When we think of carbohydrates, we think sugar and we also think energy, as the two are often interconnected. We all need energy and our equine companions are no different. Thus carbohydrates are an essential part of the horse diet, but in excess and dependent on the form ingested, problems can develop and impact overall health. In order to gain a better understanding of carbohydrates and feeding in the horse, we have to understand some basic principles. Utilized properly, carbohydrates can be a useful means of gaining and sustaining energy needs for every horse.
The horse is a forage based animal and the pasture is their main source of nutrition. They are grazing animals and hindgut fermenters, being exposed to a wide variety of different forages and even grains as they move about a field or pasture. In many cases, energy needs are felt to not be met by pasture or forage, or in some pasture turnout is not an option or quality is low. Due to this situation, we have often resorted to adding grains to our horse’s diet in order to provide an additional source of carbohydrates for energy. It is true that in some cases, as with working horses with higher needs, this is acceptable and needed, but in other cases, especially with those that are already overweight or sedentary, this supplementation practice could result in more problems.
The main concern is carbohydrate overload and this overload is being blamed for many health problems from ulcers to colic to metabolic disturbances. Whie this is true, in most cases, the situation if negative is man created, often due to supplying the added carbohydrates in too high of a level in comparison to needs or ability to digest properly. This is one reason for the recent explosion of “low starch” diets on the equine market, hoping to provide lower levels of starch while still providing a high volume grain product. In reality, carbohydates are the preferable source for energy production in the equine body, above the use of fats for energy. Despite the high prevalence and use of low starch feeds, the simple fact is that not all horses respond well to these products and different approach actually may suit them better.
Everything in moderation is the key, being relative to the situation at hand.
Carbohydrate Types in Horse Feeds
To begin the discussion, we need to get some carbohydrate types defined.
- Simple sugars (glucose, fructose, galactose)
- Disaccharides (sucrose, maltose, lactose)
- Oligosaccharides (fructans and α-galactosides)
- Mucilages/gums (soluble fiber)
- Pectin (soluble fiber)
- Hemicellulose (insoluble fiber)
Fructans are the main carbohydrate storage form produced in cool season grasses. Starches are the main carbohydrate storage form in grains, warm season grasses and legumes. Fructans generally bypass small intestinal digestion or hydrolysis and are fermented in the hindgut. Starches can be hydrolyzed in the small intestine or fermented in the hindgut, dependent on type and form consumed.
Most forages contain non-structural (sugars, starch) and structural (fructan, fiber, cellulose) carbohydrates. Plants produce simple sugars as a result of photosynthesis and store these sugars as starch or fructans for use as energy during stressful periods including winter, heat and periods of drought. Fructans levels generally are noted to begin to rise in the morning, peak in the afternoon and fall in the evening. More specifically, water soluble carbohydrates (WSC) tend to increase in spring, decline in summer, increase in fall and decline again in winter.
When looking at starch, it can be either digested or hydrolyzed in the small intestine or fermented in the hindgut. The biggest determiner of which route is the form in which it is presented. Whole grains, as an example, generally have more ‘resistant’ starch that is prone to fermentation, due to this starch being protected against digestive enzymes due to shell coating and/or cells walls. In some studies, further processing of whole grains improved starch digestibility due to breaking down of shell coat, such as grinding and milling practices, however, rolling or crimping did not demonstrate improved digestibility. (Hoekstra, 1999) In regards to glycemic index or ability to raise blood glucose levels, research data is conflicting whether whole grains or milled grains are better. (Vervoert, 2004)
The overall concern regarding starch is that if it is not digestible and consumed in excessive amounts, then it can lead to excess fermentation byproducts in the hindgut, which may contribute to various health concerns and acidosis. In my personal opinion, the operative key word here is ‘excessive’ amounts and just because a horse consumes non-digestible starch does not equate to the fact that bad things are going to happen.
What is NSC and what does it mean for my horse?
In today’s equine world, especially if you own a metabolic prone horse, the term NSC is commonplace. NSC stands for nonstructural carbohydrates and equates to the content of sugars and starch present in a feed. The analysis is performed using water, ethanol or enzyme hydrolysis to determine the carbohydrate level.
NSC may be further divided into:
- WSC (water soluble carbohydrate): simple sugars, dissacharides, oligosaccharides, fructans)
- ESC (ethanol soluble carbohydrate): simple sugars, glucose, fructose, sucrose, low molecular weight fructans)
ESC is actually viewed as being a subclass of WSC, and if we subtract ESC from WSC, we get an estimate of fructans in the food ingredient. ESC is viewed as the most practical means of determining simple sugar content in a feed source.
Glycemic response or index (GI) is a measure of how a food or ingredient impacts blood glucose levels, with a higher index indicating that it creates a quick rise in glucose readings. The glycemic index is not readily used in horse nutrition as it is in human nutrition. In humans with diabetes, for instance, the goal is to consume low glycemic index foods, to help control blood glucose levels. In one equine study, when using oats as a baseline, the glycemic index was determined for a few food groups.
Beet pulp‹ Alfalfa ‹ Timothy ‹ Carrots ‹ Oats ‹ Barley ‹ Corn
Glycemic index increases from left to right, so essentially beet pulp has a lower glycemic index than beet pulp, but oats have a higher index compared to alfalfa.
The problem with the research in this area and glycemic index, when it comes to horses, is that there are several variables at play which may enhance or even reduce the glycemic index. Those variables include meal size, rate of ingestion, amounts of digestible carbohydrates, oil content, fiber content, processing, digestibility and even absorption. The other variable that is mentioned is that often grains are mixed and even other supplements are added to the meals, all of which may create fluctuations in the glycemic index. Certainly an area that needs to be further explored, but overall, every horse is fed differently, so even with data, it would be hard to apply to every situation.
Fermentation of carbohydrates in the hindgut results in production of volatile fatty acids (VFA’s), which are necessary for health on certain levels, but can be detrimental if excessive. The main VFA’s include acetate, propionate, butyrate, lactate and valerate. Forage fermentation usualy results in higher levels of acetate, butyrate and propionate, while grains usually result in more lactate production.
In one study, it was noted that high grain consumption resulted in alterations to bacterial levels in the stomach, cecum and hindgut, enough to negatively impact fiber digestion and utilization. (Medina, 2002). Rapid fermentation of starch from grains has also been noted to increase Lactobacillus bacterial populations, which can have negative consequences on health in general and increased production of lactic acid, which may actually contribute to increased fatigue and poor performance, not to mention tie-ins with metabolic and laminitis concerns.
Do I feed grains and carbohydrates to my horse and if so, how much?
Okay, so the bottom line is that grains are needed in many instances for increased energy production. No two ways around it in some cases. What we have to realize is that the small intestine has a limited ability to hydrolyze or digest carbohydrates, and if carbohydrates are consumed in amounts larger than this, the system gets overloaded, resulting in excess carbs going to the hindgut for fermentation. Couple this with high fructan and resistant starch intake and problems can occur.
What research has told us is that there is an ‘overload’ limit, at which we begin to see spill over into the hindgut for fermentation. This limit appears to be between 2.5-4 grams of starch per kg of bodyweight per feeding (g/kg/bw). Consuming starch in this range or above usually results in decreases in pH in the hindgut, contributing to acidosis, diarrhea, colitis, overgrowth of bad bacteria, inhibition of good bacteria, leaky gut syndrome (endotoxemia) and laminitis.
So, considering this, the general recommendation is to feed starch at <2 g/kg/bw per feeding. In more sensitive horses, that range is dropped to 0.3-1 g/kg/bw of starch per feeding. If we have to feed a grain or feel it is vital, by feeding in these recommendation levels we can reduce the chance of acidosis and help to keep bacterial populations more stable.
Now, looking again at research, in many laminitis models they are inducing clinical disease through bolus administration of fructans at a dose of 7-12 g/kg/bw and in one study, they demonstrated a dose of 5 g/kg/bw was sufficient to induce laminitis. Now this dose is far above the recommended amounts, however, in theory, given the right circumstances, a horse could consume 5 g/kg/bw of starches on the right pasture in a given day. The difference here is that in the research models, they are delivering the full dose at once, while in pasture, the dose is consumed over time. More than likely, this pasture consumed dose is enough to push those pre-existing insulin resistant patients over the edge, creating clinical problems, rather than being a direct cause itself.
Let’s look at some starch, ethanol and water soluble carbohydrate (WSC & ESC) levels:
|Grain Type||% Starch||% ESC|
|Corn gluten meal||15.5||3.05|
|Forage Type||% Starch||% WSC|
|Mixed Grass/Legume Pasture||2.59||11.1|
Now, if we further take into consideration that the average recommendation to prevent carbohydrate overload situations, is to feed <2 grams of starch /kg of BW per meal, we can calculate amounts that can safely be fed based on starch percentage present.
|Feed Type||% Starch||<2 g/kg BW||<1 g/kg BW||<0.3 g/kg BW|
|Standard high starch sweet or pellet feed||50-65%||<3.3-4.4 lbs||<1.6-2.2 lbs.||<0.88-1.3 lbs.|
|Controlled starch feeds||15-25%||<8.8-14 lbs||<4.4-7.2 lbs.||<2.6-4.4 lbs|
|Low starch feeds||10-12%||<18-22 lbs||<9.2-11 lbs||<5.5-6.6 lbs|
|Corn||70%||<3.0 lbs||<1.5 lbs||<0.8 lbs|
|Barley||56%||<3.9 lbs||<1.9 lbs||<1.1 lbs|
|Oats||45%||<4.8 lbs||<2.4 lbs||<1.5 lbs|
(charts extrapolated and modified from Geor, et al. 2013)
One of the big misconceptions, in my experience as a veterinarian, is that we cannot feed whole cereal grains, especially to metabolic or carbohydrate sensitive horses. There are two reasons given for this. First reason being is that these cereal grains are simply too high in starch or carbohydrates. Second reason, is that they are not balanced nutritionally, especially when compared to an already prepared ‘low starch’ feed.
To address the first reason, yes, the whole cereal grains including oats and barley are higher in starch, but when we look at the chart above, we can see that if we feed based on guidelines, we can actually stay within the recommended amount of starch intake, that being <2 g of starch/kg of bodyweight. If we chose to feed oats, as an example, then we can actually feed 4.8 lbs per meal and stay within that guideline. If we want to reduce that starch level further, we can still feed 1.5 lbs of oats per feeding. So, in the end, it is not the grain in my opinion, but more so the amount being fed.
To address the second reason, yes, it is true that whole cereal grains are not that nutritionally balanced, but in reality we are not using them as a major source of nutrition, but more so as a needed energy source or one to just act as a medium for supplement administration. The bulk of nutrition should come from high quality forage, in my opinion, but all too often this source is not utilized and many feed low quality hays trying to make up for nutrient loss in supplemented grains. Even if we feed a ‘low starch’ grain that is supposed to be balanced in regards to nutrition, those nutrients are often added or sprayed on to the end product, in artificial or synthetic form. In order to usually benefit from those added nutrients, one must feed much higher levels of that product, which is why we often see such high feed volumes, as noted above. The truth is that most owners that do utilized these types of feeds do not feed according to label, which is not bad, but by doing this, they are not getting the balanced nutrition that is intended.
I am firm believer in supplying nutrition in its natural form via food, as much as possible. When it comes to metabolic or overweight patients, we often feel we must feed lower quality hay, often void in nutrients and actually, sometimes higher in starch that a legume source, for instance. Alfalfa has a bad reputation when it comes to metabolic patients and laminitics likewise, as we are told the carbohydrate or protein levels are too high. The carbohydrate or starch level is actually lower than a typical grass hay, but protein is higher generally dependent on maintenance to the forage prior to bailing. Legumes, including alfalfa are high in nutrient load as well, which may actually benefit the patient on many levels. In my experience, many overweight patients have actually lost weight by feeding legumes and their condition stabilized. The one concern here is providing forage consistently to these patients and that feeding 2% or less of BW of this type of forage may lead to weight gain. This is true and in many instances, a lower quality forage is provided for them to nibble on outside of regular feed times. The other option here is to increase exercise in these patients, which will help burn calories and reduce likelihood of weight gain. Pasture turnout is also acceptable, in my opinion, not only on dry lots but pastures or paddocks in which grass height has been reduced by mowing, which then reduces consumption and encourages movement.
Carbohydrates are a concern and there is no doubt about this. I do feel they are a major player in equine health, especially hindgut health, bacterial levels, metabolic concerns and laminitis, but the point is that they are not the only players in the game. In many metabolic and laminitic patients, carbohydrate levels are reduced, patients are put on low starch feeds and other regimens, but despite this, many fail to improve. This tells us that there are other players in the game or factors that are not being addressed, which is something we have discussed in prior articles, including hindgut health. I do believe that most horses do well on grains, in moderation and of the right type, favoring whole grains. Here is an article about ‘clean feeding‘ in the horse. This is just opinion and based on observations.
I hope this article helps to clarify some points regarding carbohydrates and horses.
Tom Schell, D.V.M.
Nouvelle Research, Inc.
Geor, RJ et al. Equine Applied and Clinical Nutrition. Saunders. 2013, 156-66
Chatterton, NJ et al. Nonstructural Carbohydrates in Oat Forage. J Nutri, 2006, 136:2111-2113
Watts, K. Pasture Management to Minimize the Risk of Equine Laminitis. Vet Clin Eq. 2010; 26, 361-369