Insulin dysregulation (ID) is the leading cause of laminitis, accounting for up to 94% of laminitic cases. This condition, referred to as hyperinsulinemia-associated laminitis (HAL) can result from directly hyperinsulinemia, or indirectly from tissue insulin resistance (IR), both of these core components of ID can occur individually or concurrently. The enteroinsular axis including incretins glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are proposed to play a significant role in potentiating insulin secretion in horses with ID and glucagon-like peptide 2 (GLP-2) is proposed to increase intestinal glucose absorption in horses with ID. Together, these hormones might act in an additive manner and overstimulate pancreatic b-cells in horses with ID. In absence of a clear pathogenesis for HAL, treatment has been limited to pain management and there is a strong reliance on non-steroidal anti-inflammatory drugs (NSAIDs), particularly phenylbutazone. These drugs inhibit cyclooxygenase (COX) enzymes that produce prostaglandins (PGs), which have significant roles in both inflammation and homeostasis, especially prostaglandin E2 (PGE2). Among other roles, PGE2 acts as an inhibitor of glucose-stimulated insulin secretion, GLP-1 and GIP secretion, and decreases glucose disposal. In diabetic people, NSAIDs have been demonstrated to increase insulin secretion. If a similar mechanism were true in horses, administration of phenylbutazone to manage HAL could increase insulin secretion, exacerbating hyperinsulinemia, possibly leading to further lamellae damage. Our overall objective was to understand the effect of phenylbutazone administration on insulin and glucose dynamics in horses with ID. We hypothesised that, like NSAIDs in diabetic people, phenylbutazone administration would increase insulin secretion, and that this would be mediated through the enteroinsular axis. To confirm the use of phenylbutazone by owners as the main treatment to manage HAL-associated pain, an initial survey of pony owners was conducted. Seventeen owners with a total of 105 ponies responded having previous laminitis episodes and reported their use of phenylbutazone. The survey demonstrated that phenylbutazone was commonly used for pain management of laminitis, and factors associated with phenylbutazone administration included a lower number of ponies owned by the respondent, experience with laminitis, and veterinary prescription. To determine the effect of phenylbutazone administration on glucose and insulin dynamics, a randomised placebo-controlled crossover study was conducted using 16 light breed horses (7 classified as ID by being both hyperinsulinaemic and IR and 9 classified as controls by being neither hyperinsulinaemic nor insulin resistant). After day 8 of treatment with phenylbutazone or saline, horses underwent a modified frequently sampled intravenous glucose tolerance test (mFSIGTT) to identify changes in insulin sensitivity and a complete oral glucose test (cOGT) the following day to identify changes in insulin secretion and incretin activity. The alternative treatment was administered after a 10-day washout period and the same testing protocol was followed. Administration of phenylbutazone significantly reduced glucose and insulin concentrations, with lower areas under the curve, and maximum concentrations in horses with ID following the OGT, contradicting our initial hypothesis. There was no significant effect of treatment with phenylbutazone on GIP, GLP-1, and GLP-2, in any horse, and a significant effect of ID status was only detected on GIP concentration, not on GLP-1 nor GLP-2. Administration of phenylbutazone improved insulin sensitivity index in horses with ID and no significant effect was detected in control horses. These results demonstrate that (1) phenylbutazone is used by owners with ponies suffering from laminitis to manage the associated pain, (2) phenylbutazone administration does not increase insulin secretion, and instead reduces insulin and glucose concentrations in horses with ID through improving tissue IR, and (3) incretins might not play a significant role in the alterations in insulin secretion in horses with ID. The effect of phenylbutazone administration on insulin and glucose dynamics is likely mediated by an improvement in insulin sensitivity suggesting a link between tissue IR and low-grade inflammation, as previously described in humans. Although long-term treatment with phenylbutazone is not recommended, its use does not appear detrimental to the management of horses with HAL. Understanding the role of low-grade inflammation in ID warrants further research for the management of laminitic horses.