~Dr Sagarika Barman
India has the world’s largest number of livestock and thus CH4 emissions from the livestock are very significant.Livestock is one of the major sources of anthropogenic methane emissions.Much of the livesock are ruminants such as sheep,goats,camel,cattle and buffalo- who have unique four chambered stomach (rumen).In the rumen , bacteria break down food and generate methane as by-product.The production rate is affected by factors such as quantity and quality of feed, body wight,age and execise , and varies among animal species as well as among individuals of the same species.At a global scale, livestock farming may contribute 12- 18% of total greenhouse gas (GHG) emissions (Westhoek et al., 2011).Livestock contributes about 81-92 MT methane per annum globally (IPCC,2007).It has been reported that increase in the meat, milk and eggs production will further exacerbate Green House Gas problems in absence of adequate mitigation measures.(Steinfeld et al.,2006) .
Global warming and Greenhouse effect
The atmosphere has a natural supply of greenhouse gases that capture heat and keep the surface of the Earth warm. Before the industrial revolution took off in the middle 1700s, the greenhouse gases released into the atmosphere were somewhat balanced with what could be stored on Earth. Natural emissions of heat trapping gases matched what could be absorbed in natural sinks such as when plants take in carbon dioxide when they are growing and release it back into the atmosphere when they die. . As countries became more industrialized, more gases were being added to the natural levels in the atmosphere. These gases can stay in the atmosphere for at least 50 years and longer.
Gases that trap heat in the atmosphere are called greenhouse gases. It is not about how much the earth is warming, but how fast it is warming.CO2,CH4,N2O, hydrofluorocarbons, perfluorocarbons and sulfur hexafluoride are the GHGs monitored by UNFCC.
CH4 is the second major gas after CO2 responsible for the warming of environment and ozone layer depletion.Globally, GHG emissions related to agricultural production are estimated at 15–25% of total anthropogenic GHGs (Vermeulen et al., 2012 ;Tubiello et al., 2015)
Global methane sources
- Natural- waste water, wetlands, ocean, lakes & rivers and termites & other arthropods (42%)
- Agriculture-Rice, enteric fermentation, manure, other agriculture (29%)
- Other anthropogenic-Fossil fuels, biomass burning and land fills (29%)
(EPA, 2010 & EPA, 2011)
There has been a lot of research conducted in Canada, Australia, Europe, and the U.S. on strategies to reduce methane emissions from dairy and beef operations. The main focus has been on nutritional strategies, especially cows grazing pasture.
NUTRITIONAL STRATEGIES TO REDUCE CH4 PRODUCTION
High diets is associated with high rate of ruminal digestion and passage which favour a higher propionic acid production (Kumar et al., 2013).High digestion rates of grains will also ↓pH which inhibits the growth of methanogens and protozoa .↓ acetate: propionate ratio and thus ↓ the amount of CH4 produced per unit of feed intake(Beauchemin et al.,2008).CH4 losses are relatively constant in diets with 30-40% concentrate and decreases rapidly to low values in diets containing 80-90% concentrate.
2.FORAGE TYPE & QUALITY
Legume grasses produce less CH4 per unit of DMI than grass forages .(O’Neill et al.,2012)
Matured plant (↑ CF) ↑ CH4 production per unit of OM digested.(Archimede et al.,2011).Ensiled forages produce less CH4 due to extensive fermentation which reduces digestion in the rumen.Grinding, chopping or pelleting will ↓ rumen NDF digestibility and can ↓ CH4 emission as a result of ↑ passage rate.(Knapp et al.,2014)
3.LEVEL OF INTAKE AND FEEDING FREQUENCY
Intake levels (Roughage) effect on passage rate is proportionally less than concentrate or mixed diets.Low meal frequencies ↑ propionate production and ↓ CH4 production.
A. LIPID AND FATTY ACID SUPPLEMENTATION
Inhibits Protozoa, biohydrogenation of unsaturated Fats & increase propionate production(Patra ,2012).Canola seeds, soybeans, rapeseed, flaxseeds, sunflower oil, coconut oil, linseed oil, canola oil,fish oil,lauric acid, myristic acid, capyrlic, capric acid etc.CH4 emission (g/kg of DMI) reduced by 5.6% with each 1 % addition of fats(Beauchimin et al.,2008).6% fat in the diet improved milk production and ↓ CH4 emissions appreciably (15%) in cattle(Patra, 2013).
B. IONOPHORE SUPPLEMENTATION
Monensin, lasalocid, salinomycin etc are some of the ionophore used in the diet of livestock.Interrupts transmembrane movement and intracellular equilibrium of ions in bacteria and protozoa (Tedeschi et al.,2013).
Ionophores affect CH4 production by two ways-
→ ↑ feed conversion efficiency ↓CH4 emission per unit of product
→ ↓ quantity of CH4 production per unit of DMI
- NITRATE & SULPHATE SUPPLEMENTATION
NO3 → NO2 → NH3, can be the main pathway to eliminate H2 (Ungerfeld and Kohn, 2006).Sulphate is a reducer that competes for electrons and as a result decrease CH4 production.
- PROPIONATE ENHANCER
Malate and fumarate are intermediates in the succinate-propionate pathway which directs H2 away from methanogenesis.
Removal of protozoa population from the rumen.Protozoa provides a habitat for 10-20% of rumen methanogens (Rodehutscord,2013).Responsible for 9-25% CH4 production in the rumen(Morgavi et al.,2008).Mosoni et al.(2011) reported that defaunation ↓ CH4 emission but ruminal methanogen density ↑ by 10 fold.
6.PREBIOTIC AND PROBIOTIC
Non structural CHO used with nitrate, probiotics and yeast in rumen manipulation(Ingale et al.,2013).Speculated to enhance propionate production by stimulating Selenomonas, Succinomonas and Megasphera with simultaneous inhibition of acetate producers such as Rumininococcus & Butyrivibrio(Mwenya et al.,2004).Probiotics improve microbial metabolism, DMI, Fibre digestion and milk production.Stimulate lactic acid utilizing bacteria and favours the growth of cellulolytic bacteria(Mwenya et al.,2004).
7.PLANT SECONDARY METABOLITES
Essential oils, saponins and tannins are the prospective plant natural compounds for mitigating CH4 emissions(Bodas et al., 2012 and Jayanegra et al .,2014).Condensed & hydrolysable tannins ↓ CH4 by ↓ fibre digestion & inhibiting methanogen, respectively.In vitro study, essential oils (Origanum oil, garlic oil & peppermint oil) @ 0.5g/L efficiently ↓ CH4(Patra et al.,2015)
- Any suitable solution to lower on-farm methane emission should be practical, cost effective and have no substantial adverse effect on profitability.
- Manipulating diet composition to induce changes in enteric fermentation characteristics remains the most feasible approach to lower CH4
Integrated strategies considering animal, plant and microbial factors may be sought to offer a long term solution of CH4 production without detrimental effects.
Authors: Dr Sagarika Barman
M.V.Sc Scholar (ANN)