Warmblood horses with mild, previously unrecognised insulin
dysregulation may already have subtle changes in heart structure and function,
even in the absence of obvious signs of heart disease, laminitis or other
metabolic problems. 
Recent research findings suggest that insulin dysregulation, best known for its association with laminitis and equine metabolic syndrome, could have wider effects throughout the body than previously recognised.
The study, published in the Journal of Veterinary Internal Medicine, examined whether horses with subclinical insulin dysregulation showed evidence of cardiovascular changes before developing clinical disease.
Megan Palmisano and colleagues at the University of Pennsylvania's New Bolton Center carried out a blinded cross-sectional study involving 19 client-owned Warmblood horses aged between five and 15 years. All had been referred for elective procedures and had no reported history of cardiac disease, laminitis or metabolic disorders.
The horses underwent an oral sugar test to assess insulin regulation. Eight were classified as insulin-dysregulated, while the remaining 11 had normal insulin responses. Researchers also assessed body condition score, cresty neck score, blood pressure, metabolic hormone concentrations and heart structure and function using echocardiography.
As part of the metabolic assessment, the team measured leptin and adiponectin, hormones produced by fat tissue that play important roles in metabolic health. They also used two-dimensional speckle-tracking echocardiography, an advanced imaging technique capable of detecting subtle changes in heart muscle function that may not be apparent with conventional cardiac measurements.
Compared with healthy horses, those with insulin dysregulation had larger left ventricular internal diameters and thicker interventricular septa, changes consistent with early cardiac remodelling or hypertrophy. At end diastole, the average left ventricular internal diameter measured 11.77 cm in insulin-dysregulated horses, compared with 11.10 cm in controls. Septal thickness averaged 3.10 cm versus 2.46 cm, while estimated left ventricular mass was approximately 3,849 g compared with 2,898 g.
The insulin-dysregulated horses also showed significantly lower radial strain, a measure of how the heart muscle deforms as it contracts. Average radial strain was about 49%, compared with 67% in the control group. Although conventional echocardiographic measurements generally remained within established reference ranges, these more sensitive techniques revealed subtle differences in heart muscle performance before any clinical signs were apparent.
High blood pressure did not appear to explain the findings. Only two horses were classified as hypertensive, one in each group. This suggests that metabolic or hormonal factors associated with insulin dysregulation may contribute directly to cardiac remodelling, although the study was not designed to determine the underlying mechanisms.
In people, insulin resistance and metabolic syndrome are well recognised risk factors for left ventricular hypertrophy and cardiovascular disease. Several mechanisms have been proposed, including altered insulin signalling, chronic inflammation and metabolic stress. Whether similar processes occur in horses remains uncertain. Importantly, this study demonstrated an association rather than proving that insulin dysregulation causes heart disease.
The authors conclude that horses with mild insulin dysregulation show evidence of left ventricular remodelling consistent with hypertrophy and suggest that cardiovascular changes could become part of the broader clinical picture of insulin dysregulation.
The study has several limitations. It involved only 19 horses, all of them Warmbloods, so the findings may not apply to ponies, other breeds or horses with more severe insulin dysregulation. Because the research was cross-sectional, with measurements taken at a single point in time, it cannot determine whether insulin abnormalities led to the cardiac changes or whether another factor contributed to both.
Nor do the findings mean that every horse with insulin dysregulation has clinically significant heart disease or requires echocardiographic screening. The long-term importance of these subtle changes remains unknown. Larger, long-term studies will be needed to establish whether the cardiac changes progress, remain stable or improve with management of insulin dysregulation, and whether they have implications for athletic performance or increase the risk of arrhythmias or heart failure.
For now, the study adds to growing evidence that insulin dysregulation may affect more than the feet, highlighting the need to consider its potential impact on cardiovascular health as well as laminitis risk.
For more details, see:
Megan G Palmisano, Claire Underwood, Jeaneen Sage, Darko Stefanovski, Andrew van Eps, JoAnn Slack.
Echocardiographic characteristics and evidence of ventricular remodeling in subclinical insulin-dysregulated Warmblood horses
Journal of Veterinary Internal Medicine, (2026) Vol 40, (5), aalag229.
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