Technical options for the mitigation of direct methane and nitrous oxide emissions from livestock: a review

Abstract

Although livestock production accounts for a sizeable share of global greenhouse gas emissions, numerous technical options have been identified to mitigate these emissions. In this review, a subset of these options, which have proven to be effective, are discussed. These include measures to reduce CH 4 emissions from enteric fermentation by ruminants, the largest single emission source from the global livestock sector, and for reducing CH 4 and N 2 O emissions from manure. A unique feature of this review is the high level of attention given to interactions between mitigation options and productivity. Among the feed supplement options for lowering enteric emissions, dietary lipids, nitrates and ionophores are identified as the most effective. Forage quality, feed processing and precision feeding have the best prospects among the various available feed and feed management measures. With regard to manure, dietary measures that reduce the amount of N excreted (e.g. better matching of dietary protein to animal needs), shift N excretion from urine to faeces (e.g. tannin inclusion at low levels) and reduce the amount of fermentable organic matter excreted are recommended. Among the many 'end-of-pipe' measures available for manure management, approaches that capture and/or process CH 4 emissions during storage (e.g. anaerobic digestion, biofiltration, composting), as well as subsurface injection of manure, are among the most encouraging options flagged in this section of the review. The importance of a multiple gas perspective is critical when assessing mitigation potentials, because most of the options reviewed show strong interactions among sources of greenhouse gas (GHG) emissions. The paper reviews current knowledge on potential pollution swapping, whereby the reduction of one GHG or emission source leads to unintended increases in another.

Current available strategies to mitigate greenhouse gas emissions in livestock systems: an animal welfare perspective

“…Direct emissions (through enteric fermentation and losses from manure) from livestock are estimated to contribute 11% of total anthropogenic GHG emissions (Gerber et al, 2013). Due to their greater total biomass than other livestock and their digestive strategy, ruminants are the most significant livestock producers of GHGs (Pitesky et al, 2009).…”

“…Strategies for greenhouse gas mitigation and their implications for animal welfare Strategies to mitigate enteric CH 4 and manure N 2 O emissions from livestock production have recently been reviewed (Eckard et al, 2010;Gill et al, 2010;Buddle et al, 2011;Zervas and Tsiplakou, 2012;Bellarby et al, 2013;Gerber et al, 2013;Hristov et al, 2013a and2013b). Among these, some strategies focus on reducing the indirect GHG produced during animal production such as, for example, land use change, direct on-farm energy use for livestock production or manure management.…”

“…Instead, marked improvements can be expected beyond a 35% to 40% inclusion of grain in the diet (Gerber et al, 2013). For instance, to achieve a decrease of 9.5% CH 4 in dairy cattle, Lovett et al (2006) increased non-fibre carbohydrates more than fourfold (from 338 to 1403 kg/ head per year).…”

“…Waghorn and Hegarty (2011) estimated that if feed efficiency were selected as the main animal breeding goal for ruminants, a valuable 15% reduction in CH 4 emissions could be achieved. Reductions in emissions and Ei with improved feed efficiency should also apply to N 2 O (Gerber et al, 2013), as more N efficient animal will retain more dietary N and therefore N excretion in faeces and urine will decrease. Nevertheless, risks for health and fertility traits have been identified in breeding for greater feed efficiency.…”

Methane emissions from two breeds of beef cows offered diets containing barley straw with either grass silage or brewers’ grains

“…Enteric CH 4 emissions represents a loss of feed energy to the animal (estimated at 6% to 10%), which could be used by the animal for production (e.g. deposition of lean meat; Cottle et al, 2011;Gerber et al, 2013a and2013b).…”