Nutritional interventions paired with appropriate management strategies are often effective in reducing the risk of disease onset and reducing the severity of or completely eliminating clinical symptoms associated with metabolic disorders.

Many of these conditions have similar clinical symptoms, but different etiologies, which can make a correct diagnosis difficult. Additionally, it is possible for a horse to be affected by multiple conditions.

Therefore, a thorough physical examination as well as appropriate endocrine testing in light of the horse’s health history, current clinical symptoms and coexisting conditions should be conducted to provide a well-rounded picture of what might be going on, and what the best approach to managing the condition(s) is.

Etiology

• Contemporary management practices provide many horses sedentary lifestyles while, at the same time, being fed excessive levels of concentrated rations and nutrient dense forages. Horses have evolved by nature to store energy and nutrients in times when feedstuffs are in abundance to enable survival when food is sparse.
  • Horses presented with overnutrition on a regular basis may become obese or exacerbate existing obesity, especially when coupled with limited physical activity.
  • These horses increase their fat stores, and those at risk for developing equine metabolic syndrome typically develop regional adiposity (e.g., cresty neck, fat pads at the tailhead).
• With advances in understanding equine metabolic diseases, it is recognized that fat cells (adipocytes) have a diversified physiological role extending beyond repositories for stored energy.
  • Recent studies have shown that adipocytes are capable of releasing a variety of hormones, or adipokines, that play a major role in regulation of body mass and composition.
  • Abdominal fat cells possess an enzyme that converts circulating inactive cortisone into active cortisol, which inhibits the action of insulin, and may contribute to the development of insulin resistance and hyperinsulinemia associated with high consumption rates of dietary starches and sugar.

Insulin Resistance

• Insulin resistance plays a significant role in aberrant carbohydrate metabolism, which manifests itself in a variety of disorders including Equine Metabolic Syndrome (EMS), Laminitis, and Equine Cushing’s Disease (PPID).
• Insulin resistance during late pregnancy is also common and may lead to increased risk of laminitis, complications with parturition, as well as potential impacts on fetal growth.

Genetic Disorders

• Recurrent Exertional Rhabdomyolysis (RER), Polysaccharide Storage Myopathy (PSSM type 1 and type 2), and Malignant Hyperthermia (MH) are genetic disorders where glucose metabolism and/or calcium regulation in skeletal muscle are abnormal.
  • Although the etiologies of these muscle disorders are different from those of other metabolic diseases, the underlying nutritional goal is to minimize post-prandial glucose and insulin spikes to avoid exacerbating an insulin-resistant or insulin hypersensitive state depending on the specific condition.

Developmental Orthopedic Disease

• Many different factors are thought to contribute to Developmental Orthopedic Disease (DOD), including genetics, nutritional imbalances, excess stall confinement (lack of free exercise), acute trauma and overtraining.
  • Many growing horses exhibit insulin resistance at an early age.
  • A concentrate meal containing high starch and sugar levels will elicit a high glycemic response.
  • Exaggerated glycemic responses over time may contribute to hormonal dissynchrony, which in turn affects conversion of cartilage into bone during endochondral ossification.

Dietary Recommendations

• Utilization of added fat and fiber rations to minimize the impact on post-prandial glycemic response (blood glucose and insulin increases) in lieu of large concentrate meals high in starch and sugar is recommended.
• Other specific nutrients such as magnesium, vitamin E, zinc and chromium may be useful in managing metabolic disorders, with the exception of polysaccharide storage myopathy, for which the use of chromium is contraindicated due to these horses exhibiting an abnormal (over) sensitivity to insulin.
  • Chromium is not yet approved as a horse feed ingredient, but is available in some supplements.
• Ad libitum access to clean water and salt should be available at all times.