Effects of a forage-based versus forage-replacement diet on fecal particle size, dry matter, nondigestible fiber content, and ultrasonic measurement of large colon motility in healthy horses

Abstract

Diet is a risk factor for colic, but few studies have characterized the effects of diet on fecal characteristics or gastrointestinal motility, features affected by colic. This prospective crossover study determined how 2 standard equine diets affected fecal particle size (FPS), dry matter (DM), nondigestible fiber content, and ultrasonographic measurements of large colon motility. The authors hypothesized that horses fed a forage-based diet (FBD) would have increased values in the above variables compared with those fed a complete forage-replacement diet (CFR). Twenty horses (19 QH and 1 TB; median age 16.7, range 5–26; 15 mares and 5 geldings) at Texas Tech University School of Veterinary Medicine served as subjects, 16 of which completed the study. Horses were fed 2 diets for mature horses at maintenance: coastal Bermudagrass (Cynodon dactylon) hay fed at 2% body weight (BW) with a commercially available concentrate-supplemented at 0.5% BW (FBD) and a commercially available pelleted, complete forage-replacement diet (CFR) fed at 1.35% of BW per manufacturer. After 3 d of dietary transition, followed by 13 d of acclimatization, fecal grab samples (800 g) were collected on the last 4 d twice daily via rectal palpation at 12-h intervals with times advancing 3 h each day to account for diurnal variation. Fecal DM, acid detergent fiber (ADF), neutral detergent fiber (NDF), and lignin content were evaluated. The FPS, the size distribution of solid particles in feces, was evaluated using a Gilson Sieve Shaker with screen sizes 4.75 mm, 2.36 mm, 1.70 mm, 1.18 mm, 1.00 µm, 180 µm, and a collection pan. Large colon motility was assessed with percutaneous ultrasound 3 d before fecal collection in 4 randomly selected horses daily (n = 12). Contractions at the sternal and pelvic flexures and cecum were conducted twice daily, 2 h after feeding. Statistical analysis was performed with R Studio using a Shapiro-Wilk test, Levene's test, and classic 2-way ANOVA. Results were considered significant at P < 0.05. Diet had no main effect on FPS. Fecal DM was increased in horses fed CFR (P < 0.0001). Horses fed CFR had an increased concentration of ADF (P = 0.000) and lignin (P = 0.01), but decreased NDF (P < 0.0001) compared with those fed the FBD. Horses fed the CFR had increased contractions at the sternal flexure compared with horses fed FBD (P < 0.0001). This study found that diet impacts the physical characteristics of feces and gastrointestinal motility of healthy horses, which may impact equine colic.