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12 Ruminant Contributions to Methane and Global Warming — A New Zealand Perspective G.C. Waghorn and S.L. Woodward CONTENTS 12.1 Introduction ..................................................................................................234 12.2 Relevance of Greenhouse Gases for New Zealand Producers....................234 12.3 New Zealand GHG Inventory......................................................................236 12.3.1 Methane ............................................................................................236 12.3.2 Nitrous Oxides .................................................................................237 12.4 Defining Mitigation......................................................................................237 12.5 Methane Mitigation......................................................................................238 12.6 Relationship between Diet Composition and Methanogenesis...................241 12.7 Methane Emissions from Ruminants Fed Fresh Forages ...........................242 12.7.1 New Zealand Measurements............................................................242 12.7.2 Pasture Methane Measurements outside New Zealand...................244 12.8 Condensed Tannins and Methanogenesis ....................................................244 12.9 Animal Variation in Methanogenesis...........................................................246 12.10 Management to Mitigate Methane in Grazing Animals ............................247 12.11 Feed Additives ............................................................................................248 12.11.1 Oils ..................................................................................................248 12.11.2 Ionophors ........................................................................................248 12.11.3 Removing the Protozoa (Defaunation)...........................................248 12.12 Targeting Methanogens...............................................................................249 12.12.1 Vaccine ............................................................................................249 12.13 Agronomy and Complementary Feeds .......................................................250 12.14 Nitrous Oxide Emissions and Abatement ...................................................251 12.14.1 Mitigation Options..........................................................................251 12.14.2 Animal Management and Feeding..................................................252 12.15 Whole-Farm Systems..................................................................................253 12.16 Summary and Conclusions .........................................................................255 Acknowledgments..................................................................................................255 References..............................................................................................................256 233 © 2006 by Taylor & Francis Group, LLC 234 Climate Change and Managed Ecosystems 12.1 INTRODUCTION An overview of the implications, research, and policies concerning greenhouse gas (GHG) emissions from New Zealand agriculture is presented. Most emphasis is given to methane from ruminants and to opportunities for mitigation in forage-based feeding systems. The opportunities for practical reductions in both methane and nitrous oxide emissions are indicated. The underlying principles affecting levels of methane emissions from ruminants are examined and compared with values obtained from sheep and cattle fed fresh forages. Opportunities for mitigation are presented as short-, medium-, and longterm strategies. Topics include the bases for animal variance, effects of management and diet, as well as potential mitigation through rumen additives. The risks associated with mitigating a single GHG in isolation from others are demonstrated using a model of CO2 and CH4 emissions from contrasting dairy systems and the importance of maintaining economic viability in addition to environmental improvement is central to all considerations. The information presented here is based primarily on New Zealand experience. Our mixture of sheep, dairy and beef cattle, and deer is farmed outdoors all year on pastures varying in topography, fertility, and quality with diverse climatic conditions. New Zealand has a substantial challenge to determine agricultural GHG inventory and to mitigate emissions. 12.2 RELEVANCE OF GREENHOUSE GASES FOR NEW ZEALAND PRODUCERS Methane accounts for 38% of New Zealand greenhouse gas emissions (based on Tier II estimations), which is a higher percentage than emissions in Australia (24%), Canada (13%), the U.S. (9%), and most industrialized countries, which emit only 5 to 10% of GHG as methane.1 Nitrous oxide (N2O) accounts for 17% (largely Tier I estimates) and CO2 44% of our national GHG inventory (Table 12.1). Total annual emissions are 72.4 million tonnes of CO2 equivalents, or about 18 tonnes per human.2 Countries with higher emissions (tonnes head–1 of population) include Australia (25.1), the U.S. (23.6), and Canada (22.6). In New Zealand 88% of CH4 emissions are associated with animal agriculture, of which 98% is from digestion, primarily in the rumen. A single source of CH4 provides an excellent focus for both measurement and mitigation, especially as energy losses account for about 10% of metabolizable energy (ME) intake of ruminants grazing grass-dominant pasture. Mitigation should be investigated on the basis of improved performance and efficiency of feed utilization as well as GHG inventory. Examples include halving CH4 production to provide sufficient energy for an additional 400 kg milk cow–1 lactation–1 (average annual milk production from pasture fed cows is 3700 kg cow–1). Alternatively, if total emissions could be collected from an adult cow over 1 year, the energy would fuel a midsize car for 1000 km! The New Zealand government had intended to raise a ruminant tax (dubbed the “fart tax” by farmers and media) to generate research revenue. Planned taxation (per annum) was about US$0.50 per cow and US$0.08 per sheep, but this was abandoned © 2006 by Taylor & Francis Group, LLC Ruminant Contributions to Methane and Global Warming 235 TABLE 12.1 Annual (2001) New Zealand Greenhouse Gas Emissions (as CO2 equivalents)2 Total CO2 Equivalents (tonnes × 106) % of Total New Zealand Carbon dioxide Methane Nitrous oxides PFC, HFC, SF6 32.43 27.06 12.58 0.31 44.6 37.5 17.4 0.4 Agriculture Energy Industrial Waste 35.85 30.93 3.18 2.31 51.0 39.0 5.0 5.0 Agricultural Emissions Methane From digestion From manure Nitrous oxidesa From animal production Indirect from agricultural soils Direct from agricultural soils % of CH4 or N2O 23.12 0.55 84.5 2.0 7.12 3.13 1.81 56.6 24.9 14.4 Abbreviations: PFC, perfluorocarbons; HFC, hydrofluorocarbons; SF6, sulfur hexafluoride a Nitrous oxide emissions apply to all agriculture, with some direct and indirect emissions attributable to animal agriculture. in the face of farmer protest and current annual investment (NZ$4.7m) supports about 32 full-time equivalent researchers. Approximately 55% of funds are directed toward inventory, 20% to fundamental, and 25% to abatement research. A comprehensive report on Abatement of Agricultural non-CO2 GHG Emissions in New Zealand3 summarizes all current research and identifies research priorities. There is good and increasing collaboration between Australian and New Zealand researchers with annual conferences and reports receiving direct government support. This collaboration is essential, given the relatively small investment in GHG research in both countries. Although Australia is not a signatory to the Kyoto Protocol, there is a strong commitment by federal and state governments to GHG reduction. Promotion of benefits from lower GHG emissions in terms of productivity and environmental sustainability are receiving guarded support from farmers and the public. The concept of energy wastage provides an appropriate avenue for lobbying © 2006 by Taylor & Francis Group, LLC 236 Climate Change and Managed Ecosystems farmers and agricultural professionals to secure their support for funding. New Zealand farmers are sensitive to their role as guardians of their land and to the need to maintain or improve their environment. Successful mitigation (abatement) will require a mixture of consultation, education, and awareness as well as research if it is to be successful in the longer term. Ironically, the threat of an emission (“fart”) tax has contributed awareness, although it was of little benefit for research funding. 12.3 NEW ZEALAND GHG INVENTORY 12.3.1 METHANE New Zealand agricultural production is not subsidized and follows market demands, with significant reductions in sheep numbers over the past 20 years and concomitant increases in dairy cattle and deer. The census data (undertaken every 5 years) are crucial to the Tier II method for estimating CH4 production, from livestock numbers, feed requirements, and estimated feed intakes. This Tier II inventory calculation is based on monthly measurements of animal requirements and feed dry matter (DM) intakes.2,4 Briefly, the ruminant population is defined in terms of dairy cattle, beef cattle, sheep, and deer (numbers of goats, horses, and swine are very low; Table 12.2). Each group is subdivided into categories based on farming systems, with monthly adjustment of numbers to account for births, deaths, and transfer between age groups. Productivity and performance data required to estimate feed intakes include average live weights of all categories, milk yields and composition from dairy cows, growth rates of all categories, and wool production from ewes and lambs. The ME content of diets consumed is measured and the DM intake determined from ME requirements for each population, using CSIRO algorithms.5 TABLE 12.2 Animal Numbers (3-year average), CH4 Emission Rates, and Total Annual Emissions for New Zealand in 2001 Species Sheep Dairy Beef Deer Goats Swine Horses Numbers (×106)a 41.36 4.98 4.54 1.55 0.17 0.35 0.08 Total CH4 Emissionsb CH4 /Head (kg) 10.6 74.7 56.0 20.9 8.9 1.5 18.0 tonne × 103 438.7 372.5 254.0 32.7 1.5 0.5 1.4 % 40.0 33.8 23.0 3.0 0.1 0.0 0.1 Note: Data are calculated from census data, monthly feed requirements, estimated intakes, and methane emissions unit–1 intake2. a b Adult equivalents. Excludes contribution from manure. © 2006 by Taylor & Francis Group, LLC Ruminant Contributions to Methane and Global Warming 237 These data form the basis of the Tier II inventory, with current emissions (g CH4 kg–1 DM intake) of 21.6 for adult dairy cattle, 20.9 for adult sheep, and 16.8 for sheep aged less than 1 year grazing pasture — 6.5, 6.3, and 5.1% of the gross energy (GE) intakes. The accuracy of methane emissions is given as ±50%, with a coefficient of variation of 23%.2 The census data are accurate but concerns remain over the accuracy of predicted DM intakes and CH4 emission unit–1 DM intake (DMI). Manure CH4 emissions are low and are based on calculation of total animal manure production. Annual emissions from manure are calculated to be about 0.9 kg for cattle, 0.18 kg for sheep, and 0.37 kg for deer.2 12.3.2 NITROUS OXIDES Pastoral agriculture is the source of most N2O in New Zealand. Emission estimates have been revised6 on the basis of the Inter Governmental Panel on Climate Change7 and use default values of 0.0125 kg N2O-N kg–1 N for N2O from all origins (Tier I). Emissions are derived primarily from N in animal excreta (about 53% of total) and nitrogenous fertilizers (10%) as well as other direct and indirect (leaching, runoff, volatilization) emissions. Current research suggests N2O-N losses kg–1 N of 0.007 and 0.003 are appropriate for dung and urine, respectively,8 which is substantially lower than values used in calculations of inventory. All sheep, deer, beef, and most dairy cattle waste is deposited on pasture. 12.4 DEFINING MITIGATION Methane emissions can be expressed in several ways: • • • • Gross emissions, which have significant meaning for inventory but little indication of the animals’ performance or physiological status. Low emissions may be due to low performance, and vice versa. Expressions as a function of feed intake, for example, DMI or digestible DMI. This expression enables comparisons between feeds, but high intakes by animals consuming good-quality diets (with low CH4 kg–1 DMI) may result in high gross emissions. Methane per unit of production. This appears to be a useful expression of “GHG efficiency,” especially from a systems perspective because total emissions can be judged on the basis of performance. This is a good procedure providing emissions are totaled over a cycle of events, e.g., growth of a lamb from conception to slaughter, or annual milk production from dairy cows. This procedure is easily abused, for example, when expressing CH4 unit–1 milk production, because values will be low in early lactation when maintenance is a small proportion of energy intake (and the cow has lost weight) but high in late lactation as milk yield declines and the cow (and fetus) is gaining weight. Methane mitigation should be expressed in association with other GHG and economical scenarios. For example, feeding grains with forages will © 2006 by Taylor & Francis Group, LLC 238 Climate Change and Managed Ecosystems lower CH4 yields kg–1 DMI and CH4 kg–1 milk production but large CO2 emissions are associated with soil organic matter losses (from cultivation), use of fuel, fertilizers, harvesting, drying, and transport of grain. Furthermore, costly mitigation must not disadvantage producers in a competitive world economy. Table 12.3 lists options for methane mitigation, with an indication of applicability, risk, and a timescale for commercial availability. Most consideration will be given to forages and feeding, constituent nutrients, animal management, variations among individuals, and the importance of a whole system analysis. These options can be applied in the short term with a high level of acceptability. 12.5 METHANE MITIGATION Opportunities for methane mitigation3,9–16 include short-, medium-, and long-term strategies (Table 12.3). Mitigation must also be economical, sustainable, and relatively inexpensive; persistent and high levels of methane production should not be viewed as an inevitable consequence of ruminant digestion. It can be reduced by 90% through daily administration of halogenated methane analogues13 with minor effects on performance.17 However, total elimination of methane production during digestion is unlikely to be sustainable, acceptable, or economical. Although halogenated methane compounds are potentially carcinogenic, less toxic alternatives for methanogen inhibition may become available and achieve consumer acceptance for registration and industry use. Successful mitigation strategies can either lower production of the hydrogen substrate used for methane synthesis or increase available sinks for hydrogen disposal. Rumen bacterial degradation of fiber to acetate will inevitably release hydrogen ions and sinks must be available to prevent microbial inhibition. Dairy cattle and feedlot animals provide excellent opportunities for mitigation because daily administration of methane suppressors, mitigators, or hydrogen “sinks/users” (acetogens) is practical and potentially cost-effective in animals producing high-value commodities. However, the majority of ruminants are raised under extensive grazing and mitigation can only involve occasional intervention, hence the attraction of vaccination against methanogens18 or protozoa. Animal management techniques to improve productivity may offer benefits to producers as well as lower methane emissions per unit of product (e.g., milk or live weight gain) but options will depend on government policies. For example, one solution is inclusion of grains and concentrates in ruminant diets to boost production; however, a full system appraisal of grain production, considering fertilizer, cultivation, fuel and other energy inputs, and consequent emissions of CH4, N2O, and especially CO2 shows very high net GHG emissions per unit of ruminant production, compared to production from ruminants grazing pasture.19 Any consideration of methane abatement should consider other GHG costs, economics, and environmental consequences of change. © 2006 by Taylor & Francis Group, LLC Technique Short-Term Options Maintain forage quality Application Limitations Consequencesa Potential Uptake Medium-high fertility grazing No limitations; require skilled management Improved animal performance, must limit excess fertilizer use High Feed legumes/herbs, highquality grasses All situations depending on species Costs of establishment and maintenance lower yields could lower profitability Improved animal performance but more agronomic care needed Moderate Incorporate condensed tannin into diet Widespread, especially with lotuses, sainfoin Lower yield and persistence except lotus in low fertility Very good animal performance, 13–17% reduction in methane and lower N2O emissions Moderate Specific lipids Currently limited to dairy unless expressed in forage plants Cost-effectiveness May affect product flavor High with incentive Balance rations to meet animal needs Systems involving supplementary feeding Requires nutritional knowledge and advice Improved performance from high producers. Could lessen N2O emissions by lowering N intake Moderate Select high-producing animals Normal practice High producers require good feeding and management Lower stock numbers, increased profitability High Potential for high profitability Moderate Unlikely to have detrimental consequences High with incentiveb Optimal farm management Widespread but requires good Depends on commodity prices; need skills consultant advice Widespread if trait is heritable None known but low CH4 producers may only apply to some diets © 2006 by Taylor & Francis Group, LLC 239 Medium-Term Options Selection of low methane producing animals Ruminant Contributions to Methane and Global Warming TABLE 12.3 Options for Reducing Methane Emissions, in Total or per Feed Intake or per Unit Product from Ruminants Fed Forages Application Widespread if viable Limitations Current data show inconsistent responses, variable persistence with forage diets Consequencesa If viable, an added benefit is protection from bloat and possible improved feed conversion Potential Uptake Low to medium Probiotics Dairy, unless available as slow release Minimal evidence of efficacy in vivo Unknown Unknown Halogenated compounds Could be widespread if in slow-release form Need approval and verification of persistence Consumer avoidance of products High with incentive Acetogens Dairy cows Require daily administration Responses not defined; excess acetate will not benefit high-producing ruminants fed forage Low unless incentive Defaunation Moderate, depending on diet Current technology risky, a vaccine would help. Beneficial for animals fed poor forage Moderate if safe High-efficiency animals Widespread Require selection of animals with efficient nutrient utilization Selections may be feed specific Moderate Long-Term Options Vaccines — methanogens Widespread Good opportunities hampered by lack of funding Potential for improved animal performance High Vaccines — protozoal Moderate Probably minimal OK when poor feed is available Moderate Specific methanogen inhibitors (HMG-S-CoAc and Phage) Widespread Depends on specific inhibition of methanogens Improved performance if intakes maintained High with incentive a b c Consequences refer to the animal or environment; a net reduction in CH4 kg–1 feed or product is implied. If performance is not enhanced an incentive may be required to use these materials. HMG-CoA, hydroxymethyl glutaryl-S-CoA. © 2006 by Taylor & Francis Group, LLC Climate Change and Managed Ecosystems Technique Use of ionophores 240 TABLE 12.3 (continued) Options for Reducing Methane Emissions, in Total or Per Feed Intake or Per Unit Product from Ruminants Fed Forages Ruminant Contributions to Methane and Global Warming 241 12.6 RELATIONSHIP BETWEEN DIET COMPOSITION AND METHANOGENESIS The analysis of methane data by Blaxter and Clapperton9 has served as reference for effects of intake, digestibility, feed type, and animal species on CH4 emissions unit–1 feed intake. These data appear to be based on dried feeds but relationships between methane (as a percentage of GE) and digestible energy (DE) content or level of intake were not consistent across dietary types. For example, there was no relationship between feed quality (DE content) and energy loss to methane for concentrate–roughage mixtures fed at maintenance, despite a significant correlation for dried roughages. These details appear to have been overlooked by some researchers. A more recent analysis20 failed to demonstrate any relationship (r2 = 0.052) between observed GE loss to CH4 (range 2.5 to 11.5%) and DE of the diet (range 50 to 87% of GE). These authors also showed a very poor relationship (r2 = 0.23) between the Blaxter and Clapperton9 predictions of CH4 losses from beef cattle fed a diverse range of diets and actual values. An alternative equation derived from trials with dairy cows fed mixed rations,21 based on intakes of hemicellulose, cellulose, and nonfiber carbohydrate (NFC), enabled 67% of the variance in predicted methane production to be explained: CH4 (MJ day–1) = 3.406 + 0.510 (NFC) + 1.736 (hemicellulose) +2.648 (cellulose) where NFC (DM less fiber, crude protein (CP), ash, and lipid), hemicellulose, and cellulose are daily intakes (kg). The prediction was improved by using digestible NFC, hemicellulose, and cellulose intakes, explaining 74% of the variance, but measurements of digestibility are not always available. These authors21 concluded that methane production by adult cattle at maintenance could be predicted from dry matter or total digestible carbohydrate intake, but accurate prediction at higher intakes, typical of lactating cows, requires the type of dietary carbohydrate to be determined. The intercept of equations based on fiber and digestible fiber did not pass through zero, which emphasizes the empirical nature of the relationship and precludes expression on the basis of GE intake. Complex equations developed for lactating dairy cows22 did not improve predictions over those based on carbohydrate fractions,21 and Wilkerson et al.23 concluded that estimates based on cellulose, hemicellulose, and NFC provided the highest correlation with actual methane emissions, and had the lowest errors. Use of either intakes or digestible intakes of carbohydrate fractions provided similar levels of accuracy for predicting energy loss to CH4. Prediction of emissions from animals fed contrasting diets are complicated by differences among individuals (e.g., References 24 through 26; Figure 12.1). There is also some evidence that increasing the proportion of concentrates in a diet will increase the variation between individuals.9,14,27 © 2006 by Taylor & Francis Group, LLC 242 Climate Change and Managed Ecosystems Methane production (g/kg DMI) 28 26 24 22 20 18 16 14 12 10 0 30 60 90 120 150 180 210 240 270 Days of lactation FIGURE 12.1 Methane production (g kg–1 dry matter intake) from five cows with a New Zealand Friesian genotype () and five with a North American/Dutch genotype () genotype grazing pasture and measured at 60, 150, and 240 days of lactation. (Waghorn, Unpublished data.) 12.7 METHANE EMISSIONS FROM RUMINANTS FED FRESH FORAGES 12.7.1 NEW ZEALAND MEASUREMENTS New Zealand research has focused on measurement of methane emissions from sheep and cattle fed fresh forage diets (usually perennial ryegrass-dominant pasture) throughout the season and with animals differing in age and physiological status. Four data sets have been analyzed using multiple regression to define relationships among treatment means (CH4 kg–1 DMI) and linear combinations of dietary components — soluble sugars, NFC, CP, ash, lipid, condensed tannin (CT), neutral detergent fiber (NDF), acid detergent fiber (ADF), hemicellulose (H), and cellulose (C). Analyses have been undertaken for sheep fed ryegrass-based pasture (15 data sets), sheep fed legumes and herbs alone or in mixtures (12 data sets), lactating Friesian cows fed pasture (12 data sets), and lactating Friesian cows fed a range of diets including pasture (n = 22). Perennial ryegrass feeding with sheep included ad libitum grazing24,25,28,29 and indoor feeding30,31 with forage quality ranging from immature to mature (CP 29 to 11%, NDF, 36 to 51%). Methane emissions ranged from 13 to 26 g kg–1 DMI (Table 12.4; 3.8 to 7.6% of GE). Correlation coefficients (r2) between CH4 kg–1 DMI and NFC, NDF, and ADF concentrations were 0.47, 0.28, and 0.58, respectively. Multiple regression using the criteria developed by Moe and Tyrrell21 for cattle showed only 51% of the variance in methane yield was explained by NFC, hemicellulose (H), and cellulose (C) concentrations in the DM: © 2006 by Taylor & Francis Group, LLC