Everyone has heard about insulin resistance (IR) and how it is connected to equine obesity and laminitis. IR has been a hot topic the last few years and, as is always the case, has triggered the release of a host of supplements or plans for dealing with this condition. Unfortunately, many are at best ineffective and can be harmful if they delay institution of a correct management approach.
What is it'
Insulin resistance isn?t a disease. It is a metabolic type that makes equines born with this metabolism able to maintain weight on lower-calorie, higher-fiber diets that wouldn?t be adequate for horses with different metabolisms. Horses evolved with little starch or simple sugars in their diet, which means little need for insulin release. As a result, their tissues are less responsive to insulin and it takes higher levels to achieve normal glucose after a meal high in starch or sugar.
You can't cure a horse's or pony?s insulin-resistant metabolism any more than you can change their height or coat color, nor do you have to. All it takes to achieve and maintain good health is to feed them a diet that their body can handle and maintain a good exercise program. (This diet has been published in the 2007 book Equine Podiatry, Drs. Andrea Floyd and Richard Mansmann editors, and in the journal Compendium of Continuing Education for the Practicing Veterinarian, volume 26, pages 122-130, 2004. it's the diet used by the Equine Cushing?s and Insulin-Resistance Yahoo Group, and has helped thousands of horses over the last nine years. This group is monitored by Horse Journal?s Veterinary Editor, Dr. Eleanor Kellon.)
Humans Are Different.
With type II diabetes in people, the liver is producing more glucose than the pancreas (which secretes insulin) can keep up with. People with metabolic syndrome tend to be overweight with high cholesterol levels. that's why human supplements and drugs target things like elevated cholesterol and triglycerides and any abnormally high production of glucose by the liver.
While some changes in circulating fats have been documented in horses, they're minimal compared to what is found in people, and there is no evidence to date that horses overproduce glucose as part of their insulin-resistance metabolism.
Insulin resistance is built into the horse's metabolism, and tHere's compelling evidence that this is genetically determined. While severely overweight animals of any breed are less insulin-sensitive than their leaner cousins, IR severe enough to cause laminitis is extremely rare to nonexistent in Thoroughbreds, Standardbreds, Quarter Horses, drafts and warmbloods. In contrast, ponies, miniature horses, Arabians, Morgans, and native breeds, among others, are prone to IR, especially when not regularly exercised.
A 2006 study performed by a team from the Virginia Polytechnic Institute studied a herd of 160 pastured ponies and found that the likelihood of laminitis could be predicted with high accuracy from the degree of insulin resistance. They also found strong evidence that IR was associated with a dominant gene or set of genes, with additional influence from sex (intact stallions are protected).
What do they need'
it's simple, really. When kept in regular work, IR equines can maintain a good weight and do well on a diet of hay, the necessary minerals to balance the hay, plus salt, vitamin E and flaxseed. Some horses can even be on pasture all year when regularly worked. For example, a common scenario is an Arabian in endurance work being pasture-kept, even fed a little grain, but that same horse getting overweight and laminitic within as short a period as a month if the exercise is stopped without the diet being adjusted. More-sensitive animals may need to be kept off pasture at least during the period of rapid spring growth.
If the horse or pony is already in trouble with excess weight and laminitis, exercise may not be an option. In this case, the diet must be more tightly controlled until they can get back to regular exercise after their feet heal. Hay should be analyzed to make sure the combined level of sugar and starch is below 10%. If higher, the hay will need to be soaked to lower the sugar content. Vitamins and minerals requirements are as above and can be fed in a small amount of molasses-free, well-rinsed and soaked beet pulp.
Humans have a similar health issue, and human metabolic syndrome can degenerate into type II diabetes. A variety of drugs have been developed to treat this problem, but even so the pharmaceutical companies can only make a modest difference compared to improvements the patient gets from weight loss, healthful eating and exercise. Despite this fact, horse owners continue to be drawn to a variety of supplement ingredients or alternative approaches.
The only thing that permits you to be less conservative about diet with an insulin-resistant equine is exercise. If you're looking for a supplement or drug that will allow you to feed whatever you want and not exercise the horse, forget it. While it's true that some basic nutrients and herbs can have an impact on insulin actions and symptoms of IR, there are also a great many ingredients that are actually bad for an IR horse. See our table on these pages for details.
Some supplements that proved helpful in humans and lab animals, such as chromium and cinnamon, have not panned out for horses. Some that are advancing through formal human NIH (National Institute of Health) trials ? resveratrol and Momordica ? look exciting, but even if they prove helpful for human IR they may not work the same for horses.
The cornerstone of successfully controlling IR, and the laminitis risk from it, remains regular exercise and a low-carbohydrate, mineral-balanced diet, which supplies adequate levels of the important antioxidant nutrients.
Dr. Eleanor Kellon