Fresh and preserved green fodder modify effects of urinary acidifiers on urine pH of horses.
Authors: Goren G, Fritz J, Dillitzer N, Hipp B, Kienzle E
Journal: Journal of animal physiology and animal nutrition
Summary
# Editorial Summary Researchers at the University of Munich investigated whether hay's well-documented ability to stabilise equine urine pH results from its physical structure or chemical composition, using a crossover study design with four ponies fed six different forage types (fresh grass, alfalfa hay, grass cobs, grass silage, straw, and extruded straw) with and without urinary acidifiers. Urinary acidifiers successfully lowered urine pH only in straw-based diets (from 7.8 to 5.2), whilst all diets containing fresh or preserved green plant material maintained urine pH above 7 regardless of acidifier addition; corresponding patterns emerged in blood pH, bicarbonate and base excess measurements. The research suggests that chemical composition rather than physical structure drives this stabilising effect, with chlorophyll and its metabolites proposed as the protective agent—a finding with significant implications for managing horses prone to urinary calculi or those requiring therapeutic acidification. For practitioners using acidifiers therapeutically or preventatively, these results indicate that forage quality and type substantially influence efficacy; reliance on green fodder or quality preserved forages (silage, alfalfa) may limit acidifier effectiveness, whilst straw-dominant rations show greater pH-modifying potential. Further investigation into chlorophyll's mechanisms could enable more targeted dietary strategies for acid-base management in clinical practice.
Read the full abstract on PubMed
Practical Takeaways
- •Include fresh or preserved green forage (grass, alfalfa hay, grass silage) in horses' diets to naturally stabilize urine pH and prevent acidification, particularly important for those prone to urinary calculi or receiving urinary acidifiers
- •Straw-based or low-forage diets combined with acidifying supplements will significantly acidify urine; if urinary acidification is therapeutic goal, ensure adequate green fodder intake is not inadvertently counteracting the treatment
- •Physical processing of forage (extrusion) does not preserve the acid-buffering properties of green plant material; fresh or ensiled green fodder is required for this protective effect
Key Findings
- •Fresh and preserved green fodder (grass, alfalfa hay, grass cobs, grass silage) maintained urine pH above 7.0 even when acidifiers were added, whereas straw-based diets allowed urine pH to decrease to 5.2 ± 0.38 with acidifiers
- •Blood pH, bicarbonate, and base excess were similarly stabilized by green plant material but acidified by straw-based diets with acidifier supplementation
- •Chlorophyll and its metabolites from green plant material are proposed as potential mediators of acid-base stabilization in equine urine
- •Chemical composition rather than physical structure appears critical for pH regulation, as extruded straw did not confer the protective effect of fresh or preserved green fodder