Effect of Hay Steaming on the Estimated Precaecal Digestibility of Crude Protein and Selected Amino Acids in Horses.
Authors: Pisch Caroline, Wensch-Dorendorf Monika, Schwarzenbolz Uwe, Henle Thomas, Greef Jörg Michael, Zeyner Annette
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Steaming hay is widely recommended for horses with respiratory disease because it effectively reduces dust, mould spores and airborne bacteria, but its impact on nutrient availability has remained poorly characterised. Researchers analysed six batches of hay from central Germany, comparing native and steamed samples for crude protein (CP) content, amino acid profiles, and heat-induced protein damage markers (Maillard reaction products including furosine and carboxymethyllysine). Whilst steaming did not alter total CP concentration, it significantly reduced protein digestibility: precaecal crude protein digestibility fell from 56% to 35%, with concerning losses in essential amino acids including lysine (>50% reduction), methionine plus cysteine (45% reduction) and threonine (41% reduction). The damage occurred through heat-induced protein modification, evidenced by a 67% increase in furosine and 120% increase in carboxymethyllysine in steamed samples. For practitioners managing horses with equine asthma or dust-related airway disease, this finding underscores the necessity of strategic dietary reformulation—increased crude protein intake and careful amino acid balancing become essential when steamed hay forms the primary forage source, as the reduced digestibility cannot be overlooked despite the genuine respiratory health benefits steaming provides.
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Practical Takeaways
- •Steamed hay remains beneficial for horses with respiratory disease as it reduces allergens and microorganisms, but diets must be supplemented with additional protein and amino acids to compensate for the 35-50% reduction in digestible nutrients
- •Monitor horses on steamed hay for protein status; consider adding high-quality protein sources or amino acid supplements, particularly lysine, methionine, and cysteine
- •While steaming solves respiratory problems, it creates a nutritional trade-off—ensure dietary balancing is prioritized alongside allergen reduction strategies
Key Findings
- •Steaming hay increased neutral detergent insoluble crude protein by 57% and pepsin insoluble crude protein by 15%, indicating heat-induced protein damage
- •Precaecal digestibility of crude protein decreased from 56% to 35% following steaming, with precaecal digestible crude protein falling from 37.9 to 22.5 g/kg DM
- •Maillard reaction products increased substantially (furosine +67%, carboxymethyllysine +120%), particularly affecting lysine availability
- •Essential amino acids were significantly reduced post-steaming: methionine plus cysteine decreased 45%, threonine 41%, and lysine more than 50%