Horses have a unique digestive system that is designed to process large quantities of forage. Horses on pasture often spend up to 16 hours per day grazing. There are many types of forages in vegetative (pasture) and dried (hay) forms. Most people now use hay as the main source of forage for their horses. But, how does hay compare to pasture?
Hay is different from the growing plants in a pasture because it contains only about 11% moisture, while fresh grasses and legumes usually contain over 70% moisture. To compensate for this, horses secrete copious amounts of saliva that is mixed with the dry hay when it is chewed and swallowed. By the time the digesta (hay and saliva) reaches the stomach, it contains about 90% moisture. That is a lot of saliva! Therefore, when feeding hay, it is essential to provide horses unlimited access to fresh, palatable water. When water is not available or palatable horses will stop eating dry feeds. Lack of water leads to dehydration, and dehydration leads to impaction colic, something you definitely want to avoid.
Another factor that contributes to colic is hay that contains high amounts of indigestible fiber. This happens when hay is harvested when vary mature and full of stems. While horses may eat very mature hay, it does not provide sufficient energy to maintain body condition. Consequently, they lose weight and may develop a ?hay belly? from the indigestible fiber trapped in the hind-gut.
To help one understand fiber in horse feeds, some definitions are important. Carbohydrates are classified as nonstructural (also called soluble, nonfiber) or structural (also called dietary fiber). Nonstructural carbohydrates include simple sugars (glucose, fructose), starches and glycogen (sugar stored in muscle fibers). Fibers are classified as soluble (sap, resin, gums, pectin, and mucilages), insoluble (cellulose, hemi-cellulose) and indigestible (lignin). Horses digest the soluble fibers in the foregut. The insoluble fibers are digested by bacterial enzymes in the hindgut. Lignin is not digested and passes in the manure. The older the plant, the more insoluble fiber and lignin the plant will contain.
So, how do we determine the types and amounts of fiber in a sample of hay and what type of hay should be fed to individual horses? There are two common measures of fiber in forages that can give one an idea of fiber content and quality of forages.
? Neutral Detergent Fiber (NDF) is usually provided on a hay analysis report. It is an underestimate of the insoluble fiber content of a feed. NDF includes nearly all of the cellulose and over 50% of the hemicelluloses, but also erroneously includes a high percentage of the amylase digestible starch.
? Acid Detergent Fiber (ADF) is also provided on hay analysis reports. It is an underestimate of the insoluble fiber content, because most of the hemi-cellulose is lost in the acid treatment along with the starch. However, it is the most accurate indication of a feed?s poorly utilizable carbohydrate content that is generally available.
Don?t confuse either of these two fiber analyses with crude fiber; another fiber measurement that must be listed on horse feed tags. Crude Fiber is an unpredictable underestimate of the insoluble fiber content of a horse feed, therefore an overestimation of the non-fiber carbohydrate content of the feed. This may lead to an overestimation of the caloric content of the feed and its feeding value. However, it can be useful when comparing fiber content of several feeds that contain varying amounts of fiber. I recommend feeding concentrate feeds with at least 13% crude fiber for proper digestive health.
The NDF is always larger than the ADF. Both NDF and ADF fiber measures help indicate forage quality; as they increase, forage quality decreases. High-quality forages contain NDF between 35 and 55% and ADF between 25 and 35% on an as-fed basis (usually means about 11% moisture in the hay). Lower quality forages contain NDF between 55 and 70% and ADF between 35 and 45%. Hay with the lowest ADF for a comparable amount of NDF is better-quality hay. Caution should be taken when feeding hay that's over 65% NDF, because it increases the risk of impaction colic, especially if horses aren't drinking enough water. Conversely, if horses don't get enough fiber, they might try to find it on their own by chewing on fences, stall walls or even eating their own manure. (These behaviors can occur for other reasons as well, such as boredom.)
One may be able to get a rough idea of the fiber content of hay by its appearance. Look at the hay and estimate how much digestible fiber it has based on its stem content and its leaf-to-stem ratio. Good-quality hay will have considerably more leaf than stem. Very leafy hay will be considerably lower in ADF and NDF, and it will be more digestible than something with few leaves, many seed heads and lots of thick stems. The best way to determine the nutrient content of forage is to take core samples from at least 10 bales for a nutrient analysis. For information on forage nutrient analysis, contact ADM Alliance Nutrition?s lab at 217-231-2213, use a local University Extension office, or look online for a lab that analyses forage samples for horses. High-quality forages are great for horses with high energy demands, while lower quality hays may be more suitable to horses that are overweight, easy keepers or those that are not working.
Quick Tips for Feeding Forages to Horses
- The best way to accurately determine the fiber content of forage is by laboratory analysis.
- High-quality forages contain NDF between 35 and 55% and ADF between 25 and 35% on an as-fed basis (about 11% moisture).
- Lower-quality forages contain NDF between 55 and 70% and ADF between 35 and 45%.
- Feed only hays with less than 65% NDF and make sure it is low in stems and seed heads.
- Feed hays with lower NDF and ADF to horses needing more energy and hays with higher NDF and ADF to maintenance horses.
- Make sure your horses always have palatable water available.
- The ideal amount of fiber to maintain health and condition of each horse will depend on his total ration, age, breed, workload, current condition and other factors.
For more information about the feeding and care of horses, visit ADM Alliance Nutrition?s online equine library at www.grostrong.com. For free feeding suggestions for your horses, call the Equine Nutrition HELPLINE at 800-680-8254.
Feeding and Care of the Horse. 1995. Lon.D. Lewis. Williams & Wilkins, Baltimore. Pp. 17 & 389.
Fiber in Hay: What's the Magic Number? May 01, 2008 Article # 11784. Christy West, TheHorse.com Webmaster.
Reprinted with permission from ADM Alliance Nutrition, Inc., 1000 N 30th St, PO Box C1, Quincy, Illinois, USA 62305-3115; 800-680-8254; www.grostrong.com. Judith A. Reynolds, Ph.D., P.A.S., Dipl. A.C.A.N., is the Equine Nutritionist and Equine Product and Technical Manager for ADM Alliance Nutrition, Inc.