Author ORCID Identifier

https://orcid.org/0009-0007-0463-6451

Date Available

5-1-2025

Year of Publication

2025

Document Type

Master's Thesis

Degree Name

Master of Science (MS)

College

Agriculture, Food and Environment

Department/School/Program

Animal and Food Sciences

Faculty

KYLE R. MCLEOD

Faculty

DAVID L. HARMON

Abstract

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.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2025.118

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