| Livestock Research for Rural Development 30 (10) 2018 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Livestock production systems have a very negative image when viewed against the need to reduce global warming, and to restore natural ecosystems. The approach in this paper is to put the environment first – such that land-use patterns are based on agroforestry principles, with the role of livestock being as facilitators of an integrated system that produces food and energy while facilitating sequestration of atmospheric carbon. The choice of goats as the animal component is justified by their innate “browsing” habit that enables them to selectively harvest leaves from forest biomass. Their role is strengthened when they are seen as being strongly gender-positive, as a species traditionally managed by women with a world-wide reputation for the quality of the products.
Key words: carbon footprint, ecosystems, methane, prebiotics, rumen fermentation
Livestock production systems have a very negative image when viewed against the need to reduce global warming and its secondary effect in changing the climate. “Livestock’s long shadow” was the title of the paper by Steinfeld et al (2006) that first drew first attention to the massive contribution of livestock systems to generation of greenhouses gases responsible for global warming. The major elements were methane resulting from rumen fermentation (37% of global emissions) and nitrous oxide (65% of global emissions) generated from uncontrolled fermentation of excreta. The debate on this issue has generated much research on ways of modifying the rumen fermentation to reduce methane production but less on ways of reducing nitrous oxide.
However, it is not sufficient only to reduce the production of greenhouse gases. Simultaneously, carbon dioxide levels in the atmosphere – which recently passed the 400 ppm level must be reduced to 350ppm or less. Thus, reducing greenhouse gas emissions must be accompanied by strategies leading to sequestration of carbon dioxide into biomass and soil – the logical routes to follow.
Finally the very question of producing food from animals is being questioned in view of their incrasingly negative impact on the world's natural resources (Poore and Nemecek 2018).
The first step in the way forward is to increase the fixation of atmospheric carbon into biomass, and to ensure that its final resting place is the soil. The research of Patzek (2007) (Figure 1) showed that forests are the most efficient ecosystems for sequestering carbon from the atmosphere. The biomass that is produced in agroforestry systems can contribute to all our needs in a renewable format: food for people and animals, energy, soil conservation and carbon sequestration. Trees produce human food from their fruits (the oil palm, coconut palm and sugar palm are good examples); the leaves can be the basic feed for livestock; the fibrous residue in the stems and branches are a source of renewable energy and a byproduct - biochar - that enhances fertility and simultaneous carbon sequestration in soil.
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| Figure 1. Biomass production from different ecosystems (Patzek 2007) |
Goats are the logical livestock species to participate in agroforestry systems because of their feeding habits. Their preferred way of eating is “browsing” the leaves from trees and bushes. They thus offer a natural way of fractionating forest biomass: the leaves for the goats; the residual branches and stems converted via gasification to a combustible gas and biochar, the latter acting as the vehicle to sequester carbon to the soil (Figure 2).
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| Figure 2. The role of goats in agroforestry systems |
Goats are often criticized as destroyers of the environment and this is so when their feeding behavior is not controlled; the contrary is the case when their selective feeding habits are used to advantage to create an integrated food and energy system with a potentially negative carbon footprint.
Feed intake and digestibility of a range of foliages by goats were increased when these were suspended above the feed trough compared with separating the leaves and offering them separately (Theng Kouch et al 2013). Practical feeding systems have been designed (Photos 1 and 2) which facilitate this way of offering foliages to goats.
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| Photo 1. Goats are very efficient in fractionating forages, consuming the leaves and leaving the stems for the gasifier |
Photo 2. Tree foliage fed from a suspended rack simulates browsing and facilitates managment |
The parts of the plant rejected by the goats, the branches and stems, can be converted into renewable energy by gasification (Figure 2). The products from this process are a mixture of combustible gases (mainly hydrogen and carbon monoxide) and biochar. This latter residue from gasification, originally thought to be ash, has proved to be a combination of carbon, phenolic compounds and silica-rich minerals, derived from the original biomass. When applied to the soil the effect of the biochar is to increase plant growth (Preston 2015) and - equally important - enhance the retention in the soil of nitrogen and organic carbon (Bouarovong et al 2017).
Many browse species contain anti-nutritional factors. Examples are Leucaena leucocephala, which contains the toxic amino acid mimosine; and cassava, the leaves of which contain cyanogenic glucosides that give rise to toxic hydrocyanic acid when consumed by animals. A recent development that is relevant to these and many other tree species, is the discovery that the byproducts of fermentation and distillation of grains such as barley and rice contain compounds (categorized under the general heading of “prebiotics”) that enable the action of microbial communities and the immune system to neutralize the anti-nutritional factors common to most tree species. The research of Binh et al (2017) highlighted how a feeding system of cattle based on “bitter” cassava foliage was transformed from supporting minimal growth of 50 g/day to 650 g/day by enriching the diet with 4% of brewers’ grains. The mode of action – detoxification of the cyanogenic glucosides – was evidenced by the major reduction in urine excretion of thiocyanate following supplementation with the brewers’ grains additive. These positive findings from use of brewers’ grains as a feed “additive”, supplementary to its role as a bypass protein supplement (Ffoulkes and Preston 1978; Phanthavong et al 2016) have been confirmed in experiments with goats (Figure 3), where growth rates were increased 130% from 70 to 160 g/day when an exclusive diet of cassava foliage was supplemented with 5% (as DM) of brewers’ grains. Similar benefits were reported in goats fed ensiled brewers’ grains as a feed additive to a diet of foliage from the legume tree Bauhinia acuminata (Silivong et al 2018).
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| Figure 3. Adding 5% of brewers’ grains to an exclusive diet of fresh cassava foliage doubled the rate of live weight gain of goats in Cambodia (Sina et al 2017) |
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| Figure 4. Effect of a supplement of brewers’ grains (4% in diet DM) on live weight gain of goats fed Bauhinia acuminata in combination with cassava foliage (CF) or water spinach (WS). (Silivong et al 2018) |
Biochar is a byproduct from the carbonization of fibrous residues at high temperatures. It is composed primarily of carbon and phenolic compounds and residual minerals from the original biomass. The large surface area (>30 m2/g), high pH and water-holding capacity, makes it an ideal site for the adsorption of communities of microorganisms and nutrients in biofilms (Leng 2017).
The physical attributes of biochar confer major advantages when it is applied to soil. It facilitates access of plant roots to nutrients resulting in increased plant growth, especially in poor soils (Figure 5). More important is that it helps to retain nitrogen and organic carbon in the soil (Bouaravong et al 2017), thus acting as the pathway for sequestering atmospheric carbon dioxide, an important part of the strategy to reduce global warming.
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| Figure 5.
Acid sub-soil (pH4.2) untreated (left) or after combined
application of biochar and biodigester effluent (right) (maize was planted in both soils but did not grow in the untreated soil) (Rodríguez et al 2010) | |
The qualities of biochar that facilitate its positive action in soils also apply to livestock. Growth rates in cattle were increased by 40% when biochar was included in their diet of ensiled cassava roots, urea and cassava foliage (Sengsouly and Preston 2016). Growth rates in goats fed basal diets of foliage from Bauhinia acuminata (Figure 6) and N-retention of goats fed urea-treated cassava stems (Figure 7) were increased when 1% of biochar was included in the diet, presumably because the biochar created conditions for the effective detoxification of the cyanogenic glucosides present in the cassava stems.
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| Figure 6.
Biochar increases growth rate of goats fed foliage of Bauhinia acuminate with and without wáter spinach Ipomoea acuatica (Silivong and Preston 2015) |
Figure 7. Effect of biochar on N retention in goats fed
urea-treated cassava stems with or without a supplement of water spinach Ipomoea acuatica (Thuy Hang et al 2018) |
Technological developments, aimed at reducing labor requirements, boosting productivity and facilitating economies of scale, are the driving forces leading the global trend to Mega-farms. By contrast, issues concerning the environment and animal and human welfare have had a low priority leading to widespread criticism from environmentalists.
When the analysis is made in a broader context, and environmental issues have first priority, family scale farms rate much higher (Ikerd 2016). The approach that is favored in this paper is to put the environment first – such that agroforestry principles drive the production system, with the role of livestock being as facilitators of an integrated use pattern that produces food and energy while facilitating sequestration of atmospheric carbon. The choice of goats as the animal component is justified for technical reasons already expounded in this paper. Their role is strengthened when they are recognized as being strongly gender-positive - a species traditionally managed by women with a world-wide reputation for the quality of the products.
An earlier version of this paper was submitted to the 4th Asian - Australasian dairy goat Conference that will take place from 17 to 19 October 2018 at Tra Vinh University, Vietnam.
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Thuy Hang L T, Preston T R, Leng R A and Ba N X 2018 Effect of biochar and water spinach on feed intake, digestibility and N-retention in goats fed urea-treated cassava stems. Livestock Research for Rural Development. Volume 30, Article #93. http://www.lrrd.org/lrrd30/5/thuyh30093.html
Received 19 September 2018; Accepted 19 September 2018; Published 1 October 2018