The effects of diet on the physical characteristics of feces and fiber digestibility in healthy horses

Abstract

Diet is a known risk factor for colic, but few studies have explored how diet affects fecal characteristics which are often altered in horses with colic. This prospective cross-over study evaluated the effects of two common equine diets on fecal characteristics and fiber digestibility in healthy adult horses. We hypothesized that horses offered a complete pelleted diet would exhibit increased fecal dry matter (DM) and decreased fecal particle size compared to those offered a forage-based diet. Twenty horses at Texas Tech University School of Veterinary Medicine served as subjects in the study. Horses were offered two diets following a three-day transition and ten-day dietary adaptation period, during which hay was provided ad libitum for horses in the hay plus supplementation group. During the study periods, diets consisted of either: coastal Bermudagrass hay offered at 2% body weight (BW) with a commercially available complete pelleted feed at 0.7% BW, or the same complete pelleted feed offered at 1.35% of BW. Rectal grab samples were collected twice daily for four days, dried for 96 hours at 55 °C, and analyzed for fiber content and particle size. Data were analyzed using two-way ANOVA in R Studio and the GLIMMIX procedure of SAS, with treatment as a fixed effect and period and animal as random effects. Significance was set at P < 0.05. Horses offered the complete pelleted feed had greater amounts of mean fecal particles retained in sieve 1.70 mm (P = 0.02), 2.36 mm, 180 µm, and the collection pan (P < 0.01) compared to horses offered the forage-based diet. Horses on the forage-based diet had elevated neutral detergent fiber (NDF) and fecal gross energy (GE) compared to those on the complete pelleted feed (P < 0.01), whereas horses offered the complete pelleted feed had greater ash (P < 0.01) and acid detergent fiber (ADF; P = 0.04) in fecal matter. There was a tendency for higher lignin in horses offered the complete pelleted feed (P = 0.08). Horses consuming hay with supplementation diet showed greater intake (including DM, organic matter (OM), NDF, ADF, hemicellulose (HEM), GE, and digestible energy (DE)), fecal output OM and HEM, along with a greater apparent total tract digestibility (DM, ADF, NDF (P < 0.01), and HEM (P = 0.04)). These findings demonstrate that diet influences fecal particle size, fiber fraction, and digestibility in healthy horses, factors that may have implications for gastrointestinal health and colic risk.