Information

Hill, Upland and Crofting Farmer-led Group: climate change evidence

A summary of existing evidence around Hill, Upland and Crofting (HUC) farming, including greenhouse gas emissions produced by the Rural and Environment Science and Analytical Services (RESAS) division.


Annex D – CXC Measures for LFA Cattle & Sheep

This annex contains an extract of mitigation measures from the CXC (2020) report that are specific to the dairy sector.

3NOP feed additive for cattle

3-Nitrooxypropanol (3NOP) is a chemical substance that reduces the emission of enteric methane by ruminants when added to their rations. It does so by reducing the rates at which rumen microbes convert the hydrogen in ingested feed into methane. Specifically, 3NOP inhibits the final step of methane synthesis by microbes. For housed animals, the 3NOP could be mixed in with the ration, while in grazing situations it may be possible to deliver the 3NOP via a bolus.

Overview

3NOP is a chemical that reduces the excretion of enteric methane by ruminants when added to their rations (or introduced via a bolus). It does so by reducing the rates at which rumen archaea convert the hydrogen in ingested feed into methane. Specifically, 3NOP inhibits methyl-coenzyme M reductase, the final step of methane synthesis by archaea (Duin et al. 2016).

The ingestion of a small amount of 3NOP each day is required, typically in the range of.0.05 to 0.2g NOP per kg of DMI (Javanegara et al. (2017), i.e. for cattle the effective dose is likely to be in the order of 2-3g of 3NOP/animal/day (Haisan et al. 2014, Martinez-Fernandez et al. 2018). For housed animals. the 3NOP could be mixed in with the ration. For grazing animals, it may be possible to deliver the 3NOP via a bolus (Rooke et al. 2016, p13).

Greenhouse gas mitigation summary

While 3NOP is a new mitigation measure (it was patented in 2012, Duval and Kindermann 2012) a range of experimental studies and meta-analyses have been undertaken. Most of the studies with 3NOP have focused on high quality concentrate-based diets. However Martinez-Fernandez et al (2018) found a reduction in enteric methane from beef cattle fed a roughage diet.

Table D1: Summary of studies of the mitigation effect of 3NOP
Livestock type Parameter Effect Country Year Reference
Dairy cattle Enteric methane yield -4 to -7% UK 2014 Reynolds et al. (2014)
Milk yield and fat No effect
Milk protein Increase
Beef cattle Enteric methane yield -33% Canada 2014 Romero-Perez et al., (2014)
Daily weight gain No effect
DMI Small decrease
Dairy cattle Enteric methane yield -60% Canada 2014 Haisan et al., (2014)
DMI, milk yield No effect
Daily weight gain Increased
Dairy cattle Enteric methane yield -30% USA 2015 Hristov et al., (2015)
DMI, milk yield No effect
Daily weight gain Increased
Beef cattle Enteric methane yield -7 to- 81% (varies with diet and dose) Canada 2016 Vyas et al., (2016)
Daily weight gain No effect
DMI High dose: reduced
Beef and dairy cattle Enteric methane yield -30% Canada 2016 Duin et al. (2016)
Ruminants Enteric methane yield -19 to -33% Various Various Jayanegara et al., (2017)
Beef cattle Enteric methane yield -38% Australia 2018 Martinez-Fernandez et al (2018)
Daily weight gain Increase
Beef cattle Enteric methane yield -37 to -42% Canada 2018 Vyas et al. (2018)
FCR -5%
Beef cattle Enteric methane yield -17.1% ±4.2% Various Various Dijkstra et al. (2018)
Dairy cattle Enteric methane yield -38.8% ±5.5%

*methane yield: the kg of methane per kg of dry matter intake (DMI)

Jayanegara et al. (2017) undertook a meta-analysis of 3NOP based on 12 in vivo studies from 10 articles. Their results showed that increasing level of 3NOP addition in diets of ruminants decreased enteric methane emissions per unit of DMI, while having no effect on DMI and limited effects on the production performance of both dairy cows and beef cattle. They concluded that "3NOP is an effective feed additive to mitigate enteric methane emissions without compromising productive performance of ruminants". Papers published since 2017 reinforce this conclusion. Based on the above-mentioned results, we assumed that 3NOP reduces the enteric methane yield by 30% and 20%, respectively, in dairy and beef.

In theory, the feed energy otherwise lost as methane will be transferred for animal functions; this will improve the animal performance. Assuming that 10% of the feed energy is consumed in generating methane, and that the methane reduction as a result of the use of 3NOP ranges from 20% (beef) to 30% (dairy), then the reduction of feed consumption when 3NOP is used would range from 2% (beef) to 3% (dairy). As a conservative estimate, we applied a 2% yield increase for both dairy and beef.

It should be noted that changes in enteric methane conversion factor as a result of 3NOP are likely not to be additive with other methane mitigation methods, e.g. breeding and high-starch diet.

Costs

No one-off costs arising from the measure are predicted. The main recurring costs are likely to arise from the purchase and administering of 3NOP. It has been estimated that the cost of Mootral (an alternative to 3NOP) would be $50 per cow per year (Zwick 2017). i.e. £38.

Current uptake and maximum additional future uptake

In theory, 3NOP could be used with beef cattle, dairy cattle, and sheep. The current uptake of the measure is zero. The industry is seeking approval for commercial application of 3NOP by early 2021. If it is successful, the potential uptake rate from that date is 100% in Scotland - we assumed maximum uptake on all housed animals.

Assumptions used in the MACC

Table D2: Assumptions used in the modelling
Parameter Change in value
Dairy
YM -30%
Milk yield +2%
Cost £38 animal-1
Beef
YM -20%
Live weight +2%
Cost £38 animal-1

Cattle breeding for low methane emissions

The composition of the micro-organisms present in the gut of mammals is influenced by the genetics of the host animal. Studies indicate that it is possible to select dairy cattle for low methane emission, as methane production is heritable to some extent. Inclusion of low enteric methane emission in the breeding goal could reduce methane emissions from cattle, though might limit the productivity and fitness improvements, as selection for low emission causes changes in the animal's nutritional physiology.

The measure assumes that enteric methane emission is introduced in the breeding goal and therefore animals are started to be selected considering their enteric methane emissions. The measure requires farmers buying (semen from) breeding animals with lower methane emissions. The improvements in emissions are cumulative over the years as the emissions from the individual animals get reduced by breeding. Genetic improvement in the national herd can be enhanced by using genomic tools, while farmers collect performance information on the individual animals and genetic testing, and feed this information back for breeding goal development. As well as the methane emission reductions, using genomics also means production traits can be improved.

Overview

The composition of the micro-organisms present in the gut of mammals is influenced by the genetics of the host animal (Hegarty and McEwan, 2010). It has been shown possible to select sheep for high or low methane emissions, as methane production is heritable to some extent (Pinares-Patiño et al. 2013). Studies indicate that dairy cattle have the potential for genetic selection for low methane emission too (de de Haas et al. 2011, Roehe et al. 2016). Inclusion of low enteric-methane emission in the breeding goal could reduce methane emissions from cattle, but might limit the productivity and fitness improvements to some extent, because selection for low emission causes changes in the animal's nutritional physiology.

The measure entails starting breeding for low enteric-methane emission in the national herd (via including the methane emissions in the breeding indices) and farmers buying the animals with lower methane emissions. The improvements in emissions are cumulative over the years as the emissions from the individual animals get reduced by breeding.

Genetic improvement in the national herd can be enhanced by using genomic tools. This entails farmers collecting performance information on the individual animals and genetic testing and feeding back this information to breeding goal development. By using these tools not only can the gains in methane emission reduction be achieved more quickly but production traits can also be improved.

Greenhouse gas mitigation summary

Dairy and beef production would increase (annual gain of 0.75% in milk yield, milk protein and fertility for dairy, and annual gain of 0.25% in live-weight, growth rate and fertility for beef cattle), reducing the emission intensity of products, and the enteric methane conversion factor would decrease by 0.15% of its value every year.

Costs

To realise the measure £2.5m in research investment would be needed in the UK for the dairy herd, of which 9% would be attributed to Scotland (based on dairy cow proportions between the four nations). The beef research would need another £2.5m in the UK, 21% of it falling to Scotland. Furthermore, in every five years £0.5m would be needed to fund both the dairy and the beef genomic tools in the UK. The genomic testing required on farms costs £20 for each bull (either dairy or beef). It is assumed a dairy bull would serve 500 cows while a beef bull would serve 100 cows. The productivity gains would translate into increased income from sales at the farm level.

Current uptake and maximum additional future uptake

The measure is assumed to be applicable to 45% of the dairy and 20% of the beef herd.

Assumptions used in the MACC

Table D3: Assumptions used in the modelling
Parameter Change in value
Dairy
Milk yield 0.75% year-1
Milk protein content 0.75% year-1
Cow fertility 0.75% year-1
Methane conversion factor -0.15% year-1
R&D cost £2.5M in every 5 years in the UK (9% of it in Scotland)
Genomic tool cost £0.5M in every 5 years (9% of it in Scotland)
Genomic testing £20 bull-1 (serving 500 cows)
Beef
Live-weight 0.25% year-1
Growth rate 0.25% year-1
Cow fertility 0.25% year-1
Methane conversion factor -0.15% year-1
R&D cost £2.5M in every 5 years in the UK (21% of it in Scotland)
Genomic tool cost £0.5M in every 5 years (21% of it in Scotland)
Genomic testing £20 bull-1 (serving 100 cows)

Covering slurry stores with impermeable cover

Animal excreta stored in liquid systems is a source of substantial ammonia and methane emissions, as during the storage N and the volatile solids excreted turn into these gaseous compounds. Though nitrous oxide is not generated in large quantities in slurry stores, a small portion of the ammonia turns into nitrous oxide subsequently in the environment (the process is called indirect nitrous oxide emission). Several factors affect the rate of ammonia, methane and nitrous oxide emissions, including the airflow over the manure; by covering the stores these emissions can be reduced. The presence of a slurry cover increases the ammonia concentration of the slurry and hence its nitrogen content and fertiliser value, but also the potential subsequent ammonia and nitrous oxide losses when the slurry is applied to the soil, unless low ammonia emission spreading techniques are implemented. Cover technologies include floating covers, rigid covers, natural crust and suspended, tent-like structures, and their effects on the pollutant gases are very different.

A review of experimental results showed that impermeable plastic covers have the potential to reduce ammonia and GHG emissions in parallel. However, there can be feasibility problems with floating covers if applied on slurry tanks or larger lagoons and their durability is not yet well tested. Impermeable covers do not inhibit methane formation, so the gas built up under the cover needs to be managed to avoid an explosion risk (in this measure the flaring or purification of the methane is not assumed). Furthermore, depending on the structure, rainwater can accumulate on impermeable floating covers and needs to be removed via e.g. pumping.

Overview

Animal excreta stored in liquid systems is an important source of ammonia and methane emissions because, during the storage, N and the volatile solids excreted turn into these gaseous compounds. In these systems (unless the slurry is aerated), direct nitrous oxide formation is less important as the anaerobic environment blocks denitrification (Sommer et al. 2000). However, a small portion of ammonia emissions turns into nitrous oxide (indirect nitrous oxide emissions). Several factors affect the rate of ammonia, methane and nitrous oxide emissions, including the airflow over the manure. Thus, by covering the store, these emissions can be reduced (Hou et al. 2014; VanderZaag et al. 2015).

Cover technologies include floating covers, rigid covers, natural crust and suspended, tent-like structures (VanderZaag et al. 2015). Ammonia loss is a physiochemical process controlled by the ability of ammonia in the slurry to diffuse to the atmosphere; covers restrict diffusion by creating a physical barrier. With reduced ammonia emissions, indirect nitrous oxide emissions also reduce. The presence of a slurry cover increases the ammonia concentration of the slurry and hence its N content and fertiliser value, but also potential subsequent ammonia and nitrous oxide losses when the slurry is applied to the soil, unless low ammonia-emission spreading techniques are implemented.

The effects of cover solutions on direct GHG emissions are less explored however, with variable and inconclusive results (Hou et al. 2014; Montes et al. 2013; Sajeev et al. 2018; VanderZaag et al. 2008; VanderZaag et al. 2015). Crust formation, straw addition and the use of granules, in particular, tend to increase nitrous oxide emissions substantially, often overriding the emission savings in methane and indirect nitrous oxide emission reductions (Hou et al. 2014; Sajeev et al. 2018). The effects of these covers on methane emissions are variable, with high probability of increased emissions. A review of Hout et al. (2014) showed that impermeable plastic covers have the potential to reduce ammonia and GHG emissions in parallel.

However, there are feasibility problems with floating covers, in general, if applied on slurry tanks or larger lagoons (not on small earth-banked lagoons), and their durability is not yet well tested (Amon et al. 2014). When the slurry is covered by impermeable films, the formation of methane is not eliminated, and the gas builds up under the cover and in the liquid, creating an explosion risk and escaping when the cover is opened (Montes et al. 2013). With additional devices (gas pipes and pumping system) most of the methane can be captured and converted to CO2 either by direct flaring, reducing the GWP substantially, or by purification and use in electricity or heat generation. Furthermore, depending on the structure, rainwater can accumulate on impermeable floating covers and needs to be removed via e.g. pumping.

Greenhouse gas mitigation summary

Table D4: Data from literature on abatement
Abatement Value Country Reference
Methane emissions -47% (g methane–C (kg VS)-1) Sweden (Rodhe et al. 2012)
Direct nitrous oxide emissions -100% (g nitrous oxide–N m-2) Sweden (Rodhe et al. 2012)
Ammonia emissions -80% (range: -59% - -95%) Various Review of four papers in (VanderZaag et al. 2015)

Costs

Cost information on slurry covers has been collated by VanderZaag et al. (2015) from North American and UK sources. They estimated the capital costs of floating impermeable covers to be in the range of €1.70 m-2 to €63 m-2 with a lifespan of 8-10 years and 2% annual maintenance costs for rainwater collection. The high cost solutions included negative pressure covers to keep the film tight on the slurry surface.

Current uptake and maximum additional future uptake

The slurry covers can be installed on all slurry tanks and lagoons.

Assumptions used in the MACC

Table D5: Assumptions used in the modelling
Parameter Change in value
Methane conversion factor -47%
Direct nitrous oxide emissions from storage -100%
Ammonia emissions from storage -80%

Improved health of ruminants

Endemic, production-limiting diseases are a major constraint on efficient livestock production, both nationally and internationally, and have an impact on the carbon footprint of livestock farming. UK systems are particularly vulnerable to endemic disease impacts because they are largely pasture-based. The emissions intensity of ruminant meat and milk production is sensitive to changes in key production aspects, such as maternal fertility rates, mortality rates, milk yield, growth rates and feed conversion ratios - all of which are influenced by the health status of the animal. Therefore, improving health status is expected to lead to reductions in emission intensity. Animal health is a complex topic, influenced by a plethora of diseases. It can be improved through preventative controls (such as changing housing and management to reduce stress and exposure to pathogens; vaccination; improved screening and biosecurity; disease vector control) and curative treatments such as antiparasitics and antibiotics. In this work a simplistic approach was chosen; rather than estimating the GHG effects of the prevention and control of individual diseases, a general improvement in the health status was assumed, without reference to specific management options.

Overview

Endemic, production-limiting diseases are a major constraint on efficient livestock production, both nationally and internationally, and have an impact on the carbon footprint of livestock farming (Elliott et al. 2014). UK systems are particularly vulnerable to endemic disease impacts because they are largely pasture based. The emissions intensity of ruminant meat and milk production is sensitive to changes in key production aspects, such as maternal fertility rates, mortality rates, milk yield, growth rates and feed conversion ratios. All of these parameters are influenced by health status, so improving health status is expected to lead to reductions in emission intensity (Skuce et al. 2014). However, there have been few empirical studies investigating the impact of any of the production diseases on GHG emissions intensity.

Health can be improved through preventative controls (such as changing housing and management to reduce stress and exposure to pathogens, vaccination, improved screening and biosecurity, disease vector control) and curative treatments such as antiparasitics and antibiotics.

Greenhouse gas mitigation summary

The impact of endemic disease is difficult to quantify, often relying on old data from experimental challenge studies, which do not reflect the natural presentation of many of these diseases. ADAS (2014) attempted to quantify the impact of the top cattle health 'conditions' on the carbon footprint of a litre of milk, and the reductions that could be made via veterinary and/or farm management interventions. The study concluded that a 50% movement from current health status to a healthy cattle population (assumed to be the maximum improvement achievable) would reduce the UK emissions by 1436 kt CO2e year-1, or 6%. Eory et al. (2015) used a similar approach to quantify the effect of improving sheep health, and estimated that a 50% movement from current health status to a healthy sheep population would reduce the UK emissions by 484 kt CO2e year-1 by 2035.

Several studies have been undertaken since the 2015 MACC (Eory et al. 2015), which are briefly summarised below.

UK cattle and sheep health

Skuce et al. (2016) reviewed the evidence on prevalence and impact for 12 key ruminant diseases. They identified potential GHG emissions savings for all twelve diseases evaluated, while noting that some diseases are more tractable than others. They concluded that emissions intensity could be reduced through control measures relating to:

  • milk yield and cow fertility rates (dairy systems)
  • cow/ewe fertility and abortion rates
  • calf/lamb mortality and growth rates (beef and sheep systems), and
  • feed conversion ratios (all systems).

Three diseases, one from each of the major livestock sectors, were considered more cost-effective and feasible to control: neosporosis (beef cattle), infectious bovine rhinotracheitis, IBR (dairy cattle) and parasitic gastroenteritis (sheep).

Worms in sheep

Houdijk et al. (2017) undertook experiments to determine the effect of parasitism on the emissions intensity (EI) of sheep and found that infection with Teladorsagia increased calculated global warming potential per kg of lamb weight gain by 16%. Fox et al. (2018) also undertook experiments infecting sheep with Teladorsagia and found that infection led to a 33% increase in methane yield and a significant decrease in lamb growth rates, which led the authors to conclude that "there is potential for parasitism to have an extensive impact on greenhouse gas emissions".

Worms in beef cattle

Gut worms are the most important gastrointestinal nematode parasites of grazing cattle, responsible for considerable sub-clinical disease and production loss. Bellet et al. (2016) undertook an abattoir study of prevalence and production impacts in England and Wales of Ostertagia spp. (the study also recorded the effects of rumen fluke and liver fluke). Based on this data set, MacLeod and Skuce (2019) estimated that the growth rates of cattle with a high Ostertagia burden were about 10% lower than those with a low burden. This translates into a difference in EI of 3.9%, i.e. the high-burden herd produced 3.9% more GHG for every kg of liveweight output. Assuming the overall burden could be halved with appropriate treatment implies that the EI could be reduced by 2%.

Liver fluke in beef cattle

Skuce et al. (2018) investigated the impact of liver fluke infection on cattle productivity and associated GHG emissions intensity (EI) using abattoir data from NE Scotland from 2014-2016. The study focused on a cohort of 22,349 Charolais males from a total dataset of ~250,000 cattle. Liver fluke infection resulted in a statistically significant reduction in liveweight gain of 0.023kg/day and an extra 21 days to slaughter. As a result, the EI of meat from a herd with no fluke is approximately 1% lower than the same herd with fluke. The study only focused on one impact of fasciolosis (reduced growth rates) - other effects include changes in feed conversion ratio, mortality and fertility, milk yields and quality of output (e.g. carcass conformation and rates of liver condemnation). These will have an additive effect on greenhouse gas EI, so removing fluke may have a much greater impact on EI in practice.

Lameness in dairy cattle

Lameness can reduce dairy cow milk yield, thereby increasing the EI of the milk produced. Chen et al. (2016) calculated the effect of lameness on EI, using the impacts of lameness reported in a series of studies undertaken in Europe and North America. They estimated that lameness can lead to an increase in emissions intensity of 1-8% compared to a baseline scenario, depending on the prevalence of the disease. Mostert et al. (2018) investigated the effects of three types of foot lesions in Dutch dairy cattle: digital dermatitis (DD), white line disease (WLD), and sole ulcer (SU). They found that the impacts of these lesions on milk yield and calving interval led to an average increase in milk emissions intensity of 1.5%.

Conclusion

The studies undertaken since 2015 indicate that the abatement potentials given for improved cattle and sheep health in Eory et al. (2015) are achievable (while bearing in mind that studies with negative findings are less likely to be submitted for publication). Furthermore, they provide specific examples of how the abatement potential might be achieved, i.e. by reducing the incidence of gastrointestinal parasites, liver fluke and lameness.

Costs

As improving livestock health is a very broad measure, encompassing a variety of livestock management, disease prevention and treatment options, this study, following previous studies, estimated the cost-effectiveness of the measures (based on earlier publications) and derived the costs from the cost-effectiveness.

Eory et al. (2015) estimated that improving cattle health could be achieved at an average of £-42 t CO2e-1, while the cost-effectiveness of improving sheep health would be £30 t CO2e-1. As there are many possible combinations of health challenges and treatments, the cost-effectiveness of achieving mitigation via improved health is likely to vary considerably; flocks and herds with below average health status are likely to provide scope for larger and more cost-effective reductions in greenhouse gas.

Current uptake and maximum additional future uptake

We assume that 80% of the herd could have improved animal health.

Assumptions used in the MACC

Table D6. Assumptions used in modelling
Parameter Change in value
Milk yield +6.38%
Cost £28 animal-1

Contact

Email: are.futureruralframework@gov.scot

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