Abstract
A potential strategy to limit ammonia (NH3) emissions from feedlots is the feeding of supplemental clinoptilolite (CLN), which has a high affinity for ammonium (NH4+-N). The particle size of CLN could influence its efficacy in binding NH4+-N in the rumen and in manure. Therefore, our objective was to determine the effects of feeding CLN (2.5% of diet DM) of two different particle sizes (30 and 400 µm) on ruminal fermentation characteristics, apparent total-tract nutrient digestibility, the route of N excretion, manure N profile and NH3-N emissions. We were also interested in determining the effectiveness of reducing NH3-N emissions between feeding CLN and the application onto manure surface. Six beef heifers were used in a repeated 3 × 3 Latin square design with 21 d periods. Dietary treatments were: 1) finishing ration with no supplement (CON), 2) CON + 30-µm CLN (CL-30), and 3) CON + 400-µm CLN (CL-400). Intake was measured daily. Ruminal fluid was collected on d 19 for NH3-N analysis and blood was collected 3 h post-feeding on d 21 for PUN analysis. Indwelling pH loggers were used to measure ruminal pH (d 15 to 21) and grab fecal and spot urine samples were collected from d 19 to 21 to determine total-tract nutrient digestibility and later emission analysis. To determine NH3 emissions, six rectangular vented, non-steady state, closed chambers interfaced with a Fourier Transform Infrared Spectroscopy analyzer were used. Soil was added to chambers to a depth of 10 cm before addition of manure and incubation over a 7-d period. Data was analyzed using SAS. Supplementing CLN had no effect (P ≤ 0.86) on rumen pH, serum metabolites or minerals, SCFA production, or nutrient intake. Apparent total tract CP digestibility was lower (P = 0.03) for CON heifers than CL-30 and CL-400 heifers. Ruminal NH3-N (mg/dL) was lower (P = 0.04) for heifers fed supplemental CL-30 than CON heifers; however, there was no difference between the CON and CL-400 treatments. There was no diet effect (P ≥ 0.82) on urinary total nitrogen (N) excretion. Urine urea-N (% of total urine N) was lower (P = 0.01) for CL-30 than CON and CL-400 heifers. Urine urea-N (g/d) tended to be lower (P = 0.07) for CL-30 than CON and CL-400 heifers. However, urinary NH3-N excretion (g/kg and g/d) was greater (P ≤ 0.04) for CL-400 than CON and CL-30 heifers. Fecal DM excretion, tended to be greater (P = 0.07) for CL-30 than CON and CL-400 heifers. There was no diet effect (P = 0.46) on fecal NH3-N concentration. Fecal carbon content (% DM) was lower (P < 0.01) for CL-30 than CON and CL-400 heifers. Remaining media pH and NHx-N concentration (mg/L) were lower (P = 0.01) for the soil control compared to the other treatments. Percent N also tended (P = 0.08) to be lower for the control soil than the CON, CL-30, CL-400, or the post application of zeolite (PAZ30 and PAZ400) treatments. Average daily NH3-N fluxes were lower (P < 0.01) for the first 24 h for heifers supplemented with CL-400 than all other treatments. For 48 to 168 h, daily NH3-N fluxes were lower (P ≤ 0.02) for CL-400 when compared to the CON, CL-30, and PAZ30; however, did not differ between CL-400 and PAZ400. Supplemental CLN had no effect (P ≤ 0.90) on N2O-N and CO2-N daily fluxes. Estimated cumulative NH3-N emissions were lower (P < 0.01) for CL-400 heifers than CON, CL-30, PAZ-30, and PAZ-400 treatments for 24 h measurement period. Estimated cumulative NH3-N fluxes for 48 to 168 h were lower (P < 0.01) for heifers supplemented with CL-400 than the CON, CL-30, and PAZ-30; however, no differences were observed between CL-400 and PAZ-400 treatments. Estimated cumulative N2O and CO2 emissions did not differ across treatments. Overall, feeding CL-30 reduced ruminal NH3-N concentrations and UUN excretion, however, it did not lead to a decrease in cumulative NH3-N emissions. Further, although supplementing heifers with CL-400 did not decrease ruminal NH3-N and PUN concentrations, and UUN excretion, it did reduce cumulative NH3-N emissions. Fed CLN also had a greater impact on the reduction of manure NH3-N emission when compared to the surface application. Therefore, beef producers could supplement CLN with a particle size of 400 µm to reduce feedlot NH3-N emissions, which could increase the environmental sustainability of the beef industry.