5 - Potential management practices and technologies for reducing methane emissions from agriculture

Summary

The main findings on methane mitigation options are:

  • Reducing livestock numbers is an effective method of reducing methane emissions but is not a viable financial option for livestock farmers.
  • Feeding animals better through the use of concentrate feeds will reduce emissions but is not financially viable in New Zealand's low cost systems.
  • The use of grass cultivars selected for improved animal performance could in theory decrease methane emissions per unit of animal product but no experimental evidence is available.
  • Some less common forage species (e.g. lotus, sulla) that contain high concentrations of condensed tannins do appear to produce less methane when digested by ruminants but they are difficult to incorporated into New Zealand's farm systems.
  • The effect of improved grass cultivars and alternative forage species on total emissions is estimated to produce a maximum reduction of 5%. Their impact is constrained by the limited amount of land that is re-seeded each year. If more land is re-seeded the negative impact of cultivation on carbon storage has to be considered.
  • Probiotics are feed supplements that directly affect rumen function. On the evidence available they are likely to have a small impact on total methane emissions (<1.5%)
  • Ionophores, especially monensin could reduce emissions by up to 8% if used extensively in the beef, sheep and dairy sectors. The caveat is that very little of the evidence comes from grazing animals. To reduce methane at a reasonable cost, ionophores also need to increase animal performance. There may be consumer resistance to the routine use of ionophores as they are a type of antibiotic. Ionophores also decrease the amount of N excreted by ruminants and should therefore help to reduce N2O emissions from pastures.
  • Other technologies targeted at directly influencing rumen fermentation (e.g. vaccines) are only at the early research/concept stage and are unlikely be available within the next 5 years.

5.1 - Introduction

The concentrations of methane (CH4) in the atmosphere are estimated to have doubled over the last two centuries, with much of this increase being attributed to anthropogenic sources. Current estimates of global emissions of methane range between 500,000 - 600,000 Gg. Of this 90,000 -115,000 Gg arise from livestock (Ehhalt et al. 2001). The principle source of livestock methane is enteric fermentation in the digestive tract of ruminants, although small amounts are produced by enteric fermentation in monogastric animals (pigs & poultry). The anaerobic fermentation of animal wastes also produces methane, with the amount dependant upon how they are stored and handled. When deposited directly onto pastures, dung from grazing animals undergoes aerobic fermentation and produces insignificant amounts of methane

New Zealand has a small industrial base, a small human population and large numbers of ruminants; methane is therefore an important contributor to total green house gas (GHG) emissions. Official figures (MfE 2000), give total methane emissions in New Zealand of 1590 Gg per annum, of which approximately 1400 Gg arises from ruminants. New Zealand's livestock farming systems are based on grazing ruminants outdoors all year round and the waste products of digestion are deposited directly onto pastures and so produce very little methane. In the national inventory, 99% of the methane produced by ruminants is attributed to enteric fermentation.

Enteric methane arises as a by-product of the fermentation of feed in the rumen. The rumen contains a large and diverse population of micro organisms and these break down feed to produce volatile fatty acids (VFA's), carbon dioxide (CO2) and methane. The micro organisms responsible for the production of methane are methanogens, which synthesise methane from hydrogen. The VFA's produced in the rumen are absorbed and used as an energy source but most of the CO2 and CH4 is removed from the rumen by eructation. The amount of methane produced in the rumen varies with factors such as diet type, level of feeding, size, age and species of animal. As a percentage of the gross energy consumed, between 2-15% is lost as methane (Johnson & Ward 1996). Therefore, reducing the amount of methane produced by ruminants has implications both for the concentrations of GHG's in the atmosphere and the efficiency of conversion of dietary energy into animal products.

5.2 - Currently available mitigation options

5.2.1 - Reducing livestock numbers

Official estimates of ruminant methane production in New Zealand show that between 1990 and 1998 methane reduced from 1490 Gg to 1406 Gg (MfE 2000). The main reason for this small decline is that sheep numbers dropped by 10 million and enteric methane output from sheep fell from 853 Gg to 696 Gg. However, for a number of reasons, reducing livestock numbers to reduce methane output is unlikely to be a viable option for New Zealand farmers.

Doubt has been expressed about the reliability of the methane estimates from ruminants because of the failure to take account of increases in productivity per animal (Clark 2001). The reduction in sheep numbers was driven by economic forces and not as a deliberate policy aim. It should be seen not so much as a reduction in livestock numbers but as a re-direction of investment into more profitable enterprises (ie the reduction in sheep numbers has been accompanied by an increase in the number of deer and dairy cows) and an increase in the efficiency of production of livestock products generally. The total number of livestock units has in fact only decreased by about 5% between 1990 and 1998 and, although wool production declined, sheepmeat output increased by 9%, beef production 34% (Meat and Wool Economic Service 2000a) and the amount of milk processed by 48% (Livestock Improvement Corporation 2000).

Simply decreasing livestock numbers as a method for bringing about a reduction in methane output needs to be differentiated from the changes in livestock numbers and improved animal performance that have been a feature of New Zealand agriculture in recent years. In the context of this report, decreasing livestock numbers as an approach to reducing methane implies reducing number but holding productivity per animal constant so that methane emissions fall. This has financial consequences as the revenue from livestock enterprises will decline in direct proportion to the reduction in numbers. Using 1998/1999 data for the national average beef and sheep farm (Meat and Wool Economic Service 2000b), 1999/00 data for national average dairy farm (Livestock Improvement Corporation 2000, Ministry of Agriculture and Fisheries 2001a,b) and methane emission factors from Clark (2001), Table 5.1 estimates the amount of revenue earned per tonne of CH4 and CO2 'equivalent' emitted on the average beef/sheep and dairy farm. 2 This data shows that although dairy farms produce more methane per unit of land than beef/sheep enterprises the amount of revenue generated by each tonne of methane is considerably higher on dairy farms. Farm profitability has improved in recent years but profits are highly dependent on the number of stock carried per unit area and the consequences for profitability of any reduction in stocking rate are far more severe than the loss of revenue implies. For example, on beef and sheep farms a 10% reduction in stocking rate reduces income by 10% but has a smaller impact on fixed costs (approx 5%) such that farm profits could fall by as much as 40% (G. Lambert, personal communication). In practice, reducing livestock numbers as a means of decreasing methane is only likely to be feasible in the context of producing the same amount of product from a smaller number of more efficient animals, so that the methane produced per unit of product declines.

Table 5.1. Methane production from average beef/sheep and dairy farms and the revenue generated per tonne of methane and carbon dioxide equivalents.

Sheep & beef Dairy cattle
Methane (tonnes/year) 63.5 24.6
Methane (kg/ha) 114 265
Farm revenue ($) 180,642 295,754
Revenue per tonne methane ($) 2845 12023
Revenue per tonne CO2 equivalent($)    

5.2.2 - Improving animal productivity

Improvements in the efficiency of conversion of feed into animal product will reduce the amount of methane emitted per unit of product but will not necessarily reduce the amount of methane produced in total. A reduction in the total will only occur if the amount of product produced is static or rises at a slower rate than the rate of decline in methane emitted per unit of product. The methane produced per unit of product has been falling in New Zealand for a number of years. Table 5.2 uses information from the Meat and Wool Economic Service of New Zealand (2000a) and the Livestock Improvement Corporation (2000) in conjunction with nationally compiled methane emission data (Ulyatt et al 1991, Clark 2001) to compare the amount of enteric methane emitted per kg of milk and meat produced in 1990/91 and 1998/99.

Table 5.2. The quantity of enteric methane produced per unit of milk, beef and sheepmeat produced in 1990 and 1998.

  kg CH4/1000 litres milk kgCH4/tonne sheepmeat kg methane/tonne beef
1990

38.7

1752

658
1998

33.8

1444

510

A factor in this decreased methane:product emission ratio is that output per head has increased and hence the proportion of the total energy consumed devoted to maintenance has decreased. A further factor is that methane production, as a proportion of the gross energy consumed, goes down as the level of feeding rises above maintenance because the rate of passage of feed through the rumen is increased. These two mechanisms are demonstrated for dairy cows in Table 5.3 where the standard IPCC methodology for calculating energy (IPCC 2000) is combined with the Blaxter & Clapperton (1965) methane prediction algorithm. As milk production per animal rises, methane output per animal rises but the proportion of gross energy used in the production of methane and the amount of methane emitted to produce a given quantity of milk both fall.

Table 5.3. Methane output from a typical New Zealand dairy cow (450kg liveweight) at three levels of milk production. Energy requirements calculated using IPCC methodology and methane output estimated using the algorithm of Blaxter & Clapperton (1965).

Milk Yield (litres/year) 3000 3500 4000
Methane emitted (kg/cow/year) 86.5 90.4 94.2
Methane emitted (% gross energy) 7.11 6.98 6.85
Methane emitted per 1000 litres milk (kg) 28.2 25.83 23.54

Over the last ten years it would appear that New Zealand agriculture has been able to reduce the amount of methane produced per unit of product at a rate that balances the increase in product output; methane emissions have changed little (Clark, 2001) but productivity per animal and the total quantity of livestock products produced (with the exception of wool) has increased substantially (Meat and Wool Economic Service 2000a, Livestock Improvement Corporation 2000).

Improvements in the efficiency of production in the agricultural sector should continue because New Zealand farmers are competing in a global market and have to continuously improve to survive. The genetic merit of animals has and will continue to increase due to selective breeding and the widespread distribution of genetic material from exotic breeds. Improved management techniques are continuously being developed and adopted. These will all decrease the amount of methane produced per unit of product. Whether increases in productivity per animal arising out of these processes are going to be enough by themselves to reduce New Zealand's total enteric methane emissions is questionable.

5.2.3 - Ionophores

Ionophores are antibiotics that modulate the movement of cations such as sodium, potassium and calcium across cell membranes (Pressman 1976). In ruminants they affect several pathways of fermentation. Monensin is the ionophore most studied in ruminants and most of the information in this section relates to monensin, although others such as lasalocid, salinomycin, nigercin and gramicidin are available. Monensin is used regularly in New Zealand by dairy farmers as an anti-bloat agent.

When added to the diet, ionophores are claimed to affect methane production in two ways. First they increase feed conversion efficiency and this reduces methane output per unit of product. Second, because of their effect on rumen fermentation, they directly reduce the amount of methane produced per unit of food intake.

In relation to feed conversion efficiency, a common finding is that ionophores reduce intake but maintain or increase productivity. On high concentrate diets, data from a number of trials indicates that dry matter intake is reduced by 5-6% and feed conversion efficiency increased by 6-7% (Raun 1990, Goodrich et al 1984). Less data is available from forage based diets and the results tend to be more variable. Animal performance does, on balance, tend to be increased (e.g. Parrot et al 1990; O'Kelly & Spiers 1992). Herbage intake has been measured less frequently on forage diets, but is usually unaffected or decreased (e.g. Davenport et al 1989; Huston et al 1990; O'Kelly & Spiers 1992).

Much of the evidence on the ability of ionophores to reduce methane output per unit of feed fermented comes from in-vitro studies. In a review of in-vitro studies, Van Nevel & Demayer (1996) found that ionophores in general do reduce methane output but the percentage inhibition shows a wide range (0-76%) and is related to ionophore type and dose rate. The same authors give a figure of 18% for the average reduction in methane emissions from in-vivo trials. In a review of ionophores, Nagara et al. (1997) quote a range of between of 4 and 31%. A particular issue arising from in-vivo trials is that there is some evidence of an adaptation to ionophores such that the methane reduction per unit of feed is only temporary (Johnson & Johnson, 1995). A further issue with regard to New Zealand agriculture is that there are no reports in the literature on the effects of ionophores on methane production from grazing animals.

O'Kelly and Spiers (1992), working with steers fed lucerne hay, recorded large reductions in methane output from ionophore treated animals and attempted to partition this reduction between the anorectic effect (ie the portion attributed to reduced food intake) and the specific rumen activity effect. In their particular trial, 55% of the reduction in methane was attributed to the anorectic effect and 45% to the direct effect on rumen fermentation. The implications of this are that even if there is some adaptation to ionophores, methane production would still be reduced per unit of product in situations where ionophores reduced herbage intakes.

Overall, because of their dual impact on methane production, the feeding of ionophores does show promise as a tool for reducing methane. However, measurements of methane emissions from grazing ruminants need to be made to confirm this promise and the long term effects of ionophores on methane output need to be studied. Of particular concern to some people are the long term implications of the routine feeding of antibiotics. Ionophores need to be fed at frequent intervals and, unless they can be delivered by a slow release delivery device, are only suitable for dairy cattle and intensive beef. Slow release delivery devices have been developed for cattle but similar devices do not appear to be available for sheep, although this is probably a reflection of the limited use of ionophores in sheep rather than a specific technical problem. A potential problem with monensin is that in the USA and the European Union it is not licensed for use in dairy cows. In New Zealand and Australia It is licensed for dairy cows but as an animal health product (e.g. bloat control) and not specifically for use as a means of increasing productivity or decreasing methane production.

5.2.4 - Probiotics

Probiotics are microbial feed additives developed primarily to improve animal productivity by directly influencing rumen fermentation. Wallace and Newbold (1993) reviewed data from trials involving dairy cows and growing cattle fed high concentrate diets and calculated that probiotics improved productivity by 7-8%. This would imply a reduction in the amount of methane produced per unit of product. Interest in them as a potential technology to reduce methane stems from the additional finding that in-vitro they can directly reduce methane production (Frumholtz et al 1989). However, even in-vitro, this is not a consistent effect (Martin et al 1989) and there are no reports in the literature of methane being measured in-vivo from probiotic supplemented ruminants.

Since probiotics are feed additives that are fed daily, they would appear to be only suitable for systems where feed supplements are given on a routine basis or for animals, such as lactating dairy cows, where supplementation via such means as the water supply is straightforward. This, combined with the very limited evidence that they do in fact directly influence methane output, would appear to rule them out in the short term as a possible mitigation technology for many of New Zealand's un-supplemented pasture based animal production systems. However, they may be suitable for dairy and intensive beef systems, but more work on their ability to improve feed conversion efficiency in grazing ruminants is required. Their ability to directly reduce methane in-vivo also needs to be assessed.

5.2.4 - Improved forage quality

At equal levels of intake, forages that increase the amount of milk or meat produced would decrease the amount of methane reduced per unit of methane produced. Additionally certain forages (eg those containing condensed tannins) may directly act to reduce the amount of methane reduced per unit of intake.

Improved grass cultivars developed in New Zealand, are claimed to increase liveweight gain in lambs without changing the quantity of feed ingested (Westwood and Norriss, 1999). This would imply, at the very least, a reduction in methane production per unit of product. It could also result in less methane per animal if there was a direct effect on rumen fermentation because of particular attributes of these forages. Cultivars of perennial ryegrass containing high levels of water soluble carbohydrates are also available and these have been found to increase animal performance under some circumstances (IGER 2001). However, to date no direct tests of the amount of methane produced by animals grazing these forages have been carried out.

White clover results in significantly better animal performance than the common forage grasses and less common species such as sulla and chicory have also been found to be superior to grasses (e.g. Waghorn & Sheldon 1997). AgResearch and Dexcel have measured methane production from animals grazing alternative forage species (e.g. lotus, sulla) and these indicate that they do produce less methane per unit of feed intake than other common New Zealand forages (Woodward et al. 2001). In the case of lotus and sulla, the ability to reduce methane output per unit of feed intake is thought to be a consequence of these plants having high concentrations of condensed tannins (G. Waghorn, personal communication).

At present the ability of grass cultivars selected for improved forage quality traits to reduce methane emissions per unit of feed intake has not been assessed. Alternative forage species do show promise but more information is needed both on their efficacy and on their ability to be incorporated into New Zealand grazing systems. Using improved cultivars and alternative species should decrease the amount of methane produced per unit of product. Even if improved or alternative forage species do prove to be capable of directly and indirectly influencing reducing methane emissions their impact nationally is constrained because only a proportion of pastures in New Zealand are re-sown on a regular basis (approximately 5% per annum, B. Belgrave, personal communication) and the proportion of sown species declines as pastures age. Increasing the area re-sown each year would increase the impact of improved forage species but re-seeding is expensive (annualised cost $100-$150 per hectare) and the cultivation associated with re-seeding also emits carbon dioxide. These additional carbon emissions are potentially very large if conventional cultivations are used; Crush et. al. (1992) quote a figure of an annual loss of 2.95 tonnes carbon (approx. 11 tonnes CO2 equivalents) per hectare from New Zealand soils converted from pasture to cropping.

5.2.5 - Manipulating nutrient composition

Manipulating the nutrient composition of the diet of ruminants can directly reduce methane output. For example, a high proportions of concentrates (grain based feeds) in the diet tends to reduce the protozoal population in the rumen, reduce rumen pH, alter the acetate:proprionate ratio and decrease the amount of methane produced per unit of feed intake (Blaxter & Clapperton 1965). However the proportion of concentrates in the diet needed to bring about this effect may well be over 50% (G. Waghorn, personal communication). The direct manipulations of the diet in New Zealand's pasture based systems by feed supplementation has practical difficulties for many classes of livestock (e.g. sheep) and the cost of concentrates already limits there use in New Zealand's low cost systems. Developing forages that directly reduce methane is likely to be a better option in New Zealand than feed supplementation.

5.2.6 - Animal breeding

Table 5.2 illustrates for dairy cows how improving individual animal performance reduces the methane produced per unit of product. Similar examples for beef and sheep can easily be constructed. In terms of methane production, the use of a smaller number of higher genetic merit animals to produce a given amount of product would therefore be beneficial.

It is also possible that some animals have lower methane emissions per unit of intake than others at the same level of performance. In trials with grazing sheep Pinares-Patino et al. (2000) identified some animals as 'high' and 'low' emitters per unit of feed intake in a single trial and then confirmed in a second trial that these differences persisted when the same type of diet was fed. The reasons why particular animals emittted less methane per unit of feed intake in these trials is not known but it does raise the possibility of genetic differences between animals in methane production.

Using animals of superior genetic merit has always been a feature of New Zealand farming and its continuation will help to reduce the amount of methane reduced per unit of product. In the last 10 years the sheep sector has been able to increase productivity (e.g. lambing percentages increased by approx. 20%, carcase weights by 13%) and reduce the absolute amount of methane produced. Dairy farmers have increased the proportion of higher producing Holstein/Freisian cattle in the national herd but, because of a large increase in the number of dairy cattle, methane output has increased. However a continuation of the trend towards breeding animals with higher levels of individual performance will lessen any adverse consequences for methane production of the forecast rise in dairy cow numbers.

5.3 - Future mitigation options

5.3.1 - Alternative hydrogen sinks

Methane arises from the conversion of hydrogen to methane by a specific group of micro organisms, collectively described as methanogens. Other micro organisms break down feed to produce volatile fatty acids, carbon dioxide and hydrogen. Increasing the production of one of these fatty acids (proprionate) reduces hydrogen production, resulting in less being available for conversion to methane. A number of organic acids (malate, fumarate, pyruvate) are needed as precursors to proprionate and if the rumen concentrations of these acids could be increased, proprionate production would increase and methane production would, in theory, fall. Malate is the organic acid most studied in relation to methane production although fumarate has also been the subject of some limited work.

In-vitro studies conducted by Martin & Streeter (1995) demonstrated that malate does increase proprionate production and decrease methane output. The same workers (Martin et al 1999) also found that direct additions of malate to the diet of finishing steers improved feed conversion efficiency. The literature does not contain any reports of studies where methane output has been measured from ruminants receiving malate supplementation. Fumarate has also been shown to decrease methane production in-vitro (ADAS, 1998).

The cost of organic acids (e.g. malate approx. $6000per tonne) makes it unlikely that direct supplementation of ruminant diets is an economic proposition. However, organic acids are present at relatively high concentrations in the leaf tissue of plants and it may be possible to breed forages with higher levels of these compounds. Data on the concentration of organic acids in the common New Zealand forage species is not available from the literature. Studies from the USA with lucerne, bermudagrass and tall fescue indicate that concentrations vary between species and between cultivars of the same species (Calloway et al 1997). From the limited data available in the literature it is not possible to ascertain whether the differences in organic acid concentrations found between plant species and cultivars are of a big enough magnitude to influence methane production by ruminants in New Zealand.

5.3.2 - Halogenated compounds

These compounds (e.g. bromochloromethane, hemiacetyl of chloral and starch) are potentially strong inhibitors of methane production in ruminants. For example, when added to ruminant diets at a rate of 5gms per day, bromochloromethane has been shown to strongly reduce methane for up to 15 hours after treatment (Johnson et al 1972). In addition to reducing methane these compounds tend to decrease intake, have little effect on liveweight gain and therefore increase feed conversion efficiency (McCrabb 2000). In Australia, a compound containing bromochloromethane and cyclodextrin has been found to have a very large impact on methane production (May et al 1995). When fed to cattle at hourly intervals it completely reduced methane production (McCrabb et al 1997) and when fed twice daily to cattle over an eight week period, it reduced methane output by 54% (McCrabb 2000). No information is presently available as to when this product will be on the market, what it is likely to cost and what the method of administration will be. A potential problem with halogenated compounds is that microbial populations may adapt such that methane inhibition may not continue in the long term (Van Nevel & Demeyer 1996). They are also unstable compounds which are potentially toxic to ruminants (Lanigan et al 1978) and humans. Much more work needs to be done before their potential as a mitigation tool can be assessed.

5.3.3 - Defaunation

Defaunation, the elimination of protozoa from the rumen, has been shown to reduce the amount of methane produced in the rumen. It does this in a number of ways; lowered fibre digestion, reduced methanogen populations that are symbiotically associated with protozoa, reduced hydrogen production. The reduction in methane output varies with diet and is higher in concentrate based diets than in forage based diets (Kreuzer et al. 1986, Itabashi et al, 1984, Whitelaw et al. 1984). Although it is possible experimentally to eliminate protozoa from the rumen, practical methods have yet to be developed by which protozoa can be eliminated. The long term effects on animal productivity of defaunation have not been investigated.

5.3.4 - Immunisation

A team of researchers in Western Australia have taken out two patents on a vaccine that is claimed to improve animal performance and directly reduce methane by invoking an immune response in the rumen to protozoa and methanogens. Details in the scientific literature on the product are not available but publicity material, available from CSIRO (http://www.csiro.au/index.asp?type=faq&id=Methane%20vaccine ), claims that, based on animal trials in sheep, it will reduce methane production in sheep and cattle by 11-23% and, in addition, increase productivity. The vaccine is still at the development stage and it not likely to be available for evaluation purposes until 2003/4 for sheep and 2005 for cattle.

5.3.5 - Acetogens

Acetogens are bacteria that produce acetic acid by the reduction of CO2 with hydrogen in the colon of humans (Ljungdahl 1986). They are present In adult ruminants but their populations are low compared to methanogens and methane producing reactions dominate. Research is under way in Europe to try to increase the populations of acetogenic bacteria at the expense of methanogenic bacteria (ADAS 1998). If successful, this approach would reduce methane and increase the efficiency of production since acetic acid is an important energy source for ruminants. The research is at a very early stage and it is not possible to assess how successful this approach is proving to be.

5.3.6 - Genetic modification

There is in general a paucity of information on the genetics of rumen bacteria (Teather et al 1997). However, altering the fermentation characteristics of rumen micro-organisms by genetic modification has been identified as a mechanism whereby ruminant methane emissions could be reduced (Armstrong & Gilbert 1985). Research is at an early stage and has so far concentrated on the use of molecular biology techniques to quantify and characterise rumen microbial populations (Teather et al 1997). Even if genetically altered rumen microbes did become available their acceptance by both producers and consumers is debatable. The approval of any product/organism would have to meet both national and international regulatory standards for GM organisms and products.

5.4 - Potential of mitigation options to reduce methane emissions

The potential of the mitigation technologies discussed in sections 5.2 and 5.3 are not easy to assess because of a lack of firm data on the response rates with which to make predictions. A number of the research areas being investigated are at the concept stage only and others, such as the use of probiotics and alternative pasture species, have not been rigorously investigated in grazing ruminants. Table 5.4 summarises the existing knowledge. The percentage reductions possible from these mitigation options need to be judged alongside the 0-12.5% predicted increase in methane emissions that are likely to arise as a result of increases in livestock numbers and individual animal performance over the next 10 years (Ministry of Agriculture 2001c, G. Rys, personal communication).

Reducing livestock numbers to reduce methane emissions is unlikely to be a viable economic option for most New Zealand farmers because stocking rate is an important determinant of farm profitability. However a combination of reducing livestock numbers but increasing the performance of each animal would reduce methane emissions for a given amount of product. It would also allow for the amount of product produced to be increased without changing New Zealand's total methane emissions.

Ionophores appear to have the greatest potential of the options currently available, although there is considerable uncertainty surrounding both their short and long term efficacy and acceptability. A detailed cost benefit analysis of ionophores is presented in section 5.6.

Probiotics are primarily applicable to the dairy sector. Their effect on productivity has generally been found to be small, meaning that even if they were adopted widely by dairy farmers, they would have a limited impact on total methane emissions.

Improved forages that directly reduce methane have not been well researched. Theoretically they can be used by all farmers but in practice are more applicable to the dairy and intensive beef/sheep sectors because re-seeding is physically difficult in many situations and the costs of re-seeding are high. Because of this their impact on total emissions is constrained. No information is available on the ability of improved cultivars to reduce methane although they could make a contribution because of their potential to increase individual animal performance.

The range of options available at present to reduce methane emissions is not large and no single option appears to provide a simple solution to holding New Zealand's methane emissions at 1990 levels. However, as has been pointed out in section 5.2.2., improved management practices over the last 10 years has resulted in the quantity of methane emitted per unit of product being reduced and the adoption of a combination of the approaches outlined in Table 5.4 may help this process to continue.

5.5 - Effects on other environmental parameters

The technologies available, or being developed, to reduce methane emissions can broadly be grouped into those that aim to feed animals better and those that directly manipulate the breakdown of this feed in the rumen.

If the diet of ruminants in New Zealand is improved, this will not only influence methane production but will have a beneficial effect on N2O emissions. If the amount of product produced from ruminants is held constant and productivity per animal increased because of improved feed quality, fewer animals are needed to meet a given level of production. This results in a smaller proportion of feed going into maintenance and so the total amount of feed eaten declines. If the total amount of feed eaten is reduced the total amount of faeces and urine deposited on pastures is reduced. Urine and dung deposits are the major source of N2O emissions. However there may also be some negative effects on other GHG's if improving feed quality involves soil cultivation. With any options that involve cultivation (cultivars/new species), the environmental effects of cultivation has to be considered. As noted in section 5.2.5, if the area under cultivation is increased, the extra CO2 lost as carbon from the soil and the increased use of fossil fuels will have to be offset against any savings made in methane emissions. If traditional cultivation is used, it is possible that total GHG emissions from a re-seeded area could actually be increased. At this stage it is, however uncertain whether carbon dioxide emissions from agricultural soils will need to be accounted for during the first commitment period.

Improving the efficiency of rumen fermentation may also have a direct effect on the nitrogen concentration of excreta. Improved rumen fermentation tends to reduce nitrogen losses per se and reduces the C:N ratio of faeces. Reducing nitrogen losses will help reduce N2O emissions and the lowered C:N ratio in faeces reduces faecal methane emissions. Nitrate leaching and run off from pastures is also of major concern in some areas (e.g. Lake Taupo) and any reductions in the amount of nitrogen deposited by ruminants will also be seen as beneficial for the environment. Quantifying the extent to which any of the methane reduction options discussed in this report will reduce nitrogen losses in grazing ruminants is not possible at this stage because of a lack of information. However, in a submission to the Canadian Environmental Technology Verification (ETV) Program, Elanco Animal Health claim, on the basis of work by Plazier et al (2000), that Rumensin reduces faecal nitrogen concentrations in cattle by 20%.

5.6 - Cost benefit analysis

The information needed to conduct a comprehensive cost benefit analysis on the emission reduction options discussed in this report is not available at present. The ability of the methods to actually reduce methane emissions in practical situations has not been tested. The exception to this is the ionophore, monensin. It has been the subject of a significant research. Although there are doubts about its long term suitability as a method of reducing methane, enough information is available to undertake a cost benefit analysis. For the other methods a simple summary has already been provided in Table 5.4.

Table 5.4 Impact of methane mitigation options

Options currently available
Option Applicability Potential reduction in methane Potential impact on total emissions Comments
      Uptake 20-100% Maximum value of 'carbon credits' at $20 tonne ($million)  
Reducing animal numbers All livestock 1% reduction in total methane for every 1% general reduction in animal numbers 0 0 Not a viable option for New Zealand farmers
Ionophores All livestock 20% maximum 1.6-8.1% 11.1-55.3 Delivery systems need to be developed and long term implications assessed. Assumed that they are used on adult dairy cows, breedingt ewes & 50% of growing beef animals.
Probiotics Dairy, intensive beef? ~7% per unit of product, No information per unit of intake 0.3-1.6% 2.2-11.1 Assumed to apply only to dairy animals.
Improved cultivars/ new forages All animals, resown pastures only 20% maximum

No information per unit of intake on forage cultivars

Up to 20% reduction with different forages

 1.1-5.4% 7.4-36.9 Approx 5% of land re-sown each year and effect lasts for 3 years. Assumed to apply to all dairy land & 5% of beef/sheep land. Methane reduced by 20%. New species have to be integrated in farming systems
Improved performance per animal All livestock Approx 5% for every 10% increase in individual performance 1.2-5% 6.8-34.3 Assumed that total product output is unchanged but that it is produced by a smaller number of higher producing animals.

Assumed that total product output is unchanged but that it is produced by a smaller number of higher producing animals.

The general assumptions used in the cost benefit analysis are that monensin is available as a slow release capsule that lasts 100 days. For simplicity the analysis has been restricted to adult ewes and milking dairy cows. It also has applicability in the beef sector but because of the range of beef systems, a detailed analysis is beyond the scope of this report. The impact on methane emissions only has been considered although if, as the experimental evidence suggests, monensin reduces the amount of nitrogen excreted, N20 emissions would also be reduced. Data for sheep are presented in Table A1 (a:f) and for dairy cattle in Tables A2 (a:f), A3 (a:f) and A4 (a:f) in Appendix A. For dairy cows, the cost of the slow release capsules is based on the present market cost of those currently available. An approximate cost for a similar delivery device for sheep has been provided by Elanco Animal Health. The average farm data and the number of livestock are as per section 5.2.1.

The main findings for ewes are:

  • The cost of treatment is high relative to revenue and a 15% increase in animal performance is needed to recover the cost of the treatment (Table A1(b)). This is higher than the average increase in productivity found experimentally (see section 5.2.3).
  • In terms of emissions, the cost per tonne of CO2 equivalent reduced is also high and does not fall below $50 per tonne unless the percentage reduction in methane is high (20%) or the % increase in productivity is greater than 10% (Table A1(c)). Compared to experimental data, these values are very much at the high end.
  • Although sheep in general emit over 50% of New Zealand's enteric methane, treating all ewes for 100 days reduces national emissions by a maximum of 2.7%. (Table A1(d,e)).
  • The potential total 'value' of the reduced emissions per farm depends on the ability of monensin to reduce methane, the rate of adoption by farmers and the 'value' of a tonne of CO2. On the average sheep/beef farm the cost of treatment is approximately $8000 (Table A1(b)). Assuming a value of $20 per tonne for CO2 implies that to meet this cost without any increase in productivity, CO2 equivalent emissions per farm have to be reduced by 400 tonnes. This equates to over 17 tonnes of methane.
  • If methane emissions in ewes could be reduced by 20% for the treatment period, the savings per farm are just over 2.3 tonnes of methane, equivalent to 53 tonnes of CO2. To recover the cost of treatment without any increase in productivity would require CO2 to have a value of at least $150 per tonne (Table A1(c), column 1).

Dairy cows have a high methane output per head and a large income relative to the cost of treatment, it may therefore be cost effective to administer monensin for a longer period. Tables A2, A3 and A4 explore the cost and benefits of treating dairy cows for 100, 200 and 300 days.

The main findings for dairy cows are:

  • Compared to sheep, the productivity gains needed to pay for the cost of treatment are modest, ranging from 2.5% in cows treated for 100 and 200 days to approximately 5% for those treated for 300 days (Tables A2(b), A3(b), A4(b)). These are well within the range of values found experimentally.
  • In terms of emissions, the cost per tonne of CO2 equivalent reduced falls below $50 per tonne when productivity gains (maximum 3.5%) and the percentage reduction in methane emitted per cow (maximum 10%) are within the range of values found experimentally (Tables A2(c), A3(c), A4(c)).
  • Treating for 100 and 200 days reduces annual dairy farm methane emissions by just over 6% for each 100 day period but this falls to 3.5% in the last 100 day period when the milk production per cow decreases (Tables A2(d), A3(d), A4(d)).
  • The impact on national methane emissions is relatively modest, reaching a maximum of 3.7% when all dairy cows are treated for 300 days and methane per animal is reduced by 20% (Tables A.2(e), A3(e), A4. (e)).
  • The cost of treatment per farm for 100, 200 and 300 days respectively is $3540, $7080 and $10620. Assuming a value of $20 per tonne for CO2 implies that to meet this cost without any increase in productivity, CO2 equivalent emissions per farm have to be reduced by 177, 354 and 531 tonnes respectively. Tables A2(d), A37(d) and A4(d) show that the per farm reductions in methane emissions reach a maximum of just under 4 tonnes, equivalent to 88 tonnes of CO2, when methane emissions per cow are reduced by 20% for a treatment period of 300 days. To recover the cost of treatment would require CO2 to have a value of between $100 -$120 per tonne (Table A2(c), column 1, A3(c), column 1 Table A4(c), column 1).

In summary, using monensin to reduce methane emissions is only cost effective if gains in productivity defer the cost of treatment. In dairy cows, the productivity gains needed to pay the treatment costs are modest (especially if treatment is restricted to the first 200 days of lactation) but in sheep they are higher than experimental evidence suggests they are likely to be. On a per farm basis, treating dairy cows for between 100 to 300 days could reduce methane emissions by between 6.5 and 16% if emissions per animal are reduced by 20%. On sheep/beef farms treating ewes for 100 days reduces emissions by a maximum of 3.6% per farm. If all ewes in the country were treated for 100 days and all dairy cows for 300 days the maximum reduction in total methane emissions would be approximately 6.4%. Without any productivity gains arising from using monensin, this would cost between $120 and $150 per tonne of CO2 equivalent saved.

5.7 - Conclusions

The management options for decreasing methane emissions from New Zealand ruminants are limited at present.

Reducing livestock numbers is not a desirable option because of the financial consequences. It is only feasible if farm incomes can be maintained by other means.

  • Ionophores have a proven ability to directly reduce methane emissions in the short term but their use in grazing ruminants has not been assessed nor has implications of long term use. They are also not licensed for use as a methane inhibitor and their acceptability by consumers has not been tested. The ability of ionophores to reduce methane at a reasonable cost relies on them being able to also increase animal productivity. Because of the cost of treatment relative to revenue, this is more likely to occur in dairy cattle.
  • Feeding ruminants better (improved grasses, different forage species, improved animal genetics) has the potential to directly reduce methane emissions per unit of feed intake but the evidence is limited. On the evidence available reductions in total methane emissions arising from these approaches will involve reductions in methane per unit of product and reductions in animal numbers.
  • Probiotics are only applicable to a small proportion of section of New Zealand agriculture and have no proven ability to directly reduce methane. Any reductions in methane arising from the use of probiotics, on the evidence available , are limited to reductions in methane per unit of product unless animal numbers are reduced.

Individually none of the options outlined above provides a simple, universally applicable mitigation technology. However taken collectively, if adopted, they should at the very least help defer any rise in New Zealand's methane emissions over the next 10 years.

The options currently at the research/concept stage concentrate on directly reducing methane. Information on these is limited. The most promising approach seems to be the vaccine because

  1. it may be applicable to all classes of livestock,
  2. there is evidence that it is effective and
  3. if the developers of the technology are correct in their predictions, it will be available within the next five years.

 

2 To convert CH4 into CO2 equivalents the latest IPCC ‘global warming potential’ of 23 for CH4 has been used throughout this document.

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