EFFECTS OF DIETARY ENERGY SOURCE AND STRESS ON EQUINE INTESTINAL PERMEABILITY AND INFLAMMATION

Dietary concentrate is often provided to exercising horses to meet energy requirements. However, both high-starch and high-fat diets may be associated with alterations in intestinal barrier function. To investigate this, 32 mature horses were fed one of four isocaloric dietary concentrate treatments (n = 8 per treatment): 1) a concentrate with cracked corn providing 4 g starch⋅kg BW-1⋅d-1 and 0.2 g fat⋅kg BW-1⋅d-1 (CC), 2) a concentrate with puffed corn providing 4 g starch⋅kg BW-1⋅d-1 and 0.2 g fat⋅kg BW-1⋅d-1 (PC), 3) a concentrate with puffed corn and soybean oil providing 2 g starch⋅kg BW-1⋅d-1 and 0.6 g fat⋅kg BW-1⋅d-1 (moderate-fat; MF), or 4) a concentrate with puffed corn and soybean oil providing 1 g starch⋅kg BW-1⋅d-1 and 1.2 g fat⋅kg BW-1⋅d-1 (high-fat; HF). Baseline measurements were taken during week -2 (PRE). Gradual adaptation to treatment diets occurred during weeks -1 and 0. Horses were maintained on the concentrate diets until the end of the study (week 7). Fecal pH was measured PRE and in weeks 3 and 5, and postprandial plasma glucose and insulin kinetics were assessed during week 3. Gut permeability was measured using plasma appearance of three orally-dosed non-metabolizable sugar analogues, mannitol, lactulose, and sucralose. Gut permeability and whole blood inflammatory cytokine mRNA were measured PRE and in weeks 5 and 7, and salivary cortisol was measured during a 12-hour stress test (short transport and individual housing) in week 7. Fecal pH was less (P ≤ 0.04) in horses fed CC and HF compared to those fed PC or MF. Horses fed HF had greater (P = 0.004) plasma sucralose area under the curve (AUC) than horses fed PC. Plasma sucralose AUC was also greater (P ≤ 0.06) for horses fed HF and CC than those fed MF and PC respectively. Horses fed CC had numerically greater plasma sucralose concentrations than those fed PC after 6 hours post-dosing, while those fed HF had numerically greater plasma lactulose concentrations before 6-hours post dosing. Salivary cortisol concentration remained greater than baseline during the stress test but was not influenced by dietary treatment (P = 0.08). During the week 7 stress test, peak concentration and AUC for all markers of gut permeability were increased (P ≤ 0.02) compared to week 5 (no stress), and concentrations of all markers were numerically greater before 6 hours post-dosing in week 7 compared to week 5. Whole blood IL-1β and Il-6 mRNA were increased (P ≤ 0.01) during the week 7 stress test compared to PRE and week 5. Taken together, these results indicate that dietary energy source and stress can impact equine small intestinal and hindgut permeability.