By Dr. Martin Adams, PAS Equine Nutritionist for Southern States

Dry lots are recommended for insulin
resistant horses and ponies.

Recent studies show some horses, ponies and donkeys are prone to insulin resistance (IR). Our nutritionist offers some advice on what to look for and how to prevent, cure or help horses that are insulin resistant.

Warning Signs

Evidence suggests obesity, age, inactivity, and diets high in starch and sugar contribute to insulin resistance in horses. Modern equine management providing excessive calories from improved pasture and grain feeding has resulted in obesity and problems associated with Equine Metabolic Syndrome (EMS), including symptoms such as abnormal fatty deposits along the crest, rump and above the eyes, voracious appetite, and reduced stamina. Horses that are overweight are more likely to develop IR and have an increased risk of laminitis.

Many older horses, especially over 20 years of age, can be insulin resistant due to the hormonal effects of Equine Cushing's Disease (ECD) and can include symptoms of EMS, hirsuitism (long curly hair that won't shed in spring), muscle wasting, frequent infections, infertility, and excessive water consumption, sweating or urination.

In a recent study, horses fed a high sugar and starch feed had increased IR compared to horses fed a high fat and fiber feed, even when they were not overweight.

Diagnosis

Your veterinarian diagnoses IR by measuring blood levels of glucose and insulin. A combined glucose-insulin test may be used but more likely a resting serum insulin concentration will be utilized. There are two drugs that help IR horses; levothyroxine (also called Thyro-L) helps reduce IR and increases weight loss when used over a three to four month-long period, and metformin helped reduce obesity and laminitic pain in 78% of horses in another long-term study.

Prevention

Prevention is always more economical than treatment, so use the following tips to help prevent and treat IR:

Weight loss in obese horses diagnosed with IR may allow them to return to a normal metabolic status. Adjust your feeding program to maintain proper body condition and avoid obesity. This may require limiting pasture grazing time, the use of a grazing muzzle, or limiting the amount of hay and grain fed.

Regular exercise reduces blood glucose and insulin levels, allowing an active horse to prevent IR even when fed high sugar and starch meals. However, lack of activity combined with overfeeding can result in obesity and onset of IR or EMS. Provide as much exercise and turnout for your horse as possible. Consider a sacrifice area or paddock, where pasture grass is not available but horses can be turned out daily for activity.

Maintain good soil fertility in pastures. Research shows that a well-fertilized pasture of cool-season grasses has lower levels of sugars that cause laminitis. Avoid or severely limit access to pasture grazing for IR horses in the spring and fall. Cool season grasses contain the greatest amount of sugars, including fructan sugars, which cause laminitis. Horses with IR are more likely to have a laminitic outbreak when grazing on pasture during these times.

Select hay with low levels of soluble carbohydrates. Small grain hays like oat and ryegrass have greater sugar content than grass hays like timothy and orchardgrass. Alfalfa hay and Coastal Bermudagrass are lower in sugar and starch content, but alfalfa contains more calories and feeding rate must be monitored closely. Clover hay should be avoided for IR horses; moderate quality grass hay is preferred for its low soluble carbohydrate and moderate caloric content. Soaking hay for 60 minutes in cool water reduces its soluble carbohydrate content by 30%.

Select a horse feed low in sugar and starch to reduce blood glucose and insulin levels. Beet pulp and soy hulls contain very low levels of soluble carbohydrates, so select a feed that is based on one of these ingredients. Southern States provides the soluble carbohydrate values of its horse feeds to help you select the most appropriate feed for your horse.

Proper hoof care is essential for the IR horse due to increased incidence of laminitis. Select a well-fortified horse feed to meet protein, lysine, calcium, phosphorus, zinc, copper and iodine requirements. These nutrients are especially important for good hoof growth. Also consider a horse feed or supplement containing biotin if hoof quality is poor.

Magnesium aids in regulated insulin secretion and is recommended for horses with IR. Chromium has been used to reduce blood glucose levels in horses. Select a feed with higher guaranteed levels of magnesium or consider using magnesium and chromium supplements.

When feeding small amounts of feed to decrease calories make sure your horse is receiving sufficient nutrition. Consider a balancer pellet, such as Triple Crown® Lite, 12% Supplement or 30% Supplement.

Triple Crown Lite is specially formulated for miniature horses, ponies, overweight and "easy keeper" horses. Due to its low feeding rate, concentrated nutrient profile, and low starch and calorie content it can be fed with an all forage (hay or pasture) diet.