of protein in search of a performance advantage. Carbohydrates and fats are better energy sources (more on them in a minute).
Feeding more protein than is needed is false economy for other reasons, too. Any protein that is not used immediately by the horse's system is converted to ammonia and urea molecules, which are excreted in the urine. This leads to increased water intake, increased urination, and a noticeably strong ammonia smell in the stall.
Carbohydrates For Energy
If fiber provides the maintenance energy horses need for the workings of everyday life--grazing, sleeping, wandering from pasture to pasture, maintaining his internal temperature--then carbohydrates, from cereal grains such as oats, barley, and corn, are the turbo-charged portion of the diet. The main function of grain is to provide higher concentrations of energy so that the horse can do the work we ask of him.
The amount of energy your horse needs rises in direct proportion to how fast, how long, and how hard you expect him to perform. At the lowest end of the spectrum are horses which are idle, or perhaps work only a few times a week at a very slow pace; most pleasure horses fall into this category. At the other end are racehorses, which probably work harder than any other category of equine athlete. Probably somewhere in between is your horse--whether he's a Western pleasure horse, a Grand Prix jumper, or a polo pony. His energy requirements probably are not met completely by hay or pasture.
Work isn't the only thing that can raise a horse's energy requirements above the maintenance level. Environmental conditions, his physical fitness, and his degree of fatigue all play a role. Pregnancy also counts as an increased energy demand, especially in the last three months of gestation when the fetus is developing faster than any other time during pregnancy. Lactation and growth are two other situations where energy needs are higher than usual.
Carbohydrates and starches contained in grains are the most convenient way to provide extra energy to your horse. A carbohydrate molecule is composed of simple sugars (also called monosaccharides) such as fructose, glucose, galactose, and xylose that are attached. In the gastrointestinal tract, the bonds that hold the monosaccharides together are broken by enzymes so that the simple sugars can be absorbed through the walls of the small intestine. Once they pass that barrier, they're almost immediately available for energy use by the horse.
If the energy isn't needed immediately, the body begins re-assembling the sugars in the form of glycogen so that they can be stored. Storage centers in the kidneys, liver, and muscles give the horse a substantial energy warehouse. If those locations become full, any extra monosaccharides are con-verted to and stored as fat. Both glycogen and fat can be drawn on for energy whenever they're needed. The hormone insulin acts as a glucose regulator in the bloodstream, determining how much sugar remains there and how much gets stored away.
How do you know if your horse needs grain in his diet? He'll show the signs of inadequate energy intake--a depressed attitude, weight loss, and an inability to do the tasks you ask of him.
Far more common, however (with domestic horses, at least) is an energy excess. Equines which routinely receive too much carbohydrate-rich feed will develop increased fat stores and be "hot," or difficult to manage (basically, he's looking for a place to burn off that excess energy).
In young horses, excess energy also contributes to rapid growth, which can increase the risk of developmental orthopedic (bone and joint) problems. Reducing the amount of feed in the diet (especially grains), and providing more outlets for exercise usually will take care of the problem.
All grains contain large amounts of carbohydrates and starches, but not all grains are equal. Here's what they do have in common--they're low in fiber and about 50% higher in dietary energy than average to good quality hay; and starch makes up 55% or more of a grain's total dry matter.
Grains with seed coats (like oats) tend to be lower in carbohydrates and higher in fiber than hull-less seeds like barley and corn, which are very carbohydrate-dense.
On the whole, starch digestibility by the horse is high--researchers estimate that the average horse utilizes from 87% to 100% of the starch he's given. And therein lies a problem.
When a grain meal hits the horse's small intestine, some of the starch is digested and absorbed as simple sugars, as it's meant to be, but the rest, instead of passing through the system undigested, is converted by the bacteria in the cecum to volatile fatty acids and lactic acid. If the production of these acids is rapid enough (as can happen when a horse gets a large grain meal or when he breaks into the feed room and gorges), cecal acidosis can result. This is a toxic condition that can trigger diarrhea, colic, and laminitis.
To reduce the risk of this reaction, it's wise to follow the old horseman's credo of "small meals, often." This gives the small intestine time to process the carbohydrates before the system moves everything along to the cecum. The more carbohydrates that get digested in the small intestine, the less cecal acidosis results. Because forage in the system can decrease the amount of grain processed in the small intestine, it's best not to feed hay for an hour or more before feeding grain, or for three or more hours afterward--a rule that was definitely not in the old horseman's lexicon. Other approaches that can help include giving preference to grains with fiber-rich hulls, such as oats, or choosing grains that have been processed by grinding or heat treatment (pellets, extruded feeds, and "steam-flaked" rations are three examples) to improve the digestibility of the starches.
In short, although carbohydrates can be a useful addition to your horse's diet, they need to be fed with caution. The equine digestive system really wasn't designed to deal with them very well, so moderation is the key.
Understanding how these three key dietary ingredients--fiber, protein, and carbohydrates--operate to fuel your horse's metabolism and performance should help you make reasonable choices when you're buying feed. That's not to say there still won't be a few feeding mysteries to unravel; but that's a good reason to stay tuned to this column!
About the Author
Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.