This review described the state of the science concerning the generation, measurement, and mitigation of ammonia (NH₃) emissions from beef cattle feedyards. NH₃ emissions primarily come from urinary urea in cattle manure. In the past, constant emission factors were used to inventory NH₃ emissions. Currently, NH₃ emission factors estimated by process-based mechanistic models reflecting various factors affecting NH₃ emissions in the feedyard environment are available. This review of current literature indicated the average NH₃ emissions from a beef cattle feedyard was approximately 119 g/head/day (range 24 to 318 g/head/day), and the average NH₃ flux was approximately 58 µg/m²/s (range 2 to 185 µg/m²/s). Although more realistic estimates of NH₃ emission flux from open-lot livestock facilities were being obtained using process-based models, there was still significant variation depending on the diet composition, manure management practices, and the feedyard environment, including both seasonal weather patterns and synoptic weather events. We note the need to improve inventories of NH₃ emissions into categories of crude protein percentage, manure management implemented, and feedyard environment. Some mitigation strategies can be effective, such as diet manipulation, growth-promoting technologies, and manure or pen-surface amendments. Of those, precision diet feeding to meet but not exceed protein requirements appeared to be the most practical way to reduce ammonia emissions over the animals’ feeding period; laboratory studies suggested that shorter-term reductions in emission flux may be possible with the other approaches, but they were far more speculative at this point as to both their efficacy and their cost of implementation.

Northeast Colorado’s livestock operations have been identified as a major contributor to reactive nitrogen deposition in the Rocky Mountains National Park (RMNP). We present a review on the state of knowledge concerning the emission, transport, deposition, and mitigation of gaseous ammonia (NH₃) from open-lot cattle feeding facilities located east of the Northern Front Range of the Rocky Mountains. Gaseous NH₃ mitigation strategies discussed are related to diet manipulation and management practices. Crude protein content of 11% and condensed tannins of 8% reduced the NH₃ emission by 43% and 57%, respectively. Ambiguous results for NH₃ mitigation by using water sprinklers have been reported—an increase in NH₃ emission by 27% and decrease of 27 to 56%. Manure harvesting should be evaluated in terms of maintaining proper moisture content, and not necessarily as a mitigation option. The use of chemical and physical manure amendments has shown a wide range in NH₃ mitigation effectiveness, ranging from 19 to 98% for chemical and 0 to 43% for physical amendments, respectively. The review outlined the scientific basis, practicality, and expected efficacy of each management practice. The most plausible management practices to reduce NH₃ emissions from corral surfaces in cattle feedyards are presented.

Ammonia (NH₃) emissions are of prime environmental interest due to air quality concerns, fine particulate formation, nitrogen deposition, and nutrient management in ecosystems. Proper instrumentation for measuring NH₃ concentrations is needed to quantify emissions and test mitigation strategies. Commercial measurement systems are based on a similar principle to read the signal from the sensor that responds to the target pollutant gas through a data logger; however, the cost and scientific value vary depending on the quality of the parts used. Electrochemical sensors can be used to reduce costs and increase data availability. This method research reports a process for designing, manufacturing, calibrating, and testing an electrochemical sensor-based NH₃ measurement system for a budget-oriented end-user.

Dehydrated manure from agricultural animal feedlots can become aerosolized and may potentially harbor viable antimicrobial-resistant bacteria. Little is known about the dynamics and risk of bacteria in bioaerosols originating from the feedyard environment. Nutrient deficiency, desiccation, UV exposure, temperature, and pH changes can affect bacterial viability. In this study, we investigated the impact of changes in relative humidity (RH) and UV-B exposure on enteric bacterial survival in vitro to simulate environmental conditions in cattle feedyards. Cattle manure samples were placed in two separate chambers with 73% RH and 31% RH, respectively. For the UV-B experiment, samples were placed in a chamber exposed to UV-B (treated) or in a chamber exposed to LED light (control). Samples from both experiments were spiral plated in triplicate onto selective agar media to quantify total aerobic bacteria, E. coli (total and antimicrobial-resistant (AMR)), and Enterococcus spp. (total and AMR). Results showed that enteric bacteria from cattle manure can withstand at least two stress conditions, including low RH levels and UV-B exposure. Moreover, the data revealed that antimicrobial-resistant bacteria can persist in manure under the harsh conditions that may be encountered in a feedyard environment. These findings underscore the need for mitigation strategies in feedlots to minimize the overall risk of bioaerosol formation.

Antimicrobial use in food animals selects for antimicrobial-resistant (AMR) bacteria, which most commonly reach humans via the food chain. However, AMR bacteria can also escape the feedyard via agricultural runoff, manure used as crop fertilizer, and even dust. A study published in 2015 reported AMR genes in dust from cattle feedyards; however, one of the study’s major limitations was the failure to investigate gene presence in viable bacteria, or more importantly, viable bacteria of importance to human health. Our main objective was to investigate the presence and quantity of viable bacteria and antimicrobial-resistant (AMR) determinants in fugitive bioaerosols from cattle feedyards in the downwind environment. Six bioaerosol sampling campaigns were conducted at three commercial beef cattle feedyards to assess variability in viable bacteria and AMR determinants associated with geographic location, meteorological conditions, and season. Dust samples were collected using four different sampling methods, and spiral plated in triplicate on both non-selective and antibiotic-selective media. Colonies of total aerobic bacteria, Enterococcus spp., Salmonella enterica, and Escherichia coli were enumerated. Viable bacteria, including AMR bacteria, were identified in dust from cattle feedyards. Bacteria and antimicrobial resistance genes (ARGs via qPCR) were mainly found in downwind samples. Total suspended particles (TSPs) and impinger samples yielded the highest bacterial counts. Genes encoding beta-lactam resistance (bla_CMY-2 and bla_CTX-M) were detected while the most common ARG was tet(M). The predominant Salmonella serovar identified was Lubbock. Further research is needed to assess how far viable AMR bacteria can travel in the ambient environment downwind from cattle feedyards, to model potential public health risks.

Ammonia (NH₃) emissions from beef cattle feedyards cause nutritional loss in manure and contribute to environmental pollution. Thus, the mitigation of NH₃ emissions helps sustain and promote the production of environmental agriculture. Sprinkler-based water applications have primarily been used to reduce fugitive dust and heat stress in livestock. It has also been proposed as a potential NH₃ mitigation strategy; however, its effectiveness remains uncertain for industrial use. This study evaluated the effect of controlled water application on NH₃ emissions under simulated feedyard surfaces. Several environmental conditions (addition of urine, water and manure properties, and temperature) were subjected to different treatments, including repeated water applications or chemical amendments to improve the NH₃ mitigation. Results indicated that water applications provided only a temporary mitigation effect (4–25%). NH₃ emissions rebounded (1–19%) over time as the applied water evaporated, indicating that water primarily delays NH₃ volatilization rather than permanently reducing total emissions. These findings suggest that while water applications provide short-term NH₃ mitigation, additional strategies, such as chemical amendments or repeated applications, might be necessary for sustained emission reduction. By optimizing water application methods through further research, water application can become a valuable component of NH₃ mitigation strategies for livestock operations.