Protein Source and Intake Effects on Diet Digestibility and N Excretion in Horses-A Risk of Environmental N Load of Horses.
Authors: Saastamoinen Markku, Särkijärvi Susanna, Suomala Heli
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary This digestibility trial compared six typical equine diets across six Finnhorses using a Latin square design with four three-week periods, measuring faecal and urine nitrogen excretion alongside nutrient digestibility. The research revealed that forage-only diets (haylage and hay) produced significantly greater faecal and urine volumes than grain and protein-supplemented rations, with total daily nitrogen excretion varying substantially by diet composition: hay-only diets resulted in the lowest total N output (approximately 102–103 g/day), whilst protein-supplemented diets increased urinary nitrogen loss considerably, despite improved crude protein digestibility with soybean meal compared to rapeseed or linseed meals. Critically, horses on forage-alone fed diets excreted more nitrogen in urine relative to faeces, whereas adding quality protein sources shifted excretion patterns and elevated overall environmental nitrogen load—findings that challenge the assumption that higher protein intake universally improves nutrient utilisation. For practitioners, the implications are substantial: precise matching of dietary protein to actual requirements (rather than formulaic over-supplementation based on work level alone) offers a practical pathway to reduce nitrogen pollution from stabled and grazing horses, whilst maintaining adequate digestibility and nutrient delivery through informed feed selection and sourcing strategies.
Read the full abstract on PubMed
Practical Takeaways
- •Feed high-quality protein sources strategically rather than excessive amounts to reduce environmental nitrogen pollution from horse manure—good quality protein diets require lower total N intake while maintaining performance.
- •Consider hay over haylage when seeking to minimize nitrogen excretion and environmental impact, particularly for horses not requiring intensive work.
- •When supplementing forage diets with grain and protein, soybean meal offers superior digestibility compared to rapeseed or linseed meals, potentially improving efficiency and reducing excess N excretion.
Key Findings
- •Haylage-only and hay-only diets had lower DM and OM digestibility compared to supplemented diets, but higher total N excretion through urine and feces combined.
- •Soybean meal supplementation resulted in better DM, OM, and CP digestibility compared to rapeseed meal and linseed meal supplements.
- •Horses excreted more nitrogen via urine than feces, with urine N excretion increasing when forage protein content increased or protein supplements were added.
- •Hay-only diet resulted in the lowest total N excretion (approximately 102.8 g N/day combined fecal and urinary) compared to haylage and protein-supplemented diets.