Last Updated on February 19, 2022 by Allison Price
A happy, healthy horse is one that has a good nutrition foundation. This article will provide a list of ten key points to help you understand nutrition and use it to your advantage. There is information for everyone involved in horse nutrition decisions, from the basics like the importance and benefits of forage to the more complex topics of “digestibility” versus “bioavailability”. This article is divided into ten sections or keys that each cover a different but related topic in equine nutrition.
KEY #1 – Horses eat forage.
KEY #2–But . . Forage is not complete nutrition
KEY #3–Over- and Under-Supplementation
KEY #4 – Horses’ Nutrient Requirements
KEY #5 – The Digestive Tract Parts and Purposes
KEY #6 – The Six Classes of Nutrients
KEY #7–Factors Affecting Nutrient Requirements
KEY #8 – Body Condition Scoring (and Other Measurements)
KEY #9 – Some Tricky Definitions
KEY 1 – Horses eat forage
Long-stem forage is the most important requirement in horse diet. This should be fresh grass. Free-choice grasshay is an alternative. Horses will most closely imitate their natural grazing behavior if hay is kept in front of them at all times. Horses should be fed at least 1% of body weight daily in forage. This can be divided into as many meals and snacks as possible. This is 10 pounds per day for a horse 1000 pounds. It’s not volume (flakes), but weight.
Horses suffering from Equine Metabolic syndrome (EMS), Cushing’s Disease, or other medical conditions might have to limit their grazing times in order to reduce the amount of sugars and starches they eat. Horses with founder may not be able to graze in pasture, especially if the sugar fructan content is high (e.g. spring or fall).
KEY #2–But . . Forage is not complete nutrition
Horses need more than forage. Hay and grass are deficient in certain nutrients, and hay and grass are deficient in certain vitamins . To meet the vitamin and mineral requirements of horses, fortified grains are sometimes added to their diet. Some horses do not need these calories. These extra calories come mostly from starches and sugars, which can cause problems for horses suffering from Equine Metabolic Syndrome (EMS), and Polysaccharide Storage Myopathy(PSM).
There are many ways to provide horse nutrition that doesn’t involve calorie counting. The simplest option is to provide your pasture horse with minerals or your horse on hay with a multi-vitamin/mineral supplement. A ration balancer is a feed that provides vitamins and minerals along with a protein source (amino acid). Fortified grain is the next link, as it provides vitamins, minerals and protein, as well as energy. A complete feed is what horses with certain medical conditions, such as airway disease, or dental problems, can thrive on. It is similar to having hay and grains in one bag. These products contain all the nutrients, vitamins, and protein that horses need, as well as fiber. You should always read the labels on these products to ensure you are feeding the right amount.
- Mineral or Multi-vitamin/mineral supplement: 1 – 4 ounces
- Ration balancer: 1 – 2 pounds
- Fortified grain: 5 – 7 pounds
- Complete feed: 12 – 14 pounds
KEY #3–Over- and Under-supplementation
A pleasure horse that is active and at the recommended weight, receiving forage and fortified grains may be able to meet all of his nutritional requirements. This is not always the case.
Scenario 1 – A 15-year-old “EasyKeeper” who eats grass hay only
The owner of this horse has severely restricted his diet, including removing any fortified grains. This is likely to cause him to lose weight. It may be providing the horse with protein depending on its type, cut, and quality, but it could also be deficient or unbalanced in vitamins and minerals, likely due to the way it was made. This is a case of “under-supplementation” in which a horse is not receiving the correct amount and ratios of the nutrients his body needs.
Scenario 2 – A 5-year-old racehorse with 50/50 grain and forage diet
Consider a young racehorse who is undergoing intense exercise on a daily basis. He is fed equal amounts of grass/alfalfa and sweet feed to meet his high energy needs. This horse is “over-supplemented” in vitamins and minerals due to the sweet feed. He may also be more susceptible to colic, ulcers, and even tying up.
Keys #2 and 3 refer to horses’ nutritional requirements. The next key lists the minimum daily recommended amounts of protein, carbohydrate and fat for horses.
KEY 4–Nutrient Requirements for Horses
The fifth edition of the National Research Council’s Nutrient Requirements of Horses (NRC) was used by veterinarians, nutritionists and feed manufacturers as well as students, teachers, and horse owners for many years. It was published in 1989. A 2007 update made this invaluable reference much more current. (Available for purchase at https://www.nap.edu/catalog/11653/nutrient-requirements-of-horses-sixth-revised-edition)
This NRC publication aims to summarize and review the scientific literature on nutrition and feeding horses. It also addresses the nutritional requirements of different physiological classes, including foals, yearlings and yearlings as well as adult horses at various levels of work and breeding animals. The publication was prepared by a committee who acknowledged that the suggested values might not be appropriate for all horses and that specific goals or adjustments may be required.
Horses’ NRC Nutrient Requirements:
- Fatty Acids and Fats
- Proteins and Amino acids
- Water and Water Quality
- Feeds and Feed Processing
- Feed Additives
- Feed Analysis
- Feeding behavior and general considerations for feeding management
- Unique Aspects Of Equine Nutrition
- Donkeys and other Equids
- Formulation and evaluation of rations
- Computer Model to Estimate Requirements
Chapter 12 discusses nutrition and common equine problems such as nursing, orphan foals, old age, feeding horses in cold and hot weather, and nutritional management for specific diseases. This section covers hyperkalemic periodic parlysis (HYPP), tying-up, PSSM and developmental orthopedic disease (DOD), as well as laminitis, nutritional secondary hypoparathyroidism, ulcers and colic.
The Council was not responsible for reviewing and summarizing information regarding the horse’s digestive physiology. Therefore, the next key will give a brief description of each part and purpose of the digestive tract.
KEY #5 – The Digestive Tract Parts & Purposes
Horses can be classified as non-ruminant herbivores and hindgut fermentors. The horse’s digestive tract is still similar to other species. It is composed of the following parts.
- Mechanical breakdown, mouth–food entry
- Salivary glands – food moistening, some carbohydrate digestion
- The Esophagus–transports food to the stomach
- Stomach–protein digestion
- Small intestinal (duodenum jejunum and ileum) – further carbohydrate, protein, and fat digestion; absorption nutrients
- Liver and pancreas – aid in carbohydrate, fat and protein digestion and absorption
- Large intestine (cecum colon, rectum, cecum)–water, electrolyte and nutrient absorption
- Anus–waste exit
The horse’s stomach is small relative to its overall size. It makes up about 10% of the horse’s entire digestive tract, and holds only two gallons. The colon, however, can hold approximately 15 gallons and makes up nearly half of a horse’s digestive system. These two important differences should have an impact on how horses are fed. Horses are born with small stomachs. They were designed to eat small amounts of food frequently or continuously. Large colons are actually fermentation “vats” that contain bacteria that ferment fiber which the horse cannot digest. They also produce nutrients such as energy, B-vitamins, and other nutrients. This fermentation “vat”, which can be added to with hay during cold winter days, is a great way to heat your horse’s insides.
We now know how different parts of the horse’s digestive tract work to absorb and digest nutrients. It’s time to look at these nutrients. Key #6 explains the roles of each nutrient in the horse’s body and recommends some amounts.
KEY #6 – The Six Classes of Nutrients
Six categories of nutrients are listed: water, protein carbohydrate fat, vitamin, minerals, and fat. Although all nutrients are vital to life, water is the most important. Animals can live longer without other nutrients than they can without water. 70-75% of our bodies are made up of water. Water plays two major roles in the body. It is a part of metabolism and controls body temperature. Horses generally consume between 5 and 15 gallons of water per day depending on their size, environment, workload, and other factors. It is important to have plenty of clean water at all times.
Horses require amino acids, which are the building blocks of protein. Protein is listed as a nutrient. The NRC’s Nutrient Requirements of Horses states that an adult horse weighing just over 1000 lbs and consuming minimum work needs to consume 540 grams of protein per day. This means that the diet should contain at least 8% protein. Protein is the most abundant substance in our bodies. It makes up muscle, connective tissue, and hormones. Although proteins are made up of 20 amino acids, only 10 are essential. This means that the animal must have them in their diet. Lysine is the first “limiting” amino acids because it limits the body’s ability of making proteins.
Carbohydrates are primarily used to provide energy for horses. However, their fiber component is essential for proper functioning of the large intestine. There are many ways to categorize carbohydrates, and they can all be confusing. There are two ways to categorize carbohydrates. One is to split them into structural and non-structural carbs (NSC). The structural carbohydrates include indigestible substances like lignin, which passes through horses’ digestive tract intact. There are also hemi-cellulose and cellulose. These insoluble fibers can only be digested in the colon by bacteria. Non-structural carbohydrates are single sugars such as glucose (monosaccharides), double sweets like lactose and disaccharides, medium-length sugars such fructoligosaccharide or FOS (also known by FOS), and longer sugars such as starch (polysaccharides).
Although it is not clear that horses require fatty acids, nutritionists recommend that horse diet contain at least 0.5% of linoleic, an omega-6 fatty acid. Recent research has shown that omega 3 fatty acid supplementation may reduce inflammation, particularly in the skin and respiratory systems. As a carrier of fat-soluble vitamins from the GI tract and as a precursor for prostaglandins, fat is essential for cell membrane health. Research has shown that fat can have other benefits, as high as 20% for dry matter. Fat is more energy-dense that carbohydrates and can be used to provide calories for the hardworking horse or thin horse who needs to gain weight. Fat can be used as an alternative energy source to simple carbohydrates in grains, which leads to lower excitability and better efficiency.
Vitamins are organic elements that the body requires in small quantities to maintain its essential metabolic functions. There are two types: the fat-soluble A, D. E, and K, and the water-soluble B-vitamins or Vitamin C. However, not all vitamins are necessary in normal diets. Supplementation may be required for senior horses or horses that are under stress due to injury, illness, transport, and other GI conditions.
Minerals are organic elements that have been recognized as essential for the body’s function and must be included in your diet. You can also divide them into macrominerals, which are more important than micro or trace minerals. Macrominerals include Sodium (Na), Chloride (Cl), Calcium (Ca), Phosphorus (P), Magnesium (Mg), Potassium (K) and Sulfur (S). Cobalt, Copper (Cu), Iodine(I), Iron (Fe), Manganese [Mn], Selenium [Se] and Zinc (Zn) are all microminerals. Other minerals of interest are Chromium, Fluorine (F), and Silicon (Si).
KEY #7–Factors Affecting Nutrient Requirements
The NRC recognizes these physiologic classes: pregnant mares and stallions, growing animals, lactating horses, lactating mares, nursing mares, working horses, and adults in no work. There are many subclasses within each class. Working horses can be divided into four classes: light, medium, heavy, and very heavy. These physiologic classes can be determined by their age and work load. Workload is either reproduction or exercise. There are other factors that can affect the amount and type of nutrients needed by horses, including:
- Training, competing and shipping can cause stress
- Injury or disease
- Being a “senior horse”
- “Easy keeper” vs. “Hard keeper”
- Weather and environment
- Management or housing
- High quality feedstuffs
Horses under stress might need more B-vitamins, while horses recovering from injury or disease may require more Vitamin E. Hay that has been either analyzed for low NSC levels or soaked in sugar can be beneficial to easy keepers. Hard keepers might thrive on a fat-supplemented diet. Horses will stay warm and nourished when it turns cold. Hay, not grain, is the best option. Some horses like their individual turnout and stall while others prefer group turnout on pasture. The quality of the forage, especially grain and supplements, has a significant impact on horses’ weight, energy levels, and overall health.
It can be difficult to determine how much a horse is weighing. However, the next key gives some useful tools for estimating body condition and weight.
KEY #8 – Body Condition Scoring (and Other Measurements)
It is important to know your horse’s vital signs, including temperature, pulse, respiration, and other vital indicators. You should also have a system that allows you to track changes in his weight, and body condition. There are many ways to estimate the horse’s weight. A commercial weight tape is the easiest. These tapes can be accurate depending on how close your horse is to the average horse. They can also be inaccurate by as much as 100 pounds. Weight tapes can be used to track changes. This means that if your horse loses weight on a regular basis, such as 1000 pounds on November 1, 975 pounds on December 1 and 950 pounds January 1, you can track the changes. This weight formula is a more precise way to estimate your horse’s weight.
Heart girth(in) X heart girth(in) X Length (in) = weight in pounds
The horse’s heart girth measures the circumference of its barrel measured at the top of his withers. The length is the distance between the shoulder and the buttock.
You should regularly assess your horse’s condition and weight to monitor any changes. The Henneke Body Condition Scoring Chart is a great tool to measure your horse’s weight. It provides a standard scoring system that you, your veterinarian, and your nutritionist can use. A scale can be used to measure the thickness of a dog, from the thinnest one to the largest.
2 = Very thin
4 = Moderately thin
8 = Very fleshy (fat).
9 = Very fat (obese).
Body condition score, nutrient requirements, over and under-supplementation . . . This article contains some very heavy words. Key #9 gives definitions of words that are often used in nutrition discussions.
Key #9 – Some Tricky Definitions
Nutrition words can be interchanged but may not mean the exact same thing. This section contains definitions and common misused words.
Nutrient – Any food component necessary for life support. A chemical substance that provides nutrition, such as protein or carbohydrate.
Ingredient – An edible material that can provide nutrients as a part of food.
Food- Any material containing essential nutrients, usually from animal or plant sources.
Food for animals
Food – Any substance that can be used as food. Usually, multiple foodstuffs are combined to create a balanced diet. A component of a diet that has a useful function.
Diet – A regulated selection of feedstuffs or mixtures that are provided according to a prescribed or continuous schedule. A balanced diet provides all the nutrients necessary for healthy and productive functioning.
Ration – A fixed amount of feed. It is usually expressed as a daily allowance.
Digestibility – The percentage of nutrients in food that can be absorbed from the GI tract.
Bioavailability – The amount of a nutrient that has been absorbed by the GI tract and converted into a form that the body can use.
Roughage – These are the primary food sources for herbivores that live in natural environments. They provide the majority of their diet for the majority of the year. Include pasture, green chop and hay, as well as silage, chaff, chaff, and other forms. Bulky feed with a low weight per unit of volume, high crude fiber and low digestibility of nutrients.
Digestive- The preparation of food for absorption. This may include chemical, mechanical and enzymatic actions. The overall function of digestion is to reduce food to a size or solubility that allows for absorption.
Absorption-There are many processes that allow small molecules through the membranes in the GI tract to the bloodstream or lymph system.
Hunger-a craving for food or water. It is generally a long-term phenomenon, in contrast to short-term satiety. Refers to the internal factors that induce or inhibit hunger in an animal.
Palatability – The overall acceptance and enjoyment with which an animal eats any feedstuffs or diets. The sum of all the factors that an animal perceives when it is searching for and eating food, such as texture, smell, temperature, etc.
Taste – To distinguish flavors among water or feed components.
Satiety- The state of feeling satisfied with your food. It is the opposite of hunger.
Hunger – The desire to eat. This is the opposite of satiety.
All definitions taken from Basic Animal Nutrition and Feeding, Third Edition, Church DC and Pond WG, 1988 John Wiley & Sons, Inc.
This article covered a lot! We started by discussing the importance of forage, but also explaining that it wasn’t a balanced and complete diet. Next, we talked about how horses can become deficient or oversupplemented when they are fed a standard grain diet. The NRC Nutrient Requirements of Horses was next introduced. We reviewed the horse’s digestive system, described the six classes of nutrients, then explored how factors could alter the requirements for specific nutrients. The final discussion on nutrition cannot be complete without addressing body condition scoring and methods for estimating horse weight. This article concludes with definitions of common nutrition terms and the indispensable Resource Section. This section is not complete. These are only a few of the favorites I use frequently.