Feed protein partitioning impacts horse fecal nitrogen profiles: A retrospective pilot study.

Research Overview

• This study examined how different types and amounts of protein in horse diets influence the nitrogen content and form in their feces, which is important for manure management and fertilizer potential.

Background and Objective

• Excess dietary crude protein (CP) in horses leads to greater nitrogen excretion via urine and feces.
• There is limited data on how protein fractions in the diet affect nitrogen forms in equine feces.
• The study aimed to determine if daily intakes of crude protein and a specific fraction known as neutral detergent soluble crude protein (NDSCP) affect nitrogen profiles in horse feces.

Methods

• Subjects: Three Quarter Horse geldings (male horses) used in a controlled feeding trial.
• Feeding Protocol:
  • First 14 days (GRASS phase): Horses fed coastal Bermudagrass hay at 15 g dry matter (DM) per kg body weight (BW) per day.
  • Next 14 days (MIXED phase): Horses fed a 50:50 mixture of coastal Bermudagrass and alfalfa hay at the same DM intake.
  • Additionally, horses received 0.5 kg DM/day of a concentrate containing 158 g CP/kg DM throughout the study.
• Sample Collection and Analysis:
  • Fresh fecal samples collected on day 14 of each diet phase.
  • Samples were frozen and later analyzed for nitrogen and other components by Dairy One lab.
• Statistical Analysis:
  • Compared results from the two diet phases using paired t-tests.
  • Used analysis of covariance (ANCOVA) with crude protein intake as a covariate to assess effects on fecal nitrogen profiles.

Key Findings

• The MIXED diet (coastal Bermudagrass + alfalfa) provided significantly more NDSCP per kg body weight than the GRASS-only diet.
• Fecal Ammonia:
  • Tended to be higher in feces from horses on the MIXED diet compared to the GRASS diet (approaching significance).
  • ANCOVA results confirmed significantly greater fecal ammonia with the MIXED diet when controlling for CP intake.
• Fecal Carbon:
  • Lower concentration in MIXED diet feces compared to GRASS diet feces.
• Total Fecal Nitrogen and Organic Nitrogen:
  • Both were lower in horses fed the MIXED diet compared to the GRASS diet (significant differences found via ANCOVA).

Interpretation and Implications

• Diets higher in NDSCP alter the form of nitrogen excreted, increasing fecal ammonia concentration.
• Increases in fecal ammonia suggest that protein fractionation in the diet influences nitrogen partitioning during digestion and excretion.
• Understanding these shifts in nitrogen profiles is important for horse manure management and optimizing its use as fertilizer since ammonia can volatilize or affect soil nitrogen availability differently than organic nitrogen.
• The study highlights that not just total dietary protein, but also the type and solubility of protein fractions, are important factors affecting nitrogen excretion patterns.

Study Limitations and Future Directions

• This was a small-scale, pilot study with only three horses, limiting generalizability.
• Samples were single-hand grab fecal samples, which might not capture total daily nitrogen excretion variability.
• Future studies with more animals and comprehensive sampling over time could confirm these findings.
• Further research could explore how dietary protein fractionation affects nitrogen release dynamics and nitrogen cycling when manure is applied as fertilizer.