Author(s): VASSEUR, M., GRIMM, P.2, JULLIAND, S.2, LANGEVIN, N.3, LEPERS, R.1, Institution: INSERM U1093 CAPS AND LABTOFIELD, Country: FRANCE, Abstract-ID: 2464

INTRODUCTION:
Intake of high-starch diets is a strategy for equine athletes to support energetic demand and accelerate muscle glycogen repletion after exercise. However, this strategy induces a shift in gut microbiota composition and acidosis, reducing fiber (cellulose, hemicellulose) digestion, short-chain fatty acids (SCFA) production and absorption. The predominant SCFA, acetate, is an energy substrate for muscles lowering glucose mobilization and inducing less acid production than glucose. We recently demonstrated on equine athletes that fibrolytic efficiency of gut microbiota was associated with improved aerobic capacities. The aim of the present study was to test the hypothesis that replacing a high-starch diet (HS) with a high-fiber diet (HF) would benefit fibrolytic activity of equine gut microbiota and subsequently exercise performance.
METHODS:
French Trotters regularly trained (n=21, 2.0±0.1yrs, 447±33kg) fed HS diet (starch: 1495g/day, neutral detergent fibers (NDF): 5151g/day) were included in a longitudinal test. An in vitro fermentation test was performed from fresh fecal samples during 48h to assess the fibrolytic capacity of the fecal microbiota (fibers disappearance and gas production). SCFA concentration and pH were measured in the feces. Maximal oxygen uptake (VO2peak) was determined with an incremental discontinuous test until maximal aerobic speed. Blood samples were taken at rest, immediately after the test, and after 20 minutes of recovery to measure acetate, glucose, lactate, and non-esterified fatty acids concentrations. After basal measurements, 10 horses were fed an isocaloric and isoprotein HF diet (starch: 732g/day, NDF: 5789g/day) for 4 weeks, and the 11 others remained on the HS diet. Measurements were repeated after the 4 weeks. ANCOVA analysis, with basal values as covariate and Tukey post-hoc adjustment was performed to evaluate the impact of diet on each parameter.
RESULTS:
Higher fecal pH was observed in HF (p<0.001), probably due to differences in SCFA concentration (HS: 87.7 mmol/L, HF: 65.8 mmol/L, p=0.005). In parallel, acetate proportion was higher in HF (p=0.01), while propionate proportion was lower (p<0.001). In vitro parameters did not vary between groups nor did blood metabolites (p>0.2). VO2peak (HS: 114 ml/min/kg, HF: 109 ml/min/kg, p=0.5) and maximal speed (HS: 12.2 m/s, HF: 12.5 m/s, p=0.2) did not differ between groups.
CONCLUSION:
These results confirm that replacing HS diet with a HF diet reduces gut acidosis. SCFA absorption was probably greater in HF diet, as a lower fecal concentration was observed, although this was not confirmed by blood parameters. The alteration in fecal SCFA proportions suggests a shift toward an improvement in fibrolytic activity, even if fibrolytic efficiency measured in vitro was not modified by the diet as it was assumed. This could explain why respiratory parameters and aerobic performance were not significantly affected by the diet. A greater contrast between diets seems necessary to alter performance.