More and more horse owners are looking for feeds and forages with low starch and sugar content for easy keepers, insulin resistant horses, and horses afflicted with Cushing’s disease, PSSM, RER and the risk of developmental OCD from hyperglycemia and hyperinsulinemia.
Not long ago, a feed company claimed that the glycemic index was a better measurement of starch and sugar in horse feed than the standard laboratory measurement known as NSC — non-structural carbohydrates. NSC is the sum total of starch plus WSC (water-soluble carbohydrates) and includes the subset category ESC (ethanol-soluble carbohydrates which include simple sugars and fructans).
The problem is, as of now there is no standardized version of the glycemic index for horses. And using the human model disregards the specialized forage-eater digestive systems of equines.
Of additional concern for Cushing’s horses and IR horses is that the starch percentage of feed and forage is critical to reducing the onslaught of inflammation that leads to elevated hoof pain and laminitis. These horses need to have a combined starch and ESC content no higher than 10%. According to analytical services provider Dairy One, the average starch content of oats over the years 2000–2016 was 43.8% — way too high for metabolic horses. In that same time period the starch content of alfalfa pellets was 2.19%. As you can see, the starch content of alfalfa is considerably lower than oats.
History of the glycemic index
The glycemic index was identified and developed by Dr. David Jenkins and colleagues at the University of Toronto in 1981 as part of research on which foods were best for people with diabetes. The glycemic index is a relative ranking of carbohydrates in foods according to how they affect blood glucose levels.
The current validated methods use white bread as a reference food, giving it a glycemic index of 100. For humans, foods with an index of 55 or less are classified as low-GI, and include beans, flax seeds, pumpkin seeds, most vegetables some whole intact grains, and many fruits. Medium-GI are in the range from 56–69 and include sucrose, basmati rice, unpeeled potatoes, grape juice, ice cream, bananas, and sweet potatoes. High-GI are foods are above 70 and include glucose (dextrose, grape sugar), high-fructose corn syrup, white bread, white rice, corn flakes, maltodextrin, extruded breakfast cereals, etc.
But there are variances; published glycemic index values from different studies reflect different testing methods, different experimental time periods and different portions of food. Also, the methods of testing postprandial glycemia in humans have varied. Some testing procedures used capillary blood sampling and others used venous blood draws.
There are wide variations in the same food tested. Rice and carrots have a large range of GI values, which may be due to growing conditions, soil fertility, the use of chemical fertilizers and methods of harvesting. Not all carrots are alike.
The glycemic index applied to horse feed
Only a few studies have been done on the application of the glycemic index to ingredients in horse feeds. Different studies assign different glycemic values to common feed ingredients, with the baseline being oats at 100 (similar to the baseline in the human glycemic index of white bread at 100). In the studies, the testing and evaluation of glucose and insulin response varied based on time of blood sampling withdrawal as well as cortisol influence and the small sampling of horses tested.
Sweet feed: 128.52
Jockey oats: 104.83
Wheat bran: 62.93
Beet Pulp: 24.35
Rice bran: 13.48
Soybean hulls: 7.23
Sweet Feed: 129
Whole oats: 100
Beetpulp with molasses: 94
Cracked corn: 90
Beet pulp (unrinsed): 72
Orchard grass hay: 49
Rice bran: 47
Ryegrass hay: 47
Alfalfa hay: 46
Beet pulp (rinsed): 34
Bluestem hay: 23
The fiber conundrum
In human nutrition it is believed that fiber (soluble and insoluble) as part of food has a beneficial effect on sugar metabolism — which is why many fruits and some whole grains fall under the low-glycemic index category. This is one of the arguments an equine feed company makes for abandoning the NSC percentage as a measuring standard.
Does dietary fiber alter glycemic load in horses? The answer is, we don’t know.
A study published in 2006 (Acta Vet Scand. 2016; 58 (Suppl. 1): 69) titled, “Glycaemic and insulinemic response to dietary carbohydrates in horses” looked at the effect of dietary fiber on plasma glucose and insulin concentration. The hypothesis was that different dietary fiber compositions would alter post-prandial glycemic and insulinemic index of test meals.
Their conclusion: “Meals with different fiber composition did not affect the glycaemic- and insulinemic index in horses when fed at the levels used in the present experiment.”
Meanwhile, researchers from Germany’s Institute for Animal Nutrition, University of Veterinary Medicine Hannover in Germany concluded that, “The modifying effect of dietary fiber on glycemic index seemed to be overestimated in horses… Complex diets and glycemic index needs further clarification.” [Vervuert, I & Coenen, Manfred. (2018). “Factors Affecting Glycaemic Index of Feds for Horses”.]
The following section is taken from the presentation at the European Equine Nutrition & Health Congress, March 17-18, 2006 at Ghent University, Merelbeke, Belgium titled, “Factors Affecting Glycaemic Index of Feeds for Horses” (Institute for Animal Nutrition, University of Veterinary Medicine Hannover, Hannover Germany):
“There is interest in the glycaemic response in horses for conditions such as exercise performance, obesity, insulin resistance, laminitis and osteochondrosis. There is information available on the influence of different grain sources on glucose and insulin responses in the horse, but little is known about the influence of different grain processing techniques and the effect of mixed meals (compound feeds or grain-roughage mixtures) on glucose and insulin control. Furthermore, no standardized glycaemic or insulinaemic index has yet been formulated for horses such as that for humans.
Our research group found no differences between whole oats, barley or corn in the response of healthy standardbred horses with a moderate starch intake (between 1.2 and 1.5g starch/kg) whereas increasing amounts of oat starch (1.2-1.5,2 or 4 g starch/kg) resulted in higher glycaemic responses.”
Continuing from the same study:
“Rodiek and Stull (2005) created a glycaemic index for common horse feeds assuming that the starch intake comprises 25% of equines’ daily digestible energy requirement. In general, concentrate feeds (rich in starch) were found to have the highest GI while those of forages and by-products were relatively lower. The GI of oats was used as the reference (GI: oats=100%, corn = 117%, barley = 101%, oats plus oil = 86%, wheat= 71%, carrots = 51%, timothy hay = 32% and beet pulp = 1%.”
“A simple index is needed that could help in the development of nutritional recommendations for horses for specific issues, such as insulin resistance, laminitis, or exercise performance. However, it appears that the glycemic index cannot serve as the only such criterion, as it is considerably influenced by several factors: consumption rate, nutrient composition and gastric emptying, especially in the case of mixed feeds. Furthermore a standardized methodology should be developed for the estimation of gylcemic index in feedstuffs for horses to make it possible to compare the results of different research groups.”
Starch and digestibility
For metabolic horses and easy keepers the starch and sugar content (including fructan) of feed and hay is elemental in the management of these equines. Some horses are so sensitive to starch that more than 5% starch content can increase foot soreness. Typical grains fed to horses — corn, oats, barley — are digested in the small intestine, but horses don’t produce as much of the digestive enzyme amylase as, for example, pigs do, so the starches travel to the hindgut. This can cause a buildup of lactic acid, changing the pH of the hindgut and leading to a release of endotoxins that are risk factors for laminitis.
A published study conducted jointly by Ohio State University, Department of Veterinary Clinical Sciences and Otterbein College, department of Equine Science noted that there is conflicting evidence for the difference in small intestinal starch digestibility between grains commonly fed to horses. (J. Anim. Sci. 2004, 82:2623-2629)
Several studies have shown that corn has a lower small intestinal starch digestibility (29–45% depending on prior processing) than oat starch (80–90%) or barley starch (81%) (Meyer et al., 1993; 1995 De Fombelle et al., 2001). However, other studies indicated that starch digestibility was not different between corn (80%), oats (81%) and barley (95%) (Radicke, et al., 1992).
Using the glycemic index average from the few studies on horses, we can take a rough average and see that oats (100), corn (105), and barley (95) are all too high on the index to be fed to metabolic horses and easy keepers.
Using NSC numbers from Dairy One, we can see that the average of the starch content of oats is 43.8%, for barley 54.3%, and for corn 69.3% — again, all way too high for easy keepers and metabolic horses.
But if we use the human glycemic index on these particular grains we get a slightly different picture. Remember, low-glycemic is 55 or below, medium is 56-69, and high is 70-plus. Here is how the grains are rated on the human glycemic index: oats, 58; barley (rolled), 66; corn, 53. (International Table of Glycemic Index and Glycemic Load Values. 2002, American Journal of Clinical Nutrition. Vol. 76, No.1, 5-56)
In a 2013 study published by S. R Bailey and N.J. Bamford, the authors noted that, “It is important to note the breed type when considering the likely metabolic effects of dietary carbohydrate, because there are major differences between the thoroughbred type and some other breeds of horses and ponies. Relative glycaemic index or glycaemic load may be useful in predicting peak plasma insulin but carbohydrates such as starch and fructans may have particularly marked effects on insulin sensitivity.” (S. R Bailey and N.J. Bamford. “Metabolic responses of horses and ponies to high and low glycaemic feeds: implications for laminitis”, Animal Production Science, 2013.)
This is just another scientific example of why the NSC number is so important. To manage these equines, we must know the sugar and starch content of feeds and forage.
The importance of measuring non-structural carbohydrates
Non-structural carbohydrates are the major source of energy for grazing animals. The NSC analysis is necessary to screen for elevated NSC percentage in the feeds and forage that are consumed by horses. To manage easy keepers and the various metabolic diseases in horses, knowing the NSC is essential.
Is there a place in the management of horses for the glycemic index? Yes. But we need much more research to establish a standardized index. We cannot blindly apply the human glycemic index to feed and hay.
A specific, standardized glycemic index for horses could be applied as a useful tool in the toolbox in addition to NSC percentage, but until science and research provide more glycemic index answers for horses, testing hay and feed for NSC number is a reliable and established scientific protocol.
BioStar offers three supplements that not only stay below the recommended combined starch and ESC content of 10%, but are created entirely from real whole foods, offering support for metablic horses and easy keepers:
Tri Dosha EQ: An East-Meets-West approach, with Ayurvedic herbs such as Organic Indian Gooseberry, Organic Holy Basil, and Organic Chasteberry, combined with Western minerals and foods like amino acid chelated magnesium, whole almond powder, organic hemp seeds, and spirulina.
Total NSC: 12.6% (ESC + Starch = 9.4%) (Starch: 1.0%, WSC: 11.6% [ESC: 8.4%])
Optimum HW: A formula providing a wide range of important vitamins and minerals from plants including chelated minerals, amino acids, B-complex, vitamin E, selenium yeast, and Astaxanthin. Unique to Optimum Healthy Weight is Crominex® 3+, a patented blend of Indian Gooseberry extract, Shilajit, and trivalent chromium. Crominex® 3+ supports the production of ATP for energy and stamina.
Total NSC: 9.8% (Starch: 3.9%, WSC: 5.9%)
Impulsion EQ: Offers the easy keeper and metabolic horse a blend of whole ingredients to support energy, stamina, metabolism, recovery, muscle maintenance and bone health, including protein, fiber, and fat, plus the essential fatty acids including Omega-3. Shilajit supports healthy mitochondrial function, which is important for energy, stamina, metabolism, and recovery.
Total NSC = 5.1% (Starch: 0.4%, WSC: 4.7)