The American public often is obsessed with fad diets and weight loss. Through the years, there have been diets for all occasions. For a time, the Atkins diet took the country by storm, with the low-carb diet taking center stage, and producers developing products ranging from cooking oil to beer, touting the low level of carbohydrates in their respective brands.
Now, the low-carb fad has found its way into diets for horses, with many owners demanding feed products with low levels of carbohydrates.
Many horse owners believe this will keep their horses at a proper weight and, thus, enhance their good health.
One of the problems with putting all of one's proverbial eggs in the low-carb basket is that research has not yet defined the proper carbohydrate level for all horses.
"It is an individual thing," says Mary Beth Gordon, PhD, a nutritionist with Land O'Lakes Purina Feed Company LLC, a leading producer of horse feeds and also a leader in nutritional research. "A carbohydrate level that is appropriate for one horse with Cushing's syndrome, for example, may not be right for another horse with the same condition. The same is true for horses without this condition. We just don't have the scientific data right now."
Purina is working to change that, and Gordon is one of its researchers charged with coming up with the answers.
So, the question arises, just what are we talking about here? What are carbohydrates and what role do they play in the overall nutrition/energy equation?
To answer those questions, we'll draw on the expertise of the Purina researchers. In addition to Gordon, we will present information from the likes of Katie Young, PhD, consulting equine nutritionist with Purina, and Karen Davison, PhD, manager of equine technical services for Purina.
All are involved in the ongoing research concerning starches, sugars, and carbohydrates. The information that follows has been taken from interviews, their written reports, as well as presentations to veterinarians and equine groups.
What's the Difference?
First, we should deal with terminology when discussing carbohydrates. Sugars and starches are carbohydrates, but so is fiber. Fiber carbohydrates are known as structural carbohydrates and, for the most part, are provided by the grass and hay that the horse consumes.
Sugars and starches are classified as non-structural carbohydrates (NSC) and, for the most part, are provided by grain in the horse's diet, although some also are found in grasses. Most of the NSC are broken down in the small intestine to become glucose, which is a simple sugar that provides energy. After being absorbed into the bloodstream, glucose is transported to various tissues of the body, where it is used as fuel immediately or stored as glycogen or as fat. The glycogen is stored in the muscles or liver, where it can be called upon as fuel when needed.
Once we realize that carbohydrates come from hay and grass as well as grain, the issue of cutting down on carbs becomes compounded. Nature designed horses to be herbivores that eat small amounts of food very often. Their digestive system features a small stomach and a large, involved apparatus beyond that point to break down the fiber ingested and convert it into energy or to simply pass it on through the body in the form of waste.
As Davison mentions, horses that ranged free across the North American prairies had few digestive problems as they wandered about, seeking the most lush grazing spots. These horses were not large, often standing only 12 hands high and weighing no more than 750 pounds at maturity. One of the reasons for that small size was that nutritional limitations with a grass-only diet served to inhibit greater growth.
When man intervened and began making use of the horse for war and agricultural pursuits, all that changed. No longer could grass supply enough energy for a horse that might be on the march all day and where time was critical.
Nature designed the horse's digestive system to digest small amounts of food over an extended periods. If the horse was being ridden for hours at a time or hitched to a plow for sustained periods, there was no time for extended casual grazing.
This led to feeding hay and grain to provide the needed energy, and to achieve greater size and bulk. When that became the common approach, some problems developed within the horse's delicate digestive system as more carbohydrates were added to the diet in the form of grain and hay.
Young discusses the importance of NSC and also the problems that they can cause. We reiterate that most NSC are broken down into glucose, a simple sugar.
Here, in part, is what Young has to say: "Glucose is very important for the horse to function properly, as it is the only fuel that can be used by the brain; it is used to a large extent by the hooves, and it is the only substance that can be used for making glycogen. Studies have shown that horses that use up all their glycogen and are not provided glucose to replenish the glycogen stores show greatly reduced performance capabilities. So, glucose is vital to the health and well-being of the horse. Again, glucose comes primarily from NSC."
So, are NSC "evil"? Young continues: "We know that too much NSC (particularly starch) in a horse's meal can cause problems. We want the NSC to be digested in the small intestine, but if we feed a large meal that contains so much starch that it overflows from the small intestine into the large intestine, it may cause digestive disturbances such as colic or laminitis. Studies have shown that feeding no more than 0.5% of a horse's body weight of grain in one meal will reduce the risk of grain overload into the horse's hindgut, therefore reducing the risk of colic or laminitis."
That being said, both Young and Gordon make the point that there are certain horses with particular conditions where feeding a lower level of NSC might be important in helping them maintain a stable condition. A case in point would be horses that have been diagnosed with laminitis. With those horses, feeding a diet with a low level of NSC might be beneficial in preventing a recurrence of the disease.
Another example would be the horse suffering from Cushing's. Horses with this affliction have trouble regulating the glucose within their bodies. A key element in the regulation of glucose is insulin, which facilitates removing the glucose from the blood and distributing it to the tissues where it is stored as glycogen.
In Cushing's horses, insulin is unable to properly regulate the glucose and the result often is high levels of glucose in the blood. The horse then becomes what is known as insulin-resistant. Horses with this affliction can benefit from a diet with low levels of NSC and, therefore, less glucose.
Another condition that might benefit from a lower level of NSC in the diet is exertional rhabdomyolysis or tying-up.
One form of this disease carries the label of polysaccharide storage myopathy, which surfaces more often in Quarter Horses, Paints, Appaloosas, draft horses, draft crossbreds, Warmbloods, and even a few Thoroughbreds. When polysaccharide storage myopathy is involved, non- bioavailable polysaccharides accumulate in the muscles. To phrase it more simply, glycogen accumulates in the muscle because the muscle cannot use it properly.
Thus, the muscle has an abundance of fuel, but it can't burn it. Without the energy that the glycogen is designed to supply, these horses cramp and become stiff.
Well before discussions of low-carb diets for horses originated, researcher Stephanie Valberg, PhD, of the University of Minnesota, one of the leading researchers on exertional rhabdomyolysis, recommended that horses with polysaccharide storage myopathy be supplied with an alternative form of energy, or, in other words, a diet with a low level of NSC.
A good source, she reported, would be fat, because fats are calorically dense and enter the muscle's metabolic pathways at different sites than does glycogen. She recommended high-fat supplements--such as processed rice bran products--to replace grain and sweet feed, thus providing a low level of NSC.
When More Is Better
While horses with certain maladies are helped by diets low in NSC, others that are involved in competition or vigorous exercise burn up supplies of glucose, or glucose stored as glycogen, on a regular basis and need for supplies to be replenished.
There are a variety of activities that can deplete these stores. Bursts of activity, such as in the cutting pen, can quickly deplete glycogen stores, but so can sustained exercise, such as an endurance race. It is estimated that muscle glycogen stores can be almost completely depleted during a 50- to 70-mile endurance contest.
The problem, Gordon says, is no one knows the correct level of NSC. Much more research is needed to ferret out answers. There is no data, she says, that would indicate that 10% NSC in the diet is any better or any worse for the horse than, say, 20%.
Checking a horse's body condition can provide some answers as to appropriate feeding and exercising programs, she says. The body condition score rates the horse on a scale of 1 to 9. (To download the Body Condition Score chart sponsored by Platinum Performance, see www.TheHorse.com/pdf/nutrition/bcs.pdf.)
In abbreviated form, this is how the body condition scoring system goes:
A horse with a body condition score of 1 is an animal in poor condition-- extremely emaciated. A horse with a score of 2 is a horse that is very thin, but with slight fat over the spinal processes. A 3 is rated as thin, but with fat buildup about halfway on the spinous processes. A 4 horse is moderately thin, with a slight ridge along the back and a faint outline of ribs discernible. A 5 is listed as being moderate with the back flat--no crease or ridge--and ribs are not visible. A 6 horse is moderately fleshy with a slight crease down the back and spongy fat over the ribs. A 7 is listed as being fleshy with horse perhaps having a slight crease down the back; individual ribs can be felt, but there is noticeable filling between ribs with fat as well as fat around the tailhead.
An 8 is listed as fat with a crease down the back, difficult-to-feel-ribs and soft fat around the tailhead. A 9 is extremely fat with an obvious crease down the back, patchy fat appearing over the ribs, and bulging fat around the tailhead, along the withers, behind the shoulders, and along the neck.
The ideal scores, says Gordon, are 5 and 6--moderate to moderately fleshy. When body scores are 7, 8, and 9, she says, it might mean that the owner should provide more exercise along with a reduced quantity of feed, rather than rush into a low-carb diet.
It should be noted, the nutritionists say, that not all carbs are created equal. Relative to hay and pasture, cereal grains are lower in sugar and fiber, but higher in starch. Other sugar sources, such as refined sugar or molasses, are high in sugar, but they are often fed in such small amounts that they contribute very little to the total sugar content of the diet.
The NSC content of hay and pasture also can vary. The Purina nutritionists say that grass hay averages around 13% NSC under average growing conditions. However, they add, some hays grown in extreme temperatures can be higher.
If you are concerned about the NSC content of hay, you should contact a county extension agent relative to testing.
The nutritionists say that grass pasture might, at certain times and under certain growing conditions, have high amounts of NSC that could be detrimental to the health of a horse that is NSC-sensitive.
Fad diets haven't worked with humans, and they won't work with horses. Just reducing carbohydrates in the diet is not a cure-all. If obesity problems exist, the owner would do well to first examine the exercise regimen for that particular horse and determine if it is adequate, and second, discuss the animal's diet with a veterinarian or equine nutritionist.
At the moment, there are more questions than answers in the debate concerning carbohydrates, but fortunately, the research is ongoing.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.
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