Journal Article

Characterizing ammonia emissions from horses fed different crude protein concentrations

Li, H., Weir, J., Macon, E., Warren, L. K., Wickens, C.

2017

Overview

ABSTRACT Evaluating impact of animal agriculture on air quality has been the focus of recent research. Ammonia (NH3) volatilization occurs when undigested protein in feces and urea in urine is broken down by bacteria and enzymes. Information regarding NH3 emission from equine facilities is limited, and effects of CP intake on NH3 emissions have not been investigated. Nine mature geldings were used in a 3 × 3 replicated Latin square design study to determine effects of dietary CP on potential NH3 losses from feces and urine. We hypothesized feeding horses above the CP requirement would result in an increase in NH3 emissions from urine and feces and different bedding materials would affect NH3 emissions from urine. Diets were formulated using different ratios of bahiagrass (Paspalum notatum) and Tifton-85 bermudagrass (Cynodon dactylon) hays, and a commercial vitamin mineral supplement to provide 3 different CP concentrations and labeled in relation to each other: LOW-CP, MED-CP, and HIGH-CP (10.6%, 11.5%, and 12%, respectively). Each study period consisted of an 11-d diet adaptation phase, followed by a 3-d total collection of urine and feces. To determine total nitrogen (TN) and urea-N concentrations, samples were pooled by period (n = 9). For in vitro determination of NH3 concentrations, urine and fecal samples were pooled within period by diet (n = 3) and mixed with either wheat straw or wood shavings. Ammonia emission of these samples was measured using a vessel system with an airflow rate (2.5 L/min) at 20°C over a 7-d period. Concentration of NH3 in each vessel was measured using a photoacoustic multigas analyzer. Temperature, airflow rate, and NH3 concentration in each vessel were used to calculate NH3 emission rate (ER). Data were analyzed using a mixed model ANOVA with repeated measures. Urinary TN and urea-N excretion increased as CP intake increased (P < 0.0001). Vessel urinary NH3 concentrations were not different across diets (P = 0.1225), ranging from 55.48 ppm (LOW-CP) to 101.14 ppm (HIGH-CP); however, they differed between bedding types (P < 0.0001), with straw higher than shavings (97 vs. 73.5 ppm, respectively). Cumulative urinary NH3 ER tended to be different across diets (P = 0.0550) ranging from 5.87 g/m2 to 9.97 g/m2 and bedding types (P = 0.0129), with straw being higher than shavings (11.1 vs. 6.9 g/m2, respectively). Overfeeding CP to horses can lead to increased urinary TN and urea-N excretion, which could lead to greater of NH3 in the atmosphere.

• Publisher: Oxford University Press
• Subject: Ammonia - metabolism / Animal Feed / Animals / Diet - veterinary / Dietary Proteins - administration & dosage / Feces - chemistry / Horses - metabolism / Male / Nitrogen - analysis / Nitrogen - metabolism / Paspalum / Temperature / Triticum / Urea - analysis / Urea - metabolism / Urine - chemistry