CARBOHYDRATES AND CONFUSION

Of all the nutrients, I think carbohydrates are the most confusing. The nutrients that we have discussed so far (water, protein, and fat) are fairly straight forward. After all, no one can deny that horses need access to water. And once you understand the roles of proteins and fats in maintaining the body, you are on your way to developing a suitable diet for your horse based on his body condition, age, and work level. But carbs…the terms alone can get you bogged down. Simple versus complex, non-structural versus structural, ADF and NDF…what does that even mean? Not to mention high-carb versus low-carb diets…so much to learn.

Don’t worry, this isn’t a research paper. It’s a brief overview of what carbs are, what they do, and where they are found in your horse’s diet. I’m not going to tell you how to feed your horse, as each horse is an individual and should be fed as such. That is a conversation to have with your vet and with a knowledge feed store employee or a feed rep. You won’t be an expert when you are done reading this article, but hopefully you will have a better understanding of carbohydrates as a nutrient. Those of you with an extensive background in equine nutrition will notice that there is a lot of information that doesn’t appear here, but again, my goal is to provide a good basic understanding.

We’ll break this down over the next couple of months. This month’s article will introduce you to what carbs are and what they do and will cover some of the terms that are used in evaluating and measuring carbs. Next month we’ll take a closer look at fiber, and after that we’ll talk about sugars and starches.

Let’s start with a surprising fact: you won’t find a number on your feed bag for the total amount of carbohydrates. You have to do some work to determine that number, and you’ll see why as you read this article.

Carbohydrates consist of three groups: sugars, starches, and fiber. Are you surprised to see that fiber is a carb? The most natural diet for a horse is fiber-based, so right away we can see that a no-carb diet isn’t going to work for horses. They need fiber, and we’ll talk more about that next month.

Carbohydrates are energy. You can think of them as fuel. They provide energy for your horse’s daily existence, they give him the extra energy for the increased work that we ask of him, and when fed in abundance they can put weight on a horse. Remember though that they are not the only source of energy: fat has a hand in that game too. Carbs also power your horse’s brain. According to the book “Horse Brain, Human Brain” by Janet L. Jones, PhD, the horse’s brain is 0.67 percent of his body weight but uses 25% of his body’s glucose supply. That’s right- teeny tiny brain, huge need for glucose, which is a form of sugar. (This is a wonderful book. Everyone who handles horses should read it.) Horse need carbohydrates. The big questions are what kind and how much.

You may recall from previous articles that carbs and protein have similar amounts of calories, but it is metabolically more expensive for the horse to get energy from protein than from carbs. This means that another role that carbs play is to provide energy for the horse so that his body doesn’t have to break down muscle mass for energy. Carbs, like fats, are easily broken down compared to protein. Horses are adept at storing excess carbs and fats as weight, whereas excess protein is generally excreted in urine.

I’m going to use some traditional terms for carbs in this article: simple sugars, complex sugars, starches, and fiber. You will see different terms used in other articles: storage sugars may be used in place of complex sugars and starches, and structural carbohydrates may be used instead of fiber.

What makes up a carbohydrate? Picture a chain with multiple links of three different colors. The links are carbon, hydrogen, and oxygen, and they can be connected to form many different color patterns and units of many different lengths. That chain is a carbohydrate, and the order, number, and length of the units of colored links determine whether it is a sugar, a starch, or fiber. A simple view, I know, but we don’t really want to get into organic chemistry, do we? Here is where it starts to get complicated: complex sugars (many units hooked together) can be broken down into simple sugars. Starches can be broken down into complex sugars and then into simple sugars. Both are broken down fairly easily by enzymes and absorbed during digestion in the small intestine. These simple sugars then are used as fuel by the body. Fiber is also a string of complex sugars and starches, but it is not broken down easily by enzymes. Instead, it is fermented in the cecum and large colon to release its energy. It is the act of fermentation and the resulting release of energy that provide heat to your horse in the winter. (That’s right, feeding him more hay, not corn, will keep him warmer in the winter.)

Carbohydrates are also known as saccharides. Monosaccharide is a term used for simple sugars which contain one sugar unit. These simple sugars are the smallest units of sugar. When they are further broken down, they are no longer considered a sugar. It is the breaking of the bonds holding the sugar together that releases energy. Glucose and fructose are examples of monosaccharides. Disaccharides contain two sugar units. Two examples are lactose, found in dairy products, and sucrose, more commonly known as table sugar. Oligosaccharides contain anywhere from three to 200 units, and there are also polysaccharides, which contain 200-2,000 units. As the number of units that are hooked together increases, the number of possible combinations also increases. As you can imagine, there are many. Starches and fiber fall into the polysaccharide group. Three of the polysaccharides that are fiber are cellulose, hemicellulose, and lignan. They are the compounds that give structure to plants and, in scientific terms, are “indigestible by mammalian enzymes.” That means that the horse cannot digest them. That’s what ends up in your wheelbarrow! They play a critical role though in your horse’s gut health. They help to regulate or balance the influx of the highly digestible simple sugars, they help move food through the digestive tract, they help conserve water and electrolytes for the body’s use, and they help provide metabolic warmth to the horse through the act of fermentation. Horses need fiber, and they need more fiber than they do of the other carbs.

To make things even more confusing, carbohydrates can also be grouped into two categories: non-structural and structural. Non-structural carbs are sugars and starches. They are easily digested in the small intestine. (Very little digestion of carbs happens in the stomach.) Structural carbs are fiber. You can think of them as the scaffolding of plants. They are not digested in the small intestine, but instead are fermented in the cecum and large intestine, which are part of the hindgut.

Take a moment and re-read the previous paragraph. There are a couple important points here. First, sugars and starches are easily digested by enzymes and are absorbed in the small intestine. Second, fiber is not easily digested by enzymes, instead it is fermented in the hindgut. So, we have carbs that are broken down by the horse in different methods and in different parts of the gastrointestinal track. Now buckle up- things are about to get confusing. Although the horse can break down starches in his small intestine, he has limited ability to do that, so if he eats too much starch it can overflow into his hindgut. Then we have problems. The microbes in the hindgut are adept at fermenting fiber but not accustomed to digesting starches. This can cause the overproduction of acids and gas, which can lead to colic. The overload of undigested starch can also cause the death of these very important microbes, and as they die, they can give off toxins that cause laminitis. Which grains contain large amounts of starches? Corn, oats, and barley.

To make things even more confusing, not all sugars, starches, and fibers act the same. Pectin is a good example. It is considered a structural fiber as it is the cellulose “glue” that holds together other carbs in the cell wall, but is a soluble fiber. It has little nutritional value to the horse but is very important to the plant that feeds the horse.

Ready to come up for air for a moment? Here is an interesting fact: the horse can make quick use of the starches in his diet as long as he isn’t fed too much. Humans digest starches slowly. The oatmeal that you eat for breakfast may make you feel full for several hours, but it can cause your horse to act like you just fed him rocket fuel.

Carbohydrates are measured in different ways. The number that you are looking for depends on the information that you are trying to retrieve. If you are wondering how many calories your horse is eating, then you would look for the term digestible energy (DE) which is expressed as the number of kcals. This means kilocalories, or Calories (with a capital C) or 1000 calories. This is the number we look at when we are concerned about the horse’s weight. Sometimes you may see it as mcal, which means megacalories. This appears as a small number, because one mcal equals 1000 kcal. You have to move the decimal point three places to the right to get the more familiar kcal value. Sometimes you will see it expressed as mcal/kg, especially on the European feed bags. Then you will have to convert both the megacalories and the kilograms to arrive at the more familiar kcal/lb.

If you have a horse with metabolic issues or who needs a low-carb diet, then you would be concerned with the NSCs, or non-structural carbohydrates, which consist of sugar and starches. The fixed nutrition feeds and some of the fixed formula feeds will have this information on the bag, but the least cost ingredient feeds won’t have this information. The amounts will be shown as percentages, and you will have to add the two together to find the total NSC value. It’s important to remember that this number is an average, as each batch of feed produced will have slight variations, no matter how good the quality control is at the feed mill. The percentage of NSCs on the bag indicates the average over many batches. Remember too that this represents the percentage of carbs in the bag of feed. It is not a true picture of the total carbs in your horse’s diet, as you have to take pasture and hay and even treats into consideration.

All commercial feeds, even the least-cost ingredient feeds, should show the amount of fiber that the bag contains. This will also be a percentage. Remember again that this means it is a percentage of what is in the bag, NOT what is in your horse’s total diet. It is usually listed after protein and fat, but sometimes it may be listed between the two. Read the bag carefully and don’t assume that it will always be the same position on the guaranteed analysis.

If you paid attention to the previous two paragraphs, you can see that the feed bags don’t have one number that expresses the total percentage of carbs in the bag. Depending on the feed that you give your horse, you should be able to determine the amount of fiber and you may be able to determine the sugar and starches.

Another interesting fact: most feed companies do not declare the number of kcals (or digestible energy) on the feed bag and may not have it on their website either. If you ask a feed rep (someone who works for the feed company), they will tell you that it is because there are several ways to determine DE and that they cannot be compared equally from one company to another. If you keep asking though, they should be able to provide you with the DE value of a feed. As you compare values, just keep in mind that you are likely working with a range of values and not a finite number.

To this point, we’ve been talking about the carbs in your horse’s diet that you can somewhat easily determine by looking at the feed bag. If only the rest of it were that easy! Your horse also gets structural and non-structural carbs from his hay and his pasture. That is trickier to compute. If you have your hay analyzed, you will get a picture of the digestible energy and the sugars and starches, but you will still have to do some work to interpret the results. We’ll discuss that more in the future articles on fiber and sugars and starches. Again, remember that this number is indicative of the sample that you sent in, and not all your hay bales will be exactly alike. Hay can differ from one side of the field to another, and the hay that is cut one day can differ from the hay in the same field that is cut a few days later.

For our practical purposes, pasture is nearly impossible to measure for carbohydrates. It can be done but the results won’t really help you much, given the difficulty. The sugar content of grass changes daily and changes during the day too. Grass stores up energy in the form of carbs as it receives sun during the day, then uses that energy overnight. Sunny days produce a different response in the grass than cloudy days, and cool weather and hot weather trigger different responses. About the only thing you can be confident in is that as the grass matures, it contains more of the indigestible structural carbohydrates. That’s why horses prefer to dine on the tender green grass and not on the taller stalks of mature grass. Can you even measure how much grass your horse eats in a day? There are suggested formulas, but your horse may be a picky eater who wonders around looking for the choicest bits, or he may be like my Mustang and hardly come up for air.

Your horse gets carbs from his treats too; have you considered that? Luckily feed manufacturers are starting to realize this and are producing low NSC treats. It’s all relative though, depending on how many treats you feed him. One or two per day likely won’t do too much harm, especially if he is moving around and exercising, but if you feed more then you should consider the effect on his total diet. Fruits and vegetables don’t necessarily keep him out of trouble either- carrots and apples are high in natural sugars like fructose and should be fed cautiously to horses with sugar sensitivities. We’ve all heard stories of horses that ate too many fall-drop apples and developed colic. The mature apples contain high levels of sugars and pectin, that soluble fiber that breaks down into sugars and starches. The starches can overwhelm the hindgut and lead to colic or worse. If you have a horse with metabolic issues or sugar sensitivities, consult with your veterinarian regarding his diet and treats.

If nothing else, I hope that your take-away from this month’s article is that the horse needs carbs, but we have to be careful with which ones he eats and how much he eats. We’ll go into greater depth as we look at fiber and starches and sugars in the next couple of months. Another important point to remember is that although carbs seem confusing, many times it is because of the way they are categorized or grouped. When you know what kind of information you are trying to retrieve, you will have a better understanding of the groups. Then you will be on your way to making appropriate choices for your horse’s diet.