Enteric methane emissions in grazing dairy systems.

Approximately 80% of agricultural CH4 comes from livestock systems, with 90% of that derived from enteric CH4 production by ruminants. Grazing systems are used worldwide to feed dairy cattle. Although quantifying enteric CH4 emissions in grazing systems has unique challenges, emerging technologies have made gaseous data collection more feasible and less laborious. Nevertheless, robust data sets on enteric CH4 emissions under various grazing conditions, as well as effective and economic strategies to mitigate CH4 emissions in grazing dairy cows, are still in high demand because data collection, feeding management, and milk market regulations (e.g., organic certification, grassfed) impose more challenges to grazing than confinement dairy systems. This review will cover management strategies to mitigate enteric CH4 emissions and applicability to pastoral dairy systems. The effects of enteric CH4 in the broader context of whole-system assessments will be discussed, which are key to assess the overall environmental impact of grazing dairies.

Maine organic dairy producers' receptiveness to seaweed supplementation and effect of Chondrus crispus on enteric methane emissions in lactating cows.

Introduction: There is a growing interest in utilizing seaweed in ruminant diets for mitigating enteric methane (CH4) emissions while improving animal health. Chondrus crispus is a red seaweed that grows in the Gulf of Maine (United States) and has shown to suppress CH4 production in vitro. Organic dairy producers in Maine are currently feeding seaweed due to herd health promoting benefits. However, large-scale adoption depends on technical and financial factors, as well as validation from pilot studies. Methods: A survey was developed to identify barriers and drivers towards the adoption of CH4-reducing algal-based feeds. Concurrently, a randomized complete block design study was conducted to investigate the effect of C. crispus on enteric CH4 emissions and milk production in a typical Maine organic dairy farm. Twenty-two organically certified Holstein and Jersey cows averaging 29 ± 6.8 kg of milk/d and 150 ± 69 days in milk, were blocked and randomly assigned to a control diet without C. crispus (0CC), or with 6% [dry matter (DM) basis] C. crispus (6CC). Samples were collected on the last week of the 2-wk covariate period, and wk 3, 5, 8, and 10 after initiation of treatments for a total of 12 weeks. Gaseous emissions were measured using a GreenFeed unit. Data were analyzed using the MIXED procedure of SAS with repeated measures over time. Results: All survey respondents (n = 35; 54% response rate) were familiar with seaweeds as feed, and 34% were already users. Producers who were willing to pay 0.64 USD/cow/d on average for a CH4-reducing algal-based feed, also stated the need for co-benefits in terms of cattle health and performance as a requirement for adoption. Feeding 6CC decreased enteric CH4 production by 13.9% compared with 0CC (401 vs. 466 g/d). Further, milk yield (mean = 27.1 kg/d), CH4 intensity (mean = 15.2 g of CH4/kg of energy corrected milk), and concentrations and yields of milk fat and true protein were not affected by treatments. Discussion: Producer receptiveness to CH4-reducing algal-based feeds will not only be dependent on purchase price, but also on co-benefits and simplicity of integration into existing feed practices. Feeding C. crispus at 6% of the diet DM decreased CH4 production in dairy cows by 13.9% without negative effects on milk yield and composition. Identifying the bioactive compounds in C. crispus is critical to understand the effect of this red seaweed on mitigating enteric CH4 emissions in dairy cows.

Feeding incremental amounts of ground flaxseed: effects on diversity and relative abundance of ruminal microbiota and enteric methane emissions in lactating dairy cows.

We evaluated the effects of incremental amounts of ground flaxseed (GFX) on diversity and relative abundance of ruminal microbiota taxa, enteric methane (CH4) emissions, and urinary excretion of purine derivatives (PD) in lactating dairy cows in a replicated 4 × 4 Latin square design. Twenty mid-lactation Jersey cows were used in the study. Of these 20 cows, 12 were used for ruminal sampling, 16 for enteric CH4 measurements, and all for spot urine collection. Each period lasted 21 d with 14 d for diet adaptation and 7 d for data and sample collection. Diets were formulated by replacing corn meal and soybean meal with 0%, 5%, 10%, and 15% of GFX in the diet's dry matter. Ruminal fluid samples obtained via stomach tubing were used for DNA extraction. Enteric CH4 production was measured using the sulfur hexafluoride tracer technique. Diets had no effect on ruminal microbiota diversity. Similarly, the relative abundance of ruminal archaea genera was not affected by diets. In contrast, GFX decreased or increased linearly the relative abundance of Firmicutes (P < 0.01) and Bacteroidetes (P < 0.01), respectively. The relative abundance of the ruminal bacteria Ruminococcus (P < 0.01) and Clostridium (P < 0.01) decreased linearly, and that of Prevotella (P < 0.01) and Pseudobutyrivibrio (P < 0.01) increased linearly with feeding GFX. A tendency for a linear reduction (P = 0.055) in enteric CH4 production (from 304 to 256 g/d) was observed in cows fed increasing amounts of GFX. However, neither CH4 yield nor CH4 intensity was affected by treatments. Diets had no effect on the urinary excretion of uric acid, allantoin, and total PD. Overall, feeding GFX decreased linearly the relative abundance of the ruminal bacterial genera Ruminococcus and Clostridium and enteric CH4 production, but no change was seen for CH4 yield and CH4 intensity, or urinary excretion of total PD, suggesting no detrimental effect of GFX on microbial protein synthesis in the rumen.

Building comprehensive glucosinolate profiles for brassica varieties.

Brassica plants play an important role in common agricultural practices, such as livestock feed or biofumigation, due to the bioactivity of the natural degradation products of glucosinolate metabolites. Therefore, the ability to survey comprehensive glucosinolate profiles for individual brassicas is essential for informing proper species selection for the intended application. Current methods for glucosinolate identification and quantification involve complex or unconventional procedures, and proper reference materials are not readily available. Therefore, researchers with limited resources that require glucosinolate profiles are at an extreme disadvantage. In this work, a simple and accurate HPLC-MS method was developed and validated to build preliminary glucosinolate profiles for three agriculturally relevant forage brassica varieties [turnip (B. rapa L.), canola (B. napus L.), and rapeseed (B. napus L.)]. The average glucosinolate content across three herbage collection dates for canola, rapeseed and turnip were 2.9 ± 0.9 mg g-1, 6.4 ± 1.3 mg g-1, and 14 ± 3.4 mg g-1, respectively. GLS concentrations are reported in milligrams of glucosinolate, calculated as sinigrin equivalents, per gram of dry plant material. This semi-quantitative approach for reporting total GLS content in brassicas is accurate within 15%. Several minor individual glucosinolates were identified that have not been previously reported in canola, rapeseed and turnip species, including glucotropaeolin and 4-hydroxyglucobrassicin (canola), glucoraphanin and glucoberteroin (rapeseed), and glucosinalbin and glucobarbarin (turnip). This non-targeted screen of several forage brassica varieties demonstrates the inherent variation in both the individual glucosinolate content and the total glucosinolate profile among brassicas, and highlights the importance of such glucosinolate characterization in agricultural practices. Additionally, the method developed in this study can be used as a tool for researchers with limited resources to build accurate glucosinolate profiles of brassica plants.

Spatiotemporal patterns of PFAS in water and crop tissue at a beneficial wastewater reuse site in central Pennsylvania.

Per- and polyfluoroalkyl substances (PFAS) are a collective name for thousands of synthetic compounds produced to enhance consumer and industrial products since the 1940s. They do not easily degrade, and some are known to pose serious ecological and human health concerns at trace concentrations (ng L-1 levels). Per- and polyfluoroalkyl substances persist in treated wastewater and are inadvertently introduced into the environment when treated wastewater is reused as an irrigation source. The Pennsylvania State University (PSU) has been spray-irrigating its wastewater at a 2.45 km2 mixed-use agricultural and forested site known as the "Living Filter" since the 1960s. To understand the spatiotemporal patterns of 20 PFAS at the Living Filter, water samples were collected bimonthly from fall 2019 through winter 2021 from the PSU's wastewater effluent and from each of the site's 13 monitoring wells. Crop tissue was collected at the time of harvest to assess PFAS presence in corn silage and tall fescue grown at the study site. Total measured PFAS concentrations in the monitoring wells ranged from nondectable to 155 ng L-1 , with concentrations increasing with the direction of groundwater flow. Concentrations within each well exhibited little temporal variability across sampling events, with mixed relationships between PFAS and groundwater elevation observed between wells. Further, >84% of the PFAS present in livestock feed crops were short-chain compounds, with PFAS consumed annually by livestock fed crops harvested from the site estimated to be 2.46-7.67 mg animal-1 yr-1 . This research provides insight into the potential impacts of long-term beneficial reuse of treated wastewater on groundwater and crop tissue quality.

Ruminal fermentation and enteric methane production of legumes containing condensed tannins fed in continuous culture.

A continuous-culture fermentor study was conducted to assess nutrient digestibilities, volatile fatty acid (VFA) concentrations, microbial protein synthesis, bacterial nitrogen (N) efficiency, and enteric methane (CH4) production of four 50:50 grass-legume diets, randomly assigned in a 4 × 4 Latin square design. Four legumes with different concentrations of condensed tannins (CT) were tested: alfalfa [ALF; Medicago sativa L., non-CT legume]; birdsfoot trefoil [BFT; Lotus corniculatus L., low-CT legume]; crown vetch [CV; Securigera varia (L.) Lassen, moderate-CT legume]; and sericea lespedeza [SL; Lespedeza cuneata (Dum. Cours.) G. Don, high-CT legume]. Orchardgrass (Dactylis glomerata L.) was the common forage used in all diets. Four fermentors were evaluated over four 10-d periods by feeding 82 g of dry matter (DM)/d in 4 equal feedings. Methane output was recorded every 10 min. Effluent samples were collected during the last 3 d of the experiment, composited by fermentor and period, and analyzed for pH and VFA, as well as DM, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber for determination of apparent and true nutrient digestibilities. Microbial protein synthesis and bacterial efficiency were estimated by analysis of N flows and purines. The CT concentrations were 3, 21, 38 and 76 g/kg of DM for ALF, BFT, CV, and SL diets, respectively. The SL diet had decreased fiber digestibilities and total VFA concentrations compared with the other diets. This resulted in the least total CH4 production in the SL diet. Bacterial N efficiency per kilogram of organic matter truly digested was lower in the SL diet than in the BFT and CV diets. The lowest CH4 production per unit of digestible nutrients was also found in the SL diet. Further work should be conducted to find optimal diets (by testing other legumes, rations, and sources of CT) for reducing CH4 emissions without negatively affecting ruminal digestion to maintain or improve productivity.

Evaluation of a single-flow continuous culture fermenter system for determination of ruminal fermentation and enteric methane production.

A 4-unit, single-flow continuous culture fermenter system was developed to assess in vitro nutrient digestibility, volatile fatty acid (VFA) concentration and daily enteric methane (CH4 ) production of ruminant diets. The objective was to develop a closed-vessel system that maintained protozoal populations and provided accurate predictions of total CH4 production. A diet of 50% orchardgrass (Dactylis glomerata L.) and 50% alfalfa (Medicago sativa L.) was fed during 4, 10-day periods (7-day adaptation and 3-day collection). Fermenters were fed 82 g of dry matter (DM)/day in four equal feedings. pH and temperature were taken every 2 min, and CH4 concentration was measured every 10 min. Samples for DM and protozoal counts were taken daily, and daily effluent samples were collected for determination of DM, VFA and NH3 -N concentrations. There was no effect (p > 0.17) of adaptation versus collection days on vessel and effluent DM, temperature or pH. Initial protozoal counts decreased (p < 0.01), but recovered to initial counts by the collection period. Total VFA, acetate, propionate and isobutyrate concentrations did not differ (p ≥ 0.13) among periods or days of the collection period. There was no difference (p ≥ 0.37) among days or periods in total daily CH4 production and CH4 production per g of OM, NDF, digestible OM or digestible NDF fed. Data collected throughout 4 experimental periods demonstrated that the system was able to reach a steady state in fermentation well within the 7-day adaptation period and even typically variable data (i.e., CH4 production) were stable within and across periods. While further research is needed to determine the relationship between this system and in vivo data, this continuous culture fermenter system provides a valid comparison of in vitro ruminal fermentation and enteric CH4 production of ruminant diets that can then be further validated with in vivo studies.

Projected heat stress challenges and abatement opportunities for U.S. milk production.

Cost-effective heat mitigation strategies are imperative for maintaining milk production and dairy farm profitability in the U.S. with projected climate change. This study investigated the cost-effectiveness of four heat abatement strategies, including Minimal (open barn or shading), Moderate (forced ventilation), High (fans and misting), and Intense (air conditioning). Heat stress and subsequent impacts on milk production per cow were predicted across nine climatic regions in the U.S. for early (2015 to 2034), mid (2045 to 2064) and late (2081 to 2100) 21st century, using downscaled climate projections. Heat abatements were used to adjust predicted milk production losses and illustrate the potential to reduce milk production losses due to heat stress. Economic analysis included a cost-benefit ratio calculation associated with the implementation of each heat abatement. Results showed that milk production losses were expected to accelerate across the U.S. at a mean rate of 174±7 kg/cow/decade, with the fastest rate in the Southeast region. Relative to Minimal heat abatement, Moderate, High, and Intense heat abatements increased annual milk production per cow by 3%, 4%, and 6% during early-21st century, 3%, 6%, and 11% during mid-21st century, and 3%, 8%, and 21% during late-21st century, respectively. The cost effectiveness of different heat abatement strategies generally increased with subsequently stronger heat abatements. In mid- and late-21st century, mean annual net values of High and Intense heat stress abatement implementation approached -$30 to $190 /cow and -$20 to $590 /cow, respectively, with the largest net annual benefit in late-21st century under Intense abatement. Findings from the study demonstrate the value of using downscaled climate projections to shed light on local and regional strategies to abate heat stress on cattle and mitigate potential milk production losses due to climate change.

Animal performance and environmental efficiency of cool- and warm-season annual grazing systems.

Annual forage crops can provide short-term grazing between crop rotations or can be interseeded into perennial pastures to increase forage quality and productivity. They also provide an opportunity to increase the economic and environmental sustainability of grazing systems. Cool-season annual forage crops provide high-quality, abundant forage biomass when forage availability from perennial forage species is lacking, reducing the need for stored feeds during the winter months. For example, ADG of 1.5 kg have been reported using small grains alone and in mixtures with annual ryegrass (Lolium multiflorum Lam.) while maintaining an average stocking rate of 3.5 animals/ha. No-till (NT) establishment has been shown to be as effective as conventional tillage for establishing small grain pastures. Stocker performance during the fall was not affected by tillage treatment, but during the spring grazeout, BW gain per hectare was 8% greater in NT pastures. An in vitro study showed that daily production of CH4 was 84% lower, respectively, in turnip (Brassica rapa L.) and rapeseed (B. napus L.) diets compared with annual ryegrass. Warm-season annuals are frequently used during the summer forage slump when perennial pasture growth and quality are reduced. Research has shown that brown mid-rib sorghum × sudangrass (BMR SSG; Sorghum bicolor L. × S. arundinaceous Desv.) and pearl millet (PM; Pennisteum glaucum L.R. Br.) with crabgrass (Digitaria sanguinalis (L.) Scop.) tended to have greater ADG (0.98 kg) than sorghum × sudangrass or peal millet alone (0.85 kg). However, non-BMR and BMR SSG tended to have greater gains per hectare than PM or PM + crabgrass (246, 226, 181, and 188 kg/ha, respectively). Feeding of brown mid-rib sorghum × sudangrass reduced daily production of CH4 and CH4 per gram of NDF fed by 66% and 50%, respectively, compared with a perennial cool-season forage in continuous culture. Cool- and warm-season annual pastures not only provide increased animal gains, but also increase soil cover and in vitro data suggest that annual forages (i.e., brassicas and warm-season annual grasses) decrease enteric CH4 emissions. Establishment method, grazing management, and weather conditions all play important roles in the productivity and environmental impact of these systems. A more complete life cycle analysis is needed to better characterize how management and climatic conditions impact the long-term economic and environmental sustainability of grazing annuals.

Enteric methane production and ruminal fermentation of forage brassica diets fed in continuous culture.

The aim of the current study was to determine nutrient digestibility, VFA production, N metabolism, and CH4 production of canola (Brassica napus L.), rapeseed (B. napus L.), turnip (Brassica rapa L.), and annual ryegrass (Lolium multiflorum Lam.) fed with orchardgrass (Dactylis glomerata L.) in continuous culture. Diets were randomly assigned to fermentors in a 4 × 4 Latin square design using 7 d for adaptation and 3 d for collection. Diets were: 1) 50% orchardgrass + 50% annual ryegrass (ARG); 2) 50% orchardgrass + 50% canola (CAN); 3) 50% orchardgrass + 50% rapeseed (RAP); and 4) 50% orchardgrass + 50% turnip (TUR). Feedings (82 g DM/d) occurred four times daily throughout 4, 10-d periods at 730, 1030, 1400, and 1900 h. Methane samples were collected every 10 min using a photoacoustic gas analyzer (LumaSense Technologies, Inc.; Santa Clara, CA) during the last 3 d of the experiment. Effluent samples were collected on d 8, 9, and 10, composited by fermentor, and analyzed for VFA and pH as well as DM, OM, CP, and fiber fractions for determination of nutrient digestibility. Forage samples were analyzed for CP, NDF, ADF, minerals, and glucosinolate (GLS) concentrations. Data were analyzed using the GLIMMIX procedure of SAS. Apparent DM, OM, and NDF digestibilities and true DM and OM digestibilities were similar (P > 0.28) among diets (45.1, 63.2, 44.1, 67.1, and 87.2%, respectively). Total VFA (87.2 mol/100 mol), pH (6.47), and acetate (A: 44.6 mol/100 mol) were also not different (P > 0.20) among diets. The A:P (P = propionate) ratio was greater (P < 0.01) in ARG and CAN than RAP and TUR. Daily CH4 production was greater (P < 0.01) in ARG than all other diets (68.9 vs. 11.2 mg/d). Methane, whether expressed as g per g of OM, NDF, digestible OM, or digestible NDF fed was greatest (P < 0.01) in ARG but similar (P > 0.18) among brassica diets. A significant negative correlation was observed between total GLS and CH4 production. However, when multiple regression analysis on CH4 production was completed, neither total GLS nor individual GLS were a significant component of the model. Addition of brassicas provided similar nutrient digestibility to ARG while reducing daily CH4 production, potentially making brassicas an alternative for ARG in pasture-based ruminant diets.