CARBOHYDRATES AND CONFUSION: FIBER AND FORAGE

CARBOHYDRATES AND CONFUSION: FIBER AND FORAGE Last month we had an overview of carbohydrates and their role in the horse’s diet. A quick review: carbohydrates consist of sugars, starches, and fiber. During digestion, carbs are broken down into simple sugars and indigestible matter. Sugars and starches are digested in the horse’s small intestine, and they break down fairly easily. Fiber is not broken down easily; instead, it is fermented in the horse’s hindgut (cecum and large intestine.) It is the breakdown and fermentation of carbs that provide energy for the horse for his daily activities, the extra demands that we place on him for performance, and for “feeding” his brain. Horses need carbs. The big questions are which ones and how much. This month we’ll discuss fiber. Not only is it the most important part of your horse’s diet, it should also be the largest part of his diet by volume. Fiber is found in plants. The sources that horses consume most frequently are forages such as grasses and hay, but fiber also comes from other sources such as beet pulp. The energy that is released from the fermentation of fiber fuels his everyday activities and maintenance such as breathing, moving, sleeping, and maintaining body temperature. The movement of fiber through his GI tract moves the other nutrients as well. You could think of it as a conveyor belt, as it carries the other nutrients through the digestive tract and then exits the body. Without fiber, your horse is at risk for dehydration, loss of electrolytes, colic, laminitis, and other health issues as the other nutrients “pack” in his GI tract. A steady supply of fiber helps to prevent and control ulcers also. The saliva that is produced when the horse chews the fiber can help buffer the stomach acids that are part of the cause of ulcers, and the presence of fiber in the stomach also helps to mitigate the “splash effect” of these very strong acids. I can’t say it enough: fiber is a critical part of his diet. As we’ve mentioned many times, fiber also keeps your horse warm. While starches and sugars are broken down rapidly in the small intestine, leading to a rapid availability of energy, that isn’t the case with fiber. The fermentation of fiber in the hind gut is a slow process. Instead of a rapid release of energy (the kind you are looking for in performance), it is a slow release of metabolic heat. If you want to help your horse stay warm in the winter, make sure he has plenty of hay, not corn. Not all fiber is equal though. Some fiber, such as resins, sap, and pectin, are soluble, meaning that they are digestible. Others, such as cellulose, hemicellulose, and lignin, are insoluble. These provide the structure and rigidity in plants. The horse has limited ability to digest cellulose and hemicellulose, and lignin in particular is indigestible. Soft spring grass contains little lignin, and trees contain a lot. You can easily picture the difference! As grass matures during the growing season, the amount of indigestible fiber increases. That is why hay that is cut late or past its prime is “stemmy.” The amount of lignin increased as the hay matured. This has consequences for your horse’s diet, as we’ll see in a moment. Horses are meant to be grazers. They have surprisingly small stomachs for their size, and they need a constant supply of small amounts of food. Given the opportunity, most would graze for 12 hours per day. Of course, there are variations within that. Some horses don’t seem to graze as much, and others never seem to lift their head when turned out to pasture. It’s hard to determine how much fiber is in their pasture, as it varies with the environment, the time of year, the stage of growth of the grass, the weather, the soil quality…things that we can’t control. There are ways to analyze the nutrients in grass but for the most part it is only a snapshot in time. Generally, we don’t do it. However, hay is easy to analyze. Fill a gallon-sized re-sealable bag and take it to your feed store. Most places have access to a lab that can generate a report detailing the nutrients in your hay. The report will tell you how much protein, how many calories, and the mineral content of your hay. It will also give you some insight into the quality of the fiber. The measurements related to fiber are neutral detergent fiber (NDF), acid detergent fiber (ADF), and relative feed value (RFV). Each is a measurement of a different aspect of the fiber. While each number gives you some useful information, they have their drawbacks too. Currently they are the best tools that we have though. NDF measures how much hemicellulose, cellulose, and lignin are in the hay. Remember, these are the structural carbohydrates that give plants their rigidity. The number, expressed as a percentage, tells you how much of the hay is not digestible. The higher the number, the less likely it is that the horse will eat this hay. Ideally the range should be 40-45% for hay that is fed to performance horses, with a slightly higher range considered suitable for horses at maintenance level. Hay that measures above 65% will have little nutritional value for your horse, and he probably won’t be interested in it anyway, as it is very stemmy and will poke the inside of his mouth as he chews. ADF measures the residue after the NDF test and considers the amounts of cellulose and lignin in the hay, two highly indigestible components. It differs from NDF in that the hemicellulose has been removed as part of the NDF test. This has the effect of removing most of the starches too. As with NDF, it is expressed as a percentage and tells you how much of the hay is not readily digestible. A lower number is desirable. A measurement of