Dietary soyabean oil depresses the apparent digestibility of fibre in trotters when substituted for an iso-energetic amount of corn starch or glucose.
Authors: Jansen W L, Geelen S N J, van der Kuilen J, Beynen A C
Journal: Equine veterinary journal
Summary
# Editorial Summary Previous research suggested that high dietary fat reduces fibre digestibility in horses, yet because fat had been substituted for starch in those trials, it remained unclear whether the effect was truly from fat or partly from removing starch from the diet. Jansen and colleagues addressed this ambiguity by feeding six trotters iso-energetic rations containing soyabean oil (158 g/kg DM), corn starch (337 g/kg DM), or glucose (263 g/kg DM) in a Latin square design, with the glucose treatment serving as a control that would not interfere with caecal and colonic fermentation since it is fully absorbed in the small intestine. Crude fibre digestibility fell substantially with fat supplementation (56.5 ± 7.65%) compared to both starch (70.7 ± 3.06%) and glucose (71.0 ± 1.90%), with similar depression observed for NDF, ADF, and cellulose digestibilities. This work confirms that fat exerts a specific, direct inhibitory effect on fibre fermentation independent of which carbohydrate source is used, meaning that practitioners formulating high-fat diets for performance horses should anticipate a genuine reduction in the digestible energy contributed by forage—a particularly relevant consideration when balancing rations for horses where fibre quality and quantity are critical to both performance and gastrointestinal health.
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Practical Takeaways
- •High-fat diets (like soyabean oil supplementation) reduce the horse's ability to digest fibre by approximately 14 percentage points, which may impact energy efficiency in performance horses relying on forage
- •Using starch or glucose as energy sources does not compromise fibre digestion the way fat does, making them better alternatives if maintaining fibre digestibility is a priority
- •Veterinarians and nutritionists should consider the trade-off between added fat for calories and reduced fibre digestion when formulating high-energy diets for horses
Key Findings
- •Soyabean oil (158 g/kg DM) significantly depressed apparent crude fibre digestibility to 56.5% compared to 70.7% with corn starch and 71.0% with glucose
- •Corn starch and glucose produced similar fibre digestibility rates, indicating starch does not inhibit fibre digestion when substituted for fat
- •Fat has a specific inhibitory effect on fibre utilisation that reduces energy availability from dietary fibre in horses
- •The depressed digestibility with fat feeding extended to neutral detergent fibre, acid detergent fibre, and cellulose