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Nitrous oxide (N2O) is a greenhouse gas with a higher global warming potential than carbon dioxide (CO2) or methane (CH4). The objectives of this research were to quantify enteric N2O emissions from beef cattle and determine effects of dietary nitrate (NO3) concentrations. Experiments consisted of one in vitro incubation trial and 2 live animal (LA) trials. During the in vitro trial, gas was collected from 4 forage-based and 5 corn-based diets. During the LA trials, emissions were monitored from steers in respiration chambers. In LA trial 1, 5 measurements of 256 to 720 min were conducted on a single steer within a 48-h period. In LA trial 2, measurements were conducted on 4 steers in the absence of manure. Highest in vitro N2O production was from diets containing added NO3 or alfalfa. In vitro N2O increased with dietary NO3 concentrations (r2 = 0.99), with little correlation to dietary CP (r2 = 0.17). Added NO3 decreased CH4 emissions. Mean N2O emission rates (±SD) from the LA trials were 6.93 ± 2.99 mg of N2O∙kg−1 of DMI in trial 1 and 2.20 ± 0.10 mg of N2O∙kg−1 of DMI in trial 2. Mean enteric N2O emissions accounted for 0.35% (LA trial 1) and 0.12% (LA trial 2) of CO2 equivalents. Enteric N2O emission rates were 6 to 40 times lower than values cited in earlier publications. Enteric N2O emission rates were also 58 to 108 times lower than manure emissions. Therefore, efforts to reduce greenhouse gas emissions from beef cattle should focus on enteric CH4 and manure N2O as opposed to enteric N2O.

Wet distiller’s grains with solubles (WDGS) are a common by-product feedstuff generated by the grain–ethanol industry, and it is used extensively by the cattle feeding industry. Distillers grains are typically high in protein; however, the protein in WDGS has a low ruminal degradability, and thus may result in a deficiency of RDP in the diet even when dietary CP concentrations are high. Assessment of the RDP needs in diets containing WDGS is needed to aid the cattle feeding industry in managing feed costs and potential environmental issues. To that end, we conducted 2 feeding studies to evaluate the supplemental RDP requirements of beef cattle fed steam-flaked corn-based finishing diets. In Exp. 1, 525 yearling steers (initial body weight = 373 ± 13 kg) received treatments in a 2 × 3 + 1 factorial. Dietary factors included WDGS (15 or 30% of DM) and nonprotein N (NPN; 0, 1.5, or 3.0% of DM) from urea (0, 0.52, and 1.06%). The control diet without WDGS contained 3.0% NPN (1.06% urea) and cottonseed meal. Diets were formulated to have equal crude fat concentrations. Overall gain efficiency among steers fed 15% WDGS was greatest for 1.5% NPN and least for 0% NPN (P = 0.07, quadratic), whereas gain efficiency decreased linearly (P < 0.09) as NPN increased in the 30% WDGS diets. Dressing percent was greater (P < 0.01) for the Control diet than for 15 or 30% WDGS. In Exp. 2, 296 steer calves (initial BW = 344 ± 12 kg) were fed 1 of 4 experimental diets that included a Control diet without WDGS (contained 3% NPN from urea, and cottonseed meal) and 15% WDGS diets with either 1.50, 2.25, or 3.00% NPN (0.52, 0.78, and 1.04% urea, respectively, on a DM basis). Overall gain efficiency on either a live or carcass-adjusted basis was not different among treatments (P > 0.15). Dietary NPN concentration did not influence growth performance (P > 0.21). Increasing dietary WDGS concentration resulted in decreasing (P < 0.05) diet digestibility (determined with an internal marker) and increasing (P < 0.05) N volatilization losses (determined by diet and manure N:P ratio); however, the effects of NPN level on digestibility and N losses were somewhat inconsistent across experiments. Results suggest that optimum performance for cattle fed 15% WDGS occurred when the diet contained between 1.5 and 2.25% NPN. However, no supplemental NPN was needed to support optimum performance in diets containing 30% WDGS.

Animal agriculture is a significant source of ammonia (NH3). Cattle excrete most ingested nitrogen (N); most urinary N is converted to NH3, volatilized and lost to the atmosphere. Open lot dairies on the southern High Plains are a growing industry and face environmental challenges as well as reporting requirements for NH3 emissions. We quantified NH3 emissions from the open lot and wastewater lagoons of a commercial New Mexico dairy during a nine-day summer campaign. The 3500-cow dairy consisted of open lot, manure-surfaced corrals (22.5 ha area). Lactating cows comprised 80% of the herd. A flush system using recycled wastewater intermittently removed manure from feeding alleys to three lagoons (1.8 ha area). Open path lasers measured atmospheric NH3 concentration, sonic anemometers characterized turbulence, and inverse dispersion analysis was used to quantify emissions. Ammonia fluxes (15-min) averaged 56 and 37 μg m−2 s−1 at the open lot and lagoons, respectively. Ammonia emission rate averaged 1061 kg d−1 at the open lot and 59 kg d−1 at the lagoons; 95% of NH3 was emitted from the open lot. The per capita emission rate of NH3 was 304 g cow−1 d−1 from the open lot (41% of N intake) and 17 g cow−1 d−1 from lagoons (2% of N intake). Daily N input at the dairy was 2139 kg d−1, with 43, 36, 19 and 2% of the N partitioned to NH3 emission, manure/lagoons, milk, and cows, respectively.

The increased use of by-products in finishing diets for cattle leads to diets that contain greater concentrations of crude protein (CP) and metabolizable protein (MP) than required. The hypothesis was that excess dietary CP and MP would increase maintenance energy requirements because of the energy costs of removing excess N as urea in urine. To evaluate the potential efficiency lost, two experiments were performed to determine the effects of feeding excess CP and MP to calves fed a finishing diet at 1 × maintenance energy intake (Exp. 1) and at 2 × maintenance intake (Exp. 2). In each experiment, eight crossbred Angus-based steers were assigned to two dietary treatments in a switchback design with three periods. Treatments were steam-flaked corn-based finishing diets with two dietary protein concentrations, 13.8% CP/9.63% MP (CON) or 19.5% CP/14.14% MP (dry matter basis; ECP), containing corn gluten meal to reflect a diet with excess CP and MP from corn by-products. Each period was 27 d in length with a 19-d dietary adaptation period in outdoor individual pens followed by a 4-d sample collection in one of four open circuit respiration chambers, 2-d fast in outdoor pen, and 2-d fast in one of four respiration chambers. Energy metabolism, diet digestibility, carbon (C) and nitrogen (N) balance, oxygen consumption, and carbon dioxide and methane production were measured. At both levels of intake, digestible energy as a proportion of gross energy (GE) tended to be greater (P < 0.06) in ECP than in CON steers. Metabolizable energy (ME) as a proportion of GE tended to be greater (P = 0.08) in the ECP steers than in the CON steers at 2 × maintenance intake. At 1 × and 2 × maintenance intake, urinary N excretion (g/d) was greater (P < 0.01) in the ECP steers than the CON steers. Heat production as a proportion of ME intake at 1 × maintenance tended (P = 0.06) to be greater for CON than for ECP (90.9% vs. 87.0% for CON and ECP, respectively); however, at 2 × maintenance energy intake, it was not different (63.9% vs. 63.8%, respectively). At 1 × maintenance intake, fasting heat production (FHP) was similar (P = 0.45) for both treatments, whereas at 2 × maintenance intake, FHP tended to be greater (P = 0.09) by 6% in ECP than in CON steers. Maintenance energy requirements estimated from linear and quadratic regression of energy retention on ME intake were 4% to 6% greater for ECP than for CON. Results of these studies suggest that feeding excess CP and MP from a protein source that is high in ruminally undegradable protein and low in protein quality will increase maintenance energy requirements of finishing steers.

HighlightsEnteric methane (CH4) from beef cows on pasture was measured over three seasons using three methods.Methods yielded similar results during the summer grazing season but diverged in autumn and winter seasons.Emission averaged 0.34, 0.27, and 0.29 kg CH4 cow-1 during lactation, mid-gestation, and late gestation, respectively.Annualized enteric methane emission rate for a beef cow herd grazing tallgrass prairie was 0.32 kg d-1 cow-1.Abstract. Methane (CH4) is an important greenhouse gas, and about 20% of the carbon dioxide equivalent (CO2e) greenhouse gases emitted by U.S. agriculture are attributed to enteric CH4 produced by grazing beef cattle. Grazing cattle are mobile point sources of methane and present challenges to quantifying the enteric methane emission rate (MER). In this study, we applied three methods to measure herd-scale and individual-animal MER for a herd of beef cows grazing a native tallgrass prairie: a point source method that used forward-mode dispersion analysis and open-path lasers and cow locations, an open chamber breath analysis system (GreenFeed), and an eddy covariance ratio method that used the ratio of CH4 and CO2 mass fluxes. Three campaigns were conducted during the early season (July), late season (October), and dormant season (February). The point source and GreenFeed methods yielded similar MER (±SD) values during the early season campaign: 0.38 ±0.04 and 0.34 ±0.05 kg d-1 cow-1, respectively. However, the MER values from the two methods diverged in subsequent seasons. The GreenFeed MER decreased through the late and dormant seasons to 0.23 ±0.03 and 0.19 ±0.03 kg d-1 cow-1, respectively. In contrast, the point source MER stayed the same during the late season and increased during the dormant season to 0.41 ±0.07 kg d-1 cow-1. The CH4:CO2 ratio method, which was used only during the dormant season, yielded a MER of 0.29 ±0.05 kg d-1 cow-1. The point source and GreenFeed methods measured different MER (integrated herd-scale versus a subset of individual animals) and likely sampled methane emissions at different times during the day. We conclude that the point source method tended to overestimate emissions, and the GreenFeed method tended to underestimate emissions. Enteric methane emissions from beef cows over the three grazing seasons averaged 0.39 and 0.25 kg d-1 cow-1 as measured by the point source and GreenFeed methods, respectively. An annualized enteric MER for a beef cow herd grazing tallgrass prairie was 0.32 kg d-1 cow-1. Quantifying enteric methane emissions from grazing beef cows remains a challenge because of the mobile, often dispersed behavior of grazing cattle and the dynamic interactions of forage quality, dry matter intake, and changing physiological state of cows during the year. Keywords: Beef cows, Enteric methane, Forage quality, Grazing, Tallgrass prairie.

Ammonia (NH 3 ) emission from beef cattle feedyard manure results in losses of nitrogen (N), which may negatively affect air, soil, and water quality. The magnitude and rate of NH 3 volatilization from feedyards partially depends on the amount of urinary urea excreted and dissociation of ammonium (NH 4 + ) into NH 3 following urea hydrolysis. Zeolite clinoptilolite is a naturally occurring, porous aluminosilicate mineral that can sorb and sequester cations within its negatively charged framework structure. Zeolite has been used to mitigate NH 3 losses and improve fertilizer value of compost, sewage sludge, and manure in livestock barns; however, few studies have evaluated its efficacy on open-lot beef cattle feedyards. Zeolite application to pen surfaces could be a practical and cost-effective means of reducing NH 3 losses. Objectives of this study were to (1) characterize NH 4 + sorption by zeolites with differing physicochemical properties and (2) evaluate zeolite effects on rates and cumulative losses of NH 3 following application of artificial urine to feedyard manure. Batch incubation studies with four commercially available zeolites revealed that NH 4 + sorption by zeolite was rapid (1 to 2 h) with large differences in sorption potential largely related to zeolite pH. Maximum sorption ranged from 28 to 97 cmol NH 4 + -N kg -1 zeolite. Effects of zeolite application rate [0.5% to 10.0% of manure dry matter (DM)] on sorption and desorption characteristics in a manure/artificial urine matrix were highly variable but tended to be proportional to zeolite application rate: as little as 0.5% zeolite increased NH 4 + -N recovery by up to 19%. In flow-through chamber studies, higher rates of zeolite did not reduce cumulative NH 3 emissions, as 1.0% zeolite reduced cumulative NH 3 emission by 42% and 5.0% zeolite reduced N losses by only 18% compared to unamended manure. Surface application of zeolite has potential for mitigating feedyard NH 3 losses, but specific zeolite properties influenced its effectiveness. Further studies are warranted to evaluate effects of repeated zeolite application, co-application of zeolite and urease inhibitors, and cost:benefit ratios of zeolite application at commercial feedyards.

Odor emissions from livestock production have become increasingly important in the past decade. Odors derived from animal feeding operations are caused by odorous VOC emitted from the mixture of feces and urine, as well as feed and silage which may be experiencing microbial fermentation. Distillers grains are a by-product of corn grain fermentation used to produce fuel ethanol, and this industry has grown rapidly throughout the U.S. in past years. Therefore, the use of wet distillers grains with solubles (WDGS) in feedlot cattle diets has also increased. The objective of this research was to determine specific VOC emissions from feces and urine or a mixture of both, from cattle fed steam flaked or dry-rolled corn (DRC)-based diets containing either 0% or 30% WDGS. Flux of dimethyl trisulfide was greater from feces of cattle fed DRC than steam-flaked corn (SFC) diets. No other differences in flux from feces were detected across dietary treatments for phenol, 4-methylphenol, indole, skatole, dimethyl disulfide, and flux of volatile fatty acids (VFA) such as acetic, propionic, isobutyric, butyric, isovaleric, and valeric acids (P > 0.15). Flux of skatole, acetic acid, and valeric acid from urine was greater for cattle fed SFC than DRC diets (P

Nitrous oxide (NO) emissions from concentrated animal feeding operations, including cattle feedyards, have become an important research topic. However, there are limitations to current measurement techniques, uncertainty in the magnitude of feedyard NO fluxes, and a lack of effective mitigation methods. The objective of this review was to assess NO emission from cattle feedyards, including comparison of measured and modeled emission rates, discussion of measurement methods, and evaluation of mitigation options. Published annual per capita flux rates for beef cattle feedyards and open-lot dairies were highly variable and ranged from 0.002 to 4.3 kg NO animal yr. On an area basis, published emission rates ranged from 0 to 41 mg NO m h. From these studies and Intergovernmental Panel on Climate Change emission factors, calculated daily per capita NO fluxes averaged 18 ± 10 g NO animal d (range, 0.04-67 g NO animal d). This variation was due to inconsistency in measurement techniques as well as irregularity in NO production and emission attributable to management, animal diet, and environmental conditions. Based on this review, it is clear that the magnitude and dynamics of NO emissions from open-lot cattle systems are not well understood. Further research is required to quantify feedyard NO fluxes and develop cost-effective mitigation methods.

Odor and volatile organic compound (VOC) emissions are a concern at animal feeding operations (AFOs). The issue has become more prevalent as human residences move into areas once occupied only by agriculture. Odors near AFOs are generally caused by odorous VOCs emitted from manure, the mixture of feces and urine. Wet distillers grains with solubles (WDGS) are a by-product of the ethanol industry, and WDGS have become a staple in many beef cattle finishing diets. The objective of this research was to determine specific VOC emissions from frozen feces and urine of cattle fed steam-flaked corn (SFC)-based diets containing 0, 15, 30, or 45% WDGS. No differences in flux were detected across dietary treatments for phenol, indole, skatole, or 4-methylphenol (P > 0.23). Dimethyl disulfide and dimethyl trisulfide flux in feces were not different across treatments (P > 0.35) and the flux of volatile fatty acids (VFA) such as acetic, propionic, isobutyric, butyric, isovaleric, and valeric were not different across treatments (P > 0.25). There was a tendency for dimethyl disulfide flux from urine to be greater for cattle consuming an SFC-based diet with 15% WDGS than the other diets (P = 0.10). Furthermore, flux of acetic, propionic, isobutyric, butyric, and isovaleric acid from the urine were not different (P > 0.61) across dietary treatment. There were no significant differences in odor activity value (OAV) across treatments for feces, and only a tendency for dimethyl disulfide in the feces (P = 0.09). Thus, there was no obvious indication that feeding WDGS in conjunction with SFC affects flux of odor or odorous VOC from beef manure. The summed OAV was three times higher in the urine than feces, and a single odorous compound (4-methylphenol) accounted for 97.6%and 67.3% of the OAV in urine and feces, respectively. Therefore, engineering or dietary strategies to reduce odor from beef cattle manure should focus on controlling or reducing 4-methylphenol concentrations in the urine and feces.

Concentrated animal feeding operations (CAFOs) are major sources of ammonia emitted into the atmosphere. There is considerable literature on ammonia emissions from poultry and swine CAFO, but few comprehensive studies have investigated large, open lot beef cattle feedyards. Ammonia emission rates and emission factors for a 77-ha, 45 000-head commercial beef cattle feedyard on the southern High Plains were quantified using measured profiles of ammonia concentration, wind speed and air temperature, and an inverse dispersion model. Mean summer emission rate was 7420 kg NH 3 d −1 , and winter emission rate was about half that, at 3330 kg NH 3 d −1 . Annual NH 3 –N emission rate was 4430 kg NH 3 –N d −1 , which was 53% of the N fed to cattle. Daily per capita NH 3 –N losses increased by 10–64% after the daily per capita N in feed rations increased by 15–26%. Annual emission factors for the pen area of the feedyard were 19.3 kg NH 3 (head fed) −1 , or 70.2 kg NH 3 Mg −1 biomass produced. Annual emission factors for the retention pond of the feedyard were estimated to be 0.9 kg NH 3 (head fed) −1 , or 3.2 kg NH 3 Mg −1 biomass produced.

Cattle feedyards can impact local environments through emission of ammonia and dust deposited on nearby land. Impacts range from beneficial fertilization of cropland to detrimental effects on sensitive ecosystems. Shortgrass prairie downwind from an adjacent feedyard on the southern High Plains of Texas, USA changed from perennial grasses to annual weeds. It was hypothesized that N enrichment from the feedyard initiated the cascade of negative ecological change. Objectives were to determine the distribution of soil nitrogen and estimate N loading to the pasture. Soil samples were collected from 119 locations across the pasture and soil total N (TN), nitrate-N and ammonium-N (AN) determined in the top 30 cm. Soil TN concentration decreased with distance downwind from the feedyard from 1.6 ± 0.2 g kg−1 at 75 m to 1.2 ± 0.05 g kg−1 at 582 m. Nitrate-N concentration decreased within 200 m of the feedyard and changed little at greater distances. Ammonium-N concentration decreased linearly (P < 0.001) with increasing distance from the feedyard from 7.9 ± 1.7 mg kg−1 within 75 m from the feedyard to 5.8 ± 1.5 mg kg−1 at more than 550 m from the feedyard; however, distance only explained 12% of the variability in AN concentration. Maximum nitrogen loading, from 75 to 106 m from the feedyard, was 49 kg ha−1 year−1 over 34 years and decreased with distance from the feedyard. An estimate of net dry deposition of ammonia indicated that it contributed negligibly to N loading to the pasture. Nitrogen enrichment that potentially shifted vegetation from perennial grasses to annual weeds affected soil N up to 500 m from the feedyard; however, measured organic and inorganic N beyond that returned to typical and expected levels for undisturbed shortgrass prairie.

Concentrated animal feeding operations are major sources of ammonia to the atmosphere. Control methods to reduce emissions include acidifying amendments, urease inhibitors, and absorbents. For beef cattle, decreasing crude protein (CP) in diets may be the most practical and cost-effective method to reduce ammonia emissions. Our objective was to quantify the effect of reducing CP in beef cattle diet on ammonia emissions. Two groups of steers were fed diets with either 11.5 or 13.0% CP and all urine and feces were collected. Manures from the two diet treatments were applied in a replicated laboratory chamber experiment, and ammonia emission was quantified using acid gas washing. In four seasonal field trials, manures from the two diet treatments were applied to two 10-m-diameter, circular, artificial feedyard surfaces, and ammonia emission was quantified using the integrated horizontal flux method. Manure from steers fed 11.5% CP diet had less urine, less urinary N, and a lesser fraction of total N in urine, compared with the 13.0% CP diet. Decreasing crude protein in beef cattle diets from 13 to 11.5% significantly decreased ammonia emission by 44% (p < 0.01) in the closed chamber laboratory experiment, and decreased mean daily ammonia flux by 30% (p = 0.10), 52% (p = 0.08), and 29% (p < 0.01) in summer, autumn, and spring field trials, respectively. No difference was observed in winter. On an annual basis, decreasing crude protein reduced daily ammonia flux by 28%. Reducing crude protein in beef cattle diets may provide the most practical and cost-effective way to reduce ammonia emissions from feedyards.

Temperature controls many processes of NH volatilization. For example, urea hydrolysis is an enzymatically catalyzed reaction described by the Arrhenius equation. Diet crude protein (CP) controls NH emission by affecting N excretion. Our objectives were to use the Arrhenius equation to model NH emissions from beef cattle () feedyards and test predictions against observed emissions. Per capita NH emission rate (PCER), air temperature (), and CP were measured for 2 yr at two Texas Panhandle feedyards. Data were fitted to analogs of the Arrhenius equation: PCER = () and PCER = (,CP). The models were applied at a third feedyard to predict NH emissions and compare predicted to measured emissions. Predicted mean NH emissions were within -9 and 2% of observed emissions for the () and (T,CP) models, respectively. Annual emission factors calculated from models underestimated annual NH emission by 11% [() model] or overestimated emission by 8% [(,CP) model]. When from a regional weather station and three classes of CP drove the models, the () model overpredicted annual NH emission of the low CP class by 14% and underpredicted emissions of the optimum and high CP classes by 1 and 39%, respectively. The (,CP) model underpredicted NH emissions by 15, 4, and 23% for low, optimum, and high CP classes, respectively. Ammonia emission was successfully modeled using only, but including CP improved predictions. The empirical () and (,CP) models can successfully model NH emissions in the Texas Panhandle. Researchers are encouraged to test the models in other regions where high-quality NH emissions data are available.

Methane is a greenhouse gas with a global warming potential twenty-five times that of carbon dioxide. Animal production is recognized as a significant source of methane to the atmosphere. Dairies on the southern High Plains of New Mexico and Texas are typically open lot, and major sources of methane are enteric emissions from cattle and wastewater lagoons. Uncovered anaerobic lagoons are identified by the U.S. Environmental Protection Agency as a major source of methane in dairy manure management systems. Our objective was to quantify methane emissions from the wastewater lagoons of a commercial dairy located in eastern New Mexico. Research was conducted during six days in August, 2009 at a 3500-cow open lot dairy with flush alleys. Methane concentration over three interconnected lagoons (total area 1.8 ha) was measured using open path laser spectroscopy. Background methane concentration was measured using a back-flush gas chromatography system with flame ionization located upwind in the direction of prevailing winds. Wind and turbulence data were measured using a three-axis sonic anemometer. Emissions were estimated using an inverse dispersion model. Methane concentration over the lagoons ranged from 3 to 12 ppm, and averaged 5.6 ppm; background methane concentration averaged 1.83 ppm. Methane flux density ranged from 165 to 1184 µg m-2 s-1. Mean daily methane flux density was 402 kg ha-1 d-1. Per capita methane emission rate averaged 0.211 kg head-1 d-1. Uncovered anaerobic lagoons were a significant source of methane emitted from this southern High Plains dairy, and lagoons could be a significant control point for emission reduction.

Ambient NH3 concentrations were measured at a beef cattle CAFO during the spring and summer months of 2007. Concentrations were measured every five minutes, 24-hours per day at a sample intake height of 3.3 m using a chemiluminescence analyzer. On site weather data was collected concurrently. Emission rates were estimated using a backward Lagrangian Stochastic model (WindTrax 2.0.7.8). Mean 24-hr concentrations for spring were 0.498, 0.597 and 0.568 ppm for March, April and May, respectively. Corresponding fluxes for March, April and May were 57.76, 123.10 and 86.34 µg m-2 sec-1, respectively. Summer mean ambient concentrations were 0.684, 0.702 and 0.568 ppm for June, July and August, respectively. Summer fluxes were 85.27, 75.06 and 71.56 µg m-2 sec-1 for June, July and August, respectively.

Ammonia emissions from cattle feedyards may comprise 40% or more of nitrogen intakes. Decreasing ammonia emissions would improve the fertilizer value of feedyard manure and decrease potential adverse effects on the environment. Two trials were conducted to evaluate the effects of fat and zeolite on potential ammonia emissions from a feedlot surface. In the first trial corn oil, alum, a urease inhibitor, or potassium zeolite were added to simulated feedlot surfaces in lab-scale chambers and ammonia losses were captured using an acid solution. In trial two, five beef steers were fed one of five finishing diets (0% added fat, 3% added fat, 6% added fat, 3% fat+1% zeolite, or 3% fat+2% zeolite) in a 5 x 5 Latin square. During the last 5 days of each period feces and urine output were collected in stalls to determine nutrient digestion and retention. Feces and urine from each steer were used in the lab-scale flow-through chambers to estimate potential ammonia losses. In trial 1, zeolite and fat additions decreased ammonia losses by 51 to 86%; however the effects were not additive. In trial 2, apparent protein digestion, nitrogen retention, and nitrogen excretion were not affected by dietary fat or zeolite. In vitro ammonia losses were not significantly affected by dietary zeolite; however in vitro ammonia losses were greater (P < 0.05) when steers were fed diets containing no added fat. These results suggest that fat and zeolites can potentially decrease ammonia emissions from beef cattle feedyards.

Concentrated animal feeding operations are major sources of ammonia emitted to the atmosphere. There is a considerable literature on ammonia emissions from poultry and swine, but few studies have investigated large, open lot beef cattle feedyards. We used the micrometeorological flux-gradient method to estimate ammonia emissions during six field campaigns in three seasons. Profiles of ammonia, wind speed and air temperature were measured on towers located within feedyard pens. Atmospheric ammonia concentration was measured using either acid gas washing or chemiluminescence. Mean daily ammonia flux in summer averaged 72 µg m-2 s-1, and in winter, 39 µg m-2 s-1. Springtime fluxes were highly variable and averaged 79 µg m-2 s-1; high springtime fluxes were attributed to greater ammonium concentration in manure and high wind speeds. Ammonia-N emisson rate averaged 3930 and 2150 kg d-1 in summer and winter, respectively, which was 45% and 27% of fed N. Assuming that the mean of summer and winter emission rates represented a mean annual emission, ammonia-N loss was 36% of fed N, and an annual emission factor for feedyard pens based on total yearly per head production was 11.0 kg NH3-N head-1 yr-1. Ammonia emissions increased after N in cattle rations was increased from 13.5% to 14.5%. Ammonia emissions estimated using the flux-gradient method were 22 to 36% less than those derived from an inverse dispersion model. Uncertainty in the Schmidt number and possible violation of the assumption of homogeneous flow could have contributed to the lower flux estimates of the flux-gradient method. Optimizing fed N through practices such as phase feeding could help minimize ammonia emissions. Longer term, more continuous monitoring of ammonia emissions is needed to better define annual variability, emission rates and factors, and facilitate development of process models.

Dynamic, flow-through flux chambers are sometimes used to estimate ammonia emissions from livestock operations, however, ammonia emissions from the surfaces are affected by many factors which can be affected by the chamber. Ammonia emissions estimated using environmental flow-through chambers may be affected by air exchange rate; however, chamber fluxes have not been directly compared to the flux from the same source when unaffected by a chamber. We compared measured ammonia losses from an unaffected source to the same source when the air exchange rate ranged from 0 to 4 turnovers per minute. To simulate a feedlot retention pond, buffered ammonium sulfate solutions with pH values of 7.6, 8.6, or 9.6 were used as the ammonia source. To simulate a feedlot surface, similar solutions were added to a cellulose media. With both surfaces, ammonia losses increased with increased air flow. Losses at 0.5 turnovers/min were 25% or less that of losses from the unaffected sources. At low flow rates source strength differences were sometimes not accurately determined. There is a large spatial variability in ammonia flux from pen surfaces (CV = 23 to 192%). Because of this variability, the number of ammonia flux estimates required to be 95% confident that the estimated mean is within 20% of the true mean (determined as CV2/100) ranges from 5 to 369. The results of these studies suggest that dynamic flux chambers will not give accurate estimates of ammonia losses from either liquid or solid surfaces when flow rates are less than 10 to 15 air exchanges per minute and that large numbers of samples and(or) proper experimental design are required when using chambers for treatment comparisons.

We conducted field experiments to evaluate how factors such as sweep air flowrate, time since urine deposition, and flux chamber footprint area affect ammonia fluxes from open-lot feedyard and dairy surfaces as measured using three different flux chamber designs. The chambers included a 26.5-cm diameter chamber (North Carolina State University design), a 49-cm diameter chamber (EPA-type design), and a 1.2 m x 2.4 m rectangular chamber (West Texas A&M University design). Clean sweep air collected upwind of the feedyard (

A laboratory study was conducted to evaluate how rate and timing of urease inhibitor application affects ammonia emissions from simulated beef cattle feedyard surfaces. The urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT) was applied at rates of 0, 1 and 2 kg/ha, at 8, 16, and 32 day frequencies, and with or without simulated rainfall. Synthetic urine was added every 2 days to the manure surface. Gaseous NH3 was trapped in a sulfuric acid solution using a vacuum system and analyzed for nitrogen using automated procedures. NBPT applied every 8 days was most effective, with the 1 and 2 kg/ha NBPT treatments resulted in 49 and 66% reduction in NH3 emission rates, respectively. The 8-day, 1 kg/ha NBPT treatment had the most promising cost/benefit ratio of 0.48. Simulated rainfall reduced the NH3 emission rates slightly as compared to the non-rainfall treatments, though the differences were not statistically different.

A laboratory study was performed to compare ammonia emissions from simulated feedlot surfaces. Beef cattle manure was collected from open lot pens at the USDA-ARS feedlot in Bushland, TX. Treatments within the pens consisted of two dietary crude protein concentrations (11.5 and 13%) and two protein sources (urea and cottonseed meal). Manure collected from the pens was placed into Tupperware® chambers in the laboratory. Chambers were sealed and ammonia was trapped in an acid solution for 15 days using a vacuum system. Results suggest that as the protein concentration in the diet increases, potential daily ammonia emissions increase. The source of crude protein had little effect on ammonia emissions.

A dynamic flow-through chamber system and continuous analyzers were used for on-site measurements of ammonia-nitrogen (NH3-N) and hydrogen sulfide-sulfur (H2S-S) fluxes from commercial feedlot surfaces in northwestern Texas during two week period in the summer of 2002. Manure pack moisture content, pH, and TKN were measured daily to characterize its relation with NH3-N fluxes. The preliminary average NH3-N and H2S-S flux from the feedlot surface were 1,669 ± 1,212 NH3-N µg/m2/min and 1.884 ± 1.497 H2S-S µg S/m2/min. Manure pack temperature and TKN was found to have a weak correlation with NH3-N flux.

The antimicrobial susceptibilities of 421 Pasteurella haemolytica and 158 P. multocida isolates recovered from cattle with respiratory disease were determined with a microdilution minimal inhibitory concentration test system. Isolates were analyzed for patterns of resistance to ampicillin, ceftiofur, erythromycin, gentamicin, penicillin, spectinomycin, sulfachlorpyridazine, sulfadimethoxine, tetracycline, and tylosin. All isolates tested were found susceptible to ceftiofur and sulfachlorpyridazine. Pasteurella haemolytica isolates were resistant to ampicillin, penicillin, sulfadimethoxine, tetracycline, and tylosin. Pasteurella multocida isolates were resistant to sulfadimethoxine, tetracycline, and tylosin.

Ammonia and hydrogen sulphide flux and dry deposition velocity were estimated using micrometeorological vertical gradient flux method at a commercial cattle feedyard of approximately 50,000 head of beef cattle and average 14.4 m²/head (150 ft²/head) stocking density. Ammonia-N and H2S-S loss had general diurnal patterns with the highest fluxes in daytime and lowest fluxes in nighttime that correlated to temperature changes and active evaporation process during daytime. The highest average deposition velocities also occurred during daytime with unstable atmospheric conditions and the lowest during nighttime with very stable conditions. There are exponential relationship between NH3-N flux and ambient temperature with R² = 0.57 for NH3 (NH3-N flux = – 1.46 + 7.96e0.077*Temperature) and R² = 0.22 for H2S-S (H2S-S flux = – 0.75 + 0.8e-0.013*Temperature).