The effect of replacing nonstructural carbohydrates with soybean oil on the digestibility of fibre in trotting horses.
Authors: Jansen W L, van der Kuilen J, Geelen S N, Beynen A C
Journal: Equine veterinary journal
Summary
# Editorial Summary Replacing structural carbohydrates with fat in equine concentrates compromises fibre digestibility, according to research comparing high-oil and high-starch feeding regimens in trotting horses. Six mature competition horses consumed either a control diet (corn starch and glucose-based) or a test diet where soybean oil provided 37% of net energy, with both diets balanced for total energy; the high-fat diet significantly reduced the apparent digestibility of crude fibre, neutral detergent fibre and acid detergent fibre by 8.0%, 6.2% and 8.3 percentage points respectively. The mechanism appears to involve excessive fat reaching the large intestine, where it suppresses fermentation by cellulolytic bacteria critical for fibre breakdown. This fat–fibre interaction has meaningful implications for practitioners: feeding tables typically overestimate the energy yield from forage when combined with high-oil supplements, potentially leading to miscalculation of ration energy density and unintended dietary imbalances. Whilst high-fat feeding offers advantages for reducing starch-related issues in performance horses, formulators and nutritionists should account for the depressed fibre utilisation when predicting actual energy delivery and adjusting forage inclusion rates accordingly.
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Practical Takeaways
- •High-fat concentrate diets (soybean oil) significantly impair fibre digestion in trotting horses despite isoenergetic formulation with starch-based concentrates
- •Energy tables may overestimate actual energy availability from hay and forage when combined with high-fat concentrates due to reduced fibre digestibility
- •Consider the fat-fibre interaction when formulating performance horse diets; high-fat feeding may require adjustment of forage quality or quantity expectations
Key Findings
- •Replacing nonstructural carbohydrates with soybean oil reduced crude fibre digestibility by 8.0 percentage units (P = 0.007)
- •Neutral detergent fibre digestibility decreased by 6.2 percentage units (P = 0.022) with high-fat diet
- •Acid detergent fibre digestibility decreased by 8.3 percentage units (P = 0.0005) with high-fat diet
- •High dietary fat intake may suppress cellulolytic bacterial fermentation in the equine large intestine, reducing overall fibre utilisation