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

Overview

• This study investigates how two different equine diets— a forage-based diet versus a complete pelleted feed—affect the physical characteristics of horse feces and how well fiber is digested in healthy adult horses.
• The research aims to understand diet-driven changes in fecal properties that may be linked to the risk of colic, a common and serious digestive disorder in horses.

Background and Rationale

• Colic, or abdominal pain in horses, is a major health concern with diet being a key risk factor.
• Previous research on how diet affects fecal characteristics and fiber digestibility is limited, even though these factors are related to gastrointestinal health.
• Fecal characteristics often change in horses with colic, hence understanding normal dietary effects is important.

Study Design and Subjects

• A prospective cross-over study design was used, allowing each horse to receive both diets with a washout period.
• Twenty healthy adult horses at Texas Tech University’s School of Veterinary Medicine participated.
• Two dietary treatments were tested:
  • Forage-based diet: coastal Bermudagrass hay offered at 2% of body weight with a complete pelleted feed supplement at 0.7% of body weight, with hay available ad libitum during adaptation.
  • Complete pelleted diet: the same pelleted feed offered at 1.35% of body weight without additional hay.
• The study included a 3-day transition period followed by a 10-day dietary adaptation phase before fecal sampling.

Methods and Measurements

• Rectal grab fecal samples were collected twice daily for four days during each diet period.
• Samples were dried for 96 hours at 55°C to determine dry matter content.
• Fecal particle size was analyzed using sieving at different sizes (including 1.70 mm, 2.36 mm, 180 μm).
• Fiber fractions were measured:
  • Neutral detergent fiber (NDF)
  • Acid detergent fiber (ADF)
  • Lignin (a component of fiber)
  • Hemicellulose (HEM)
• Fecal gross energy (GE) and ash content were assessed.
• Apparent total tract digestibility of fiber fractions was calculated based on intake and fecal output.
• Statistical analyses included two-way ANOVA and GLIMMIX in SAS, accounting for treatment effects and random effects of period and animal.
• A significance threshold of P < 0.05 was used.

Key Findings

• Fecal Particle Size: Horses fed the complete pelleted diet had larger mean fecal particles retained in multiple sieve sizes compared to the forage-based diet group (significant differences at 1.70 mm, 2.36 mm, 180 μm, and collection pan; P ≤ 0.02).
• Fiber Profile in Feces:
  • The forage-based diet resulted in higher neutral detergent fiber (NDF) and fecal gross energy (GE) levels (P < 0.01).
  • Feces from horses on the pelleted feed had higher ash content (P < 0.01) and acid detergent fiber (ADF) (P = 0.04).
  • There was a trend (P = 0.08) toward increased lignin in feces of pelleted diet horses.
• Intake and Digestibility: Horses on the forage-based diet plus supplementation showed greater intake of dry matter, organic matter, fiber fractions (NDF, ADF, HEM), gross energy, and digestible energy.
• They also had increased fecal output of organic matter and hemicellulose, indicating more fiber passing through.
• Apparent total tract digestibility for dry matter and fiber fractions (ADF, NDF, HEM) was higher in the forage-based diet group (P ≤ 0.04), indicating better fiber digestion.

Interpretation and Implications

• Diet composition substantially influences fecal physical characteristics such as particle size and fiber composition.
• The forage-based diet promoted higher intake, improved fiber digestibility, and altered fecal fiber profiles compared to the complete pelleted diet.
• Larger fecal particle sizes with pelleted feed suggest less effective fiber breakdown or differences in mastication and fermentation.
• Differences in fiber fractions like NDF, ADF, and lignin relate to how fiber is processed in the digestive tract, which can impact gut motility and microbial health.
• These fecal characteristics and digestibility differences may help explain how diet influences colic risk since fecal alterations are often seen in colic cases.
• Understanding the effects of common horse diets on fecal traits can guide feeding practices to maintain gastrointestinal health and reduce colic incidence.

Summary

• This study provides important insight into how different diets affect fecal traits and digestion of fiber in horses.
• Forage-based diets lead to smaller fecal particles, higher fiber digestibility, and different fecal fiber profiles compared to complete pelleted feeds.
• These changes are relevant for nutritionists and veterinarians aiming to optimize horse diet formulations to protect against colic.