Characterizing ammonia emissions from horses fed different crude protein concentrations

Area of Science:

• Animal Science
• Environmental Science
• Agricultural Science

Background:

• Ammonia (NH) volatilization from animal agriculture impacts air quality.
• Limited data exists on NH emissions from equine facilities.
• The effect of dietary crude protein (CP) on equine NH emissions is not well understood.

Purpose of the Study:

• To investigate the impact of varying dietary crude protein (CP) concentrations on potential NH losses from equine feces and urine.
• To determine if different bedding materials influence NH emissions from equine urine.

Main Methods:

• Nine geldings were fed diets with LOW-CP, MED-CP, and HIGH-CP concentrations (10.6%, 11.5%, 12%) in a replicated Latin square design.
• Urine and fecal samples were collected, pooled, and mixed with wheat straw or wood shavings for in vitro NH emission analysis.
• Ammonia emission rate (ER) was measured over 7 days using a vessel system and photoacoustic multigas analyzer.

Main Results:

• Urinary total nitrogen (TN) and urea-N excretion increased significantly with higher CP intake (P < 0.0001).
• Urinary NH concentrations did not differ significantly across diets (P = 0.1225) but were higher with straw bedding (97 ppm) vs. shavings (73.5 ppm) (P < 0.0001).
• Cumulative urinary NH ER tended to be higher across diets (P = 0.0550) and was significantly higher with straw (11.1 g/m) vs. shavings (6.9 g/m) (P = 0.0129).

Conclusions:

• Overfeeding CP in equine diets increases urinary nitrogen excretion.
• This increased nitrogen excretion has the potential to elevate atmospheric NH emissions.
• Bedding type, particularly straw, plays a significant role in NH volatilization from equine urine, independent of dietary CP levels.