Agricultural production, especially in the case of livestock like dairy, is a significant contributor to climate change through the production of greenhouse gases (GHG) like carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), as well as other air pollutants like ammonia (NH3). However, increasing productivity led the U.S. dairy industry to reduce its negative environmental impacts through intensification or dilution of maintenance. In chapter 2, the aim of the study was to update a previous environmental impact assessment comparing the carbon footprint of Cheddar cheese production by Holsteins versus Jerseys in 2009. The functional unit of this analysis was 1 million metric tons of energy-corrected milk. A deterministic model simulated the two populations, establishing 16 life groups per breed needed to meet the functional unit. Production metrics like milk yield and milk components were sourced from the Council of Dairy Cattle Breeding National Metrics database for the year 2020. The software AMTS.Cattle.Pro was used to design total mixed rations for each individual life stage and breed to meeting the energy and nutritional needs of each animal. Feeds informed the background systems used to calculate land and water use, and associated feed emissions were calculated via economic allocation with emission factors sourced from ecoinvent 3.10. AMTS.Cattle.Pro also estimated daily nutrient and manure excretion, daily enteric CH4, and voluntary water intake. Total GHG emissions were converted to carbon dioxide equivalents (CO2e) using AR6 global warming potential (GWP) values. The results found milk yield increased for Holsteins and Jerseys by 29% and 26%, respectively, from 2009 versus 2020. Certain key performance indicators like land use decreased for Jerseys and Holsteins due to less feed intake associated with smaller populations. However, water use increased because irrigation was included in this assessment, but not in the original 2009 study. Overall, the carbon footprint for Jersey milk production was 1.6 kg CO2e/kg ECM and the carbon footprint for Holstein milk production was 1.8 kg CO2e/kg ECM, which was higher than the carbon footprints of the original assessment, likely due to the different GWP values used. Overall, both breeds made advancements in productivity, helping to offset increases in resource consumption. And the carbon footprint for Jersey production was 89% of the Holstein carbon footprint, meaning the Jersey population had an environmental impact more similar to Holsteins in 2020 compared to their environmental impacts in 2009. In chapter 3, the aim of study 2 was to investigate the effects of Eminex® on GHG and NH3 emissions from fresh dairy slurry and dairy lagoon water. Eminex® had previously reduced total GHG emissions by 99% under anaerobic and temperature-controlled conditions, but had not tested in liquid-based systems. For experiment 1, feces and urine were collected from lactating dairy cows and mixed into a homogenous slurry, prior to being allocated into twelve individual bowls with 2.2 kg/bowl. Each bowl was randomly assigned a treatment: high, low, and a control with an n = 4/group. Upon receiving treatment, bowls were sampled beneath individual OdoFlux chambers for 7 days to measure for CO2, CH4, N2O, NH3, and ethanol (EtOH) emissions. Samples were collected to determine changes to manure quality. For experiment 2, lagoon water was collected from a commercial dairy, and distributed to 12 stainless 208-L stainless steel barrels. Two treatments (n = 4/treatment) were administered: high (1 kg/m3 lagoon water), and low (0.5 kg/m3 lagoon water); and control (n = 4). Four barrels at a time were sampled over two, nonconsecutive 14-day periods, using OdoFlux chambers, monitoring CO2, CH4, N2O, and NH3. Slurry total solids, total nitrogen, and total carbon was similar across all treatment groups (P > 0.05). Acetic acid concentration in slurry increased in Eminex® treated groups compared to control (P < 0.05). All slurry GHG emissions, except for N2O, declined (P < 0.05). Results showed that the high Eminex® treatment compared to control reduced CO2, CH4, and NH3 emissions by 49.3%, 30.4%, and 34.9%, respectively (P < 0.05). In lagoon water, total nitrogen increased with treatment (P < 0.05), while total solids and total carbon remained similar between all three treatments (P > 0.05). Volatile fatty acid concentration in lagoon water also saw a trend for increasing acetic acid concentration in Eminex® treated groups compared to control (P < 0.1). GHG emissions from lagoon water also decreased over time (P < 0.05). The high Eminex® treatment emitted 12.0% less CO2 (P < 0.1), 85.1% less CH4 (P < 0.05), and 82.7% less N2O (P < 0.05). However, both Eminex® treatments, compared to control, increased NH3 volatilization over time (P < 0.05). With improvements to manure composition with increasing nitrogen content, as well as significant reductions in GHG emissions, Eminex® is a promising manure additive that could mitigate the negative environmental impacts of manure management systems. Further research is needed to continue verifying its potential in different settings and at the commercial level. The final study in Chapter 4 investigated the effects of Eminex® on the microbiome of slurry and lagoon water. Samples were collected from fresh slurry and dairy lagoon water during study 2. Samples were DNA extracted prior to being sent out to an independent laboratory for shallow shotgun metagenomic sequencing (SSMS). Results of the SSMS showed that the relative abundance of the phylum Proteobacteria decreased with Eminex® treatment in lagoon water, but increased in relative abundance with Eminex® treatment in slurry. Other phyla, like Firmicutes and Actinobacteria increased in relative abundance with Eminex® in lagoon water, but not in slurry. Pathogenic phyla, like Fusobacteria, did not increase in relative abundance with Eminex® treatment in slurry, but increased substantially in untreated slurry. A principal component analysis (PCA) was also performed and confirmed distinct microbiomes between slurry and lagoon water. The PCA also noted that the high Eminex® treatment, compared to the low Eminex® treatment, elicited a faster microbiome change. This suggested that Eminex® could be applied more effectively earlier in the manure management chain. Lastly, a linear discriminatory analysis showed that bacterial populations were at their highest in the two Eminex® treatments at day 28, and highest in the control by day 56. Ultimately, the Eminex® treatment resulted in significant changes to the manure microbiome, helping to explain how this additive reduces GHG and NH3 emissions. Looking at the microbiome demonstrated that the Eminex® doses can be decreased and still be effective. Future research would benefit from exploring the metabolomics associated with microbes exposed to Eminex® and exploring the effects of different treatment protocols of emissions and the manure microbiome.

The environmental impact of cattle includes enteric and manure management derived greenhouse gas (GHG) emissions and reactive nitrogen (Nr) production. In the United States, beef and dairy cattle are responsible for 27.4% and 5.2% of total methane (CH4) emissions through enteric fermentation and manure management, respectively (EPA, 2024). Concurrently, beef and dairy cattle manure management accounts for 8.4% of total GHG emissions from agriculture, while agricultural soil management (including manure fertilizer application) accounts for 49% of total agricultural GHG emissions (EPA, 2024). Feed additives are a well-studied technique with potential to reduce enteric GHG emissions. With respect to additives, containing plant secondary metabolites (PSM), or constituent molecules derived from PSM, it remains an open question as to whether these molecules retain bioactivity throughout the gastrointestinal tract. If so, these feed additives could then continue affecting GHG and Nr production in manure. Additionally, improved diet formulation can aid in increasing digestibility, delivering more nutrients to the animal and less in manure (feces and urine). In Chapter 2 of the present dissertation, the objective was to determine the effect of plant secondary metabolite-based feed additives on fecal chemistry, and how these chemical properties would lead to differences in GHG emissions and Nr when feces were amended to different soils and at different water content levels. This was achieved by recovering feces from a live-animal trial where 24 Angus and crossbred Angus steers were divided as a randomized incomplete block design to determine the effects of the feed additive treatments Agolin (AG) or Mootral (MT) as compared to cattle on an un-supplemented diet (UN) as controls. The AG treatment was fed at 1 g/day dry matter (DM) and MT was fed at 23.5 g/day DM. Fresh fecal samples were collected from all animals per pen after cattle had been on treatment for 4 weeks, and were amended to two different soil types: sandy loam and clay, at two different water holding capacity (WHC) levels: 50% and 90%, in a completely randomized factorial design laboratory incubation. Soil-only control (CON) samples were prepared alongside feces-amended samples. The GHGs and Nr were recorded for 30 days. The AG (-73.2 mg kg-1) versus MT (-60.5 mg kg-1) treatment had lower cumulative mineralized N (Nmin) in the clay, 90% WHC category ( p < 0.01). The AG (98.2 mg kg-1) versus MT (144.5 mg kg-1) treatment had lower carbon dioxide (CO2) emissions in the clay, 90% WHC category (p < 0.01), and higher CO2 emissions in the sandy loam, 90% WHC category (p < 0.01). Cumulative nitrous oxide (N2O) emissions were not different among feces-amended soils and soil-only controls and were only affected by soil type, with clay having higher emissions than sandy loam (p = 0.01). Cumulative CH4 emissions were only affected by the three-way interaction of treatment x soil type x WHC. We conclude that the C and N dynamics as influenced by AG and MT inclusion in the diet are transient and highly dependent on soil characteristics. Chapter 3 of the present dissertation entails a similarly designed laboratory incubation with a focus on how crude protein content in the diet affects GHGs and Nr in feces-amended soils. Three levels dietary crude protein were achieved by mixing corn dried distillers grains with solubles (DDGS) into diets at the University of California, Davis feedlot which were fed to three groups of cattle randomized to each treatment diet. Levels of DDGS inclusion in treatment diets were: deficient (DEF; 19.63% DM), balanced (BAL; 27.28% DM), and excess (EXS; 28.82% DM). Feces were collected from Angus steers on each treatment and amended to a sandy clay loam and a clay loam at 50% and 90% WHC. In a 32-day incubation experiment, EXS (961 µg kg-1) had greater cumulative N2O than DEF (686 µg kg-1) and BAL (392 µg kg-1) at 90% WHC in both the sandy clay loam and clay loam (p < 0.01). BAL also had lower N2O than DEF in the clay loam at 90% WHC (p < 0.01). The soil type and WHC variables impacted emissions, leading to increased variability among treatments. Reduced DDGS in the diet provided sufficient dietary N for animal performance while minimizing excreta N emissions. In Chapter 4 of the present dissertation, a feed additive blend of quebracho and chestnut extracts along with a carrier from cereals rich in saponins was fed to dairy cattle at 0.15% DM for 64 days. A group of 24 multiparous dairy cows were blocked by parity, dry matter intake, baseline CH4, and days in milk, and randomized to receive the quebracho treatment (BPX) or an un-supplemented diet (CON). In this study, fecal chemistry and fecal microbiota were analyzed over the course of the animal trial by collecting samples from each animal on days 0-, 16-, 32-, and 64 of the study. Using 16S rRNA gene amplicon sequencing, a total of 1,538 amplicon sequence variants were identified. Phylogenetic diversity of microbiota exhibited a treatment  day effect (p < 0.01). Fecal C and N exhibited a corresponding treatment  day effect (p < 0.01); however, differences were only seen between BPX and CON on day 16, indicating a potential transient effect of the feed additive, where the microbiota and N partitioning returned to baseline after a slight perturbation. Differences in fecal chemical properties were also observed, with BPX having greater levels of indole-3-lactate than CON (p = 0.01). This corroborates known effects of tannins on microbial protein degradation. Greenhouse gas emissions were also measured for feces in a 14-day laboratory incubation, no differences were observed between BPX and CON for N2O (p = 0.45), CH4 (p = 0.69), or CO2 (p = 0.97). While feed additives like those tested here, have been implemented successfully, our results suggest that the microbiota can tolerate low doses of a tannin-based product, leading to no long-term changes. Higher doses may be more efficacious, but cost prohibitive. Our results stand alongside a paucity of currently published results investigating the effects of a PSM-based feed additive on feces amended to soil. Further research on the biotransformation of the active ingredients in the gastrointestinal tract, and minimum inhibitory concentrations toward microbes in manure and soil is needed to best align dosing with animal health and performance and intended effects on manure and soil chemistry.

Cattle production and meat consumption have long been criticized for their environmental impacts and contribution to climate change. In the United States, this has led to increased research into way to mitigate environmental impacts from cattle production as well as alternative foods to replace beef and its associated impacts. The goal of the present dissertation was to review current literature related to the environmental impacts of cattle and meat alternatives and to present research related to mitigating emissions from cattle production as well as research into the comparative impacts of both beef and plant based meat alternatives.

Chapter one presents a review of current literature on the sustainability of beef in meat alternatives. This literature review covers three primary areas of environmental impacts that are most prevalent in the literature on environmental impacts of cattle: climate change, land use, and water use. Further discussed are the nuances that accompany evaluation of these impacts from cattle production. Environmental impacts of plant based meat alternatives (MA) are then discussed with a particular focus on Beyond Burger (BB) and Impossible Burger (IB), the two most prevalent MA in the US due to their similar taste and textural profiles compared to ground beef (GB).

Chapter two investigates a novel feed additive aimed at promoting environmental stewardship while maintaining or improving the efficiency of cattle production. Selective β modulator (lubabegron; LUB), recently approved by the United States Food and Drug Administration (FDA) to be fed to feedlot cattle during the last 14 to 91 d of the feeding period, was evaluated clinical efficacy for reductions in gaseous emissions/kg of final BW or HCW when different doses of LUB were fed to feedlot cattle over a 91-d duration. A 4 × 2 factorial arrangement design was utilized with the factors of dose (0.0, 1.25, 5.0 or 20.0 g/ton DM basis) and sex (steers or heifers). Three cycles were conducted (112 animals/cycle) with each dose × sex combination being represented by a single cattle pen enclosure (CPE; 14 animals/CPE) resulting in a total of 168 steers and 168 heifers (BW = 453 ± 34.5 kg). Five gases were evaluated based on CPE concentrations relative to ambient air: NH3, CH4, N2O, H2S, and CO2. Lubabegron was shown to reduce emissions of NH3 while simultaneously increasing the pounds of beef produced, demonstrating that feed additives are a promising tool towards reducing environmental impacts of cattle production.

Chapters three and four aimed to gain a more complete picture of the sustainability of GB compared to BB or IB through two means: (1) first in chapter three, national and international economic impacts of decreasing GB consumption in the US in response to the introduction of BB and IB were investigated; and (2) in chapter four, the widespread US environmental impacts associated with a decrease in GB consumption and corresponding increase in BB and IB consumption in the US were evaluated. Contrary to previous work comparing these products, the present research utilized a methodology which accounts for the complicated national and international supply chains associated with the production of these products beyond their direct inputs.

In chapter three, the Global Trade Analysis Project (GTAP) Model was used to assess the effects of reducing GB consumption in the US on both US and global economies. A 15% reduction in US GB, resulted in rather significant impacts on the US economy. Most notably, national and international consumption behaviors changed which resulted in changes to the structure of world trade. In the US, the reduction in GB consumption resulted in loss of labor (up to 9.9% of labor for the US GB sector and 4.1% for the US cattle sector) as well as substantial reductions in land used for cattle production. Similarly, reductions in labor and land use were observed for the top four countries that the US imports of lean trimmings of GB from (Australia, Canada, Mexico, and New Zealand).

In chapter four, GTAP and the multi-regional input-output database, EXIOBASE, were utilized to perform a macro-life cycle assessment (M-LCA) of GB, BB, and IB. Compared to conventional LCA, this method makes it possible to account for the detailed production systems associated with GB, BB, and IB. When replacing 15% of GB consumption with either BB or IB, environmental impacts were variable. When considering impacts to the GB sector alone, replacement with BB resulted in overall reductions to climate change impacts (i.e., greenhouse gas emissions), land use, water use, and energy use. Meanwhile, replacement with IB resulted in reductions of climate change and land use impacts from the GB sector but had the potential to increase overall water and energy use. When considering the effects of changes in the GB sector on a national scale: Climate change impacts (i.e., greenhouse gas emissions) declined minimally (0.08%), with the new GB sector contributing to 0.66% of national emissions. Land use declined by up to 1.6%, nationally. Meanwhile, water use, and energy use had mixed effects at the national level for both BB and IB, each having the potential to increase national resource use, though by relatively small amounts

When considering the sustainability of these GB compared to BB or IBs, it remains difficult to draw clear conclusions on which product might be superior, but it is clear that BB and IB will not produce the profound positive impacts suggested by their respective companies.

Cattle and their waste products are considered a major source of greenhouse gas (GHG) emissions. In the United States, animal agriculture accounts for 38% of methane (CH4) emissions with 28% arising from enteric fermentation, and 10% from manure management. With California being the leading dairy state in the United States, it is increasingly important that strategies for reducing gaseous emissions in lactating dairy cows and management of their waste within the state be investigated. In studies 1 and 2, the objective was to determine the efficacy of various commercially available plant secondary metabolites (PSM) at reducing GHG and ammonia (NH3) emissions without negatively impacting the productive performance of dairy cows. The PSM’s investigated were: (1) a commercial essential oils blend comprised of eugenol, coriander seed, and geranyl acetate (Agolin® Ruminant; Agolin SA, Bière, Switzerland), and (2) a commercial blend of quebracho and chestnut tannins with saponins (SilvaFeed® BX; SILVATEAM SpA, San Michele Mondovì, Italy). In each study, twenty early- to mid-lactation Holstein dairy cows were blocked by days in milk and parity in a randomized complete block design, and were assigned one of two treatments: PSM or control (n=2/block). Cows were individually fed, group-housed in a free-stall pen, and were milked twice daily. The treatments were administered as a top dress at each of two feedings per day. Cows were sampled for enteric CH4, carbon dioxide (CO2), nitrous oxide (N2O) and NH3 emissions in head chambers (HC) for 12 hours on treatment days 0, 14, 28, 42, and 56 in study 1, and 0, 16, 32, and 48 in study 2. Enteric GHG and NH3 emissions, energy-corrected milk (ECM; kg), milk component yields (kg) and proportions (%), and dry matter intake (DMI; kg) were analyzed for pairwise comparison in R. In study 1, supplemental Agolin® tended to decrease enteric N2O intensity, and significantly decreased enteric CH4 and NH3 intensity (g or mg gas/d/kg ECM). Enteric NH3 production decreased significantly with Agolin supplementation, though there was no effect on CH4, CO2, or N2O production (g or mg gas/d). Enteric GHG and NH3 yields (g or mg gas/d/kg HC DMI) did not differ between treatment types in study 1. In study 2, SilvaFeed® BX tended to decrease enteric CH4 and CO2 production (g/h), significantly decreased N2O production (mg/h), and tended to increase NH3 production (mg/h). Supplementing cows with SilvaFeed BX resulted in an increase in slurry NH3 emissions (mg/h/m2), though the GHG’s were unaffected. No differences were found in ECM, milk fat yield, milk protein yield, and DMI in PSM-fed cows in both studies 1 and 2. Study 3 investigated the ability of a commercial biological wastewater applicant (BiOWiSH® AQUA; BiOWiSH Technologies Inc., Cincinnati, Ohio) for reducing NH3 emissions in the effluent from anaerobic digesters. Effluent was collected from an anaerobic digester and was homogenized and distributed equally between 18 steel drums. The drums were placed in a 6x3 (row x column) grid with treatments allocated and applied according to a double Latin square. Treatments were comprised of positive control (aeration but no BiOWiSH), negative control (no aeration and no BiOWiSH), and the experimental treatment (both BiOWiSH and aeration). Gaseous emissions were measured continuously across 56 days, with each column being measured for 24 hours every 3-4 days. Ammonia emissions did not significantly differ between the experimental treatment and the positive control. Both the experimental treatment and the positive control had higher NH3 emissions than the negative control. Future research should assess the mitigation potentials of each of the feed additives and the applicant at varying dosage levels.