Aleurone supplementation enhances the metabolic benefits of training in Standardbred mares: Impacts on glucose-insulin dynamics and gut microbiome composition

Berit Boshuizen ^1,2,3* Lorie De Maré ^1,3 Maarten Oosterlinck ⁴ Filip Van Immerseel ⁵ Venessa Eeckhaut ⁵ Constance De Meeus ^1,3 Lindsey Devisscher ⁶ Carmen Vidal Moreno De Vega ^1,3 Maarten Willems ^1,3* Jean Eduardo De Oliveira ⁷ Guilherme Hosotani ⁷ Yannick Gansemans ⁸ Tim Meese ⁹ Filip Van Nieuwerburgh ⁸ Dieter Deforce ⁸ Katrien Vanderperren ¹⁰ Elisabeth-Lidwien J.M.M. Verdegaal ^1,11,3 Cathérine Delesalle ^1,3

• ¹ Department of Translational Physiology, Infectiology and Public Health, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
• ² Wolvega Equine Clinic, Oldeholtpade, Netherlands
• ³ Research Group of Comparative Physiology, Ghent University, Merelbeke, Belgium
• ⁴ Department of Large Animal Surgery, Anaesthesia and Orthopaedics, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
• ⁵ Department of Pathobiology, Pharmacology and Special Animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
• ⁶ Department of Basic and Applied Medical Sciences, Faculty of Medicine and Health Sciences, Ghent University, Ghent, East Flanders, Belgium
• ⁷ Cargill Research and Development Centre Europe, Vilvoorde, Belgium
• ⁸ Deparment of Pharmaceutics, Laboratory of Pharmaceutical Biotechnology, Ghent University, Ghent, Belgium
• ⁹ Department of Pharmaceutics, Laboratory of Pharmaceutical Biotechnology, Ghent University, Ghent, Belgium
• ¹⁰ Department of Morphology, Imaging, Orthopedics, Rehabilitation and Nutrition, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
• ¹¹ Equine Health and Performance Centre, School of Animal and Veterinary Sciences, Roseworthy Campus, University o Adelaide, South Australia, Australia

Aleurone, derived from the bran layer of grains like wheat and barley, has demonstrated positive effects on energy metabolism in pigs, mice, and untrained horses, influencing glucose-insulin dynamics and gut microbiome composition. Training itself enhances insulin sensitivity in horses, similar to the improvements in performance capacity observed in human athletes. This study aimed to investigate whether aleurone supplementation provides additional benefits to training by modulating insulin metabolism and gut microbiota in Standardbred mares. Methods: Sixteen Standardbred mares (aged 3-5 years) participated in a cross-over study with two 8week training periods separated by 8 weeks of detraining. Each horse received either 200 g/day aleurone supplementation or a control diet. Insulin metabolism was evaluated using oral (OGTT) and intravenous (FSIGTT) glucose tolerance tests, measuring parameters such as Maximumglucose, AUCglucose, Maximuminsulin, AUCinsulin, Time to peakinsulin (OGTT), Acute Insulin Response to Glucose (AIRg), glucose effectiveness (Sg), and disposition index (DI) (FSIGTT). Fecal samples underwent metagenomic analysis to assess alpha and beta diversity and microbial composition. Results: Training Aalone: Training significantly improved OGTT parameters by decreasing Maximuminsulin (P = 0.005) and AUCinsulin (P = 0.001), while increasing Time to peakinsulin (P = 0.03), indicating enhanced insulin sensitivity. FSIGTT results also showed a decrease in logAIRg (P = 0.044). Training with Aleurone: Aleurone supplementation further reduced FSIGTT AIRg (P = 0.030), 49 logAIRg (P = 0.021), and basal glucose (P = 0.030) while increasing glucose effectiveness (Sg; 50 P = 0.031) and β-cell function (P = 0.025). These findings suggest aleurone improves insulin sensitivity, glucose disposal, and fasting glucose regulation beyond training.Microbiome analysis revealed training decreased Pseudomonas, associated with dysbiosis, while aleurone reduced inflammation-associated Desulfovibrio. Beta diversity metrics showed no significant changes.