Insulin Ranges in Horses
In horses, insulin concentration is one of the most important blood measurements used to assess how effectively the body regulates glucose (blood sugar) and whether the horse may be developing insulin dysregulation, a hallmark feature of Equine Metabolic Syndrome (EMS).
Under normal physiological conditions, insulin facilitates the uptake of glucose into insulin-sensitive tissues such as skeletal muscle and adipose tissue while also regulating lipid metabolism, protein synthesis, and cellular energy balance. By promoting glucose storage and utilization, insulin helps maintain blood glucose concentrations within a narrow physiological range. In a healthy horse, blood glucose concentrations are controlled and relatively stable. Following a meal, glucose concentrations rise slightly, stimulating insulin secretion. The released insulin signals tissues throughout the body to absorb and utilize glucose, after which insulin concentrations return toward baseline. However, in horses with insulin dysregulation, tissues become less responsive to insulin's actions, a condition often referred to as insulin resistance.
This distinction is important because, unlike diabetes mellitus in humans, horses with insulin dysregulation frequently maintain normal blood glucose concentrations despite substantial metabolic dysfunction. Therefore, insulin concentrations are often considered more informative than glucose concentrations when evaluating metabolic health in horses. Hyperinsulinemia (high insulin levels) is now recognized as a primary risk factor for the development of endocrinopathic laminitis, a painful and potentially debilitating condition affecting the laminar tissues of the hoof. Therefore, assessing blood insulin levels are an important management step.
Table 1: Physiological ranges of blood insulin levels in horses (pmol/L).
Management of insulin dysregulation typically involves a multifaceted approach that includes dietary modification, weight management, exercise where appropriate, and ongoing monitoring of metabolic markers. In recent years, there has been increasing interest in the use of nutritional supplementation as a complementary strategy to support metabolic health. While supplements are not intended to replace proper dietary management, certain nutritional interventions may help support normal glucose metabolism, insulin sensitivity, body composition, muscle maintenance, and overall metabolic function. As a result, nutritional supplementation is increasingly being incorporated into long-term management programs for horses with a history of elevated insulin concentrations, with the goal of helping maintain healthy metabolic function and supporting the improvements achieved through broader management practices. In order to understand how these products effect insulin in the horse, regular blood testing remains essential to objectively evaluate metabolic status and monitor changes in insulin regulation over time.
Oki’s Journey
Oki is a Quarter Horse gelding who underwent endocrine blood testing by Halton Equine Veterinary Service in April 2026 as part of an evaluation of his metabolic health. Resting blood samples were collected and analyzed for insulin and glucose concentrations, which are routinely used to assess insulin regulation in horses. The measured insulin concentration reflects the amount of insulin circulating in his bloodstream at the time of sampling. Elevated insulin concentrations indicate that the pancreas is producing increased amounts of insulin to maintain normal blood glucose concentrations, a characteristic feature of insulin dysregulation.
Initial laboratory testing in April 2026 identified an elevated resting insulin concentration of 362 pmol/L, exceeding the laboratory reference interval (<300 pmol/L). This finding is consistent with mild hyperinsulinemia and suggests the presence of insulin dysregulation. Hyperinsulinemia is clinically important because persistently elevated circulating insulin concentrations are strongly associated with an increased risk of endocrinopathic laminitis in susceptible horses. Despite the elevated insulin concentration, Oki's resting blood glucose concentration measured 6.1 mmol/L, remaining within the laboratory reference interval (3.7–6.7 mmol/L). This combination of elevated insulin with normal glucose is commonly observed in horses with compensated insulin dysregulation, where increased insulin secretion maintains normal blood glucose concentrations.
Figure 1: Blood insulin concentrations in Oki in April 2026 before being supplemented with Structure Muscle and in June 2026 after supplementation (pmol/L).
Following the April 2026 bloodwork, Oki was started on Structure Muscle as part of his nutritional management program. No additional dietary or management changes were reported. Repeat resting blood samples were collected in June 2026 to monitor changes in metabolic status over time. At follow-up, resting insulin concentration had decreased from 362 pmol/L to 306 pmol/L (Figure 1), while glucose concentration remained well within the normal reference interval, decreasing from 6.1 mmol/L to 5.4 mmol/L (Figure 2).
A notable finding from Oki's bloodwork is the reduction in resting insulin concentration following the initiation of Structure Muscle supplementation. Between April and June 2026, insulin decreased from 362 pmol/L to 306 pmol/L, representing an approximate 15.5% reduction over a two-month period. Although the June concentration remained marginally above the laboratory reference interval, the decrease suggests an improvement in insulin regulation compared with the initial assessment. Importantly, glucose concentrations remained within normal limits at both sampling periods, indicating that glucose homeostasis was maintained throughout the monitoring period.
Figure 2: Blood glucose levels in Oki prior to being supplemented with Structure Muscle (April 2026) and while supplemented with Structure Muscle (June 2026) measured in mmol/L.
While only two blood samples are currently available, the results demonstrate an encouraging early trend toward improved insulin regulation. Horses with insulin dysregulation often exhibit variability in insulin concentrations due to factors such as season, pasture access, body condition, stress, and exercise. Despite these potential influences, Oki's insulin concentration declined over the monitoring period while glucose concentrations remained stable within the normal reference interval. Continued monitoring will be valuable to determine whether insulin concentrations continue to decline into the normal range over time.
Figure 3: Before (left; April 2026) and after (right; June 2026) supplementation with STRUCTURE Muscle
Overall, Oki's bloodwork demonstrates an early improvement in metabolic status following the introduction of Structure Muscle supplementation. Compared with the initial April 2026 concentration, resting insulin was 15.5% lower by June 2026 while maintaining normal blood glucose concentrations. Although the follow-up insulin value remained slightly above the laboratory reference interval, the downward trend suggests a reduction in compensatory insulin secretion and may indicate improving insulin sensitivity. Additional serial monitoring over the coming months will help determine whether this positive trend is sustained and whether insulin concentrations ultimately normalize.