Effect of Donor Diet on In Vitro Digestibility of Forages by Fecal Inoculate.
Authors: Godwin Taylor, Webb Gary, Lancaster Philip
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Effect of Donor Diet on In Vitro Digestibility of Forages by Fecal Inoculate When using equine fecal samples as microbial inoculants for laboratory forage digestibility testing, the donor horse's diet fundamentally shapes which microbes are present and their metabolic capabilities. Taylor and colleagues investigated this variable using six Quarter Horses in a crossover design, collecting faecal samples after 22 days on either high-grain or high-forage diets, then using these samples to ferment four test forages in vitro whilst measuring dry matter digestibility (DMD), neutral detergent fibre digestibility (NDFD), and acid detergent fibre digestibility (ADFD). Fecal inoculants from grain-fed donors yielded significantly higher NDFD values for forages high in NDF and low in crude protein (P = 0.04 and 0.03 respectively), suggesting the grain-adapted microbiome possessed enhanced fibre-degrading capacity under these specific substrate conditions—a counterintuitive finding worth exploring further. Individual horse variation also significantly influenced both DMD and NDFD results, indicating that standardising donor selection protocols is as important as controlling their diet. For practitioners relying on in vitro forage analysis, these findings underscore that donor diet history should be documented and controlled, particularly when comparing digestibility across different forage types or making nutritional recommendations based on laboratory results.
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Practical Takeaways
- •When selecting fecal donors for in vitro forage digestibility testing, consider the donor's current diet—grain-fed horses may provide better microbial communities for evaluating high-fiber, low-protein forage digestion
- •Results suggest standardizing donor diet protocols in laboratory digestibility studies could improve consistency and comparability of in vitro testing results
- •For nutritional assessment of forages, match donor horse diet to the target feeding scenario when possible to obtain most relevant digestibility predictions
Key Findings
- •Fecal samples from horses fed grain diet produced higher neutral detergent fiber digestibility (NDFD) of forages with high NDF and low crude protein (P = 0.04 and 0.03)
- •Significant horse effect observed on dry matter digestibility (DMD) and NDFD (P ≤ 0.05)
- •Donor diet influences hindgut microbiome's ability to digest neutral detergent fiber in vitro
- •Equine fecal inoculates provide comparable results to cecal fluid for in vitro dry matter digestibility procedures