Feeding Horses: General Principles

Editor's Note: This is from Understanding Equine Preventive Medicine by author and veterinarian Bradford G. Bentz, VMD. The book is available from www.ExclusivelyEquine.com.

A complete review of equine nutrition is beyond the scope of this text; however, some basic principles that relate to preventive medicine are worth mentioning. It is always advisable to seek specific suggestions from a nutritionist in developing a feeding program. Feeding programs should meet the individual horse's needs, as these requirements vary with the amount and type of forage and grains fed, amount of pasture available, use of the horse and amount of exercise, and individual metabolism and ambient environmental temperatures. Diets typically should be designed around forage (hay) and grass.  Analyzing the hay to identify the amount of energy in calories it provides as well as its mineral content can help achieve a well-designed feeding program.  Commercially available grain mixes and pelleted feeds vary to meet the energy and mineral needs of most horses that are used for various types of work or for horses with different needs (performance, broodmares, youth, overweight, geriatric horses).

Another critical component of a feeding program is access to a clean, fresh water source.

Because diets composed entirely of cereal grains are associated with higher risks of diarrhea, colic, acute laminitis, exertional myopathy (tying-up), hyperactivity, and obesity, it is recommended that a grain or concentrate mix make up no more than half (by weight of dry matter) of the total amount of feed.  Those horses that are less than one year of age or those being used for sprint-type exercise may be fed up to 70 percent grain mix, but a maximum of 50 percent grain by weight of dry matter of the diet is generally safer. This amounts to about one pound of forage dry matter (weight corrected for water content) per 100 pounds of body weight. Feeding inadequate forage to a horse that is not on pasture may significantly increase the risk of diarrhea, colic, founder, wood chewing, feces eating, and in young horses, mane and tail chewing.

Harvested forages should be fed in manners that minimize forage loss and loss of nutritional value, fecal contamination, and dust inhalation during consumption.  Containers or racks that catch leaves and loose forage and keep forage off the ground can be useful.  Hay racks, feed troughs, and feed bunks may serve these purposes.  Hay consumption from feeders or feed bunks that are placed above the horse's shoulder height increases the likelihood of material getting into the horse�s eyes and dust inhalation while eating.  Horses should be fed individually to assure that each horse gets its appropriate ration and to reduce competition for these rations.  Hay from round bales is commonly fed but should be avoided.  Feeding round bales is associated with increased incidence of colic, mold spore inhalation that leads to toxin ingestion or the development of chronic respiratory disorders such as COPD, and increased likelihood of botulism.

To help prevent digestive dysfunction, limit grain intake to about 0.5 pounds of grain/100 pounds of body weight per feeding. This grain should be fed to the horse in two to three daily meals. Infrequent meals may induce changes in intestinal motility and blood flow and increase the risk and occurrence of colic, a condition that primarily affects stabled or paddocked horses and is uncommon in horses on pasture.  The risk and occurrence of colic in horses that are not on pasture can be reduced by having long-stemmed forage available as much as possible and allowing the horse to eat it freely.  Again, long-stemmed hay and pasture should be the basis for all feeding programs. Grain should be fed in as small an amount as possible and only if forage and pasture are unable to meet any additional caloric requirements.  The exceptions would include feeding programs for horses with teeth problems that may do better on a complete pelleted feed, or if good-quality forage is unavailable or is considerably more expensive than grain.

Mineral requirements for horses may vary with age, activity, and for the mare, reproductive status. Balance between dietary calcium and phosphorous intake is important for all horses.  Growing horses, broodmares in the last trimester of pregnancy, and broodmares that are lactating need more of these minerals.  Regardless of the requirement level, these two minerals must be balanced. Diets that fall below an equal ratio of calcium to phosphorous lead to calcium deficiency, which can be caused by inadequate calcium intake or excess phosphorous intake. Clinical disease associated with this condition causes excess parathyroid hormone secretion (known as "nutritional secondary hyperparathyroidism"). Excess parathyroid hormone causes calcium and phosphorous to be mobilized from bone "reserves" and may lead to bone demineralization, enlarged facial bones, shifting leg lameness, and generalized bone and joint pain.

Dietary changes should be gradual, over several days or weeks. Increasing the amount of grain at a rate of no more than 0.5 pounds daily until the desired level is reached is believed to be a safe approach. Faster rates of change may be associated with the development of colic and/or founder. Furthermore, decreases should be gradual for horses on a high-grain diet that are being rested or retired from strenuous training.  Horses in regular strenuous exercise that are given a day's rest should receive less grain that day and should have turn-out in an area of sufficient size to allow them to run (unless being rested for an injury).  Horses being put on lush green pasture should be given all the hay they are accustomed to receiving before being put out onto the pasture.  If possible, the amount of time spent on such pasture should be gradually increased by one hour each day.  After the fourth or fifth day, it is usually safe to leave the horse on the pasture. The more plentiful and lush the pasture, the more important these procedures are for safe introduction to the pasture.

About the Author

Bradford G. Bentz, VMD, MS, Dipl. ACVIM, ABVP (equine)

Brad Bentz, VMD, Dipl. ACVIM, ABVP, ACVECC, owns Bluegrass Equine Performance and Internal Medicine in Lexington, Ky., where he specializes in advanced internal medicine and critical care focused on helping equine patients recuperate at home. He’s authored numerous books, articles, and papers about horse health and currently serves as commission veterinarian for the Kentucky State Racing Commission.

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