Livestock Research for Rural Development 33 (3) 2021 LRRD Search LRRD Misssion Guide for preparation of papers LRRD Newsletter

Citation of this paper

Adapting systems of livestock production to be compatible with global commitments to restore the health of planet Earth; ecosystems that remove atmospheric carbon and provide, food, feed and renewable energy

T R Preston1, R A Leng2 and María E Gomez Z3

1 Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia
2 University of New England, Armidale, NSW, Australia
3 Cra 24ª, 3-74, Cali, Colombia


It is recommended that in order to respond to the emergencies of climate change and accompanying loss of biodiversity, ruminant feeding systems in the tropics would be best based on foliages from trees and shrubs complemented with carbohydrate-rich byproducts, (with high fermentability) of agro-industrial crops such as cassava and sugar cane. The leaves of trees and shrubs provide the required “bypass” protein and in addition compounds which reduce enteric methane production. At the same time, they enhance the production of propionic acid from the feed consumed and hence glucose supply to the animal.

Key words: biomass, carbon, ecosystems, global warming, reforestation, shrubs, trees


Some weeks ago, Greta Thunberg, the Swedish schoolgirl and climate activist, accused the world political leaders of “speeding in the wrong direction” on issues affecting climate change. More recently (22 Feb 2021) António Guterres, Secretary-General of the UN, made the strongest warning yet that, quote “Humanity is waging a senseless and suicidal war on nature that is causing human suffering and enormous economic losses while accelerating the destruction of life on Earth”. These exchanges indicate that it is more dramatic to document the impacts of global warming (Figure 1) than the loss of biodiversity accompanying inappropriate practices of land use (Photo 1).

Figure 1. Trends in climate indicators since 1880

We believe that, as a group of researchers in natural sciences, we have a major responsibility for the above changes, as we have not recognized (or accepted) a positive way in which we can affect the environment (developing more sustainable farming systems), through our direct contribution to environmental change of our research.

Photo 1. Harvesting soybeans in Latin America. Source: (Guardian Newspaper, 2020) photo. Yasuyoshi (Chiva. AFP) 2019

Those of us with a lifetime of research have an opportunity to apply our experience and address the present challenges to our farming systems and world food supply, by identifying appropriate ways of using the worlds natural resources. We must identify and develop more sustainable farming systems that support an effective level of food production and at the same time support rural livelihoods and preserving biodiversity and the overall reduction of the world production of greenhouse gases.

Livestock have been an integral component of farming systems because of their role as sources of  food, power and recycling of essential nutrients in manure fertilizer. Both of these roles have profoundly changed with advent of fossil fuel burning machinery, including the production and application of chemical fertilizers. As a result, livestock are increasingly prioritized for the production of high-quality nutrients in the form of, milk, eggs and meat. In turn this has led to the intensification of production systems and the emergence of “mega-farms” (Photo 4). Supplying these farms with feed (Photo 1) and disposal of animal excreta inevitably generate greenhouse gases from transporting these inputs and outputs. These are in addition to the greenhouse gases produced in digestion. More attention is now being given to the environmental cost of sourcing these feed inputs. The acquisition of soybean as a critical protein feed ingredient by the animal production industries (Photo 3) has required more land available for its production and indirectly stimulated deforestation particularly in exporting countries.

The environmental cost of food production

It has been reported (Guardian Newspaper 2020) that thirty percent of the “carbon” footprint of the European Union has been ascribed to the production of meat and milk and associated products. Part of the explanation for these claims can be seen in the review of the environmental impact of food production in global farming systems. In this report, estimates were made of the land area needed to row the food. and the quantity of greenhouse gases associated with t the production of 100g of edible protein (Table 1). The comparisons are dramatic: the production of 100g of edible protein requires the use of 144 m2 of land if the system is specialized beef production from grazing animals, compared with 7.3 m2 of land when the protein is derived from beans. Differences in associated greenhouse gas emissions from the two systems are equally dramatic.

Table 1. Environmental cost producing beef, milk and beans (Poore and Nemecek 2018)


Land area, m2/year*




Beef: milk









#GHG, kg CO2 /100 g protein in the product; * m2 of grazing area to produce 100 g protein as beef

There is, however, a more efficient way to produce beef and this is as a byproduct from milk production (Beef-Milk in Table 1). In this system, land area required to produce 100 g protein is reduced from 144 to 22 m2 Greenhouse gas emissions are similarly reduced.

Fifty percent of calves born in most dairy herds are male and in the majority of cases these are slaughtered a few days after birth yielding meat of very poor quality as almost devoid of fat. This is a most inefficient way to use this resource. A recent report in the UK (Guardian New paper 2020) drew attention to the loss every year of more tha100,000 male calves slaughtered soon after birth because of lack of a market (or lack of knowledge of how to produce quality beef from the dairy herd).

Sixty years ago, a system of intensive fattening of such dairy male calves was developed in Scotland, UK (Preston and Willis 1974), The dairy calves after early weaning were fed a high energy diet, based in barley grain, which encouraged fat deposition at an early age, ensuring beef of high quality. The animals reached 400 kg, liveweight at less than 12 months of age. With such a system (Beef-milk in Table 1) the land area required was much reduced as were the emissions of greenhouse gases. These advantages over specialized “single-purpose” beef systems are because the feed cost during pregnancy to produce the “male” calf is “paid for” by the associated production of milk.

The “dual-purpose” system

This system had its origin in tropical Latin-America where Spanish settlers had promoted specialist beef production whit imported breeds from Europe and later from India. Initial attempts to obtain milk from these animals were not successful as the mother cow would not release the milk to "human hands". However, it was observed that if the offspring of the beef cow was involved in the milking system, then milk could be taken from the udder manually provided that the calf first sucked the teats to stimulate the milk "let-down" and was present adjacent to the mother cow until milk "let-down" ceased. After this point was reached, mother and offspring were released together so that the calf could thoroughly take advantage of residual milk not accessible to human hands.

This elementary system has snice been refined to incorporate milking by machine but always respecting the "cow-calf" relationship (Photos2-3). Research during the last few years has demonstrated the many advantages of the "restricted suckling system" (Sahn et al 1995; Mejia et al 1998): Total milk yield ("milked" + "suckled") and, calf growth rate are increased, the udder is healthier (mastitis almost eliminated whit out antibiotic’s) and animal welfare is improved.

Photos 2 - 3. Restricted suckling is part of the dual-purpose milk-beef system in Colombia (Photo Maria E Gomez)
Feed imports versus local production

Imports of maize and soybean (Figures 2 and 3) have negative consequences for global warming and biodiversity. Ocean freight (Photo 5) generates greenhouse gases; and monoculture farming systems (Photo1) in the counties of origin leads to loss of biodiversity through deforestation and mega farming.

Photo 4. Fattening beef cattle in feedlots in USA (Cory Booker 2020)

Photo 5. The volume of the shipment is one of the largest ever achieved anywhere in the world and is enough to fill 3400 trucks (soybean from Brazil to Netherlands).
Source: photo: Claudio Neves

Figure 2. Importation of maize in Colombia
(million tonnes/year) /USDA 2020)
Figure 3. Importation soybean in Colombia
(million tonnes/year)/ USDA 2020)

All these developments have negative consequences for the environment and rural livelihoods.

Removing carbon from the Earth’s atmosphere

More than 100 countries have pledged to achieve net zero carbon emissions by 2050, which means they will emit no more carbon dioxide than is removed from the atmosphere by, the oceans and Earth’s terrestrial systems. It is generally believed that this will be achieved by actively restoring forests. Planting trees is a useful slogan but a more appropriate one could be that it is more likely to achieve such a goal: ‘by establishing farming systems that extract and store carbon in a ‘useful’ form. In this respect there is a need to think differently according to latitude as the policy for tropical regions will have to be different from that for temperate regions of the Earth. This has been discussed by Kormondy (Figure 4).

Figure 4. Biomass production from different ecosystems (Kormondy 1969)

Fast-growing multi-purpose trees and shrubs, and semi-perennial crops such as sugar cane and cassava stay green all the year round and on a world basis extract annually more carbon from the atmosphere than most forests (Figure 4). At the same time, they contribute food, feed and/energy. Thus, reforestation needs a much broader definition and studies to evaluate this hypothesis are urgently needed.

Tree leaves as sources of “bypass protein” and compounds that influence methane production from ruminants

The major issues that determine the nutritional value of a feed for ruminant in the tropics s were defined by Preston and Leng (1987) as: (i) ethe capacity to provide essential amino acids as protein that will escape the rumen (bypass protein) for subsequent enzymatic digestion in the intestine; and (ii) the nature of the rumen fermentation in terms of the production of methane. More methane means less propionic acid (Figure 5) and therefore less glucose at sites of metabolism, therefore reduced animal productivity.

Figure 5. The negative relationship between methane production and
propionic acid id in the rumen of cattle (Whitelaw et al 1984)

Specifically, the issue is the degree to which feed will provide glucose precursors (glucogenic amino acids and propionic acid) and essential amino acids as bypass protein in addition to microbial protein production. From the point of view of climate change, the issue is the potential production of methane in the animals, digestive tract. From the viewpoint of the animal, less methane means increased productivity. It is a “win-win” situation.

The fermentation patterns high in propionate produce less methane and are the main source of glucose for the ruminant at animal. Thus, feeds must be evaluated in terms of their capacity to provide both bypass protein and glucose precursors (ie: propionic acid).

Recent data (Figures 6 and 7) show that there are major differences between grasses and leaves of trees and shrubs suitable as animal feed. Grasses, in the digestive tract produce more than twice as much methane compared with the edible tree leaves that are readily consumed by ruminants. The differences are apparent irrespective of whet the grasses whether the sole diet (Figure 6) or were fed as supplements in a high-energy diet (Figure 7). The other finding in common to both sets of data is the close correlation between rate of gas production and the proportion of methane in the gas (Figures 8 and 9). The implication of these findings is that if rumen fermentation is reduced then more feed components will escape rumen fermentation and be available for digestion in the intestine and/or acetogenic fermentation in the cecum-colon (see Phonethiep et al 2016).

Of particular significance in the data in Figure 7 is that the highest methane values were produced when the supplement was water plant Ipomoea aquatica which is a popular highly digestible vegetable for people in SE Asia.

Figure 6. Production of methane from grasses and trees in rumen in
incubations in Malawi (Maselema and Chigwa 2017)
Figure 7. Methane production from grasses, shrubs and
trees in Lao PDR (Preston et al 2019)

Figure 8. In an in vitro rumen incubation, the methane concentration
in the gas increase with rate of gas production
Figure 9. In an in vitro rumen incubation, the proportion of methane in the gas
increases as the solubility of the protein in the substrate increases

Thus, the planting of trees and shrubs, that: produce leaves rich in bypass protein and compounds that reduce methane production will be good for mitigation of climate change for biodiversity and for ruminant productivity.

Examples of the strategy of trees replacing grasses for ruminant production
The silvopastoral system

In this system forage trees such as Leucaena are planted in a proportion of the grazing area; usually about 25-30% (Photo 6). The merits of this system are evident in the higher milk production (Figure 10) as a result of the improved feed supply and in "welfare" as the trees provide shade as feed well of higher quality (Photo 6). In this instance the strategy was not complete as the cattle on the silvopastoral system continued to receive "balanced concentrates". With and estimated offer level of but 17% protein from the combination of pasture grass and Leucaena, a more appropriate supplementation would have been with cassava root or sugar cane molasses.

Figure 10. Effect of the silvopastoral system on milk production
in two season Hernández-Rodríguez R 2019

Photo 6. The cow head for the area planted with Leucaena where the feed supply and the shade provided by the trees are an obvious attraction. (Hernández-Rodríguez 2019)

Photos 7 and 8 show the further developments of the silvopastoral system. Foliage from the guásimo tree is rich in tannins which help to protect the protein from degradation in the rumen ensuring its "bypass" properties. Tithonia diversifolia contains phenolic compounds that result in decreased methane production in vitro.

Photo 7. Silvopastoral system with Guazuma
in Colombia. (Suarez J F 2020)
Photo 8. Intensive Silvopastoral System with Tithonia
in Colombia. (Uribe F)

Data from Indonesia (Figure 11) show the advantage of supplementing goats with tree legume foliage rather than a grass (Pennisetum purpureum). The results with Indigofera zollingeriana are especially encouraging in view of the high biomass production of this legume tree (Photo 9).

Photo 9. Indigofera zollingeriana in Indonesia

Figure 11. Growth rate of goats was based 40% when foliage of Indigofera zolligeriana
replaced elephant grass as the protein. Source: (Anis et al 2020)
Trees and shrubs and soil fertility

Trees and shrubs have to be assessed from several angles: as sources of feed for livestock and wildlife; as timber, fuel and biochar, and for their benefits to soil fertility. In an experiment on sloping land in North Vietnam (Nguyen et al 2010), adjacent plots were established with the shrub Tithonia diversifolia (Photo 8) and the grass “Panicum maximum” as feed for goats and rabbits respectively. The annual DM production was similar for Tithonia and Guinea grass, but production of protein was some 40% higher for Tithonia.

After two years dedicated to forage production the plots were sown with maize. Maize yield was some 40% higher from the plots previously cultivated with Tithonia. It can be assumed that the beneficial carryover effects of the Tithonia were due to its extensive root system making key nutrients (eg: P) available for the subsequent crop of maize.

Figure 12. Biomass DM production of Tithonia alone (Pti), combined with
Guinea grass Ti-GG, compared with Guinea grass alone (GG)
Figure 13. Crude protein production of Tithonia alone (Pti), combined with
Guinea grass Ti-GG, compared with Guinea grass alone (GG)

Figure 14. Yields of maize green biomass and roots in the plots before and 6 months after planting the Tithonia and Guinea grass
[Tithonia alone (Pti), combined with Guinea grass Ti-GG, compared with Guinea grass alone (GG)]
Nguyen et al 2010



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