Inflammation Resolution and Nutritional Modulation of Equine Joint Health: Ex-perimental Models, Biomarkers, and Functional Outcomes

Joint inflammation is a major cause of lameness and reduced athletic performance in horses. Although considerable progress has been made in understanding joint disease, experimental approaches that stimulate synovitis and therapeutics that target inflammation resolution remain incompletely understood. This thesis aimed to characterize early equine joint inflammation using complementary in vivo and in vitro models and to evaluate the effects of oral nutraceutical supplementation on inflammatory, cartilage metabolic, and pro-resolving responses. Study 1: A dose lower than that reported in literature of a recombinant equine interleukin-1β (reIL-1β) synovitis model was developed to determine the minimum dosing of the inflammatory stimulus required to induce measurable biochemical responses in synovial fluid, accompanied by a functional response. In n=3 horses, intra-articular administration of 75 ng reIL-1β produced a mild, transient inflammatory response characterized by increased synovial fluid prostaglandin E₂ (PGE₂) without overt lameness over a 24-hour period. Objective gait analysis identified changes in poll movement asymmetry that correlated with PGE₂ concentrations, however, did not extend past inter-session variability, supporting the model as an ethically acceptable approach for investigating subclinical synovitis. Study 2: The 75 ng reIL-1β model was validated in a larger cohort of horses (n=11) through assessment of inflammatory, cartilage turnover, and pro-resolving biomarkers together with objective gait analysis. The model produced increases in synovial fluid PGE₂ and nitric oxide (NO), while objective gait analysis detected only subtle movement asymmetries that remained within reported biological variability, confirming the mild and self-limiting nature of the inflammatory response. Study 3: The effects of an omega-3 polyunsaturated fatty acid nutraceutical (STRUCTURE-Joint) were evaluated using the validated synovitis model from studies 1 and 2. Supplementation increased synovial fluid NO, PGE₂, and resolvin D1 (RvD1) concentrations, reduced joint circumference, and altered systemic blood results, suggesting modulation of inflammatory and pro-resolving pathways rather than simple suppression of inflammation. Study 4: A second oral nutraceutical containing sodium hyaluronate, Boswellia serrata extract, and curcumin was evaluated using the same synovitis model. Supplementation reduced joint circumference together with synovial fluid NO and CS846 concentrations, indicating modulation of inflammatory signaling and cartilage metabolic responses following inflammatory challenge. This study utilized the non-clinical 75 ng reIL-1B injection to better understand the potential therapeutic effects of this nutraceutical on joint inflammation. Study 5: An in vitro lipopolysaccharide-stimulated porcine cartilage explant model was used to determine whether the effects of STRUCTURE-Joint were mediated directly through cartilage tissue. Although supplementation did not reduce NO production or glycosaminoglycan (GAG; cartilage matrix turnover), high-dose supplementation increased RvD1 concentrations under inflammatory conditions, supporting a role for omega-3 supplementation in promoting inflammation resolution rather than direct chondroprotection. Collectively, this thesis establishes a reproducible model of subclinical equine synovitis for investigating the initiation and modulation of early joint inflammation. It also demonstrates that nutraceuticals produce formulation-specific biological responses, influencing inflammatory signaling, cartilage metabolism, and inflammation-resolution pathways. These findings advance the understanding of early equine joint disease and provide an experimental framework for the future evaluation of evidence-based nutritional strategies aimed at preserving joint health, athletic performance, and long-term soundness in horses.