Basic Horse Nutrition
By March 14, 2005
Welcome to Kent University study on basic horse nutritional concepts. In this section we will explain the important concepts in horse nutrition starting first by explaining the equine digestive tract and horse’s general nutrient requirements.
The horse digestive system is classified as a non-ruminant herbivore. As a non-ruminant, the horse does not have a multi-compartmental stomach similar to cattle, but rather a simple stomach similar to a human’s. Herbivore means that horses can live on a diet of plant material. We will see in this presentation that the horse’s lower digestive tract is design such that it can utilize the plant material fairly efficiently.
Having an understanding of the anatomy of the horse’s digestive tract, will help you better understand its nutrient requirements and recommended management.
This provides a schematic drawing of the horse’s digestive tract. Important parts of the digestive tract that will be addressed include the mouth, esophagus, stomach, small intestine, cecum, and large intestine. The slide provides the lengths and capacities of the different segments digestive tract to give you a feel for the size.
As with other mammals, the mouth apprehends the food, chews the food and mixes the food with saliva to produce a moist bolus. For the horse, the teeth are important for harvesting and chewing food. The upper jaw is wider than the lower jaw. The average 5 year old adult horse has a total of 40-42 permanent teeth on the upper and lower jaws.
A horse owner needs to frequently check the teeth of the horse and obtains the services of a veterinarian if there is a problem. A common dental problem is the development of sharp enamel points causing painful abrasions on the tongue and cheek. These can be corrected by the vet grinding down the points. This process is called floating the teeth.
The esophagus is the muscular tube running from the back of the throat to the stomach. An obstruction of the esophagus is commonly referred to as a choke. A true choke seldom happens. Because of the muscular cardiac sphincter valve leading into the stomach from the esophagus, it is almost impossible for horses to vomit. In the event of over consumption of feed, it is more likely the stomach will rupture than for the horse to vomit. It is a rarity that a horse’s stomach ruptures.
For a horse’s size, its stomach has a relatively small capacity – only about 7% of the empty weight of the gastro-intestinal tract. The small size limits the size of the meal, therefore, horses typically eat many small meals in a day. In the stomach, feedstuffs are mixed with enzymes that break down the feedstuffs. The rate of passage of feedstuffs through the stomach can be relatively quick if the horse consumes a large meal. When a horse consumes an excessive meal, the digestive capacity is overwhelmed, and the undigested feed material flows though the stomach and small intestine and into the cecum. Undigested starch in the cecum can result in health problems for the horse.
From the stomach the digesta flows into the small intestine. This is the major site for digestion of protein, fat, and soluble carbohydrate. Enzymes secreted in the stomach and small intestine mix with the food to digest it into smaller components. These small components are absorbed across the wall of the small intestine. As with the stomach, rate of passage of the digesta through the small intestine is relatively rapid.
The cecum and colon of the horse is referred to as the hind gut. This section of the gastro-intestinal tract is relatively large – 64% of the empty weight of the gastro-intestinal tract. In this region of the GI tract the horse utilizes the fiber fraction of the diet which provides energy to the horse. The cecum is a blind sack approximately four feet long. Food enters at the top of the organ and is expelled at the top. The microbes in this microbiological vat break down feed not digested in the small intestine. Most importantly the microbes digest the fiber (roughage) fraction of the diet. The microbes product vitamin K, B-complex vitamins, proteins and fatty acids. Vitamins and fatty acids are absorbed, but little if any protein is absorbed. Beyond the cecum in the lower GI tract is the colon. Food may reach here in as little as 7 hours and will stay here for 48-65 hours. Microbial digestion continues in the colon. In the colon, vitamins, fatty acids and water are absorbed. Also in the colon, fecal balls are produced from the undigested food material. The short chain fatty acids produced in the hindgut provide a substantial portion of the energy from the diet.
In the next section, the general nutrient requirements of horses will be discussed. It is important that the essential nutrients a horse requires be included in its diet.
Water is not always thought of as an essential nutrient, but it is ultimately important that water be generously provided to horses. In fact water comprises 50 to 70% of the body and is essential for the horse and is required for transport of nutrients to body and waste products from body tissues.It is important to keep water in front of horses at all times except under abnormal circumstances. Typically water intake is 10-12 gallons per day, but in some situations their demand for water increases. Exercise and work can cause the horse to sweat which increases water intake. Warmer environmental temperatures increases water intake. Lactating mares have a greater water demand.
During seasons of cold temperatures, make sure the water is not near freezing. Cold water temperatures (near freezing) will reduce the water intake which can cause health problems. Because of the horse’s relatively small stomach size, the drink size is limited. Energy is the fuel for maintaining normal body functions and temperature. The diet should provide energy to meet the demand of the lifestyle of the horse. Major sources of energy in the horse’s diet include carbohydrates in grains, and fat. As discussed earlier horses utilize complex carbohydrates (fiber) of hay and pasture. Microbes in the hindgut ferment the fiber which results in the production of fatty acids. These fatty acids can provide a significant amount of energy to the horse.
The amount of energy required in the horse’s diet is dependent on the size of the horse and the life stage of the horse. Generally, the larger the horse, the greater the horse’s energy requirement. Increasing the work load of the horse increases the energy requirement. At maintenance, a 1100 lb horse requires 16,400 Kcal digestible energy, whereas, the same size horse performing intense work requires 32,800 Kcal digestible energy. A lactating mare weighing 1100 lb, the first third of lactation, requires 28,300 Kcal. These numbers are only estimates, the feeding amounts may have to be altered to retain the proper body condition of the horse. Underfeeding energy to a horse will result in the horse losing body condition, whereas, overfeeding will result in a horse becoming overly fat.
Like all mammals, horses require protein in their diets. Actually dietary protein is comprised of long chains of amino acids, the building blocks of life. Amino acids are the building blocks of muscle and other structural tissue. As important, amino acids are components of some enzymes and hormones that are essential for metabolic processes. To optimize growth, sustain the working horse and maximize milk production of a mare, it is important to have the proper amount and balance of amino acids in the diet. Horses in these life stages require more amino acids to build muscle and other proteins.
Also of importance in the diet of horses is mineral supplementation. The essential minerals are typically divided into the major minerals and trace minerals. The major minerals include calcium, phosphorus, sodium, chloride, potassium, magnesium, and sulfur. Calcium and phosphorus are of particular importance because of their profound effects on growth and development. They are the chief constituents of teeth and bone. Phosphorus is essential for energy metabolism and calcium for the transmission of nerve impulses. It is important to maintain the proper Ca:P ration in the diet of horses. For the total diet, it is recommended the Ca:P be 1.5-2.0:1.0 and for the grain mix 1.1-1.4:1.0. Most importantly, the horse requires sufficient phosphorus in the diet.
Feeding salt to the horse provides the major minerals, sodium, and chloride. Feeding free choice salt to horses is necessary when they are working hard and sweating profusely and when the commercial grain product does not have added salt. Potassium, magnesium and sulfur are usually present in the diet in sufficient quantity without supplementation.
As the name suggests, trace minerals are required in the diet in very minute amounts. In most horse feed products manganese, zinc, selenium, copper, and iodine are included. As with the major minerals, it is important that the trace minerals be added to the feed at the correct amount in the proper ratio to each other. Inorganic trace mineral sources included zinc sulfate (zinc), manganese sulfate (manganese), copper sulfate (copper), calcium iodate (iodine), sodium selenite (selenium). These are not the only sources of inorganic trace minerals, but are the ones most commonly used.
In many horse products, organic trace minerals partially replace the inorganic trace minerals. Organic trace minerals are trace minerals combined with an amino acid, peptide, carbohydrate, etc. Once combined with an organic compound, they seem to have a great biological availability. Generally, organic trace minerals are more expensive than their inorganic counterpart. Research data indicates that in some animal species, organic trace minerals improved reproductive performance and enhanced immune function.
As with minerals, vitamins are required in the diet in minute amounts. Vitamins are generally classified into two categories, fat-soluble and B-vitamins. The fat-soluble vitamins include vitamins A, D, E, and K. The vitamins are stored in the body and their absorption is facilitated by the presence of fat in the diet. It is recommended that vitamins A, D, and E be supplied in the diet. Generally, bacteria in the intestinal tract synthesize sufficient vitamin K. Vitamin E is especially important because of its involvement in supporting immune system function which sustains health. Also, vitamin E is an important antioxidant in that it helps maintain the integrity of cell membranes. B-vitamins include riboflavin, thiamin, biotin, pyridoxine, niacin, choline, pantothenic acid, and vitamin B12. These vitamins are synthesized in the hind gut of the horse. Many horse feed products are supplemented with these vitamins to ensure sufficiency in the diet of growing horses and horses under stress. B-vitamins are important for production of healthy hooves, prevention of anemia, strength and maintenance of bones and joints.
The tissues of horses can generally synthesize sufficient vitamin C for its needs. However, senior horses and horses under stress may not be able to produce enough vitamin C to maintain their health so products for these classes of horse are many times supplemented with vitamin C. Vitamin C like vitamin E enhances immune response and is a potent antioxidant, helping to reduce metabolic stress. Many nutritional enhancer products are marketed to horse owners. Yeast culture is a product demonstrated through research trials, to enhance the microbial fermentation in the hind gut of the horse. This results in improved nutrient digestibility. Other demonstrated benefits include reducing risk of digestive upsets, improved feed intake, enhanced growth of foals and improved stamina of performance horses.
Important concepts to remember are that the horse is a non-ruminant herbivore – it has a digestive system that requires forage (hay or pasture) in the diet. The horse’s relatively small stomach limits its meal size. The starch fraction of the horse’s diet is digested in the stomach and small intestine and mostly absorbed in the small intestine. Whereas, the fiber fraction of the horse’s ration is broken down by microbes in the cecum and colon. Energy from the starch fraction, fat, and fiber in the diet is the fuel for maintaining normal body function, regulating body temperature and performing work.
Other important concepts include the energy requirement per day for a horse is dependent on the horse’s life stage, weight, and the level of work the horse is performing. Remember, amino acids are the components of protein and are the building blocks of muscle and functional proteins such as enzymes and hormones. Horses require minerals particularly calcium and phosphorus in the proper balance in their diet. Vitamins and trace minerals are required in small amounts in the diet, but are important for metabolic functions in the body.