by R.A. Leng
Environmental change, over the next 50–100 years, due to the warming effect of the accumulation of gases in the atmosphere will clearly influence man and his well-being and will introduce change to many areas of the world.
Although there has been modelling of future climate change, the major observation is that these models are as yet producing limited useful information. Computers have the ability to consider a multitude of variables but the computer is limited by the knowledge base and magnitude of the unknowns. In fact, it can be quickly ascertained that modelling, at best, is defining what is not known in terms of what will effect change in temperature, rainfall and sea levels, let alone sea currents, wind, sunshine hours, soil moisture and the incidence of pests and diseases of man, animals and plants.
Some prediction (no matter how uncertain) are welcomed by the population at large (e.g. increased environmental temperatures in Europe) but the uncertainties indicate that for any benefits there will also be major disadvantages, both economic and social. For example, high temperature and increased evaporation rates and the lower resultant soil moisture content, may result in the death of large areas of planted and natural forest in Northern Europe; rain in previously dry areas may lead to large scale soil erosion and wide scale flooding of major agricultural lands in the fertile delta country will occur if sea levels increase by 0.3 meters by 2050.
The major conclusion is that disadvantages are likely to outweigh any advantages and the unknowns make it essential to put into action technologies to slow green-house gas emissions and stabilise atmospheric gases as soon as possible. The long lag time between gas production, mixing in the atmosphere and therefore warming together with the reluctance of governments to put into practice legislation to limit, in particular, carbon dioxide production from fossil fuels, suggests that there will be a rise in world environmental temperatures of 0.5 to 1°C in the next 25–50 years. (see IPCC report 1990).
A major point is that no one country can point to a low level of “environmentally dangerous gases” production as being a reason for non-compliance with a general lowering of emissions. Virtually all countries contribute a small proportion of the greenhouse gas and it is, therefore, necessary for all countries to take action. In other words it needs action world wide and “every little bit helps”.
A distinction must be made between temperature rise due to gas accumulation in the atmosphere and depletion of the ozone layer through reaction with atmosphere contaminants. The two are linked but the depletion of the ozone layer (this layer protects the animals/plants from deleterious dose rates of UV irradiation) is largely a result of reaction of the ozone with atmosphere contaminants. Ozone depletion is not highly related to the subject of environmental change and gas accumulation in the atmosphere as discussed here. However, increased ultra-violet radiation at the earths surface will have major detrimental effects on plant growth.
THE GREENHOUSE EFFECT
A Simple Description
The greenhouse effect, or increasing world temperature, is clearly ascribable to the major industrial countries as some 50% of the increased retention of energy by the atmosphere is a result of the accumulation of carbon dioxide from combustion of fossil fuel. Industrialised countries presently use 70% of the world's oil production and it has been much higher in the past. (Figs 1 & 2).
Figure 1: Relative contribution (%) of greenhouse gases to atmospheric warming (Source: World Resources Institute).
The other gases that contribute to increasing temperatures arise from a variety of activities and some of the gases have been created by man. Methane is an important component of the increasing gases in the atmosphere and is the one most associated with animal agriculture. Methane has a thermogenic effect some 4–6 times that of carbon dioxide.
The rates of accumulation of methane and carbon dioxide in the world's atmosphere have changed dramatically in the last 10 years. Prior to this, the rise in world temperatures and composition of the atmosphere had changed little, but is now in what appears to be an exponential period (Figs 3 and 4). Undoubtedly the contamination of the atmosphere with carbon dioxide, methane and other gases must be stabilised or the future of the earth is threatened.
Methane production appears to be a major issue although it presently contributes only 18% of the overall warming. It is accumulating at a fast rate, and is apparently responsible for a small proportion of the depletion of the protective ozone layer. Methane arises largely from natural anaerobic ecosystems, rice paddies and fermentative digestion in ruminant animals (Fig 5).
Figure 2: Relative contribution by continent to the emissions of carbon dioxide (Source: World Resources Institute).
Figure 3: Trends in emissions of CO2 (Source: World Resources Institute).
Figure 4: Trends in atmospheric methane accumulation (Khalil and Rasmussen, 1986).
Figure 5: Relative contribution of biological resources to the global production of CH4 in the atmosphere (Bolle et al., 1986).
Animal Agriculture and the Greenhouse Effect
Animal production plays four important roles in the release of gases into the atmosphere:
Ruminants in ‘natural’ production systems are inefficient and, in general, production increases depend on an expansion of numbers. There is a growing appreciation that efficiency per animal can be improved many fold with simple technology inputs which would have an impact on all four aspects of the contributions to global warming discussed above.
The most important approach to be discussed in relation to the amelioration of greenhouse gas production by ruminants is to increase the efficiency of animal production from available resources and develop the capacity to produce more from less animals.
REQUIREMENTS FOR ANIMAL PRODUCTS
With largely stabilised human populations in the industrialised countries and a high standard of living generally, the demand for animal products has plateaued or declined (see for example MAFF/(1985– 1988) and the emphasis in animal agriculture is on the production of higher quality products. This has led to a dependence of ruminant systems based on concentrate feeds, a higher production rate per animal and reduced animal numbers. For example, there has been a marked increase in milk production through “better nutrition” relying on concentrate diets and genetic improvement of dairy cows. The result has been a marked reduction in the total number of animals required to supply local milk requirements. These increases in production per animal in North America and EEC countries that have arisen from simple technology inputs are indicated in Table 1.
The demand for food in the industrialised world is stable but production is increasing at 1.5% per annum (FAO, 1986). Policies to take land out of farming or to limit farm management options and animal numbers has reduced overall animal numbers, but meat/milk production has been maintained by technologies that increase the efficiency of production. From a global warming view point this is mostly advantageous, although there is a very high environmental cost of feeding high grain based diets to ruminants. Such concentrates can only be produced by high fossil fuel inputs and is often only economic because of subsidies. Les intensive production systems depending on grass or grass products in developed countries exhibit some of the same problems of low efficiency as those animals in developing countries which are restricted to roughage based diets (see below):
The Developing Countries
Throughout the last 30 years crop and livestock production has more than doubled throughout the third world, although there are large differences between regions, however, increases in human population, urbanization and improved income levels have increased demand for food to such an extent that surpluses are still rare. Imports of meat, milk and cereal grains in most developing countries are increasing by about 10% per annum (see FAO, 1951, 1971 and 1986). The demand for animal products will continue to increase for some time, if the patterns of food consumption by people in developing countries follows the patterns that occurred in developed countries (see Fig. 6).
Increases in animal production in the developing countries has been mainly a result of increasing animal numbers (Jackson, 1981). The lack of increase in efficiency of animal production is well documented and is emphasised by the average milk yields per cow over the 10 years from 1976–1986 (Brumby, 1989) (also see Table 1). This low productivity is exacerbated by long calving intervals and a late age at puberty in the cows in developing countries. It should be emphasised however, that it is also a feature of ruminants fed low quality forages in any country.
New feeding strategies for animals fed on low quality forages (e.g. crop residues, tropical pastures etc.) coupled with better genotypes, improved management and disease control, particularly in India (NDDB, 1989), has changed this situation enormously.
Table 1. The change in the average milk yield per cow in industrialised and third world countries.
|Percentage increase (%)|
(1976 to 1986)
A major difference in approach to feeding ruminants in tropical developing countries that has been recently developed has the potential to revolutionise ruminant production from forages. For example enormous increases in milk production can be achieved in the tropics without the use of ‘fossil-fuel-expensive’ grain based concentrates, relying rather on byproducts of agriculture. These are the only truly available feed resource for the large ruminant populations in the foreseeable future. The low inputs of concentrates into such systems and levels of production that rival those achieved in the industrialised world, provide major indications for change in management of both developed and developing countries alike.
Figure 6: Food consumption/percentage of diet for meat, wheat & rice and coarse grains. (Marks & Yetley, 1987 and Brumby, 1990).
Population Densities of Large Ruminants
The above discussions suggest that ruminant populations are not likely to increase in the industrialised world and, with ever increasing technology inputs, numbers are set to decline (as has already occurred with milking herds) - but continuing technology inputs will be highly fossil fuel dependent.
Conversely, there is likely to be a huge increase in demand for food products in the countries that are developing, of which a greater proportion of the demand is likely to be for animal products. To meet this demand local production must be increased to an extraordinary extent and it is most desirable that the impact on the environmental contamination is minimised.
of essential nutrients for microorganisms (after Leng, 1982). The ranges of YATP are shown for: The demand for draught power in countries with large numbers of small farmers is likely to expand rather than contract in the future and must not be left out of any considerations. This large group (80 million draught oxen in India alone) receives the least inputs and yet they are probably one of the major factors in food production and they limit the use of costly fossil fuels in developing countries.
Environment-friendly development of livestock production systems demand that the increased production must be met by increased efficiency and production per ruminant and not through increased numbers. The need to increase numbers would put huge pressures on many resources including forests and land that might be afforested.
Methane Production from Ruminants
World ruminant population densities and estimated methane production rates are shown in Table 2 in comparison to some monogastric species including man.
Global Methane Production
Methane gas accumulation is at a rate of 1% per annum and methane contributes 18% to global warming.
Ruminants from all species produce a relatively small proportion of the global production i.e. 15–20% of the total methane generated. However, the domestic ruminants represent one of the few sources that could be manipulated. It is estimated that beef and draught animals contribute 50%, dairy cows 19% and only 9% is from sheep (Crutzen et al., 1986). The methane is generated largely in the fermentative digestion of feed by microbes in the rumen.
The data in Table 2 indicate an approximate even split of numbers of ruminant animals between the developing and developed countries; that large ruminants contribute the greatest to world methane accumulation, and that other domestic and wild herbivores and man contribute an insignificant proportion.
The simple approach to the calculations adopted by Crutzen et al. (1986) may, however, be a little misleading although they are the best estimates available.
It is most important to emphasise that it is the rates of methane production per unit of product produced over a life time which is important in identifying where it is possible to make a major reductions in methane emissions. This is the major philosophy developed in the rest of this presentation.
Productivity of ruminants fed poor quality forages
The vast majority of ruminants in developing countries and a major proportion of the national herds of industrialised countries are supported on the by-products of agriculture or graze forages of relatively poor nutritional value.
In general, growth rates, milk production and reproductive rates in these systems depending on forage of variable quality are extremely low compared with the genetic potential of these animals (mostly about 10% and rarely exceeding 30%).
Mostly cattle grow to maturity or slaughter weight over 4–5 years, cows produce their first calf at 4–5 years and then, on average, every two years. Milk production on these feeding systems is often below 1000 litres/lactation. Cows may be kept largely to produce draught oxen and in some specialised systems they are kept for the production of dung (which is valued as a fuel) and a number of other minor purposes (e.g. as a investment, for recreation and for religious purposes).
Table 2: Estimates of methane emissions from animals (adapted from Crutzen et al., 1986).
|Animal type and region|
Developing + Australia
|Mules & Asses||54||10||0.5|
|Wild ruminants and|
* includes Brazil and Argentina
** total estimate for emissions from domestic animals has an uncertainty factor of ± 15%
Slow growth, low milk yield and poor reproductive performance results in poor feed conversion and a large methane output relative to product output.
Methane production in ruminants fed ‘poor quality’ forages
Methane output relative to product output of ruminants depends on two factors:
Efficiency of rumen fermentation
Digestion of feed by ruminants depends on a diverse group of micro-organisms in the rumen. These
organisms ferment feed materials into volatile fatty acids (VFA) a process that produces methane
(CH4), carbon dioxide (CO2) and utilises the energy (ATP) derived to convert feed to microbial cells.
The partitioning of the feed components into VFA or microbial cells and the release of CH4 and CO2
on a number of factors. Feeds that allow a high efficiency of microbial cell synthesis produce low amounts of methane per unit of feed digested (see Leng, 1982).
With cattle fed on a poor quality forage a number of essential microbial nutrients are usually deficient in the diet and microbial growth efficiency in the rumen is low. In these conditions CH4 produced may represent 15–18% of the digestible energy and correction of these deficiencies may reduce this to as low as 7%. The relationships between products of fermentative digestion and the efficiency of the microbial ecosystem in the rumen is shown in Figure 7.
Efficiency of feed utilisation by ruminants fed crop residues or other fibrous feeds.
Liveweight gain. Research in the past 20 years has clearly illustrated that supplementation of cattle on low quality forage based diets effects productivity through increasing efficiency of feed utilisation.
A mixture of nutrients as can be supplied for instance in a molasses urea multi-nutrient block/lick ensures an efficient microbial digestion in the rumen. Also small amounts of protein meal that are directly available to the animal (i.e. bypass protein) stimulate both productivity and efficiency of feed utilisation (the evidence and theory is discussed by Preston and Leng, 1987).
Traditional feeding standards are based on the metabolisable energy (ME) content of a feed. The general relationship between ME/kg of feed and growth (g gain/unit of ME intake) are shown in Figure 8. The results of a number of feeding trials with cattle on straw or low quality pasture and silage based diets supplemented with protein meals are shown in the same Figure. The efficiency of growth and methane production is shown in Figure 9. These data clearly show the massive reduction in methane production per unit of liveweight gain that is possible by using a strategic supplementary feeding system that accommodates the requirements of the rumen organisms and balances the absorbed nutrients to the animals requirements.
The data in Fig. 10 show the effects on methane production of balancing the rumen and for protein supplementation calculated for experimental data with growing animals of Saadullah (1984). This indicates the massive potential reduction in methane production per unit of liveweight gain that can result from supplementation (Leng, 1989).
Provision of molasses urea blocks to draught oxen would have a major effect on methane production, reducing it to half the present production rate.
The same principles of supplementary feeding have been found to stimulate milk production of dairy animals. Without going into detail, the methane produced per unit of milk produced under traditional feeding of local dairy cows or imported Friesians in India or Friesians under temperate country management are shown in Fig. 11. production in relation to lifetime milk production and includes the effects of supplementation on age at first calving, intercalving interval and improved milk yield of supplemented animals (Leng, 1987).
Figure 7: Relationship between the production of microbial cells and volatile fatty acids and methane in fermentative digestion in ruminants.
The relative efficiency of the system (indicated as YATP) is governed largely by the availability of essential nutrients for microorganisms (after Leng, 1982). The ranges of YATP are shown for:
Figure 8: Schematic relationship between diet quality (metabolisable energy/kg dry matter) and food conversion efficiency (g liveweight gain/MJ ME) (source Webster, 1989).
The relationships found in practice with cattle fed on straw or ammoniated straw with increasing level of supplementation. Australia (◊, O, •) (Perdok et al., 1988), Thailand (∆) (Wanapat et al., 1986) and Bangladesh (□) (Saadullah, 1984). Recent relationships developed for cattle fed silages supplemented with fish proteins (Olafsson and Gudmundsson, 1990) (Å) and tropical pastures supplemented with cottonseed meal (Godoy and Chicco, 1990) (*) are also shown. This illustrates the marked differences that result when supplements high in protein are given to cattle on diets of low ME/kg DM.
Figure 9: The relationship between the metabolisable energy content of a feed (M/D, MJ/kg) and the methane produced/kg gain.
The relationship shown by a broken line is based on the metabolisable energy system in practice in
the U.K. (Webster, 1989). The other relationships are results from results quoted in Figure 8. Perdok
et al., 1988 (◊, o, •), Saadullah, 1984 (□), Wanapat et al., 1986 (∆), Godoy and Chicco, 1990
Olafsson and Gudmundsson, 1990 (♦). (The data are calculated from Figure 7).
Figure 10: (A) The effects of improving the efficiency of rumen fermentative activity on methane production/kg of digestible energy consumed. (B) The production of methane/kg gain in supplemented cattle (feed conversion efficiency (FCR) 9:1) or unsupplemented cattle (FCR=40:1) fed straw based diets (after Saadullah, 1984).
Figure 11: The methane produced per unit of milk production in unsupplemented (fed traditionally) or supplemented (new feeding systems) cows in India with moderate levels of production.
Methane gas content of the atmosphere is increasing at 1% per annum. To stabilise methane in the atmosphere, global methane production needs to be reduced by 10–20%.
Large ruminants produce some 15–20% of the global production of methane. Ruminants on low quality feeds possibly produce over 75% of the methane from the world's population of ruminants. Supplementation to improve digestive efficiency in these animals could at times halve this methane production per unit of feed consumed. Together with supplementation to improve efficiency of feed utilisation and increase product output may thus reduce methane production per unit of milk or meat by a factor of 4–6.
Provided animal numbers in national herds are decreased as demand is met, the production of methane from the large populations of animals fed poor quality forages could be reduced to below 50% and perhaps even to as low as 20% of its present rate.
It is probably not feasible to restructure the cattle industries of the countries involved. The socio-economic implications are difficult to predict, but the start made in India with up to 1 million head of cattle, and with a potential to reach 7–10 million animals in the immediate future, is highly desirable because it increases milk production with a concomitant decrease in actual methane production and methane production per litre of milk.
Social, anthropological, economic and political considerations have been the major determinants of ‘aid programmes’ but the growing ‘environmental crisis’ due to increasing content of gases in the atmosphere leading to global warming is likely to dominate many issues confronting aid-agencies in the future.
The achievements in India can be repeated in most countries that depend on poor quality forages and even silages for ruminant production. India is fortunate in having large amounts of protein meals as by-products which can be used for animal production. In other countries protein meals may be scarce or under-utilised. The future for increased animal production in these countries is to identify protein sources and proceed to find economic mechanisms for producing meals that contain a high proportion of bypass protein. The developed world may need to encourage this by subsidising such activities or by refraining from draining _these protein sources from the developing world to support subsidised over-production in the industrialised countries (see Borgstrom, 1980). The world trade in protein meals is shown in Table 3.
Table 3. The trade in oilseed cakes between industrialised and third world countries (Borgstrom, 1980).
|Imports||Exports||Net imports||Net exports|
The increases in efficiency of animal production that result from the new nutritional strategies will, if widely applied, increase animal productivity to the extent probably needed by the expanding human population in developing countries. However, it needs a retraining of technologists in these countries to absorb the new concepts and a move away from temperate country teaching of ruminant nutrition.
The tropical climate can be used to the advantage of the developing countries where ruminant production can be more efficient (see Leng 1991).
Acceptance of these feeding strategies could reduce the need for land clearing and pasture establishment in the fragile areas of the world which have been so prone to erosion following clearing. It may also allow for considerable change in the use of such pastures with reforestation as a highly desirable first option. In addition, reduced world ruminant populations would reduce incidental release of methane from decomposing dung and reduce the inputs of fossil fuels required in much of the infrastructure.
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