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National Association of Competitive Mounted Orienteering
Equine Nutrition - By Walt Olsen

Basic Concepts in Equine Nutrition
Diseases of Dietary Origin

Horses and Grazing
Estimate Your Horse's Weight

Basic Concepts in Equine Nutrition

It's not just what your horse eats, but what, how much, and when they eat and drink that can help your horse stay healthy and happy. This information is to review the differences between the "simple-stomached" creatures (ourselves, dogs and cats, etc) and the horse. We will take a look at how domestication has impacted the horse's digestive system and how that impacts their general health.

The horse is considered a "post-gastric fermenter" meaning that after the simple stomach and small intestine, a large portion of the horse's digestion comes from the fermentation of fiber within the later portions of the digestive system. Actually about 60% of the energy a horse gets from his food can come from volatile fatty acids produced by the bacterial fermentation of fiber within the large intestine.

The bulk of the average horse's feed ration is hay (as it should be). The nutritional quality of hay can vary greatly between a pure grass hay like timothy, which has a digestible energy content of about 1.8Mcal/kg and a crude protein content of about 7.5 %, and a high-quality legume hay such as alfalfa, which has a digestible energy content of about 2.2Mcal/kg and crude protein content over 15%.

The nutritional content of hay can also be affected greatly by weather conditions at the time of harvest and other processing factors. If buying a large amount for storage it is best to have it tested to see what the protein is and the TDN, digestibility numbers.

The nutritional requirements of an individual horse vary with the stage of growth, sex, healing if injured, recovery from illness, climate and exercise. The average 1,100-pound mature gelding requires 16,400 kcal (calories or 16.4Mcal) with 660 grams of crude protein for daily maintenance. The horse would require 20 pounds of timothy grass hay or 16.3 pounds of alfalfa for daily maintenance. If this horse is a mare with foal she would require 28,000kcal ( 28.0Mcal) for daily maintenance, with 34.2 pounds of timothy or 28 pounds of alfalfa, a CMO horse of the same weight, working intensely would require 32,000kcal (32Mcal) for daily maintenance with 39 pounds of timothy or 32 pounds of alfalfa to meet the energy needs for the event. A horse can only eat about 3% of its body weight in dry matter per day.

The mare and CMO horse would need a higher energy density feed (such as grain) to meet energy needs. A general rule of thumb for daily maintenance is to feed 2% of the horse's body weight in pounds of average quality mixed grass hay, so it follows that the average 1,000 pound horse would require about 20 pounds of mixed grass hay a day to maintain weight.

The best and cheapest way to determine weight is to weight using a tape, most tapes are about $3.45 to $5.00 in most mail order catalogs. It is wise to buy a scale for hay and grains. You should feed your grains by weight if at all possible.


There are 22 amino acids used in the construction of proteins, the proteins within a foodstuff are broken down by digestive system into individual amino acids and are absorbed. From there the amino acids are used to build new muscle tissue and can be used to produce energy where there is a problem with nutritional elements in the graze, but comes at the expense of heart and other muscles.

More on protein, it is not a certain percentage of protein, but an actual gram amount, that should be used to meet requirements. It should also be noted that a certain quality of protein is necessary for it to be utilized. The amino acid lysine is the so-called rate-limiting amino acid for the horse, meaning there must be a certain minimal amount of lysine (23 grams per day for our 1,100 gelding) in order for the dietary protein to work.


Carbohydrates can be simple (also called soluble carbohydrates or monosaccharides), such as glucose and various other sugars, or complex, such as starches, fiber and the less soluble portion of grains. The grains have both soluble carbs (the inner parts of the seed or kernel) and insoluble carbs (the outer parts of the seed and remainder of the plant).

The digestibility of the grains is also affected by the processing. For example, crimped /rolled oats or cracked grounded corn have soluble carbohydrates that is better available to the digestive process than their ÒwholeÓ counterparts. Most of these soluble carb's are broken down and absorbed in the small intestinal portion of the horse's gastrointestinal system with the insoluble passing on to the colon and cecum to be fermented by bacteria to produce volatile fatty acids. The glucose and fatty acids are then used by the horse's chemistry to produce energy or are stored in various tissues as fat reserves for later energy production.


Fats are also broken down and absorbed by the small intestine. From there the fats can either enter the biochemical energy production pathways or be stored for release later. Recent research has shown that the fats can make up to 10-20% of a horse's daily energy requirements and be well utilized.Ê Facts are showing up from this research that horse's afflicted with muscle diseases ( such as tying up and glycogen storage disease ) can benefit by lowering the soluble carb's (grain ration) in their diets and increasing the amount of energy that is provided by fat. Fats contain two times the energy production ability on a gram to gram basis compared to soluble carb's or protein. There are many new feeds on the market with more fats and less carbohydrates in them. Ask at your local feed store or feed outlet which is best. Then read the label and decide for yourself.


Water is the most important nutrient. Your horse could live for weeks without ingesting any feed, but two to three days without water would cause severe illness or death. The average 1,000 pound horse drinks over 4.5 gallons of water per day. Fresh water is needed to for fill this requirement at all times.

Research for this material came from the Nutrient Requirements of Horse's, by the National Academy Press, 1989 edition, Feeding and Care of the Horse by Lon Lewis and from Washington State University 4-H material.

Diseases of Dietary Origin

Eating the wrong foods (or the wrong amounts of the right foods) can have bad consequences in your horse.

"You are what you eat" does have a bearing upon the case to horses with regard to health and well being. Although horses have evolved to eat plant material, not all plants are safe to eat. Some food substances directly exert toxic effects, while others grow fungi that do so. Availability and type of food are important issues to intestinal health and nutritional balance.

In addition, imbalances of nutritional compounds such as micro-minerals, energy, carbohydrates, and protein can have adverse effects on your horse's health. In young horses musculoskeletal problems can occur, one is called (DOD) or developmental orthopedic disease resulting from a variety of multi-factorial issues, but nutritional imbalances are known to strike a young growing horse. DOD is linked to an imbalance of calcium and phosphorus, and /or a deficiency in micro-minerals such as copper, zinc, and manganese; over feeding of these minerals can cause is just as likely a cause as imbalanced nutrition in stimulating this disease.

Too many calories enable a growing horse to become fat, with subsequent overload of developing joints. Hormonal changes associated with a rich diet also can affect joint metabolism. Mineral imbalances have destroying effects on joint cartilage development. It is known that high phosphorus and relatively low calcium levels will cause cartilage defects. High zinc levels can suppress copper absorption and result in a diet that is relatively deficient in copper.

Adverse effects of an imbalanced diet are amplified by other high-risk factors. The potential for rapid musculoskeletal development is dependent on genetics as well as on nutrition. Rapid growth adds stress to a growing skeletal system, bones, and joints when they can least withstand the added body mass.

A diet deficient in selenium can create muscle problems. The NRC (National Research Council) requirements list the required amount at 0.1 mg/kg of the diet. Foals might exhibit stiff and painful muscle disease and cardiac problems, while older horses have recurred episodes of tying up. Selenium deficiency occurs in certain geographic areas such as the Northwest and northeastern United States. However, caution must be taken not to supplement with too much selenium as toxicity can occur. The maximum tolerable level is 2 mg per kg of the diet, according to the NRC.

Some of us add to the lack of selenium here in the Northwest by putting

selenium salt blocks in a free choice area to keep our horses from chewing wood or bark off of trees that may be in the pasture areas. The adverse effects of too much selenium could trigger several adverse effects, including colic, diarrhea, hair loss and separation of the hooves from the coronary band.

Moldy corn poisoning, also known as blind stagers, is associated with consumption of corn that has been contaminated with the fungus Fusarium moniliforme. This fungus thrives on corn plants that have been stressed by drought, disease, or insects prior to harvest. High humidity and moisture encourage the growing of this mold. Exposure to high doses of this fungus over a short period of time results in liver toxicity; while low doses ingested over a longer time result in brain damage or moldy corn poisoning. Signs to look for include decreasing appetite; changes such as depression, anxiety, and neurological signs such as circling, blindness, difficulty chewing or swallowing. It's time to call your Vet. Do not wait!

Another problem that causes death in your horse comes from Botulism in the dietary form and occurs in horses which have ingested feed contaminated with this toxin produced by the bacterium Clostridum botulinum. The toxin forms when a decomposing animal or bird is accidentally baled with the hay or is processed with pelleted or cubed feed. Haylage or silage that is improperly prepared without sufficient heating allows for continued decay of organic material and production of the toxin. Moist or rotten hay, especially legume hay, can also spawn growth of anaerobic bacteria responsible for generating the toxin. Botulinum toxin is extremely potent and lethal resulting in death. Check you bales of hay for critters that might have been included in your hay when you bought it. If you bought it from a feed store, gather all you bad hay up and take it back; if you bought off a truck on the side of the road, then you are most likely to be stuck.

Skin problems can be caused by plant ingestion. Certain plants contain photo reactive pigments that are absorbed into the blood when a horse eats the plants. In the presence of ultraviolet light from the sun, these then react in areas of non-pigmented skin, and the horse sunburns. Two main plants are the problem in this situation: St. Johns wort (Hypericum perforatum) and buckwheat (Fagopyrum esculentum).

Other bad plants are and will cause problems to the liver and can cause death if taken in large doses are: Tansy ragwort or groundsels (Senecio spp.), hound's tongue (Cynoglossum spp.), horsebrush (Tetradymia spp), alsike clover (Trifolium hybridum). Legume hays have also been implicated in setting up these conditions for skin problems.

Respiratory problems other wise known a chronic obstructive pulmonary disease (COPD) can be caused by various allergens. Like an asthmatic person, a horse can be afflicted by respiratory allergies that come from mold and mold spores in hay. Poor quality roughage or hay that has high moisture content is prone to mold growth. Or hay that has been sprayed with a preservative to keep it from molding as is the case of most of the alfalfa being shipped out in containers from Washington State to Japan and points east. In that case if the hay is rejected by brokers for overseas shipment then that hay comes on the local market it must be soaked to get ride of the preservative before you can use it. A large flake of hay soaked for several hours will turn the water red; it is then safe to feed.

When a susceptible horse is exposed to these molds, a cascade of inflammatory events begins in the lungs. The end result is an emphysematous-like condition known as COPD or inflammatory airway disease (IAD), historically called heaves. What might start as an intermittent and infrequent cough can become more persistent as more lung tissue is affected and the lower airway becomes more sensitive to the effects of environmental allergens. It is not just presence of dust and mold that causes the COPD syndrome; respiratory viruses or chronic respiratory infections also create similar damage.

Fescue toxicosis occurs when tall fescue, a common pasture and hay forage for horses throughout the United States and Canada, is infected with a fungal plant parasite that lives on another parasite and causes a fungus; creating problems with our friend the horse.

Knowing the risks that these and other feeds pose to you horse's health is the first step to avoiding problems. You should discuss local plant/hay/feed risks with your local county extension agent and your veterinarian so that you can formulate a plan of action to remove any dietary problems from your horse's diet.

This material was taken from research material supplied by WSU, School of Veterinary Science, Pullman WA, and from material obtained from the UC @ Davis CA

Horses and Grazing

The word Horse brings up images of graceful, powerful animals roaming across miles of rolling hills, stopping from time to time to graze on lush green grass. In the real world, such scenes are rare, in today's world many horses live without grazing at all.

Urban sprawl has contributed to a lack of suitable pasture, in desert areas; grass is not easily grown and maintained because of lack of rain. Over 14Ó of rain is needed to keep a pasture in the very dry areas, so turnouts provide exercise opportunities only. These are among the many conditions that keep horses from grazing normally.

Too Much Grass:

There are some horses that shouldn't be allowed to graze, or whose grazing time needs to be controlled. Research has indicated that lush, green grass can contain up to 20% soluble carbohydrates. A horse grazing free-choice on this spring grass may be consuming as much sugar as contained in a large grain meal, which is a considerable risk factor in some horse's and can lead to a very overweight horse or one who founders.

The grazing patterns of pregnant mares turned out on fescue pastures should be restricted as well, fescue contaminated with the endophyte Acremonium coenophialum produces reduced or absent milk production and placentitis in mares, retained fetal tissues, and other complications.

Another health problem that might be affected by pasture access is allergies. Some allergy sufferers might not fare too well on pasture Ð in some cases, summer heaves can be caused by pasture allergies. Keep in mind that heaves cases also suffer if left standing around in a dusty barn all day. Controlling dust is one way to lessen the severity of this condition, but horse owners also should address this issue during feeding. Wetting or soaking the hay prior to feeding, as well as feeding soaked beet pulp or hay cubes.

Aside from the basic nutrients, grass hay is full of antioxidants, bioflavonoids and isoflavonoids, so a good grass hay and your choice of commercial feed is your best buy. If you live in the rainy northwest like I do, there is a good chance that pastures and local grass hay may be low in nutrients, which means we must use some supplementation. A trace mineral block is the best way to add minerals into your feeding plan. Again check your feed bag for what is in it, what is the protein amount? What is the fiber amount? How much fat is there? What is the grain consisting of? Oats? Wheat? Sun-cured alfalfa?

I use several different feeds depending what that particular horse is doing for me, a horse that pulls a buggy and is an older horse is fed a feed with crude protein of 14.0% and crude fat of 4.5% and crude fiber of 16.0%, during the winter I boost the fiber up using wet beet pulp that is 18% which is fed to all the horse's and Jim the mule who receives a feed of 10% crude protein once a day along with feed choice grass hay

The younger horses used in our sport are fed free choice local grass hay and currently a blended product called TACO which has 12% crude protein, crude fiber of 18% and crude fat of 2.5% and is high in vitamins, all feeds are certified to be free of noxious weed seed and free of Ruminant meat and Bone Meal. Vitamin A runs from 3,000 IU/LB to 20,000 IU/LB, Vitamin D from 300 IU/LB to 1000 IU/LB and Vitamin E from 35 IU/LB to 1500 IU/LB. Selenium is at 0.3 ppm.

All livestock are fed a measured amount of feed and I use a 16 oz plastic scoop filled to the top.

The key to no pasture or limited pasture is free choice grass hay instead of the limited amounts of rich legume hay, if large round bales are available this is the way to go with a non-pasture or poor pasture and a lot of livestock to feed. Even with a set feeding schedule, hay should always be available.

In removing horses and mules from pasture, we have altered their natural way of life. As a result, some behavioral and health-related issues can develop. Sheer boredom can produce habits such as chewing, kicking and cribbing. These stable vices generally result in a damaged barn, but they have the potential to cause serious health conditions.

My research for this material has come from Dr. Paul Siciliano PhD, a nutritionist and associate professor at the Dept of Animal Sciences at Colorado State University, from a book called Simple Horse Nutrition, and from the University of California at Davis, CA.



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