Some horses with insulin dysregulation (DI) may be obese, but it is not necessarily a given. Insulin dysregulation (ID) is the presence of one or more of the following: basal or fasting hyperinsulinemia, tissue insulin resistance, or exaggerated insulin response to ingested nonstructural carbohydrates (i.e. starch, simple sugars, and fructans, and/or exaggerated insulin response to intravenously provided simple sugars). Horses or ponies with ID are at increased risk of laminitis, and diet is central to managing any animal with ID. Obesity, age, and breed type play a role in horses’ increased risk of ID. Unfortunately, it is impossible to look at an individual horse/pony and state categorically they are or are not ID. Diagnostic testing is, therefore, essential, not only for identification, but also for monitoring purposes. Choosing the appropriate test, as well as regular monitoring, is often key. Nutritional management advice is not uniform, especially because not all ID animals are obese and, therefore, the nutritional goal could actually be weight gain rather than weight loss. Not all horses and ponies show the same insulin response to a particular diet. The response will likely vary with many factors, including the time of the year. Therefore, diagnosing and managing a horse/pony with ID can be challenging for many reasons, and a coordinated approach between the owner, treating veterinarian (and possibly specialist/referral veterinarian), the diagnostic laboratory, and the nutritional advisor can often be beneficial, especially in the more complex cases. Supporting the advice provided at all points is background peer-reviewed scientific research. The treating veterinarian is central to this coordinated response. They need not only to recognize the potential for an individual animal to be ID, but they need to work with the owner/caregiver to develop a plan targeted to the individual animal—taking into account what feeds/forages are available, as well as any constraints around facilities/equipment, etc. The owner/caregiver must “buy” into the plan to understand the importance and relevance. The treating veterinarian, or consultation with a specialist veterinarian, needs to choose the best test(s) for an individual based on current research and recommendations.4,5 Additionally, it is best to use an equine-specific laboratory that is knowledgeable in areas utilizing validated laboratory assays. The laboratory needs to provide guidance as to the interpretation of the laboratory results based on current recommendations backed by leading researchers.1,2 Having a nutritionist who is experienced in managing such cases within your support team and up to date on the latest published research is helpful in deciding what diet to feed, especially when things do not seem to go to plan. Feeding and management The following tips are helpful for improving insulin sensitivity and reducing insulin response to the diet3: Remove cereal grains and sweet/complementary feeds that have a high/moderate non-structural carbohydrate (NSC) (i.e. starch, simple sugars, and fructans) content from the diet. Feed multiple small, low NSC providing meals/day. The maximum NSC intake level/meal may depend on the individual6 and how low a post-prandial insulin response is required. Restricted or zero access to pasture may be required. Feed a diet based on grass hay (or hay substitute) with a low NSC content (less than 10-12 percent DM), together with a fortified forage balancer. Feed for maintenance of moderate Body Condition Score (4.5-5.5/9 BCS)—this may require a weight loss/weight gain or maintenance diet. Increase free and/or structured exercise (if clinically/practically possible). Feeding and management advice should be guided by clinical situation and laboratory results: monitoring is key.7 A sample case Courtesy of Antech The following case shows how a coordinated approach can be of value. There was a 16-year-old pony mare with sudden reluctance to walk on hard ground. The owner was concerned about laminitis. The mare was kept on pasture during the day and in the stall at night with free choice hay. She was fed a restricted starch and sugar complementary feed. The primary care veterinarian confirmed laminitis based on the clinical examination (increased digital pulses, hoof rings, stilted gait, and heat in the feet). Treatment for acute laminitis was initiated. The veterinarian also noted the mare was obese with a BCS of 7/9 and regional adiposity. Management concerns were discussed regarding diet and weight reduction. Diagnostic testing for endocrine disease, including ID, was discussed. Consultation with an equine internal medicine specialist was recommended to formulate a diagnostic plan to address any underlying endocrine abnormalities potentially contributing to laminitis. Testing options for ID would include an oral sugar test (OST) or testing the response to the current diet, including hay and pasture. The owner was not convinced the current diet was a concern, as she was only getting a small amount of grass and was on a restricted starch and sugar complementary feed. Therefore, the decision was made to test the current diet rather than the OST to help understand if her diet was a factor in the laminitis. Recommendations The mare initially undertook a basal insulin following overnight stalling with a flake of hay, but no complementary feed; then took a sample after being at pasture for one hour. Results The insulin reference range for the specialist laboratory used was 0-42 uU/mL. Insulin was 62 uU/mL after being in the stall, insulin one hour post restricted starch and sugar complementary feed was 125 uU/mL, but insulin after being on the pasture was 472 uU/mL. Equine nutritionist specialist discussion Recommendations were made with respect to weight loss Increase exercise as tolerated but only on soft footing Reduced overnight hay intake to 1.5 percent BW DM—13 lbs Replaced the complementary feed with a forage balancer Put on a grazing muzzle when out on the pasture with its cohorts Checked forage provided when stabled had a NSC content of less than 12 lbs DM Monitoring program Four weeks later The mare had clinically improved and was moving freely. She had a significant reduction in body condition (5.5/9) as monitored by a weight tape and was active in the pasture. The response to the change in the complementary feed portion of the diet was evaluated and improved but still elevated at 75 uU/mL—advising to divide the forage balancer across three meals per day. Eight weeks later The resting blood sample that was taken, which had an insulin value of nearly 900 uU/mL, found she had managed to get her muzzle off in the pasture for around an hour just before the testing. Put on a strict dry lot along with previous nutritional recommendations The mare continued to be clinically healthy Amy Polkes, DVM, DACVIM, is the equine veterinary diagnostic specialist at Antech Diagnostics. Pat Harris, MA, PhD, VetMB, DipECVCN, MRCVS and RCVS specialist veterinary clinical nutrition (equine), is director of science at Mars Horsecare and head of Waltham Equine Studies Group, Waltham Petcare Science Institute. Amanda Adams, PhD, is associate professor at University of Kentucky, Gluck Equine Research Center. References Adams & Polkes 2022: Review of factors to consider when using the OST to diagnose IDAAEP 2022. EEG 2020: Equine Endocrinology Group. 2020. Frank N, Bailey SR, Bertin FR, de Laat M, Kritchevsky J, Tadros L. Recommendations for the diagnosis and treatment of equine metabolic syndrome (EMS). Harris PA 2022: Considerations when feeding the ID equid. AAEP abstract (in press). Jocelyn N.A., Harris P.A. and Menzies-Gow N.J. (2018) Effect of varying the dose of Light corn syrup on the insulin and glucose response to the oral sugar test. Equine Veterinary Journal 50(6) 836-841 Knowles, E.J., Elliott, J., Harris, P.A. Chang, Y.M. and Menzies-Gow, N.J. (2021) Predictors of laminitis development in non-laminitic ponies. Equine Veterinary Journal (in press) Macon, E.L., Harris, P., Bailey, S., Barker, V.D. and Adams, A., 2022. Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared to non‐insulin dysregulated controls. Equine Veterinary Journal; 54:574-583 Macon, E.L., Harris, P., Barker, V.D. and Adams, A.A., 2022b. Seasonal Insulin Responses to the Oral Sugar Test in Healthy and Insulin Dysregulated Horses. Journal of Equine Veterinary Science, 113: p.103945
