| Livestock Research for Rural Development 28 (3) 2016 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Discussions on climate change and the livestock industry are skewed toward the effects on livestock rather than how livestock contribute to it. This review highlights how the activities of the livestock industry impacts on climate change. Methane forms about 44 % of livestock emissions. The rest is shared between Carbon dioxide (27%) and Nitrous oxide (29%). Cattle emit the highest, about 65 % of the livestock production emissions. With respect to activities, feed processing and production and enteric fermentation from ruminants are the two major sources of emissions, contributing 45 % and 39 % of total emissions respectively. Manure storage and processing forms 10 % and the rest is attributed to transportation and animal processing. On product-basis, milk from cows and beef are responsible for the most emissions, contributing 20 % and 41 % of the sector’s total greenhouse gas (GHG) outputs respectively. Storage of manure and supply of feed forms the bulk of emissions in pig production while supply of feed form the bulk in poultry. It is concluded that the livestock industry be given a bit more consideration in the efforts to minimize the effects of anthropogenic activities on GHG emissions.
Key words: greenhouse gas, enteric fermentation, methane, mitigation, ruminants
Since the initial meeting of the United Nations Framework Convention for Climate Change (UNFCCC), climate change has been realized as a major global problem (United Nations 1992). Agriculture is still the major contributor to most African economies (Hussein et al 2008). Agriculture is the biggest domestic producer across the world and employs from 70 % and 90 % of the total work force (FAO 2007). In addition, agriculture provides about 50% household food requirements and about 50 % household income. Majority of the revenue is generated by pigs, chickens, sheep, goats, beef and dairy cattle. These five species of livestock generate 92 % of the overall revenue from livestock in Africa. In most rural communities, livestock is the only property of the poor, but it is highly susceptible to climate changes and extremes (Easterling et al 2007; FAO 2007; Thornton et al 2007; Calvaba 2009). The influence of climate change is anticipated to increase the susceptibility of livestock industry and reinforce current factors that are having impact on livestock farming systems (Gill and Smith 2008). Agriculture contributes to climate change and it is affected by climate change (Aydinalp and Cresser 2008). The facts and figures of these are quoted in many studies and reports (IPCC 1996) and are mainly based on commercial agriculture (Koneswaran and Nierenberg 2008). The relevance of livestock in the provision of food, employment, incomes and risk insurance is widely known (Perry and Sones 2007; Herrero et al 2009). Similarly, there is an increasing awareness within the policy and research communities that fast growth in consumption and production of livestock commodities is contributing to variety of environmental problems. The main notable issue being livestock's significant contribution to anthropogenic emissions.
In 2006, a FAO publication entitled ‘Livestock’s long shadow – Environmental issues and options’ indicated that the influence of livestock on the environment was much greater than it was considered. This publication provided detailed perspectives on the impact of livestock on water, biodiversity and climate change. The issue on climate change and 18 % estimated contribution of livestock to overall GHG emissions is the concern that attracted the most attention. Dairy production is a significant contributor of GHG emissions (Weiske et al 2006; Smith et al 2007). Both manure and enteric fermentation contribute some 80 % of methane emissions from agricultural activities and about 30–40 % of the overall anthropogenic methane emissions (FAO 2006).
Activities of humans result in four long-lived GHG emissions: carbon dioxide (CO2), halocarbons, methane (CH4) and nitrous oxide (N2O). Fossil fuel usage mainly increases global carbon dioxide concentrations (IPCC 2007a; IPCC 2007b). It is expected that climate change will have a moderate impact on livestock industry in the United States since most livestock are housed and fed supplemental diets (Adams et al 1999). The case is different in developing countries where animals spend more time grazing at the mercy of the weather. It is to be anticipated that animal management will be more prepared to change in the climate under these situations. Climate affects livestock indirectly and directly. Some of the direct effects are from wind speed, air temperature, humidity and other climatic factors affect performance of animals: viz milk and wool production, growth and reproduction (Houghton 2001).
The anticipated worldwide demand for meat is likely to double between 1999 and 2050 (Steinfeld et al 2006). The total number of meat-producing animals will have to be increased to meet the demand, which will result in an increase in emissions. This significant increase in demand will be mainly because of population and income increment (Delgado et al 1999). Without critical action, emissions are not going to decrease. Emissions will rise as demand for milk, eggs and meat continues to increase globally. Estimated growth in population and incomes are likely to move consumption higher, with expected milk and meat patronage to double by 2050 (FAO 2006b).
The objective of this study was to highlight the effects or impacts of livestock production and its related activities on climate change. This was done by reviewing literature from 44 peer reviewed papers in well reputed journals.
The three gas emissions in livestock production are nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4). CH4 is the most important gas produce in agriculture (IPCC 1996). CH4 and N2O have nearly 20 and 300 times global warming potential than that of CO2 respectively (IPCC 1996). The overall contribution of Agriculture to global warming is within 18 % - 20 %. Livestock production represent about 5-10 % of the total from agricultural activities (IPCC 1996). Milk production and its related production of meat contribute about 4 % and production of milk alone is nearly 2.7 % (IPCC 1996).
It is not easy to quantify the overall emissions from livestock-related activities because of non-existence of accurate data, the variability of the systems of livestock production across the world, and the limitation of recognizing all life-cycle activities and their associated emissions. The FAO (2006) estimated 18 % anthropogenic GHG emissions from livestock industry is disapproved by Goodland and Anhang (2009) who noted that the figure under-tallies emissions from certain production activities, underestimates demand, and absolutely omits some categories of emissions. They estimated that livestock production is contributing about 51 % of anthropogenic GHG emissions. Goodland and Anhang (2009) revealed that, CO2 from livestock respiration was ignored as a source of the GHGs from the FAO study (2006).
The overall GHG emissions from livestock supply chains are approximately 7.1 gigatonnes CO2-equivalent annually for the 2005 reference point forming about 14.5 % of all emissions induced by humans (IPCC 2007a).This figure conform with FAO’s previous report (FAO 2006), although that was based on a much more complex analysis involving ‘major methodological refinements’ and ‘improved data sets’. Comparism of relative contributions is not possible due to variation in reference duration. The FAO (2006a) study compared its estimate based on a 2001 -2004 reference period and with the overall CO2, CH4 and N2O anthropogenic emissions estimated by the World Resource Institute (WRI) for the year 2000.
About 44 % of the livestock industry emissions are in the form of CH4. Nitrous oxide and carbon dioxide represent 29 % and 27 % respectively. Livestock supply chains emit 9.2 gigatonnes CO2-eq of CO2 annually or 5 % of anthropogenic CO2 emissions (IPCC 2007b). According to IPCC (2007b), 44 % of anthropogenic CH4 emissions or 3.1 gigatonnes CO2-eq of CH4 every year and 53 % of anthropogenic N2O emissions or 2 gigatonnes CO2-eq of N2O are produced annually.
Cattle are the most significant contributor to livestock production emissions with approximately 4.6 gigatonnes CO2-eq, forming 65 %. Poultry, Pigs, small ruminants and buffaloes have lower emission levels, with each contributing between 7 – 10 % of the livestock emissions. Ignoring domesticated ruminants would also have influence with respect to populations of wild ungulates, as these species could survive in ‘vacated niches’. In some cases GHG emissions from wild ruminants may even be higher than from domesticated ruminants because they have been selected over generations for efficiency. These information point to the reality that, calculating emissions from livestock systems is very complex and needs to be examined with solid conceptual models of social, environmental, economic and global change.
The most efficient protein production industry is poultry egg and meat production (Williams et al 2006). Production of poultry meat is the most efficient environmentally (that is the smallest footprint of carbon/ unit product), then followed by pork and mutton (mainly lamb) with beef being the least efficient (Williams et al 2006). This is due to many factors including the low breeding stock of poultry overheads (thus hens fecundity are much greater; 250 progeny / hen / year versus one calf /cow), feed conversion efficiency, genetic selection resulting in high weight gain and improvement in formulation of diet (Williams et al 2006).
Pigs and poultry consume feeds of high-value and depend on arable land as their needs nutritionally are mainly met by arable crops. The production of poultry and pigs rely on mainly feed concentrates. In view of this, their actual environmental effects are related to production out of the farm and feed concentrates delivery on-farm (Van der Werf et al 2005). With regards to the effect of climate change on consumed primary energy, ruminants are approximately 50 % higher than chicken or pig production (Williams et al 2006). However, the production of meats of ruminant involve more burdens than poultry meat or pork, but ruminants can be nourished from land that is not good for arable crops (Williams et al 2006).
Milk from cattle contributes 20 % (1.4 gigatonnes CO2-eq) and beef 41 % (2.9 gigatonnes CO2-eq) of total livestock emissions. Small ruminant milk and meat release 6 %, pork production 9 %, buffalo meat and milk 8 % and meat and eggs of chicken 8 %. The remaining are emissions from products that are not eaten and other poultry species (MacLeod et al 2013a; 2013b). Beef is the product with the greatest emission intensity (that is the amount of GHGs emitted / unit of produced output) with a mean of more than 300 kg CO2-eq/ kg of protein. Beef is followed by small ruminant meat and milk with means of 165 and 112 kg CO2-eq / kg of protein respectively. Chicken products, pork and cow milk have lower averages of emission intensities globally, below 100 kg CO2-eq/ kg of edible protein (MacLeod et al 2013a; 2013b).
Intensities of emissions vary immensely among producers of ruminant, pork, chicken eggs and meat. The variations are due to different ‘agro-ecological conditions’, management of supply chain and farming practices observed both across and within systems of production. Many mitigation alternatives can be revealed between the gap of producers with greatest emission intensity and those with least emission intensity.
Types of feed crops identified are second grade crops, feed crops with no co-products, crop residues and by-products from food crops. For instance, wastes from household food used to feed pigs in the backyard are assumed to have an emission intensity of zero because emissions are fully attributed to household food. Similarly, crop residues such as maize stover related emissions are low due to the fact that, most of the emissions are assigned to the main product (maize grain). By-products of slaughterhouse such as skins, blood and offals were allocated zero emission. Case studies revealed that by-products can contribute about 5-10 % to the overall revenue at slaughterhouse gate, for instance pork and beef in the Organization for Economic Cooperation and Development countries (MacLeod et al 2013a; 2013b).
Emissions from deforestation related to expansion of pasture were estimated only for Latin
America. This simplification was due to the observation that, during the period 1990–2006, substantial expansions of pasture and simultaneous reduction in forest area occurred in Africa and Latin America. However, grazing does not seem to be an important deforestation driver in Africa. In Latin America, the estimation of emissions was limited to the four countries representing more than 97 % of the regional area converted from forest to pasture (i.e. Chile, Nicaragua, Brazil and Paraguay). Greenhouse gas emissions related to change in land-use were assigned to the regions and systems that utilize feed resources linked to deforestation. Trade matrices were employed to track international flows of soybean cake and soybean and to calculate the proportion of soybean products from deforested lands in the ration of animals. Emissions related to the pasture expansion into forest areas in Latin America were assigned to production of beef in those countries in which the conversion was carried out.
Goodland and Anhang (2006) suggested the use of a twenty year global warming potential (GWP) for CH4 of 72. The debate on the quantum of warming that CH4 causes is ongoing (Shindell et al 2009). Scientific progresses have led to the rectifications in CH4 GWP values over the past ten years. Infact, the IPCC, in its 4th Assessment Report, seriously revised the GWP from 23 to 25 to add stratospheric water vapor and indirect effects of CH4 on ozone. It should be recognized that, at the period of writing the FAO (2006a) report, the GWP of 23 over a 100 year duration was valid and acceptable. Methane has an atmospheric lifespan of 12 years, in the short run it contributes more than the factor 25 to current global warming as suggested, but this influence decays almost to nothing after 20–30 years. Therefore, CH4 is a very significant gas to aim at for short term reduction in radiative forcing. However, the GWP is a measure to give special attention to in mitigation practices, for which the scale of a century is currently considered appropriate, although still under debate (Shindell et al 2009). The IPCC has appreciated the value of alternative metrics (e.g., Global Temperature Potential) but indicated that further research is needed (Plattner et al 2009). Selection of a time horizon is a scientific relevant issue, but also a political one based on the relative weight given to short versus long lived GHGs.
Research in mitigating emissions has targeted chemical compounds with a specific inhibitory influence on the rumen. Some of the most successful compounds tested in vivo were cyclodextrin (Lila et al 2004), bromochloromethane (BCM), 2-bromo-ethane sulfonate (BES) (Immig et al 1996; Mitsumori et al 2011) and chloroform (Knight et al 2011). These methane inhibitors statistically reduced CH4 emission by up to 50 % in vivo in goats, sheep and cattle.
Electron receptors which are CH4 reducing agents have currently received research attention. Examples are fumarate, sulphates, nitroethane and nitrates (Gutierrez-Banuelos et al 2007; Brown et al 2011) have been given much research attention. Leng (2008) revealed a comprehensive review of the earlier literature on nitrates. More current studies with sheep (Sar et al 2004; Nolan et al 2010; van Zijderveld et al 2010) and cattle (van Zijderveld et al 2011a, van Zijderveld et al 2011b; Hulshof et al 2012) have shown interesting results with nitrates reducing enteric CH4 release by up to 50 %. Potential challenges with these compounds include ruminal ecosystem adaptation, with one peculiar situation where nitrate constantly decreased CH4 emission from lactating dairy cows during four consecutive 24-day periods (van Zijderveld et al 2011b), but has not been studied in animal experiments for a long duration. The toxicity problem has been given much research attention and was concluded that feeding management may prevent nitrite formation from nitrate in the rumen.
Leng (2008) also emphasized the critical relevance of adaptation of the animal to nitrate gradually and that diets low in protein is the natural background for successful use of nitrates as a CH4 mitigating compound. The rumen ecosystem has to adjust to dietary nitrates and obtain the ability to reduce nitrates rapidly to NH3. This is due to the fact that, by the gradual and marked increase in nitrate reducing bacteria activity after the introduction of nitrate in the diet and the presence of special microbial groups in nitrate-adapted animals (Allison and Reddy 1984). Therefore, in the studies of Nolan et al (2010), Van Zijderveld et al (2010; 2011a; 2011b) and Hulshof et al (2012) nitrate was slowly introduced in the diet to allow adaptation, and no health issues occurred.
Plant bioactive compounds (PBAC) comprise of a variety of plant secondary compounds, specifically saponins, essential oils and tannins and their active ingredients. Saponins and tannins have been studied extensively and most promising potential for mitigating emissions. Tannins as tanniferous plants or feed supplements have occasionally, but not all the time (Beauchemin et al 2007a), shown as a potential for minimizing enteric methane production by up to 20 %. Hydrolysable and condensed tannins are mainly distributed in browse and warm climate forages and are normally considered anti-nutritional. However, they can reduce intestinal nematode numbers and permit acceptable level of production in the presence of a parasite burden (Niezen et al 1995; Niezen et al 1998a, Niezen et al 1998b; Terrill et al 1992). Tannins will definitely be anti-nutritional when dietary crude protein levels are limiting production because they decrease amino acids absorption. (Waghorn 2008). Structure, concentration and molecular weight of condensed tannins affect the diet nutritive value and it is important to note that the benefits of reduced CH4 yields do not overshadow any harmful effects of tannins on nutrient digestion and production as indicated by Grainger et al (2009) with dairy cows on pasture supplemented with grain. In this study, methane release was decreased by up to 30 %, but production of milk of the cows was also decreased by about 10 %.
Extensive research has been done on polyphenolic compounds especially condensed tannins, in temperate forages under the European Union-supported “Healthy hay” and ‘Marie Curie Legume Plus’ programmes (http://sainfoin.eu/), but yield of tropical and temperate tanniferous legumes is normally less than that of corresponding grasses and agronomic properties sometimes restrict their use. Nevertheless, animal health and nutritional benefits of tannin such as anthelmintic, bloat safe and reductions in methanogenesis and especially N2O emissions and nitrogen fixation in soils for plant growth makes these plants attractive for environmentally sustainable ruminant production. A more current study with goats indicated that a diet containing 5.6 g/kg DM tannins (both condensed and hydrolysable) decreased the gross energy factor from 7.9 (control) to 6.0 % of gross energy intake, but organic matter digestibility was lowered by 10 %-units and CP digestibility by 14 %-units (Bhatta et al 2012). Crude protein digestibility was also decreased when diets containing a lower tannin concentration (2.8 g/kg DM) were fed. The effect of tannins is determined by their composition (Waghorn 2008; Goel and Makkar 2012). As reported by Pellikaan et al (2011b), in vitro gas and CH4 production depended on tannin characteristics, such as solubility, type (condensed vs gallotannins vs ellagitannins), browning rate and cis-trans configuration. In that study, myrobalan and valonea tannins were most effective at lowering CH4 release, with only a minor influence on total gas production. Of the nine saponins studies summarized by Goel and Makkar (2012), six reported reduced CH4, from about 6 – 27 % (per unit of body weight or dry matter intake or absolute production). In three of these studies, however, organic matter digestibility was reduced and in the other three, there was no report on digestibility. From this analysis, it appeared that there was no difference in the CH4-mitigation effect between triterpenoid saponins (Quillaja saponaria), Y. schidigera and Q. saponaria and steroidal saponins (Yucca schidigera) which have been studied the most as saponins sources because they are available commercially.
Studies from China have studied the CH4-mitigation impact of tea saponins (triterpenoid) on enteric CH4 production and animal performance (Wang et al 2012). Hu et al (2006) fed goats graded levels of tea saponins ( 0, 3 and 6 g/day) and reported an increase in intake of feed and average daily gain with the 3 g/day dose. Wang et al. (2009) reported about 15 % reduction in CH4 emission by sheep fed 170 mg/day extract of Y. schidigera. Mao et al (2010) reported no impact in the application of 3 g/day of tea saponins on average daily gain of lambs but a 28 % reduction in CH4 emission. Zhou et al (2011) reported a 6 – 10 % decreasing effect of tea saponins on CH4 release in restricted-fed sheep. There is a lot of evidence that lipids such as animal fat or vegetable oil can reduce CH4 emission in the rumen. The influence of lipids on rumen archaea cannot be isolated from their overall suppressive impact on protozoa and bacteria. Several researchers have attempted to create prediction factors for the influence of feed lipids on rumen CH4. Eugene et al (2008) reported a 9 % decrease in enteric CH4 release in dairy cows due to supplementation of lipid diets, but this was associated with a 6.4 % reduction in dry matter intake which caused no difference in CH4 per unit of dry matter intake. However, these workers also indicated no impact on 4 % fat-corrected milk which, combined with the decrease dry matter intake, caused a trend for increased efficiency of feed with supplementation of oil. Further, when estimated per unit of fat-corrected milk, CH4 emission reduced with lipid supplementation. In general, it is believed that higher grain inclusion or feeding of forages with higher content of starch such as whole-crop cereal silages in ruminant diets reduces enteric CH4 release. Beauchemin et al (2011) calculated that carrying out extensive forage feeding for growing beef cattle would significantly increase greenhouse gas intensity by 6.5 %. In the same way, Pelletier et al (2010) reported 30 % higher total greenhouse gas production for pasture-finished cattle compared with cattle fed in a grain-based feedlot system. Feedlot cattle in North America are mainly fed high grain diets that are more than 90 % grain on a dry matter basis to achieve optimum profit. In these systems, gross energy can be as low as 2 – 3 % (Johnson and Johnson 1995). Beauchemin et al (2011) estimated that prolonged grain finishing of cattle from 170-210 days would decrease greenhouse gas emission of beef production by 2 %. The decreased enteric CH4 production is mainly due to shorter time to market and reduced CH4 energy emitted as percent gross energy of grain versus forage-based diets. There would also be less CH4 release from manure because its production would be lowered by 11.3 % due to the improved digestibility of grain (Beauchemin et al 2011). Intake of feed is a relevant factor for enhancing feed efficiency, improving productivity of animal and both CH4 and N2O emissions. Mertens (1994) and Allen (2000) have reported extensively on regulation of feed intake in ruminants. The physical factors are palatability and fill limitation and physiological factors are related to production of rumen propionate that control intake of feed. According to Mertens (1994) intake of feed is influenced by management practices such as frequency of feeding, feed accessibility, method of presenting the feed and animal handling. Other factors related to feed are feed palatability and physical properties of feed such as plant species, chemical composition, nutrient availability and processing and animal factors such as appetite, the capacity to ingest food and energy demand. Dietary neutral detergent fibre concentration is among the most significant regulators of feed intake through the so-called fill limitation mechanism (Mertens 1994). Thus, neutral detergent fibre content of the diet and its intake are very important for achieving maximum animal productivity and reducing greenhouse gas productions.
Harvesting forage at an early maturity stage improves its content of soluble carbohydrate and decreases the lignin level of plant cell walls thereby increasing its digestibility (Van Soest 1994) and reducing enteric methane emission per unit of digestible dry matter (Tyrrell et al 1992; Boadi and Wittenberg 2002). Processing through its influence on energy losses, passage rate and digestibility can be an effective enteric CH4 mitigation option although it may not be economically feasible in some production systems. Hironaka et al (1996) showed that pelleting of alfalfa can decrease CH4 emission, but this was not economically feasible due to increased cost of production and was not likely to be environmentally friendly due to high energy input.
A study by Hales et al (2012) using respiration calorimetric chambers with steers compared steam-flaked versus dry-rolled corn and reported increased digestibility. The steam-flaked corn feeding caused about 17 % less CH4 production per unit of dry matter intake. Breeding straw for improved nutritive quality is highly recommended and shows promising for enhanced production and decrease CH4 intensity in southern India (Blümmel et al 2010).
Sauvant et al (2011) indicated that CH4 emission per kilogram digested organic matter decreased in a linear format with increasing dietary crude protein (CH4, g/kg digestible OM = 40.1 – 0.32 × CP, percent DM; n = 59 experiments). That is decreasing dietary protein levels will likely increase fermentable carbohydrates content, which in turn will likely increase CH4 emission. These relationships have to be considered when regulating dietary nitrogen to decrease manure NH3 and N2O productions. Fibre addition to the diet of monogastrics can change the route of nitrogen excretion from urine to faeces and thus reduce NH3 and N2O productions from slurry. These relationships can be complex and usually, the impacts on greenhouse gas emissions should be studied on a whole-farm scale. Care must be taken that dietary regulations do not influence production of animal or gains at one level of the production system, are not offset by losses at another (Jarret et al 2011; Klevenhusen et al 2011).
Strategies for reducing N2O emissions from livestock productions have been summarized by de Klein and Eckard (2008). These researchers discussed the following abatement strategies, with respect to ruminant grazing systems:
1. Dietary amendments: for example, addition of salt through its diuretic impact dilutes nitrogen
in urine and may lead to decrease N2O emissions by 5 – 10 % . Also supplementation
of the diet with inhibitors of nitrification through a slow-release bolus that is excreted unchanged in urine has a potential of 30-60 % N2O emission.
2. Dietary tannins as feed supplements or fed through high-tannin forages shifts nitrogen excretion from urine to faeces and causes reduction up to 60 % in urinary nitrogen excretion.
3. Fertilizer management: The source, timing and rate of fertilizer application in relation to soil temperature and moisture conditions are important factors for decreasing N2O emissions from soil. That is 2 to 13 % potential reduction of N2O emissions.
4. Nitrification inhibitors: direct application of nitrification inhibitors on the soil has a great potential to decrease N2O productions resulting from deposition of urine.
5. Effluent management (with reference to stored manure): The method of application and timing are critical for decreasing N2O emissions with 50 % reduction potential.
6. Irrigation and drainage as related to soil moisture have up to 60 % N2O reduction potential.
Poor fertility increases greenhouse gas emissions from animal production systems. This is mainly due to the fact that poor fertility causes producers of livestock to keep more animals per production unit and obtain more replacement animals to maintain flock size. Garnsworthy (2004) provides an example of the link between improvements in dairy cow fertility in the United Kingdom and its influence on CH4 and NH3 productions, concluding that improving fertility could decrease CH4 emissions by 24 % and NH3 emissions by 17 %, mainly by reducing the number of replacements animals in the herd.
The total emission from livestock related activities ranged from 18-51%. Methane formed 44% which is the highest and cattle and it products are the main contributors to livestock emissions. In terms of activities, feed production and processing and enteric fermentation from ruminants are the two main sources of emissions, representing 39 % and 45 % of total emissions respectively.
It is recommended that potential mitigation and adaptation factors that could be incorporated into beef and dairy production systems should include:
• Ensuring more efficient nutrition
• Using continuous genetic improvement to produce more efficient animals such as reproductively sound, smaller, lighter in colour, high feed to meat conversion, high feed to milk conversion and milk output and substantial tolerance to disease.
• Modifying systems of production in order to leave a smaller carbon footprint with less emission, lower energy requirements and fewer waste products.
• Breeding more drought-resistant crops and pastures for dairy consumption.
• Implementing friendly environmental and more effective farming practices.
Slurry storage and housing of pigs contribute to the bulk of greenhouse gas and NH3 which is an indirect source of greenhouse gas emissions from pig production systems (Van der Peet-Schwering et al 1999). These emissions can be minimized by lowering the concentrations of NH3 and urea in the slurry, reducing the pH and temperature of the slurry and reducing the surface area of emission.
Many housing systems have been developed to reduce emissions. A combination of feeding techniques and housing seems most promising to attain a considerable reduction in emissions at moderately low cost (Van der Peet-Schwering et al 1999).
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Received 6 February 2016; Accepted 16 February 2016; Published 1 March 2016