Reducing emissions from agriculture – the role of new farm technologies

Appendix 1: Detailed Analysis of Candidate Technologies

A1. Seaweed (Asparagopsis)

Functional Group: Livestock Management and Production

Sub-Functional Group: Feed Management ; Feed Supplements

Overview

Seaweed is a term for a diverse range of marine microalgae. Seaweeds are phylogenetically classed as Rhodophyta, Phaeophyta, or Chlorophyta, but are more commonly referred to as red, brown or green seaweed, respectively. Some seaweed species (particularly red species) contain halogenated methane analogues, such as bromoform (CHBr₃), which inhibit methane production by reacting with vitamin B12, suppressing the cobamide-dependent enzyme methyl-coenzyme (CoM) reductase step in methanogenesis. The species exhibiting the highest potential for enteric methane reduction is the red species Asparagopsis taxiformis.

GHG saving potential

There have been a small number of trials testing the efficacy of Asparagopsis for enteric methane reduction in live animals (in vivo) (beef:2, dairy:2, sheep:1). Seaweeds fed in these studies were harvested in Keppel Bay, Australia, or in the Azores, Portugal. Baseline diet and feeding duration varies widely between studies. There have been a wider range of laboratory (in vitro) studies (n=13). The in vitro studies investigate a wide range of seaweeds (red: 12, green: n=5; brown: n=5; mixed: 1) harvested from a variety of locations including Australia, Portugal, Korea, the USA and Canada.

All identified in vivo studies reported a significant reduction in methane yield for at least one dosage level. The average observed reduction in enteric methane emissions from beef cattle was 56.0 ± 9.4%, for dairy cattle 22.2 ± 9.75%, and for sheep 53.0 ± 13.78%. However, due to the small number of in vivo studies, these reductions are associated with wide 95% confidence intervals (beef: 37.6 to 74.3%; dairy 3.1 to 41.3%; sheep 26.0 to 80.0%). Mean inclusion rates of seaweed in these studies were 0.59 ± 0.19% feed organic matter (OM), ranging from 0.05 to 3% OM, with significant reductions in methane yield found at dosages as low as 0.1% OM in dairy cows (Roque et al., 2019) and beef cattle (Kinley et al., 2020).

The in vitro studies found an average methane reduction of 55.0± 7.3% for red species, 16.0 ± 5.2% for brown species and 34.6 ± 5.9% for green species. In studies where A.taxiformis was used, mean methane reductions of 74.0± 11.1% were achieved and where inclusion rates were≥2% OM, reductions in methane were consistently greater than 95%.

The below table summarises enteric methane reductions reported through in vivo studies. OM – organic matter; DMI – dry matter intake.

Abatement	Value	Country	Reference
Sheep
0.5 to 3% feed OM	-15.3% to -80.7% CH4 yield (g/kg DMI)	Australia	Li et al., 2018
Beef
0.25 / 0.5 % feed OM	-69.7% / -79.8% CH4 yield (g/kg DMI)	USA	Roque et al., 2021
0.05 / 0.1 / 0.2 % feed OM	-9% / -38% / -98% CH4 yield (g/kg DMI)	Australia	Kinley et al., 2020
Dairy
0.1 % feed OM	-42.7% CH4 yield (g/kg DMI)	USA	Roque et al., 2019
0.25 / 0.5 % feed OM	+3.6% / -29.4% CH4 yield (g/kg DMI)	USA	Stefanoni et al. 2021

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-	The effect will be greatest with Asparagopsis taxiformis
Manure CH4
Manure N2O
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions	Uncertain	Emissions associated with pre-farm production are uncertain but likely to be relatively small
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions	Uncertain	A study in Australia saw an uplift in productivity in red seaweed(Kinley et al., 2020)
	Rating
Confidence in mitigation effect
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Not known. Kinley et al (2020^[9]) Found that the uplift in productivity would lead to cost savings. A study in Wisconsin of Red Seaweed on beef steers found a reduction in feed costs in finishing cattle with no effect on meat quality^[10].

Applicability

Seaweed products used in efficacy experiments are simple preparations (dried and ground seaweed meal) that could be used directly on farm or incorporated into a range of feed products including pelleted compound feeds and potentially in feed blocks, tubs or licks as a means of reaching grazing livestock.

Interaction effects

Seaweeds are nutrient rich foods, including iodine and heavy metals, e.g., arsenic, mercury, lead, aluminium, cadmium, rubidium, silicon, strontium and tin (Moraiset al., 2020). Although these micronutrients are generally not at levels high enough to cause toxicity, bioaccumulation of arsenic, lead (Moraiset al., 2020) and iodine (Makkaret al., 2016)can occur and this level will vary dependent on the type, species and environmental conditions the seaweed was produced under (Roledaet al., 2018).Publications have concentrated on transfer of iodine from the animal to products for human consumption (particularly milk, e.g. Antayaet et al., 2019). However, high levels of iodine consumption by the animal can cause toxicity, leading to nasal and lacrimal discharge, coughing, pneumonia and skin irritation (Hillman and Curtis, 1979).More research into the conditions leading to high levels of trace nutrients is needed and great care must be taken that levels of minerals and heavy metals in the total ration do not exceed permitted or recommended levels.

A recent publication from The Netherlands (Muizelaar et al., 2021) has questioned the safety of bromoform for the animal. They examined the organs of two dairy cows slaughtered after receiving 67g of A. taxiformis per day for 22 days and found inflammation of the rumen wall and loss of papillae. They also detected Bromoform in milk, but this was not consistently across the experimental period.

Short-lived biogenic bromine-containing compounds, such as bromoform and bromochloromethane, emitted from seaweeds can cause ozone depletion (Wisher et al., 2014). The loss of ozone in the atmosphere leads to an increase in UVB rays reaching the Earth’s surface which is harmful to human, animal and plant health. Increased farming of seaweed, particularly red species rich in bromine-containing compounds such as A. taxiformis, could lead to increased emissions of bromocarbons. Estimates ranging from a 6 to 11 times increases in bromocarbon emissions from Malaysian red seaweed farms have been projected with increasing production (Leedham et al., 2013). However, a paper currently in review concludes that Asparagopsis farming in Australia, at a scale sufficient to provide supplement for 50% of Australian cattle, would have an insignificant effect on atmospheric ozone (Jia et al., 2021). More research is required to gain consensus.

Bromoform (the main active methane-mitigating molecule in Asparagopsis) has been linked to hepatic and renal toxicity in rodents: data in ruminants appear lacking (see Muizelaar et al., 2021). The concentration of this compound in livestock diets is not currently regulated.

A2. Other Feed Supplements

Functional Group : Livestock Management and Production:

Sub-Functional Group: Feed Management ; Feed Supplements

Overview

The following feed supplements are close to or on the market and are not considered further in this review:

Product name

Bovaer 10

Active principle

3-nitrooxypropanol

Supplier

DSM Nutritional Solutions, CH

Regulatory category

Feed Additive

Regulatory status

Authorised for lactating ruminants (EU)

Not yet authorised in UK

Product name

SilvAir

Active principle

Nitrate

Supplier

Cargill Animal Nutrition, USA

Regulatory category

Feed Material

Regulatory status

Nitrate is permitted as a source of NPN and Ca

Product name

Mootral

Active principle

Garlic

Supplier

Mootral, CH/UK

Regulatory category

Feed Material

Regulatory status

Garlic is a permitted feed material

Product name

Agolin Ruminant

Active principle

Plant extracts (essential oils)

Supplier

Agolin, CH

Regulatory category

Feed Additive

Regulatory status

Not authorised (under review by EFSA)

Product name

RumiTech

Active principle

Plant extracts (essential oils)

Supplier

Harbro, UK

Regulatory category

Feed Additive

Regulatory status

Authorised as sensory Feed Additive, not authorised as zootechnical Feed Additive (to reduce methane emissions)

A wide variety of feed supplements have been evaluated for effects on methane, over several years. For clarity, they are grouped here by mode of action. In summarising their efficacy, we have drawn mainly on the recent reviews of Arndt et al. (2021, an output from the Feed and Nutrition Network of the Global Research Alliance on Agricultural Greenhouse Gases) and Honan et al. (2021).

Direct inhibitors of methanogenesis

Halogenated compounds

Asparagopsis seaweed may prove to be a practical delivery mechanism for the halogenated compound bromoform, as discussed in a previous section.

Other halogenated compounds including bromochloromethane (BCM), bromoethanesulphonate (BES) and chloroform (the subject of research since the mid-60s) all inhibit the last step in the methanogenesis pathway. However, in contrast to 3-NOP, which specifically inhibits the enzyme, methyl-CoM reductase, these halogenated compounds inhibit the supply of methyl-coenzyme M. Early research reported marked reductions in methane production, but also rapid adaptation so that these reductions did not persist. Tomkins et al. (2009) encapsulated BCM (which is volatile) in cyclodextrin and were able to lower methane production in feedlot steers by 50-60% for at least 90 days. However, BCM has an ozone depleting effect and its use is restricted, leading Tomkins et al. (2009) to doubt that it would ever be commercialised as a methane mitigator. With the current focus on seaweed as a source of bromoform, it is hard to see potential in direct use of synthetic halogenated compounds as methane mitigators.

Statins

It has been known for several years that statins (e.g., lovastatin, mevastatin) inhibit the enzyme HMG-CoA reductase that is rate-limiting to the biosynthesis of a key component of the methanogen cell membrane (interestingly, this same pathway is involved in cholesterol synthesis, explaining the medicinal use of statins to prevent hypercholesterolaemia). Abrego-Gacia et al. (2021) reviewed six in vivo studies in which statins reduced methane yield by an average of 19%. Statins came from various sources, which may explain the wide variation in response in methane yield (from +3% to –42%).

Use of the same high purity statin preparations used in human medicine as feed supplements is probably unaffordable. However, statins are produced by various fungal species which can be grown quite simply on agricultural residues through solid-state fermentation. While this may offer a route to low-cost, home-produced supplements (especially suitable for use in developing countries), it may also be a disincentive to the development of supply chains of commercial supplements, especially as prior art (dating back to at least the publication of Miller and Wolin, 2001) is an obstacle to the protection of intellectual property (patent and commercial applications exist for the use of statins to suppress enteric methane in humans, and in environmental bioremediation).

The production of statin-rich fermentation products under controlled industrial conditions, offering appropriate quality control, has not, to our knowledge, been explored.

Nitrocompounds

Research, primarily in the US, has investigated effects of various nitrocompounds, including nitroethane (synthetic), 3-nitro-1-propionate and 3-nitro-1-propanol (naturally occurring) (Latham et al., 2016). The mode of action may be a mix of electron acceptor (like nitrate) and direct inhibitor, although the mode of action remains unclear. Research on these nitrocompounds, and the possibility of identifying naturally-occurring plant extracts enriched with them, is continuing (e.g., Bozic et al., 2022). However, with the focus on commercialisation of 3-NOP and nitrate, it seems unlikely that direct inhibition of methane by these other nitrocompounds will be developed into commercial practice.

Alternative sinks for hydrogen

Sulphate

Like nitrate, reduction of sulphate is thermodynamically favourable and will remove hydrogen from the rumen. Like nitrate, the amount of sulphate that can be added before issues of toxicity arise is limited, placing a ceiling on the amount of methane that can be prevented. Toxicity is due to the end product of sulphate reduction, hydrogen sulphide, which is inhaled after eructation from the rumen, leading to the condition polioencephalomalacia. Novel nitrate oxidising sulphide reducing bacteria, with the potential to minimise ruminal accumulation of both nitrite and hydrogen sulphide (both undesirable), have been identified, but little seems to have been done to develop them as viable probiotics for the purpose of methane mitigation.

Distillers’ grains contain a higher level of sulphate than other concentrate ingredients. One opportunity to use sulphate to deliver a small but real reduction in methane is to recognise its contribution when formulating concentrate feeds using distillers' grains.

Organic acid salts (fumarate, malate, succinate).

The reduction of fumarate, malate and succinate to propionate consumes hydrogen that would otherwise be used to make methane. There would be no major regulatory or practical barriers to the use of these salts as feed supplements, if found to be effective. Despite evidence of efficacy in vitro (reductions in methane yield of around 10%), responses in vivo have been generally small, leading Arndt et al. (2021) to classify fumarate as ineffective.

Further work is needed to explore interactions between these salts (as hydrogen sinks) and other strategies (e.g., use of direct methane inhibitors). One idea to improve the efficacy of fumarate is to add a probiotic microorganism to accelerate its reduction to propionate. One might then foresee a three-way combination: a methane inhibitor, fumarate as an alternative hydrogen sink, and a probiotic to promote the metabolism of fumarate. Combining different approaches in this way, even if technically successful, would add significant cost, and each element would require regulatory approval.

Biochar

It has been proposed that biochar, with its very large surface area, may itself act as an alternative electron sink, and one recent paper reported a 10% reduction in methane in growing steers (see Honan et al. (2021) for reference and discussion). However, biochar may affect emissions through other mechanisms, so responses may be variable and unpredictable. Further research is certainly justified.

Reductive acetogenesis

The reduction of CO₂ by H2 to form acetate is an alternative to its reduction to form methane, and reductive acetogenesis dominates over methanogenesis in the guts of, for example, termites and marsupial mammals. However, at hydrogen concentrations typical of the rumen, methanogenesis is thermodynamically more favourable than reductive acetogenesis. Addition, as probiotics, of bacteria capable of reductive acetogenesis has not, hitherto, successfully lowered methane emissions in vivo.

It recently been shown that ruminal concentrations of hydrogen rise after feeding, with a lag before a rise in methane production. Hydrogen levels also rise when methane is inhibited directly, for example by 3-NOP. Is it possible that strains of reductive acetogens can be found that make a positive contribution, perhaps only for short period of the daily feeding cycle, in combination with other approaches to methane mitigation. There is at least evidence of continued research in this area.

Lower hydrogen production

Ionophores

Monensin is the best known and most researched ionophore antibiotic. These are naturally occurring, lipid soluble substances which are products of microbial fermentation (originally isolated from soil microorganisms). Monensin acts to change the end products of fermentation, favouring the production of propionate and thus generating less hydrogen.

There have been ~25 in vivo studies (dairy: 10; beef: 8; buffalo: 3; goat: 3; sheep: 1). Studies used a variety of forages for periods lasting from 5 to 200 days, and production response was measured in 18 of these studies. A total of 29 in vitro studies were also identified. Across in vivo studies, a mean reduction in methane yield of 6.7 ± 1.6% was observed (dairy: 5.9 ± 2.5%; beef: 5.1 ± 3.5%; buffalo: 8.5 ± 1.5%; goat: 4.4 ± 2.5%; sheep: 11.0 ± 6.8%) with significant reductions found for at least one experimental condition in 13 studies. One study measuring methane emissions from beef steers over a ten-week period (using the SF₆ method) found a depression in emissions for 3-5 weeks, but the effect was transient (Guan et al., 2006). Significant differences in methane emissions have been found between treatment and control animals after extended periods of time in dairy cows (180 days, Odongo et al., 2007) and beef cattle (161 days, Hemphill et al., 2017). In vitro studies found mean reductions in enteric methane of 29.2 ± 3.1% with significant reductions observed for at least one dosage level in 22 studies.

Monensin was previously authorised in the EU as a feed additive to improve growth and feed efficiency in cattle, except lactating cows. This use in cattle was prohibited from January 2006. A preparation (bolus with controlled rumen release) was authorised as veterinary medicine for the prevention of ketosis in cows. This product is recommended to be dosed 3-4 weeks before calving and is expected to deliver monensin into the rumen for 95d. The contribution of methane mitigated during this time to the carbon footprint of milk production is not currently recognised.

Defaunation

Hydrogen-producing protozoa live in symbiosis with methanogenic archaea, and it has long been recognised that a reduction in the protozoal population (partial defaunation) is associated with lower methane emissions, partly by removing their associated methanogens and partly by reducing hydrogen production.

A variety of approaches to defaunation have been researched and are mentioned briefly below. None has yet found specific application for the purpose of methane mitigation.

Saponins. Supply chains of saponins (mainly from Yucca and Quillaya plants) have been developed for other industrial purposes and they have found some use in animal agriculture to lessen odour from manure and improve ruminal N metabolism. They are well-known as methane inhibitors (see Newbold et al. (2018) for summary), but it is equally well-known that the rumen can adapt and cleave the two components of the saponin, so that effects on methane are not persistent. Novel strategies to prevent the breakdown of saponins in the rumen (which accounts for the loss of activity) have been researched (Ramos-Morales et al., 2013) but not developed commercially.

Condensed tannins. Condensed tannins may exert several effects on rumen fermentation, including defaunation (but also decreasing fibre digestion and acting as a hydrogen sink, with the exact mechanism likely being dependant on the source or type of tannin). Effects on methane production are highly variable, and may be due to a negative effect on dry matter feed intake with increasing tannin concentration (Aboagye and Beauchemin, 2019).

GHG saving potential

Abatement			Value	Country	Reference
Monensin
24 mg/kg DMI (Dairy cows)			-2.9% CH4 yield	Canada	Benchaar et al., 2020

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-	Some feed additives focused on productivity with reduced methane as a side effect
Manure CH4	-
Manure N2O
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions	?	Unknown interaction effects with other supplements
	Rating
Confidence in mitigation effect	Low
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Unknown

Applicability

This technology is applicable to farmed animals (cattle,sheep, pigs). These come as additives to feed so should be straightforward to apply.

Interaction effects

Relatively few studies have examined interactions between different methane-mitigating feed supplements, although we could hypothesise that supplements acting through different mechanisms might have synergistic, or at least additive effects. For example, Duthie et al. (2018) tested nitrate and distillers’ grains, as a source of unsaturated fatty acids, alone or in combination. Effects on methane yield were additive. Patra and Yu (2015), working in vitro, found additive effects of nitrate, sulphate and saponin.

Barriers to research on combinations of additives include the understandable priority of technology owners to invest in their own products, and the economic challenge of using more than one mitigating agent in practice, if true synergy can be found. Further structured, hypothesis-driven study of combinations of additives is certainly scientifically justified.

A3. Rock dust

Functional Group : Land Management

Sub-Functional Group : Nutrient Management

Overview

Enhanced weathering of silicate rock materials contributes to the removal of carbon dioxide from the atmosphere (Beerling et al. 2020; Beerling et al. 2018). It has been proposed that crushed rock dust could be applied at large scales to cropland soils to enhance carbon dioxide removal from the atmosphere. Through weathering processes, carbon dioxide is transformed into organic carbon (mostly in the form of bicarbonate ions) which is transferred though watercourses to the oceans where the carbon is deposited and stabilised of thousands of years. Carbon may also be stored in soils in the form of carbonates. Silicate rocks such as basalt have a higher capacity for CO₂ removal than normal liming materials (calcium and magnesium carbonate), and existing infrastructure for lime application can be used to spread silicate rock dust. It has been reported that enhanced weathering has the potential to remove between 0.5–5 Gt CO₂ yr^–1 at a global scale by 2050 (Fuss et al. 2018), which makes the scale of sequestration comparable with soil carbon sequestration and afforestation.

The image shows spreading rock dust in a typical arable field (Source: Yale University, 2021^[11])

GHG saving potential

The main greenhouse gas saving potential from enhanced rock weathering comes from carbon dioxide removal from the atmosphere. Abatement potential by agricultural soils in the UK has been estimated between 0.2 and 0.8 tonnes of CO₂ per tonne of basic rock (Kantola, 2017; Renforth, 2012). Notably, the sequestration potential will vary depending on the chemical composition of the rock material. Ultrabasic rocks with especially high magnesium and calcium contents can sequester > 1 tonne of CO₂ per tonne of rock applied (Kantola, 2017). There is some evidence that rock minerals may also contribute to the reduction in methane and nitrous oxide emissions from soils, whilst boosting the productivity of arable soils (Blanc-Betes et al. 2021; Das et al. 2019).

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	0
Manure CH4	0
Manure N2O	0/-
Soil N2O: applied N	0
Soil N2O: grazing	+/-
Energy CO2: fieldwork	+
Energy CO2: other	+
CO2 liming and urea	-	Rock dust will balance soil pH, reducing liming requirements
CO2 sequestration below ground	-
CO2 sequestration above ground	0
Pre-farm emissions	+	Mining and processing silicate rocks into dust is energy intensive
Post-farm emissions	0
Substitution of higher C products	0
Production increases by more than the emissions	0/-
	Rating
Confidence in mitigation effect	Medium
Cost-effectiveness**	Low
Confidence in cost-effectiveness	Medium

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Costs of rock weathering include the production and distribution of rock waste and in field application costs. Total costs have been estimated at £44–£361 per tonne CO₂ captured. Major costs are related to the energy required for transport and processing of silicate materials.

Applicability

This technology is applicable to any managed soil, provided spreading machinery can operate on the terrain. Direct application in the open ocean has also been proposed.

Interaction effects

Potential benefits to plant nutrition have been reported through the application of certain rock materials, increasing the nitrogen and phosphorus nutrition of crop plants the(Jones et al. 2021). Rock dust from materials such as basalt also provide a substitute for lime application

A4. Biochar

Functional Group : Land Management

Sub-Functional Group : Nutrient Management

Overview

Biochar is a carbon rich material, similar to charcoal, produced through the pyrolysis of organic material. Pyrolysis releases half of the carbon in organic feedstocks and fixes the rest in aromatic chemical structures which resist decomposition (Lehmann, 2021). The application of biochar to agricultural soils has the potential to enhance soil carbon storage over millennia and improve soil health and crop productivity. Biochar production can also be coupled with energy generation and carbon capture and storage to produce low carbon heat and electricity.

Over the past decade, the application of biochar to agricultural soils has received considerable attention. The benefits of biochar to soil health, carbon storage, and crop productivity have been extensively demonstrated in tropical areas with degraded and dry soils (Smith, 2016). A handful of studies also indicate small benefits to crop yields across arable systems in temperate countries (Hammond, 2013). Notably, the high pH of biochar could be especially beneficial for soils in Scotland, where nearly half of all agricultural areas sampled by the Farm Advisory Service suffer from reduced productivity due to low soil pH.

The image shows the process by which biochar support plant growth (Source: Chukwuka et al., 2019^[12])

Biochar has additional applications beyond use as a soil amendment. It is commonly used as a feed additive across Europe with proven benefits to livestock emissions, productivity, and health (Schmidt, 2019). Biochar can also be added to manures and composts to reduce emissions during decomposition, though further research is required to validate and quantify these benefits. Finally, biochar can also be included as a component of sustainable growing media for conventional horticulture and vertical farms.

GHG saving potential

Biochar production and application reduces greenhouse gas emissions by increasing soil carbon stores, reducing agricultural and energy related emissions, and improving crop productivity (Lehmann, 2021). Total GHG abatement will vary depending on organic feedstock, production technology, and predicted effects on crop yields. UK studies estimate an abatement potential of 0.7-1.4 t CO₂eq/ oven dry tonne (Hammond, 2011; Shackley & Sohi, 2010).

The challenge in confidently estimating the abatement potential of biochar as a soil amendment lies in assessing its impacts on crop productivity and soil nitrous oxide emissions (Borchard, 2019: Kammann, 2017). Many studies suggest biochar application reduces soil nitrous oxide emissions, but conflicting and divergent results suggest further research is needed to fully understand these effects. Effects on crop productivity vary with climate, soil type, and crop type, and these impacts have proven difficult to predict or explain (Lehmann, 2021).

Though the evidence base for biochar as a feed and manure additive is less developed, studies suggest significant reductions can be achieved. As a feed additive, biochar can reduce enteric methane emissions by as much as 20%, though reductions around 10% are more common across the literature (Kammann, 2017). Adding biochar to cattle slurry has been shown to reduce nitrous oxide emissions by as much as 63% (Brennan, 2015). Furthermore, biochar-containing manures may contain higher plant-available nutrients, which could further reduce emissions through enhanced crop productivity (Schmidt, 2019).

Life cycle assessment of horticultural growing media has demonstrated that replacing horticultural peat with biochar reduces emissions by 238 co2eq per cubic metre due to offset emissions from energy production and avoided emissions from peat use (Fryda, 2018).

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-	When used as a feed additive
Manure CH4
Manure N2O	-	When used as a manure additive
Soil N2O: applied N	-
Soil N2O: grazing	-
Energy CO2: fieldwork	+	Biochar application will require fuel use
Energy CO2: other
CO2 liming and urea	-	Possible reduction in liming requirements
CO2 sequestration below ground	+
CO2 sequestration above ground
Pre-farm emissions	+/-	Biochar production causes upstream emissions, but these can be offset if pyrolysis is coupled with energy production
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions
	Rating
Confidence in mitigation effect
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

The cost of biochar depends heavily on the production technology and organic feedstock used. In a 2010 study, Shackley & Sohi estimated costs from production to field application at £0–430 per tonne. The lowest cost options use water feedstocks such as garden waste, food waste, or sewage sludge. Profitability is also higher for systems which produce biochar and renewable energy. Shackley et al. 2011 estimate the cost of abatement for biochar between -144 and 208 £/tCO₂.

Applicability

Biochar can be applied to any managed soil but is mainly seen as advantageous as a soil amendment for arable fields and grasslands. Alternative uses of biochar apply to other agricultural systems; biochar can be used as a feed or manure additive across livestock enterprises and as a component of sustainable growing media in indoor agriculture systems.

Interaction effects

Biochar is a relatively low-risk technology. Contaminated feedstocks could present as area of negative impacts. For example, heavy metals are not removed in the biochar production process. Additionally, carcinogenic polycyclic aromatic hydrocarbons may be produced during pyrolysis, though there is limited information available on this. Finally, potential impacts on freshwater systems related to black carbon runoff require further assessment (Tisserant, 2019).

A5. Microbial Proteins

Functional Group : Livestock Management and Production

Sub-functional: Alternative proteins/ Microbial proteins

Overview

Microbial protein is referred to as single cell protein (SCP), although some of the producing microbes, such as filamentous fungi or filamentous algae, may be multicellular. Single Cell Proteins are based on the continuous fermentation of micro-organisms and emerge from growing yeast, bacteria or microalgae. Their potential is in replacing mostly soya bean meal (SBM) within animal diets with the appropriate amino acid and nutritional composition. The fast growth rate of yeast and bacteria means that these organisms present a promising economical method for large-scale oil and protein production, but inputs of carbon chains are required.

Yeast and bacteria-based SCP have been included in aquaculture feed. In 1990s in Finland, it was commercialised for pig feed. SCP from yeast is being examined as a feed for dairy cattle, chickens and pigs, there is some evidence that certain species have the potential to replace in-feed antibiotics as well due to its antimicrobial properties.’ Commercially available options include Feedkind Terra and Profloc (Nutrinsic Inc)

Some studies have found that microalgae can be used as a protein source for lactating dairy cows in intensive milk production systems, which makes them a suitable substitution for Soya bean meal or faba beans^[14].

GHG saving potential

The GHG impact has not been studied in any depth. However, is considered as a replacement for soya based meal and is therefore carbon off-setting. Some pointers that can be found in the literature is that since it does not really rely on Haber-Bosch based N fertiliser, there is much less footprint compared to protein production in conventional agriculture (Singa et al., 2021). In addition, accounting for nitrate losses from agricultural land-based protein production needs to be considered as well.

One study did look at LCA of SCP vs SBM (Spiller et al 2020) and observed the latter being worse in terms of human health impact and ecosystems impact but better in terms of resource use overall (energy-related aspects), which differed between types of SCP production systems.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4
Manure CH4
Manure N2O
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions
Post-farm emissions
Substitution of higher C products	-	Replacement for SBM though within limits
Production increases by more than the emissions
	Rating
Confidence in mitigation effect
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Costs has been estimated at £0.84-£1.60 per kg dry end product, which is more than that of soybean meal, currently trading at around £0.36 per kg(April, 2022).

Applicability

Applied to most animal sectors, including aquaculture. Each sector has its own barriers, and whilst most advances in fish feed and poultry/pigs still work to apply to ruminant sector.

Interaction effects

Unknown

A6 Underground Soil Sensors

Functional Group : Land Management

Sub-Function: Soil Monitoring/Sensors

Overview

Underground soil sensing uses a number of sensors and devices that can help in the real-time monitoring of soil fertility. These sensory devices incorporate various communication protocols for relaying the sensory data (Ghosh et al., 2021^[15]). Essentially this means a number of sensors buried and distributed under the soil. Wireless sensors pose the least disturbance to soil structure and having fewer aboveground cables reduce the risk of undesired equipment damage and potential data loss(Levintahl et al., 2021^[16]). These sensors form an array which continually monitor soil health parameters for crop growth, e.g. water and nutrient intake. The sensor usually communicates through a base station, or an echo station to increase the signal. These measures then integrate into a package which offers a dashboard of real time data and allow farmers, with an appropriate software package, to support decision making in terms of early warning system to support crop growth and consequently benefits overall yield but reduce excess inputs. Could also be coupled with other precision agriculture approaches.

The product is buried underground at various depths, at shallow depth and at root depth. This depends on type of crop, e.g., cereals at 30 cms or root crops which will be deeper. Planting density is based on field characteristics but around 6 per field(?) is recommended as the base. A battery life of 20 years allows these to be buried without disturbance.

A commercially available product is recently launched but mostly tested on a small number of trial farms in Finland and specialist horticultural enterprises in South Africa. The system is used in sports turf management, hence could be applied to intensively managed grassland systems if deemed cost-effective.

GHG saving potential

Main benefits are to improve yield per ha, by identifying interventions but also prevention of over application of nutrients and irrigation as sensors provide root health outputs. When coupled with precision farming equipment this could offer precise application of water and fertiliser.

No study on underground sensors and GHG savings exist but a number promote the idea that this would have benefits. Hence, we cannot quantify the impact but identify that savings would be on nutrient application. Also, an effect of reduced crop failure may have positive, if marginal, effects on CO² above ground sequestration.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4
Manure CH4	-	Targeting application of nutrients
Manure N2O	-	Targeting application of nutrients
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground	-	Effect of reduced crop lost before sprouting
Pre-farm emissions
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions
	Rating
Confidence in mitigation effect	Low	No estimates or trials exist
Cost-effectiveness**	High	Significant cost for implementation with arguably marginal gains
Confidence in cost-effectiveness	Medium	Continued costs on subscriptions to understand metrics may not create a return.

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Cost of a basic package of 6 sensors - estimated at around £6,000 including a 36 month subscription to the monitoring app^[17]. Dependant on depth, size and characteristics it's likely that 6 sensors will not be enough to cover Scottish fields, given the variance in gradient and structure. A yearly subscription is needed to translate the sensors into a viable metric and potentially locks the farmer into a rolling contract. Presumably some linking up of data with machinery will support targeted application of fertiliser, hence data needs to be easily transferable to other manufacturers.

Applicability

Mostly applied to intensive, high value products - fruit for example, though overall this sector has a lower carbon footprint than general cropping or specialist cereals farms. If rolled out to cropping sector, then potentially would have greater applicability to root crops, in particular potatoes, which may provide a positive return on investment. Conceivably can be used on intensive grassland but may struggle to get a return.

Interaction effects

Note the technology will be water saving in dry years. There may be CO² emissions from power use if the decision-support tool relies on large scale computing arrays.

A7 Cloud-based bioinformatics

Functional Group : Crop Management

Functions: Crop improvement

Overview

Bioinformatics is defined as the application of tools of computation and analysis to the capture and interpretation of biological data. Cloud based computing platforms provide the oppourtunity to link data on plant breeding parameters and, usually apply machine learning or, in some cases, artificial intelligence, to identify patterns which then support decision making.

Cloud based platforms are either publicly available open source for scientists/breeder or commercially owned for a subscription service. Some small start-ups are appearing which target aspects such as soil biology analysis (https://biomemakers.com/), species monitoring for pest control (https://www.bioverselabs.com/) and reduction of antimicrobial resistance with engineered alternatives (https://www.next-biotics.com/technology)

There seem to be no services directed at Scottish or UK farmers generally but would require tech investment to target UK species and provide a market that provides a return.

GHG saving potential

The benefits of the systems would be to add to decision making in terms of improving crop production - yield and reduced pests - and soil health - nutrients and management - through targeted solutions.

The benefits may be offset by the carbon emissions generated from large scale computing arrays. Grealy et al (2022)^[18] identified the significant power consumption needed to support analytical services but this could be managed through, e.g., renewable energy sources.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4
Manure CH4
Manure N2O
Soil N2O: applied N		Soil testing - though no assessment of whether this is more accurate than standard soil testing
Soil N2O: grazing
Energy CO2: fieldwork	-	More precise timing of machinery runs in field
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground	-	Reduced wastage, potential higher crop yield and harvesting
Pre-farm emissions	+	Energy use from computational arrays
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions
	Rating
Confidence in mitigation effect	Low
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Potentially subscription based model. A cost of service model may emerge for targeted advice.

Applicability

If tailored to Scottish conditions could cover all arable areas, though would need to prove better than current low-tech options, e.g. soil analysis.

Interaction effects

Should increase productivity and reduce management time

A8 Biological nitrification inhibitors

Functional Group : Crop management and production

Sub-Function: Targeted nutrient management

Overview

Biological nitrification inhibitors are natural products released into the soil by plants because of the release of secondary metabolites that can reduce the nitrous oxide emissions associated with nitrification by soil microorganisms (de Klein et al. 2022). Their action is analogous to synthetic nitrification inhibitors such as DCD which can be added to the fertiliser products to reduce nitrous oxide emissions associated with nitrification. Nitrification is known to be a significant source of nitrous oxide emissions from soils, and BNIs have been demonstrated to inhibit the conversion of ammonium nitrogen to nitrate in both field and laboratory studies. A wide range of plant species have been identified as contributing to BNI, including temperate forage species such as plantain (Plantago lanceolata). It is also possible to use products derived from plant materials such as Neem oil, which is widely used in India to coat urea fertilisers providing a mitigation option that is based upon nitrification inhibition. The understanding and performance of nitrification inhibitors in plant communities and their potential application for managed agricultural environments is at an early stage, and application of this technology is likely to require further research.

GHG saving potential

The greenhouse gas saving potential of BNIs is almost entirely related to their ability to reduce soil derived nitrous oxide emissions. Studies in tropical grasslands have shown a potential for BNIs to reduce N₂O emissions in the field by up to 90% (Subbarao et al. 2013). There is more limited evidence for the impact of BNIs in temperate systems, but work in New Zealand has shown that nitrous oxide emissions may be reduced by more than 50% for the use of plantain within species rich swards (de Klein et al. 2020; Luo et al. 2018; Simon et al. 2019). The mechanism of this effect is not entirely clear, as it could result from the direct effects of plant exudates on soil nitrification rates but could also result from digested forages having an impact on nitrification rates in the urine deposited by grazing livestock.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-
Manure CH4	-
Manure N2O	0 / -
Soil N2O: applied N	+
Soil N2O: grazing	+
Energy CO2: fieldwork	+
Energy CO2: other
CO2 liming and urea	-
CO2 sequestration below ground	-
CO2 sequestration above ground	-
Pre-farm emissions	+
Post-farm emissions	-
Substitution of higher C products	-
Production increases by more than the emissions	-
	Rating
Confidence in mitigation effect	Medium
Cost-effectiveness**	High
Confidence in cost-effectiveness	Low

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

In most circumstances the costs would be expected to be relatively low for this mitigation measure. The implementation would be likely to involve the use of mixed swards containing plants such as plantain in grasslands. In such grassland systems costs are likely to be close to zero or potentially even negative if there are ancillary benefits of mixed swards (for example fertiliser savings or increased resilience to drought). In arable systems it could involve the use of intercropping or the application of crop residues containing biological nitrification inhibitors. In the circumstances they would be a small marginal cost but again this would depend on any ancillary benefits that were offered by the alternative management approach.

Applicability

In the first instance, use of BNIs as a mitigation option would be most likely to be applicable to grazed grasslands. This would involve the use of multi-species swards which have been demonstrated to deliver multiple benefits in terms of increased nutrient use efficiency reduce nitrous oxide emissions and increased resilience to climate change (Cummins et al. 2021).

Interaction effects

There is some evidence that multi species swards containing BNI’s can also contribute to a reduction in methane emissions in ruminant livestock (Loza et al. 2021). Reductions in the rate of nitrification in soils would be expected to result in reduced nitrogen leaching, and potentially increased nitrogen use efficiency following fertiliser application. Given that this mitigation measure is dependent on natural biogeochemical cycling in the impact of existing plant species on nutrient cycles, it is unlikely that there would be any negative impacts associated with the application of this technology.

A9 Genetic profiling/Genomic testing in breeding programme

Functional Group: Livestock improvement

Sub-Function: Genetic profiling/Genomic testing in breeding programme

Overview

Genomic selection uses molecular DNA marker (single nucleotide polymorphisms, SNPs) located in the genome of animals to estimate the link between animal genomics and the traits under selection, e.g., milk yield, lifespan, fertility, to select the best animals at a younger age with higher accuracy than traditional selection (Meuwissen et al., 2001). Over the last decade, the use of genomic selection in dairy breeding programmes has more than doubled the rate of genetic gain in the net profit index of the traits under selection (e.g., United States, García-Ruiz et al., 2016; Australia, Scott et al., 2021). This genetic improvement results in a reduction in GHG emissions per kg product referred to as GHG emission intensity. Methane emissions from enteric fermentation in ruminants is the largest contributor to agricultural GHG emissions and have been reported to globally contribute to 39% of CO₂-equivalent GHG emissions from livestock (Gerber et al., 2013). In the Dutch dairy population, De Haas et al. (2021) predicted a 13% reduction in methane intensity from 2018 to 2050 using the present breeding goal, which could be increased to 24% if methane emissions are measured e.g., with sniffer technology in the milking parlour. In the UK, AHDB recently introduced a breeding index, EnviroCow that focus on traits such as cow lifespan, milk production, fertility, and feed advantage with the aim to select cows with the least GHG emissions in their lifetimes for each kg solids-corrected milk. However, the improvement could be substantially higher when methane emissions are accurately and cost-effectively measured or predicted by a proxy trait. A proxy trait accurately predicting methane emissions have been identified to be the rumen microbiome composition (Roehe et al., 2016; Auffret et al., 2018; Lima et al., 2019; Martinez-Alvaro et al., 2021). They have developed a rumen microbiome-driven breeding strategy using genomic selection which has the potential to decrease methane emissions and improve feed conversion efficiency without the need to measure those traits

GHG saving potential

The potential reduction in methane intensity due to existing breeding using genomic selection are predicted by de Haas (2021) to be 13% over about 30 years and can be increased to 24% using measured methane emissions using e.g., sniffer technology. As breeding is cumulative and permanent, these reductions in methane intensity due to breeding are equivalent to 0.45% and 0.88% per year, respectively.

Using genomic selection within the microbiome-driven breeding strategy, Martinez-Alvaro et al., (2022) predicted based on methane emissions of beef cattle recorded in respiration chambers of the SRUC Beef Research Centre a reduction of up to 17% per generation depending on the intensity of selection and breeding only for reduction in methane emissions. Considering that in a breeding programme using genomic selection, a generation interval of 2.25 years can be achieved, the genetic gain per generation would be equivalent to an up to 8% reduction in methane emissions per year or cumulatively up to 50% in 10 years.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-	Mainly targeting enteric methane emissions
Manure CH4	-	Indirect due to improvement of feed efficiency
Manure N2O	-	Indirect due to improvement of feed efficiency
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions	-	Selection on production and fitness traits associated with GHG emission intensity
	Rating
Confidence in mitigation effect	High
Cost-effectiveness**	High
Confidence in cost-effectiveness	High

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Breeding for traits presently under selection and related to methane intensity are cost neutral. If there are more emphasis on these traits in the breeding goal, then there is expected to be a loss in genetic gain in traits not or unfavourable related to methane intensity.

Using microbiome-driven breeding has additional cost involved in taking rumen samples and analysing the samples to determine the rumen microbiome composition. However, this has to be done only for a relatively small reference population (4000 animals) and the rumen sampling could be incorporated, e.g., in beef during testing of cattle for feed conversion efficiency.

Applicability

Genomic selection is applied in all livestock species (mostly dairy, pig and poultry, at a lesser extend in beef and sheep). Microbiome-driven breeding using genomic selection is developed for ruminants to reduce methane emissions but could be also used for improvement of feed conversion efficiency and animal health traits, which are reducing methane intensity.

Interaction effects

Selection for low methane emitting animals is expected to have no negative effects on animal health and productivity as shown in a selection experiment on sheep in New Zealand (Rowe et al., 2019).

A10 Fluoride and tannin additive to manure

Functional Group: Livestock Management and Production

Sub-Functional Group: Further Methane Management

Overview

Manure storage and management is a significant source of national ammonia, nitrous oxide, and methane emissions. Tannic acid and sodium fluoride (TA-NaF) have been shown to eliminate the majority of ammonia and methane emissions from stored manures whilst reducing disruptive odours by half (Dalby, 2021). Tannic acid is a naturally occurring plant compound which disrupts bacterial cell membranes, while sodium fluoride acts as an inhibitor of ammonia-producing enzymes (Svane, 2020). Compared to other manure additives, such as sulfuric and nitric acids, TA-NaF contributes to greater emissions reductions and lower environmental health and human health risks (Dalby, 2020b).

Tannic acid and sodium fluoride are already produced at an industrial scale for other uses. Tannic acid is a common food additive with additional uses in wastewater treatment and medicine. Sodium fluoride is a common ingredient in dental care products and is also used as an insecticide. Their synergistic activity in reducing manure emissions is a recent discovery by researchers in Denmark as part of the "Next Generation Manure Ammonia Reduction Technology" project (Dalgaard, 2020). The product is currently undergoing further trials, and a patent application has been filed. Additional trials are needed on a range of manures and manure management systems to fully understand the impacts of TA-NaF on manure emissions.

GHG saving potential

In experiments with pig manure, TA-NaF has demonstrated a 95% reduction in ammonia emissions, 99% reduction in methane emissions, and 50% reduction in odour (Dalby, 2020b). This is a highly promising result, but other studies at lower dosages have not identified any emission reductions (Dalby, 2021). Thus, further research is needed to confidently establish the abatement potential of this technology. In addition to direct emission reductions, TA-NaF will reduce nitrogen losses from manures, improving crop productivity and potentially reducing emissions related to synthetic fertiliser use.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4
Manure CH4	-	Significant reduction in manure methane
Manure N2O
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions	+	Embedded emissions related to chemical production
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions
	Rating
Confidence in mitigation effect
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Major costs associated with this technology are related to high costs of tannic acid (Dalgaard, 2020). Minimum effective dosage will improve economic performance, but financial support will likely still be required for farmers to adopt TA-NaF as no clear productivity benefits have been defined.

Applicability

Major trials have mainly studied impacts on emissions from pig manure, but TA-NaF could be applicable to manures from any housed livestock system. A small set of experimental evidence suggests methane inhibition is greater for TA-NaF applied to cattle manure (Dalby, 2020a).

Interaction effects

Tannic acid is a natural product which naturally degrades faster than other manure additives. Fluoride can be toxic to wildlife and plant life at high doses, but the concentrations in treated manures do not exceed those found naturally in soils. Possible inhibitory effects on crops and soil microbiota from application of treated manures should be evaluated before widespread adoption (Dalby, 2020b).

A11. Methane Vaccine

Functional Group: Livestock Management and Production.

Sub-Functional Group: Further Methane Management.

Overview

In the course of microbial fermentation in the rumen H2 is produced. Methanogens (methane producing microbes) oxidise this H₂ to reduce CO₂ to form CH₄. There is currently interest, particularly in New Zealand, on the use of vaccinations to decrease the number of methanogens present in the rumen. The vaccine works by triggering an animal’s immune system to generate antibodies in the saliva which then pass into the animal’s rumen and suppress growth and function of methanogens.

GHG saving potential

Methane vaccines are still in the development stage, with ongoing work assessing efficacy. Summaries of saving potential, both in vitro and in vivo, are given in the “mitigation summary” section below.

Mitigation summary

Recent systematic review (Baca-Gonzalez et al. 2020) has assessed the potential of vaccines for methane reductions in ruminants (both in vitro and in vivo). Efficacy ranged from 7.7% to 69% methane reduction, there were also multiple studies which were unsuccessful in vivo.

Effect of vaccine production on methane emissions (table adapted from Baca-Gonzalez et al. 2020)

Effect on methane production

12.8/14.8% ¹ methane reduction in vitro

Compared Groups

Sheep vaccinated with methanogen mix vs. Pre-vaccinated/vaccinated with adjuvant or PBS

References

Baker et al. 2020

Effect on methane production

26.26% ¹ methane reduction in vitro

Compared Groups

Sheep vaccinated with methanogens mix vs. adjuvant and PBS

References

Baker et al. 2020

Effect on methane production

Unsuccessful in vivo

Compared Groups

Sheep vaccinated with mixes of three or seven methanogens vs. adjuvant and PBS

References

Wright et al. 2004

Effect on methane production

12.8% methane reduction in vivo 7.7% methane reduction in vivo, corrected for dry-matter intake

Compared Groups

Sheep vaccinated with mix of three methanogens vs. adjuvant and PBS

References

Wright et al. 2004

Effect on methane production

Unsuccessful in vivo

Compared Groups

Sheep vaccinated with mix of seven methanogens vs. adjuvant and PBS

References

Wright et al. 2004

Effect on methane production

Unsuccessful in vivo

Compared Groups

Sheep vaccinated with three methanogens vs. adjuvant

References

Clark et al 2004

Effect on methane production

Unsuccessful in vitro

Compared Groups

Sheep vaccinated with three methanogens plus additional methanogens vs. adjuvant

References

Clark et al 2004

Effect on methane production

Unsuccessful in vitro

Compared Groups

Three semi purified IgY from hens vaccinated with three methanogens vs. semi purified IgY from prevaccinated hens

References

Cook et al. 2008

Effect on methane production

20% methane increase with anti-Methanobrevibacter ruminantium IgY 15% methane increase with anti-M. smithii IgY corrected for dry-matter disappearance

Compared Groups

Three freeze-dried egg powders from hens vaccinated with three methanogens vs. freeze-dried egg powder from prevaccinated hens

References

Cook et al. 2008

Effect on methane production

34% methane reduction with anti-M. smithii IgY 52% methane reduction with antiMethanosphaera stadtmanae IgY 66% methane reduction with their combination, corrected for dry-matter disappearance

Compared Groups

Three freeze-dried egg powders from hens vaccinated with three methanogens vs. freeze-dried egg powder from prevaccinated hens

References

Cook et al. 2008

Effect on methane production

Unsuccessful

Compared Groups

Three freeze-dried egg powders from hens vaccinated with three methanogens vs. freeze-dried egg powder from prevaccinated hens

References

Cook et al. 2008

Effect on methane production

49–69% reduction, corrected for dry-matter disappearance

Compared Groups

Freeze-dried egg powder from pre-vaccinated hens vs. without egg powder addition

References

Cook et al. 2008

Effect on methane production

Unsuccessful in vivo

Compared Groups

Sheep vaccinated with five methanogens vs. adjuvant and PBS

References

Williams et al. 2009

Effect on methane production

29% ¹ methane reduction in vitro

Compared Groups

Sera from sheep vaccinated with M. ruminantium M1 whole cells vs. prevaccinated sheep sera

References

Wedlock et al. 2010

Effect on methane production

40% ¹ methane reduction in vitro

Compared Groups

Sera from sheep vaccinated with M. ruminantium M1 cytoplasmic fraction vs. pre-vaccinated sheep sera

References

Wedlock et al. 2010

Effect on methane production

Unsuccessful in vitro

Compared Groups

Sera from sheep vaccinated with M. ruminantium M1 wall fraction vs. prevaccinated sheep sera

References

Wedlock et al. 2010

Effect on methane production

Unsuccessful in vitro

Compared Groups

Sera from sheep vaccinated with M. ruminantium M1 wall fraction with trypsin vs. prevaccinated sheep sera

References

Wedlock et al. 2010

Effect on methane production

40%¹ methane reduction in vitro

Compared Groups

Sera from sheep vaccinated with derived-protein M. ruminantium M1 wall fraction vs. prevaccinated sheep sera

References

Wedlock et al. 2010

Effect on methane production

Unsuccessful in vivo

Compared Groups

Goat vaccinated with protein rEhaF from M. ruminantium M1 vs. animal vaccinated with elution buffer plus adjuvant

References

Zhang et al. 2015

¹ Approximate values from article figures.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-	Note lack of efficacy
Manure CH4	-	As above
Manure N2O
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions	-
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions
	Rating
Confidence in mitigation effect
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Unknown

Applicability

Applicable to sheep, dairy and beef cattle worldwide. Possibility to be administered the same time as other routine vaccines.

Interaction effects

Unknown, still in development stage, however this will likely be assessed in the future.

A12. Smart Cattle Sheds

Functional Group : Livestock management and Production

Function: Further methane management

Overview

Design of a networked housed cattle system. No single definition exists but would be composed of linked up a) animal health monitoring system, b) management of microclimate, c) methane extraction. The monitoring system is connected to a low power low range wireless communication technology.

The proposed system wirelessly collects real-time information from sensors installed in the cow and the cattle shed, and the collected data are analysed by the integrated management system, delivered to the user, and automatically controlled by the application.

A number of projects have explored the design of a shed, for instance the Cornell University's new Teaching Dairy Barn or the Tark-Laut EU funded project^[20] focused on managing the microclimate with housed cattle. Animal mounted sensors (pedometers, ear-tags, collars) record activity, feeding times, temperature, rumination, and feed to a dashboard.

GHG saving potential

Claims of GHG Savings tend to focus on optimising livestock production. Ostensibly this would mean an improvement in productivity, through prevention and early diagnosis of health problems, improved welfare and energy saving on farm in terms of managing the micro-climate. Further, the SRUC Green Shed project tested extraction technology to remove methane and burn it through an anaerobic digester as a means to bring in a circular economy approach.

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-	Maybe reflective of improved health and welfare status
Manure CH4	-	Potential for removal and reuse as energy
Manure N2O
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other	-	Closed sheds offer chance to capture heat
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions	+/-	Applies to housed cattle, e.g. finishing beef or dairy-beef
	Rating
Confidence in mitigation effect	Med
Cost-effectiveness**
Confidence in cost-effectiveness

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

High capital cost would need payback over time. Mostly conducted in public sector organisations. No commercially available product is available and mostly at proof-of-concept stage.

Applicability

Applies to cattle which are housed in winter but would be reflective of intensive nature to provide a return. High technology mostly associated with dairy farming

Interaction effects

Unknown

A13. Connected animal mounted sensors

Functional Group : Livestock management and Production

Function: Improved technical efficiencies

Overview

The use of precision livestock farming (PLF), or agritech, tools on farm is increasing globally, with farmers utilising technology in the daily management of their herds and enterprises. When exploited to their full potential, PLF solutions can aid management and improve animal health (Neethirajan, 2017), welfare and production (Berkmans, 2014), can monitor or reduce greenhouse gas (GHG) emissions (Hammond et al., 2016), improve overall farm operational performance (Michie et al. 2020) and improve traceability of livestock products (Morgan-Davies et al., 2015), among others. However, some farmers do not utilise PLF solutions to their full potential, often utilising only a small amount of the functions available to them.

Whilst not intended to influence GHG emissions directly, PLF technologies, such as those intended to improve health and welfare, can do so by improving the efficiency of the animals and therefore the farm. There is a direct link between GHG emission intensities and animal efficiency (Grossi et al., 2018). The more efficient an animal is, i.e., the more productive, the lower the environmental impact is per unit of product, such as milk or meat (Grossi et al., 2018).

The use of PLF tools and techniques on farm not only improves the health, welfare, and production of the animals themselves, but reduces the overall carbon footprint of the enterprise. Optimising resource use by improving animal production efficiency through PLF techniques has the potential to maximise the profitability of pasture-based and housed systems and improve the environmental sustainability of ruminant production.

Mitigation summary

Whilst not intended to influence the GHG emissions of a farm, PLF technologies, such as those intended to improve fertility, can do so by improving the efficiency of the animals and therefore the farm. There is a direct link between GHG emission intensities and animal efficiency (Grossi et al., 2018). The more efficient an animal is, i.e. the more productive, the lower the environmental impact is per unit of product, such as milk or meat (Grossi et al., 2018). Technologies designed to improve efficiencies can be split into three broad categories applicable to both beef and dairy systems, and in both grazing and housed situations:

• Technologies designed to reduce slaughter age (e.g., automated weigh crates, 3D cameras, animal mounted systems to monitor intake and growth of animals)
• Animal mounted sensors designed to monitor and improve fertility. This covers oestrus detection, pregnancy detection and calving detection.
• Technologies designed to improve animal health and welfare (e.g., animal mounted sensors and accelerometers, rumen pH boluses to monitor rumen dysfunction).

Impacts of PLF introduction on whole farm emissions and emissions per unit of product have been modelled using an established carbon foot printing tool (Agrecalc; SAC Consulting). This was carried out on both average Scottish beef and dairy farms (using data from CTS) - results are summarised below:

BEEF (spring calving upland Suckler system, Bowen et al. 2022a and b)

Five scenarios were modelled, and emissions compared to baseline: using technology to reduce slaughter age by one, two and three months, and technology designed to improve fertility, and improve health and welfare. All scenarios reduced both total farm emissions (2.4 - 7.4%) and emission intensities (1.5 - 11.9%).

DAIRY (8000L all year-round calving; Ferguson et al. 2022 and Bowen et al 2022b)

Three scenarios were modelled, and emissions compared to baseline: using technology to improve fertility, improve fertility and milk yield, and improving health and welfare. All scenarios, except improving fertility and increasing milk yields (0.7% increase), showed reductions in whole farm emissions (0.4 - 0.9%) and all scenarios reduced emissions intensities (3.0 - 9.0%).

Mitigation summary

GHG categories	Effect*	Notes
Enteric CH4	-
Manure CH4	-
Manure N2O	-
Soil N2O: applied N
Soil N2O: grazing
Energy CO2: fieldwork
Energy CO2: other
CO2 liming and urea
CO2 sequestration below ground
CO2 sequestration above ground
Pre-farm emissions
Post-farm emissions
Substitution of higher C products
Production increases by more than the emissions
	Rating
Confidence in mitigation effect	High	Information provided here is based on modelling carbon footprints of beef & dairy farms (Agrecalc). Assumptions for modelling based on published literature, communication with technology companies and expert opinion.
Cost-effectiveness**	Medium	Good ROI but over multiple years (not instantly cost-effective)
Confidence in cost-effectiveness	High	Many PLF solutions readily available on market, cost known barrier to uptake

* ”-“ GHG reduction, “+”: GHG increase, “ ”: no significant effect

** low: =< £0/ tCO₂e, moderate: £0/ tCO₂e< >SCC, high: >SCC

Cost

Cost dependent on technologies used:

£20 to £250 per animal mounted sensor plus additional cost for basestation, software, repeaters and installation (ranging from £1,000 to £10,000 depending on system/manufacturer). This includes sensors to record activity, rumination, temperature, location, pH, oestrus, health etc.

£7000 for automatic weigh crate (e.g., BeefMonitor weigh system) plus £1500 for additional solar panel system for outdoor use

Applicability

Applied to both beef and dairy cattle. Also applicable across production systems regardless of if cattle are housed or outside grazing.

Interaction effects

Systems designed to improve health etc. therefore, unlikely to have detrimental effects to the animal. Combining various technologies will increase reductions in GHG emissions observed.