The Effect of Diet Composition on the Digestibility and Fecal Excretion of Phosphorus in Horses: A Potential Risk of P Leaching?
Authors: Saastamoinen Markku, Särkijärvi Susanna, Valtonen Elisa
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Phosphorus excretion through equine faeces represents a significant environmental concern, particularly as horse populations expand and paddock-based management concentrates nutrient outputs in localised areas. Finnish researchers investigated whether dietary composition could influence phosphorus digestibility and faecal excretion by feeding six horses six forage-based diets (ranging from hay-only to hay plus varying concentrate levels) and conducting total faecal collection over a controlled Latin Square design. Phosphorus digestibility remained remarkably low across all diets (2.7–11.1%), though concentrate supplementation marginally improved digestibility alongside crude protein and organic matter; horses excreted approximately 20.9 g phosphorus daily (7.6 kg annually), with hay-only diets producing the smallest excretion (20.0 g/day). Critically, roughly 88% of faecal phosphorus existed in soluble form—highly vulnerable to runoff and leaching—indicating that equine dung poses environmental risks comparable to other livestock manures if not carefully managed. For practitioners, the findings suggest that inorganic phosphorus supplementation should be scrutinised in mature horses undertaking light work, as current feeding practices often exceed retention requirements and unnecessarily elevate environmental burden through faecal losses; this has implications for pasture management protocols, concentrate formulation reviews, and strategic manure handling on equestrian facilities.
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Practical Takeaways
- •Minimize supplemental inorganic phosphorus in mature horses doing light work to reduce environmental contamination risk from manure—the current dietary practices may be contributing unnecessarily to water pollution
- •Recognize that horse manure management is as critical as other livestock for environmental protection; the high soluble phosphorus content (88%) means proper storage and application practices are essential to prevent water leaching
- •Consider hay-only or low-concentrate diets where workload allows, as these reduce daily fecal phosphorus excretion by approximately 1 gram per day compared to concentrate-supplemented feeding
Key Findings
- •Phosphorus digestibility varied from 2.7 to 11.1% across forage-based diets, with concentrate supplementation slightly improving digestibility (p = 0.024)
- •Horses excreted an average of 20.9 ± 1.4 g/day of phosphorus in feces, equivalent to 7.6 kg per year
- •Approximately 88% of fecal phosphorus was in soluble form, making it vulnerable to runoff losses and leaching into water systems
- •Hay-only diet resulted in the lowest fecal phosphorus excretion (20.0 g/day, p = 0.021) compared to concentrate-supplemented diets