STRATEGIES TO MITIGATE CLIMATE CHANGE THROUGH METHANE EMISSION REDUCTION IN DAIRY CATTLE OR GREEN DAIRYING
Dr. Pramod Prabhakar, Assistant Professor -cum – Jr. Scientist, MBAC, Agwanpur, Saharsa, BAU Sabour, Bhagalpur.
Livestock plays an important role in climate change. Livestock systems, including energy use and land-use change along the supply chain, accounted for an estimated 14.5% of total global greenhouse gas (GHG) emissions from human activities in 2010. More than half of these (about 65%) are related to cattle. Direct emissions from livestock and feed production constitute some 80% of total agriculture emissions, and thus need to be part of any effort to reduce the contribution of food production to global climate change.
As concern about climate change rises, researchers are working to develop innovative strategies to limit greenhouse gas emissions.
Methane makes up 14 percent of greenhouse gas emissions globally and is 28 times more potent than carbon dioxide at trapping heat in the atmosphere.
Methane is a potent greenhouse gases responsible for global warming.Various strategies likegenetic selection for production traits, feeding of highly digestible forages, use of feed additives, rumen manipulation andration balancing will reduce enteric CH4 emissionsand cause an increase in animal performance by conserving energy and reducing feed costs associated with animal maintenance. Ruminant animals loose about 4-12 per cent of gross energy intake in the form of methane, which is not only detrimental to environment but also results in energy loss to animals. Feeding a balanced ration can prevent this loss.
Greenhouse gases like carbon dioxide (CO2), methane (CH4) and nitrous oxides are produced as a result of agricultural and livestock activities. The gross energy loss in form of methane in cattle is around 2-15% of their ingested energy .The world’s 1.3 billion cattle account for some 73% of the 80 Tg of methane produced by livestock worldwide each year. Enteric CH4 is the most significant single source of greenhouse gas emissions of the world. Over the past three centuries, the amount of atmospheric methane has grown up by 2.5 folds. In 2005, out of the total 87.9 Mt carbon dioxide emissions from the agricultural sector, 50% were from enteric fermentation in cattle, 16% from sheep and 0.3% from other animals .On average, mature beef cows emit 350 g CH4/day in the tropics and 240 g/day in temperate zones. Similarly dairy cows emit 430 g/day at peak lactation .It has been reported that CH4 promotes stratospheric ozone depletion .The water vapour that is added to the stratosphere when CH4 is oxidized may provide surfaces for heterogeneous reactions that destroy ozone. At this rate, methane is expected to cause 15 to 17% of the global warming over the next 50 yr .Reducing CH4 emissions can increase animal performance by conserving energy that could be redirected to milk production or weight gain. Efforts have been made through research in last decade by the animal nutritionist for finding methods to reduce methane emissions. Since global warming potential of methane is 23 times higher than carbon dioxide, so reduction in methane emission can impact the global warming at early. The strategies should be lower methane production by our livestock.
METHANE PRODUCTION
Very recent radiocarbon (C14) isotope measurements on atmospheric methane indicate that approximately 20 and 30% is originated from fossil,gas drilling, venting, mining and wetlandemissions. The remaining 70 to 80% of atmospheric carbon is derived from sources like enteric fermentation, natural wetlands, biomass burning, rice production and waste treatment .Microorganisms in the rumen referred to as methanogens, convert H2 and CO2into CH4 and water. This process lowers the amount of H2 in the rumen. Methane production is the main way that H2 is used in the rumen.The collaboration between fermenting species and H2-utilising bacteria is called “interspecies hydrogen transfer.). The type of carbohydrate fermented influences methane production most likely through impacts on ruminal pH and the microbial population. Fermentation of cell wall fiber yields higher acetic: propionic acid and higher methane losses .Moe and Tyrrell (1979) found fermentation of soluble carbohydrate to be less methanogenic than cell wall carbohydrates. Studies conducted with forage-fed sheep found that 87 % of enteric CH4 originates from the reticulo-rumen, the remainder being generated from the hindgut .Out of the total CH4 produced in the hindgut, Murray et al. (1976) found the majority (89 %) are absorbed and expired through the lungs. The remainder was excreted via the anus.
MEASUREMENT OF METHANE PRODUCTION
There are many methods available which would be suitable for measuring CH4 produced from the various stages of animal production. However, several factors need to be considered in order to select the most appropriate technique like the cost, level of accuracy required and design of the experiments to be undertaken.
Gas Chromatography
The principle of gas chromatography is individual partitioning of different gases in the sample between a mobile phase and a stationery solid phase. After separating the components in the gaseous mixture, each component was identified by its retention time on the column and quantified by a subsequent detector .Quantification of methane is accomplished by comparing the peak height and retention time of the sample to standards of known concentration. Gas chromatography is highly accurate and precise
Fourier Transform Infrared (FTIR) Spectroscopy
A number of gases of interest in climate change research could be uniquely and simultaneously determined byFTIR technique .In FTIR spectroscopy the unique infrared absorption of different molecules are used to quantify their concentration
Tuneable Doide Laser Absorption Spectroscopy
This is based on the absorption of an infrared laser beam as it travels along a path through the gas sample. The sensitivity of the TDL based instruments depends on the pathand strength of the absorption line.
Semiconductor Chip Sensor
This sensor can detect hydrogen, CH4 and CO gas within 5 min and with a sensitivity of 0.1 ppm for each gas. The correlation between CH4 concentrations detected by semiconductor chip sensor and gas chromatography was 0.86 .
Respiration Calorimetry
Itconsists of animal chambers, head boxes, orventilated hoods and face masks to collect emitted gases from cattle. The principlebehind open-circuit indirect-respiration techniques is thatoutside air is circulated around the animal’shead, mouth, and nose and expired air collected.Methane emissions aredetermined by measuring the total air flow throughthe system and the difference in concentration betweeninspired and expired air.
Tracer Gas Technique
Methane emission from ruminants can also be estimated by using the Calibrated Tracertechnique. The tracer can either be isotopic or non-isotopic. Isotopic methods involve the use of 3H or 14Cinfistulated animals .Nonisotopic tracer techniques are also available for measurement of CH4 emissions by using sulphur hexafluoride (SF6), an inert gas tracer.Using the continuous infusion technique, sampling of gas takes place in the dorsal rumen and specific activity of the radio-labeled methane gas can be calculated.
RUMINANT ENTERIC METHANE MITIGATION
Enteric methane mitigation is not so much successful, but with appropriate policies, technologies and management practices, it may be possible to achieve reductions in methane inhibition of up to 75% .However, most technologies to control methane production from ruminants have not proved cost-effective and some may result in the underutilisation of low-cost fibrous feed resources. Some commonly usedprocedures for methane mitigation are:
a. Level of Intake-
As the daily feed eaten by any givenanimal increases, the percentage of dietary GE lost asmethane decreases by an average of 1.6% per level of intake .
b. Diet Type- feeding more amounts of grains in the diet reduces the methane production. Diets containg more corn grain produces 30% less methane as compared the diets having more barley grains. Supplementing diets containg fats & oils reduces methane emission. Use of corn silage and small grain silages, rather than grass silage, and hay, can also lower CH4 production.
c. Type of Carbohydrate- Fermentation of cell wall fibre yields higher acetic: propionic acid and higher methane losses (Beeveret al., 1989). Moe and Tyrrell (1979) found that fermentation of soluble carbohydrate to be less methanogenic than cell wall carbohydrates.
d. Addition of Lipid- Addition of long-chain polyunsaturated fatty acids decreased methanogenesis by providing an alternative metabolic hydrogen acceptor to reduction of CO2 .
e. Addition of Ionophore- Ionophore additions to beef cattle diets, particularly monensin, decreases acetic: propionic acid ratio and methane losses .The decrease in methane production isapproximately 25%.
f. Propionate Enhancers- Martin has suggested that dicarboxylic organic acids such as malate and fumarate may alter rumen fermentation in a manner similar to ionophores. Lopez et al. (1999) observed that when fumarate, a precursor of propionate, was added to rumen simulating fermentors, propionate production increased with a stoichiometric decrease in methane production. Ouda et al. (999) found that acrylate, an alternative precursor of propionate, also depressed methane production in rumen.
g. Rumen Manipulation- Microbial population of rumen can be changed to decrease methane production. Various methods are used for rumen manipulation:
• Defaunation:Defaunation of the rumen of cattle fed a barley diet decreases methane production by approximately one half .However, defaunation of animals receiving highforage diets did not reduce methane losses.
• Probiotics:Aspergillusoryzae has been seen to reduce methane by 50% which was directly related to a reduction in the protozoal population. On the other hand, addition of Saccharomyces cerevisiae to an in vitro system reduced the methane production by 10% .
• Antibiotics:Monensin is a naturally occurring polyether antibiotic that reduces methane production mainly by selective reduction of acetate formation and associated H2 production.
• Halogenated compounds: Halogenated compounds such as chloroform and BES (2-bromoethanesulfonic acid) have direct inhibitory effects on methanogenic bacteria and reduce methane production both in vitro and in vivo .
• Addition of natural compounds: Natural compounds such as Paranthocyanidins(condensed Tannins)mystiric acid and various oils reduces methane production .
h. Animal Management- Animal selection for increased production, use of growth promoting agents, and application of more refined ration balancing technologies are various strategies to reduce CH4 emissions.
i. Vaccination or Immunisation- Baker(1995) has proposed that it may be possible to immunise ruminants against their own methanogens with associated decreases in methane output.
NDDB has set up a laboratory for methane emission measurement in dairy animals under field conditions. Field trials are conducted in different categories of animals to measure methane emission before and after feeding of balanced ration to generate a baseline data. Studies conducted so far revealed that by feeding a balanced ration, it is possible to reduce methane emissions by 10-15 per cent per kg of milk in cows and buffaloes.
Mitigation of Enteric Methane Emission from Dairy Animals in India Through Nutritional Intervention
Reference-On request
