Both human and equine populations in the United States are trending toward a serious epidemic – obesity. With domestication of the horse and improvements in technology, we as horse owners and care-takers, have inadvertently subjected the equine population to “over-nutrition”. Many pastures that horses graze are well cared-for and the grasses are unlimited. Many other horses are fed the most premium-quality hay source available. Nearly all of these horses are also fed once or twice daily rations of a high calorie grain. The unfortunate reality is that many of the horses on these high-nutrition diets are not ridden or exercised hard enough to compensate for the over-consumption of calories.
Obesity is a serious concern in humans because of its link to type 2 diabetes. As a basic concept, type 2 diabetes in humans and insulin resistance in horses are very similar diseases. Horses with insulin resistance are typically identified as having higher resting glucose and insulin concentrations in the blood and show physical signs of obesity. Obesity in horses contributes to a plethora of potential problems such as organ failure, increased oxygen requirements, problematic pregnancies, developmental orthopedic diseases, insulin resistance and laminitis.
Obesity and insulin resistance are two conditions that fall under the “Equine Metabolic Syndrome” umbrella, and they have become major health concerns in the equine industry primarily due to their link with the development of laminitis. Laminitis is a painful and potentially career ending condition where laminar tissues which connect the bone to the hoof wall become inflamed and the attachment weakens. This is very painful to the horse and can cause chronic lameness.
Insulin resistance begins when a horse routinely consumes excess amounts of sugar and starch. Excess sugar and starch can come from both forage and grain. Green grass is often overlooked, but it can be one of the highest sugar sources in a horse’s diet. As cells within the body are presented with excess amounts of glucose (the simplest form of starch and sugar), the body triggers the production of more insulin to clear that glucose. Over time, as the body is subjected to more and more glucose, the cells become less sensitive to the exact needs of insulin, so insulin continues to be excreted in excess until finally the insulin-producing mechanism fails.
For the last 30 years we have used a standard method of assessing body fat mass in horses. The Henneke system assigns a numerical body condition score (BCS) on a scale of 1-9 based on subcutaneous fat deposits. According to the Henneke system, a horse with BCS 7 (fleshy) would be considered overweight, and horses with BCS 8 (fat) and 9 (extremely fat) might be considered obese. Horses prone to insulin resistance tend to accumulate fat in two distinct areas; the neck (commonly termed “cresty neck”) and the tail-head.
It was estimated in 2008 that 51% of horses in the United States are overweight, and that number has continued to increase. Obesity is important because it is the first visible sign that a horse could be developing insulin resistance. Obese horses are 80% less sensitive to insulin, meaning they are much more likely to develop insulin resistance. Horses that have fat deposits on the neck, thoracic, or tail-head regions but have a body condition score of less than 7 are at higher risk of developing insulin resistance.
One of the most important steps to ensuring a long healthy life-span of your equine athlete is proper management of their weight and body condition. The ideal body condition score ranges between 4.5 and 6 depending on the breed, discipline, and work load of the horse. When managing the diet, the first step is understanding the nutrient content of the hay that your horse eats. Have your hay analyzed by a laboratory, and then balance the ration with a grain or supplement that provides the missing nutrients. Horses that are not ridden daily may not need grain, but instead would benefit from only a vitamin and mineral supplement.
There are many low-carbohydrate grain options available, but be sure to ask the manufacturer for the actual starch and sugar content. Just because a feed has a low starch name does not necessarily mean it has safe levels of starch and sugar. For reference, the current recommendation for horses with an equine metabolic condition is for the total percent of non-structural carbohydrates (starch + sugar) in the diet to be 12 percent or less. Keep in mind 12% NSC is a total diet number, so you must consider how much starch and sugar is coming from the forage portion of the diet as well. I encourage you to work with an equine nutritionist to assess body condition and help determine the best diet for your horse.