Having a "free" horse dumped on me with special nutritional needs I've had to do TONS of research on this. What I have found through this trying time is that this info. Also helped my collicky horse, my underweight horse, and my average Joe horse as well!
Quoted from Equus and safer grass.org
"A New Generation in Feeding
Almost as soon as researchers discovered the links between sugar, starch and metabolic disorders, feed companies began to respond with appropriate products to help horse owners better feed their horses.
Researchers have discovered feeds high in starches/sugars can also make horses more prone to tying up, muscle soreness, ulcers, colic, and contributes to poor hoof quality, hoof sensitivity, and laminitis. In addition, a young horse that is still growing and may experience developmental orthopedic disease, may also benefit from a diet low in non-structural carbs. Recent studies at Virginia Tech proved the propensity to rich grain based diets and a high-concentrate diet instead of relying on a more appropriate high fiber, forage first diet greatly increases the incidence of colic and gastrointestinal disease.
The goal now is to reduce unhealthy sugars, starches and other non-structural carbohydrates (NSC) in equine diets that can cause metabolic disturbances and imbalances in the digestive system while still providing more than adequate calories and nutrients. .
Some of these feeds may be marketed (for now) as special needs feeds (horses prone to laminitis, tying up, IR, Cushings or seniors, etc), but a rapidly growing number of vets and scientist believe no horse really needs a feed with a NSC level higher than 15-20% and these feeds are good feeds for any horse and will help prevent such issues from ever developing.
Before deciding which feed is best for your horse, however, it’s helpful to have knowledge of how the equine digestive tract processes sugars and starches. And too, with one of the leading causes of death in horses being laminitis, second only to colic, every horse owner should have an understanding of how laminitis can be triggered. You’ll also want to know which ingredients are generally found in feeds designed to reduce a horses risk, as well as some guidelines for incorporating these feeds into your overall preventative management plan. With this information, this nutritional balancing act will be much easier to pull off.
Just as with humans, managing carbohydrate intake in a horses diet is a good idea. There are two types of carbohydrates In your horses diet:
Nonstructural Carbohydrates (NSCs) are the sugars and starches inside a plant cell. The sugars include glucose, fructose and sucrose. Starches are long chains of glucose and fructose molecules. Fructans are chains of fructose molecules.
With the exception of fructan, NSCs are primarily digested in the foregut of the horse (the stomach and small intestine). Enzymatic digestion here quickly breaks down starch into glucose, the body’s main energy source. This, in turn, causes a rapid rise in the horses glycemic response—the increase in blood sugar– stimulating the release of increased amounts of insulin. Recent research breakthroughs have directly linked high blood insulin levels with laminitis. While it may not produce full blow laminitis in some horses, it still very well may cause the hooves to become sensitive or appear not as healthy (brittle, chip easily, prone to cracks, flat soles rather than concave).
To keep a digestive system healthy in any horse you want to feed in a manner that keeps his glycemic response as close to what you’d see with a hay diet or if he were getting a natural diet in the wild (which would consist of fairly dry variety of grasses (not rich green grass))----which that glycemic response level is nearly none at all.
The glycemic responses triggered by traditional feeds vary, but corn, oats, barley and molasses (the bases of most feeds) create the biggest swings.
Structural Carbohydrates make up the cell wall of plants. The primary structural carbohydrates are cellulose and hemicellulose, both referred to more traditionally as fiber. These are digested in the hindgut, the cecum, and large intestine. This is where the horse is designed to have the bulk of it’s digestion occur and where it is easiest for the horse to break things down efficiently. The digestive action of the structural carbs, which is done by microbes that ferment the fiber, is slower than that of the NSC’s and does not appreciably elevate glycemic response. Just as it’s healthier/easier for us to process/digest more efficiently the sugars of a piece of fruit compared to that of a piece of candy.
Most horses are designed to be able to digest a diet compromised of both types of carbs, in varying proportions. However if any horse consumes more NSCs than his foregut can fully metabolize, they spill over into the hindgut, where the sugars are fermented by lactic acid producing microbes (this can also contribute to seemingly inexplicable tying up or muscle soreness in horses).
The resulting increase in acidity of the hindgut leads to digestive disorders...anything from gas, to colic, ulcers, as well as laminitis. Remember if your horse has poor feet–thin walls, thin soles, prone to cracks, sensitive, etc., ALWAYS look at the diet first, it almost always is the culprit! Changing the diet up won’t hurt the horse, and very well may benefit him immensely so it’s worth the try. You’ll need to stick with a diet change for at least 3 months before you’d see a noticeable change in the new hoof growth.
So, feeds designed to provide energy and nutrients, without the excess NSCs, provide calories in forms that maximize healthy hindgut digestion and reduce glycemic response.
What exactly is in these "Low-NSC" feeds?
Low-NSC feeds are quickly replacing the standard traditional grain based feeds like corn, oats, barley and molasses. Some of the most common ingredients include:
Soybean Hulls– Thin "skins" surrounding soybeans, the hulls are removed during processing for oils. Soybean hulls cause a low-glycemic response and are extremely high in digestible fiber. They are a popular ingredient in low-NSC feeds. (Note that peanut hulls, oat hulls, or barely hulls, are not acceptable substitutions. Because of how they are grown peanut hulls can be tainted with dangerous mycotoxins. Oat and barley hulls are nutritionally empty.).
Rice Bran– The outer layer of grain, bran is removed during the millingto produce white rice. Rice Bran is high in fat in an easily digested nutritious form (which also makes it good additional supplement to safely put weight on horses). Healthy fat is a safe calorie source for horses. Rice Bran is the best way to provide this without the mess of oils. Rice bran is very different than Rice Hulls however, which only provide empty calories, or wheat bran which is low fat.
Beet Pulp– After the sugar is extracted from sugar beets, pulp is the vegetable matter that remains. Beet pulp is very high in digestible fiber, but it’s glycemic content will vary depending on how it is processed. If the sugar is extracted from the the pulp and no molasses is added to make it palatable, for instance, beet pulp is a low glycemic energy source. This is how it is processed for the low NSC feeds...but this may not be the case for all feeds (such as some senior feeds that are often beet pulp based, don’t let that lead you to believe it must be low NSC. In reality they add a lot of unnecessary molasses to those feeds. So if you are unsure, stick with a reputable company that has a nutritional analysis on the label.)
Oils– Almost 100 percent fat, oils are a safe source of energy. Soybean oil is popular in low NSC feeds, but other types such as Canola or Rice Bran oil are also used. The trouble is with oil you can only put so much in a feed without affecting the quality...particularly with a pelleted feed since it will just fall apart with too much oil, and feeds with too much oil will spoil faster. Avoid adding any oils that may compromise the sugar/starch levels such as corn oil.
Hay Meal– Any type of hay chopped into extremely small pieces is considered hay meal. These are a great source of fiber (keep this in mind too when feeding a horse that may have a hard time chewing long stem hays such as a senior horse or a horse with a tooth problem or prone to choking). The NSC of hay meal depends on the type of hay....be it timothy, bermuda, alfalfa, etc. and even the particular batch it came from and when/where it was grown. Again these reputable feed companies build their reputation on their feeds so they are very careful and know what they are buying, test regularly and you can trust their overall analysis.
Wheat Middlings– These byproducts (sometimes called "midds") of flour processing are very high in fiber. But they can be relatively high in starch depending on the source. Once again, a good feed company will be careful to test before adding to any feeds so they can guarantee their NSC percentage.
Note: Most NSC feeds are made to be fed with hay in order to create a well balanced diet. The bulk of a horses diet being roughage hay is extremely necessary though for digestive health and function, and it’s slow to digestion also reduces spikes in insulin levels.
Don’t let feeding a low NSC feed give you a false sense of security however. Still always be cautious of new grass....spring grass, fall grass, or when after a drought and you receive a lot of rain...it can be VERY high in NSC, as well as alfalfa. Stressed over grazed nubs of grass will typically have a higher NSC content than non-stressed tall grass and owners will be surprised when their horse shows some signs of laminitis when to them they seemingly "have no grass" in the pasture.
Even the lowest NSC feed will not protect a horse from digestive upset and metabolic disturbances and other possible consequences of grazing a rich pasture. When new grass appears keep a close eye on your horses. Sensitive horses should either be dry lotted during this time or fitted with a humane grazing muzzle.
While we should not aim to eliminate all sugars and starches from a horse’s diet, we should aim to decrease them and eliminate those that come from non-healthy sources such as molasses, grains, etc. and quite simply, most traditional feeds are just far too high NSC percentage, particularly since they are also being fed with hay, and perhaps even grass and/or alfalfa...all providing NSCs of their own. "
I've got tons more where this came from if you want to get a little more educated on the subject.... a friend of mine does seminars on Equine Health and barefoot trimming. Man, have I learned a alot from them!