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 30-35% ADF is considered readily digestible, while measurements slightly above that is suitable for horses at a maintenance level- but please, consider a ration balancer, as it is probably low in protein and other nutrients too. Hay that measures above 45% doesn’t provide much energy for horses.

RFV is a way to categorize your hay. It isn’t a number that you use in calculating your horse’s diet, but it can help you determine if your hay is suitable for your horse’s nutritional requirements. Typically, it will tell you if the hay is suitable for a horse in heavy work (nutritious and easily digestible), moderate work, light work, or maintenance/special dietary needs (low sugars and starches). There aren’t any ideal measurements for RFV because not every horse has the same requirements. If you know your hay’s RFV, then you are able make better decisions about your horse’s overall diet.

Here is a quick test that you can do on your own, no lab equipment required: take a handful of your hay and crush it into a ball. If it folds and compresses easily, then it is soft and pliable, and your horse will find it easy to chew. If you can’t easily make a ball with it, or it scratches your hands and feels like rigid stems, then it is overly mature, and your horse won’t find it as enjoyable. After all, would you want something like that in your mouth? Of course, there is no way that you can determine the protein, calories, carbs, and other nutrients by handling your hay. So, while you have that ball of hay in your hand, pop it into a plastic bag and take it to your feed store for analysis!

An analysis is great if all your hay comes from one source. If you buy several bales at a time from different places or from a feed store that gets hay from different sources, that won’t be much help. It will tell you what you’ve already fed. In this case, you could ask your feed store what they are seeing for nutritional trends in hay. If you have a horse that is sensitive to changes in his feed and prone to digestive upsets, you might consider a digestive supplement to help keep his GI tract happy. This works by helping to regulate the pH balance in his GI tract. If you have a horse that needs to limit the sugars in his diet, having an idea of the hay values in your area can help you make informed decisions when choosing commercial feeds.

Ok, let’s come up for air. Consider this very important point: we all know that you should go slowly when making changes to your horse’s commercial feeds. The same applies to changing fiber sources. If you are changing barns, ask to take some of the hay that your horse has been eating so that you can transition him to the new hay. As you start feeding this year’s hay, mix it with some of last year’s hay. Fiber is the largest part of his diet, and a sudden change means a big adjustment for the microbes in his hindgut. You want to make the transition as safe and comfortable as possible. Makes sense, right?

Hay and pasture are not the only fiber sources available for horses. Beet pulp and bran are sources, as are rice bran, oats, barley, alfalfa meal, and other grains and plant-based products. They are not all equal though, as some contain more soluble fiber than others and the quality of the fiber can differ. Consider too that the benefit of the fiber may well be outweighed by the high levels of starches and sugars. In the case of oats, the high starch content may be tolerable if you have a racehorse, but not a great choice for your beginner lesson horse. Bran, in particular, is not a great source of fiber because its calcium/phosphorus ratio is inverted, or opposite of what it should be. A little bit once in a while won’t hurt your horse but it should not be a regular part of his diet unless you have balanced the calcium and phosphorus amounts. Beet pulp, on the other hand, is an excellent source of digestible fiber, and is the fiber of choice in most senior feeds and complete feeds. It is what is left of sugar beets after the sugar has been extracted, so it has very little residual sugars.

The sources listed in the paragraph above are the fiber ingredients that you are most likely to see in concentrated feeds. The feeds may have more than one kind of fiber. You can tell which is the most abundant by its location in the ingredient list. The closer it is to the beginning, the higher the concentration. It’s interesting to note that in the middle-of-the-road feeds, those with higher fiber tend to have less digestible energy (think calories.) There are many premium feeds though that are both high-fiber and high-calorie. The calories generally come from the addition of fats. Many feeds will also state the NDF and ADF in their guaranteed analysis.

You might also notice that your feed bag lists “crude fiber.” This is the best estimate that the feed company can give for the percentage of fiber in that bag of feed. Remember that this is the percentage of fiber just for the feed, and not for your horse’s overall diet. If you want to calculate the total amount of fiber that he eats, you will have to consider the hay and grass that he consumes as well.

We discussed earlier why your horse needs fiber, and what can happen to his digestive system if he doesn’t get enough. But what happens if he gets too much? Yes, he can get fat, but it isn’t because of the indigestible parts of the fiber. It’s because of all the digestible calories that are also in the fiber. The stuff that is indigestible passes through him and comes out the other end and fills your wheelbarrow. My husband has a theory that the amount of poop a horse produces is greater than the amount of food that he eats…he may have a point. And yes, horses can get a hay belly. As that fiber is moving through his system, it can take up a lot of room, especially if it is indigestible and isn’t thoroughly broken down. This is where the ADF, NDF, and RFV numbers can help you. The more digestible the hay is, the more nutrients the horse can extract from it. But remember that he still needs indigestible fiber to keep that conveyor belt moving.

How much fiber does a horse need? Horses are individuals and should be fed as such, but the general rule of thumb is that a horse should eat 2% of his ideal body weight a day, and this should be mostly forage. Obviously, there are exceptions. Some horses need to gain weight, some need to lose weight. Some horses need to eat 3% of their body weight, others may need as little as 1.5%. Knowing the calorie count of your hay can help you determine how much he should eat. Horses that need to lose weight are ideal candidates for that less digestible and less nutritious hay, as long as you make sure they are still getting enough protein, vitamins, and minerals. As always, talk with your vet for recommendations and a knowledgeable feed store for options.

As we wrap up, let’s review the most important points again. Your horse needs fiber, which is provided mainly by forages such as grass and hay. Forages should be the largest part of his diet, whether he is a performance horse or a back-yard retiree. The quality of the forage matters because some is more digestible than others. Not all forages are equal, and not all horses have the same nutritional requirements. Have your hay analyzed so that you know what you are feeding.

There is much more that we could discuss regarding fiber and forage, but I hope this gives you an idea of how important it is in your horse’s diet and causes you to think about how you provide fiber to your horse.