17 Can a yeast-derived prebiotic improve insulin response in aged horses?

Abstract

Research has shown aged horses to be disproportionately affected by insulin dysregulation. Therefore, the objective of this study was to test the hypothesis that feeding ActivAge® (AA), a unique yeast-derived prebiotic purported to improve metabolic health, would lower insulin response in aged horses. Ten Quarter Horse geldings (19 ± 0.6 yr; 587.5 ± 22 kg) were utilized in a randomized design, with a 42d feeding period, followed by a 28d washout, then a crossover 42d feeding period. All horses received 0.36 kg/45.5 kg BW/d Purina® Equine Senior® (ES) paired with either 0.45 kg/d of a pelleted supplement containing AA (TRT) or no supplement (CON). All horses were offered 1.25% BW/d Timothy hay. All hay and concentrate feedings were split into 2 equal feedings at 0700 and 1430. Horses were housed in stalls with individual drylot turnouts. The glucose-insulin response to feeding (GIRF) was recorded on d28, and horses underwent a combined glucose-insulin tolerance test (CGIT) on d35 in each feeding period. For both tests, horses were catheterized for blood samples and no hay was fed before or during the sampling periods. For GIRF, horses were offered their AM meal and serial (every 30 min) blood samples were obtained from −30 through 360 min. For the CGIT, horses were administered IV dextrose (150mg/kg) and insulin (0.1U/kg) and serial blood samples were taken at −30, 0, 1, 5, 15, 25, 35, 45, 60, 75, 90, 105, and 120 min. Serum was analyzedfor glucose and plasma was analyzed for insulin via colorimetric ELISA (Mercodia). Additionally, serum samples were collected via venipuncture every 2 wk, 2 h post AM meal, and analyzed for glucagon-like protein 1 (GLP-1) via an equine specific ELISA (MyBioSource). Data were analyzed via ANOVA using the MIXED procedure (SAS 9.4). Horses in both CON and TRT had similar glucose responses to feeding. No differences were observed in peak glucose response or area under the curve (AUC) for glucose. The insulin response during the GIRF was impacted by treatment with a trend for TRT having a lower insulin level (P = 0.07) and a decreased AUC (P = 0.02) compared with CON. For the CGIT, CON and TRT had similar glucose curves during the test, however there was a trend for the AUC for insulin in TRT to be lower compared with CON (P = 0.10). Horses in both the CON and TRT had similar starting levels of GLP-1 at d 0 but with time, GLP-1 levels rose in CON while they stayed lower in TRT over each 42-d feeding period (P < 0.001). In conclusion, feeding horses ActivAge® appears to affect insulin, but not glucose response, in standardized testing. Changes to GLP-1 secretion by enterocytes may be a mechanism behind this phenomenon.