Effects of processing barley on its digestion by horses.
Authors: Vervuert I, Voigt K, Hollands T, Cuddeford D, Coenen M
Journal: The Veterinary record
Summary
# Editorial Summary Vervuert et al. (2008) investigated how three common barley processing methods—rolling, micronising and extrusion—affect starch digestion and fermentation in horses, using glycaemic and insulinaemic responses alongside breath hydrogen and methane as markers of pre-caecal starch digestibility and hindgut fermentation. Four horses received each barley type at 2 g starch/kg bodyweight daily during separate 10-day periods, with blood and breath samples collected following a 12-hour fast and test meal. Extruded barley produced the highest peak glucose and insulin concentrations, followed by micronised barley, whilst rolled barley generated the lowest metabolic response—indicating that processing intensity inversely correlates with starch reaching the caecum. Breath hydrogen peaked within four hours for all diets (rolled: 98.3 ppm, micronised: 59.3 ppm, extruded: 96.1 ppm) with considerable individual variation but no significant differences between groups, though rolled barley showed a non-significant trend towards greater methane production. For practitioners, these findings suggest that whilst processing method substantially influences the glycaemic load—relevant for metabolic horses, gastric ulcer cases and those requiring controlled energy—the degree of hindgut fermentation may be less predictable than anticipated, underlining the importance of monitoring individual responses rather than assuming processing type alone dictates post-caecal starch availability.
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Practical Takeaways
- •Barley processing method significantly affects starch digestibility: extruding barley maximises pre-caecal digestion and glucose/insulin response, while rolling results in more starch reaching the caecum
- •Rolled barley may increase risk of hindgut fermentation and associated problems (colic, laminitis); extruded or micronised barley are preferable for horses requiring processed grain
- •When feeding processed barley, consider individual horse variation in response and monitor for signs of hindgut disturbance, particularly with rolled grain
Key Findings
- •Extruded barley produced the highest peak serum glucose and insulin concentrations, indicating greatest pre-caecal starch digestibility
- •Rolled barley produced the lowest peak serum glucose and insulin concentrations, suggesting poorest pre-caecal starch digestibility
- •Breath hydrogen increased within 4 hours of all barley diets with no significant differences between processing methods (rolled 98.3 ppm, micronised 59.3 ppm, extruded 96.1 ppm)
- •Breath methane concentrations were highly variable with a trend toward higher values after rolled barley, indicating variable post-caecal fermentation patterns