Reducing the carbon foot print of pig production in the tropics with local feed and breed resources

T R Preston

Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Cali, Colombia
reg.preston@gmail.com

Abstract

Promoting research on feeding forages to pigs must be seen in the wider context of appropriate farming systems to provide both food and energy from renewable resources. A fundamental feature of this strategy is that the alternative feed and energy resources can be grown on the farm as this will: (i) directly benefit the poorer farmers, who have limited cash resources to purchase inputs from outside the farm; (ii) be an active response to the need to promote sustainable rural development as a response to pressures to increase employment opportunities; (iii) reduce the dependency on transport which almost certainly will have an increasing cost as renewable energy replaces “cheap” fossil fuel.

This review has shown that:

All or part of the protein in diets for pigs can be supplied from the leaves from shrubs such as cassava and mulberry, from vegetables such as sweet potato and herbs such as Bore and Taro, and from water plants such as duckweed (Lemna spp) and water spinach (Ipomoea aquatica). All or part of the energy can be obtained from the juice in sugar cane, from the roots of cassava, from the petioles of Bore and Taro and from the fruit of the oil-palm. Forages can make a greater contribution to the diet of pigs: (i) during the reproduction phase compared with growth and finishing; and (ii) when native “indigenous” breeds are used as compared with breeds genetically selected for high growth rates and lean carcasses. The use of vegetative protein sources is facilitated when they are accompanied by energy sources that are low in both fiber and protein. A low content of fiber in the energy source creates "space" in the digestive tract of the pig for fiber present in the leaves of forages. Thus, there is potential for a natural synergism between sources of energy and protein in tropical latitudes. When energy sources low in protein (eg: sugar cane juice, cassava roots, sweet potato tubers, or banana fruit and palm oil) are combined with leaves which normally have well balanced arrays of amino acids, it is possible to reduce the overall level of protein in the diet since the amino acid array in such a combination of feeds will more closely approximate to that in the "ideal" protein (See Wang and Fuller 1989).

Preliminary experiments suggest that the foliage of Taro and probably of Boring can be a complete diet at least for indigenous breeds such as the Mong Cai in Vietnam and the Moo Lath in Laos. It is strongly recommended that future research in this area should be with herbariums plants that combine both energy (in the petiole) and protein) in the leaves.

Key words: biomass, climate change, forages, herbaceous-plants, “ideal” protein, indigenous breeds, integrated systems, prebiotics, volatile fatty acids, yeast-fermented rice

Introduction

Scientific consensus is that there should be no net increase in global atmospheric caron beyond the year 2050 (NetZero50). To meet this challenge systems of food production must change as agriculture, as presently practiced, is a major contributor to global greenhouse gas emissions and loss of biodiversity. In previous reports in this series of position papers (Preston et al 2021abc) we have described ways of achieving these goals as the relate to feeding systems for ruminant livestock. Pigs and chickens are probably the greatest offenders as global production systems have been dominated by the feeding of maize and soya bean the production of which is a major driver of global deforestation (Photo1).

Photo 1. Burning the Amazon product soybeans (The Guardian, Newspaper 2021)	Photo 2. Maritime transport: a major source of carbon emissions (Photo Claudio Neves https://www.allaboutfeed.net/animal)

The genetic makeup of farmed livestock has changed dramatically in the last 100 years and is especially evident in pig and poultry species, Local breeds and ecotypes of both species are in world-wide decline, facing a losing battle in the ever increasing demand for faster growth rates and improved feed conversion (and for leaner meat especially from pigs and chickens).

Associated with these trends have been the standardization of diets. It is probable that the majority of pigs in the world are fed om maize and soybean; and have been raised/housed in cages for part, if not the whole, of their lives.

However, these intensive systems (typified by the term ”factory farms”) are beings increasingly criticized on grounds of animal welfare, such that as from 2022 housing pigs in cages will not be permitted in all countries in the European Union, Farmers are objecting as they argue that providing more space to allow pregnant pigs enough space to build a nest where they ca n gave birth, and subsequently take care of their piglets without trampling on them. However, these reactions (of farmers) have to be viewed in the light of opportunities for learning that the ancestors of indigenous breeds have passed on to their progeny.

The potential role of indigenous breeds in farming systems designed for NetZero 50 is well illustrated by the mothering ability of the indigenous Mong Cai breed in Vietnam. Over the ages Mong Cai sows have learned to adapt to their simple environment; raising large litters and tending them with care and affection A Mong Cai sow would never trample on her offspring despite the confined space in a simple 1.5x1.5 m pen (Photos 3 and 4).

Photo 3. No need for a farrowing cage when the Mong Cai give birth!	Photo 4. A Mong Cai mother takes good care of her multiple offspring despite the confined space

Learning applies also to their diet. An example of a “negative” learning experience was evident in an experiment in Vietnam with piglets of the indigenous Mong Cai breed and those of an “imported” Large White breed (Rodriguez and Preston 1996b). The objective of the experiment was to test if there were differences between the breeds in their capacity to utilize a “novel” feed based on local resources: a mixture of sugar cane juice and fresh duckweed (Lemna minor).

There was a marked contrast in the response of the two breeds when presented for the first time with this combination of natural feeds (fresh juice from sugar can and “fresh duck weed” a plant that is found widely in Vietnams as an invader of natural water surfaces). The Large White piglets absolutely refused to eat the mixture of sugar cane juice and duck wee. In contrast the Mong Cai consumed the feed with relish. The experiment had to be abandoned as the “Large White” pigs refused to adapt to the new feed and deliberately eject the duckweed from the feed trough.

A repeat experiment was done with crossbred piglets (from a Mong Cai mother heminested whit Large White sire to replace the purebred Large White piglets. The crossbred pigs behaved like their purebred Mong Cai counterparts, suggesting that their reaction to “natural” feeds had been passed on from dam to progeny.

We consider this difference between breeds to respond to tier environment as reflect the environments in which their ancestors were raised. Traditional the Mong Cai breed was a feature of family farms in which this feed supply would be waste from the household supplemented by whatever the pigs could scavenge in their immediate neighborhood. By contrast the Large While have adapted to a long history of domestication and feeding systems based on “nutritionally balanced standards”. The contrasting feeding behavior of the Large White genotype, the product of genetic selection and the Mong Cai, the product of natural selection is attributed to these major environmental differences in their background.

It is relevant to reflect on why Min Cai sows take greater care of their offspring compared with: Large White sows? Selection for growth rate has been the major driver of genetic selection in the Large White breed. In turn, increased growth rate reflects a high intake of feed which in turns reflects eating behavior. One has only to observe a group of pigs of an improved breed in their eating behaviors. Competition for feed is evident and this is illustrated by the way some pigs become dominant at the feed trough. Thus, high growth rate may result in part from aggressive behaviors which is the opposite train to what is required for good mothering ability.

From the point of view of these reviews the lessons learned are of major relevance when the objective is to make maximums use of forages in pig feeding systems.

The challenge of “NetZero50”

It is axiomatic that future livestock production systems should take advantage of genotypes that have evolved in conditions where the impact of low-cost fossil fuel been least, as in the examples of the indigenous pug breeds in Vietnam. If foliar biomass is to play a major role as a feed resource for livestock – including pigs – there will be an important role for those breeds that are the result of natural selection in an environment least affected by the need to replace reliance on fossil fuel by maximum use of renewable energy derived from the sun.

This review therefore considers only those potential forage resources that lend themselves to production under such a scenario. The conclusions and recommendations are predicated on the potential role of forages as multi-purpose resources in a fossil fuel-free world.

Challenges and limitations regarding pig production and reproduction

It is also relevant to consider the economic, political and environmental developments, that have impacted on the world scene since 2006, and how these might change the shape of livestock production systems in the future.

Even if the challenge of NetZero50 is achieved average air temperatures will be increased. Increasing temperatures will bring about environmental changes will be unfavorable to the growth of ‘temperate’ crops such as cereal grains whereas ‘tropical’ crops such as cassava, sugar cane and bananas /plantains and members of the Araceae family will benefit. Such changes will create opportunities for the development of alternative feedings systems, especially for pigs.

Ecological issues

The declining fertility of soils is attributed to mono-cropping, excessive use of chemical fertilizers and loss of soil organic matter. Perennial plants such as trees and shrubs are viewed more favorably especially if they are leguminous. A recent development, of relevance to soil health, has been the appreciation that biochar produced by incomplete carbonization of biomass has multiple benefits through its role as a support for microfilms and at the same time serving as a means of removing carbon from the atmosphere and sequestering it in the soil (Lehmann and Joseph 2009). Perennial plants that serve as a source of feed and of feedstock for biochar production will have comparative advantage over specialist short season crops grown primarily for feed. Thus, promotion of perennial trees and shrubs will have an impact on future feed supplies for livestock including pigs.

Economic growth and economies of scale

The concept of exponential economic growth fueled by increasing demand for goods and services is now discredited with deflation and excessively high rates of unemployment being the norm in most of the industrialized countries. This puts a question mark over present trends towards “mega” farms, especially of pigs where units with thousands of animals in a confined space are the norm, reflecting the impact of technological progress and associated destruction of employment as machines displace people. Creating opportunities for work that is socially as well as economically attractive is especially relevant in agriculture as a means of reversing the trend to urbanization that creates demand for energy-rich services such as transport of feed and waste removal.

Family farms; a model for the future?

The challenge facing all developed economies (and all countries as technology lifts them out of poverty) will be to identify and promote meaningful employment, especially for young people. Agriculture in industrialized countries no longer is a major source of employment. It is still the major employer in most developing countries. There are good reasons for making every effort to reverse the present calamitous trends of migration to cities. Farming systems based on integrated use of resources for food and energy can offer a lifestyle eminently suitable for all members of the family, and with many of the attractions previously offered only in cities (especially entertainment and communication) now available through access to the internet with affordable technology.

It is proposed that family farming offers solutions to most of the problems listed above provided that technologies are in place to provide the comparative advantages that rural living will have over dwelling in mega-cities. The use of forages especially those derived from perennial trees and shrubs will be a fundamental component of these future family farming systems, not only for pigs but for most classes of livestock.

Forages for pigs; the issues

Nutritional requirements of pigs raised on forage-based diets

In order to plan an appropriate strategy for making greater use of forages in pig diets, it is important to appreciate the nutritional attributes of forages and their potential role in pig production. Generally, the forages which are appropriate for this purpose will be seen as potential sources of protein since, in general, they will have a high leaf to stem ratio and the leaves of most plants will have from 15 to 25% crude protein in the dry matter. This is a positive attribute. However, leaves (and more so the stems and petioles) in forages will be relatively high in cell wall components which means that the leaves are less digestible than traditional protein-rich feeds derived from fish byproducts and oilseeds. Thus, as a general rule, forages will be seen as potential sources of protein but with the disadvantage of being only moderate sources of energy.

An important factor associated with the use of leaves as protein sources for pigs is the opportunity to reduce overall levels of protein in the diet, as compared with conventional feeding systems when protein is derived from cereal grains and oilseed meals. This is because the leaves of plants are the growing points, and the protein is mostly in the form of enzymes which necessarily must have the optimum balance of amino acids for tissue growth. In this respect, leaf protein closely resembles the “ideal” protein (Wang and Fuller 1989). By contrast, the nutrients found in cereals and in oilseeds function mainly as an energy reserve for germination, until the plant forms its first leaves which then capture their energy from the sun through photosynthesis.

The implication for pig nutrition is that when the protein source has a balance of amino acids similar to the “ideal” protein, then total protein levels can be reduced by 30 to 40% compared with the case of diets based on cereal grains and oilseed meals (Figure 1).

Figure 1. Requirements for amino acids in sows fed a diet with an "ideal" protein (Wang and Fuller 1989) compared with the traditional maize-soybean diet according to NRC (1988) (from Speer 1990)

An extensive study was made in the Mekong delta in Vietnam (Le Thi Men et al 1997) to test the feasibility of reducing protein supplies to sows during pregnancy and lactation in accordance with the concept of the “ideal” protein (Figure 1). This required the use of an energy source that contained minimal protein and fiber (cassava root was chosen for this purpose) and a protein source that had a balanced array of amino acids and was locally available. Duckweed was the appropriate candidate as the main source of protein as it was widely available on the natural water surfaces in the Mekong delta and satisfied the premise that as a rapidly growing vegetative plant it would have a balanced array of essential amino acids. A local pig breed (Bauxyin), long adapted to the Mekong delta conditions, was chosen as the experimental animal.

Figure 2. Reducing protein level of indigenous sows during pregnancy for, 200 to 150 g/d did not affect litter weight at weaning (Le Ti Men et al 1997)	Figure 3. Effects on litter weight at weaning replacing the control protein 50% fish meal:50% soybean with 100% duckweed (Le Thi Men et al 1997)

Litter wight at weaning was not affected by reducing the level of protein during gestation (Figure 2). but were improved by feeding duckweed (Figure 3), compared with the control fish meal and soybean. It was concluded that a combination of a low protein/low fiber energy source (cassava root) with a high protein forage (duckweed) could replace all the cereal grains and 50% of the conventional protein source with improved reproductive performance, and that such a combination of feeds permitted the overall protein supply during pregnancy to be reduced from 200 to 150g/day.

Integrated production of livestock feed and energy and the role of forages as feed for pigs

A hypothesis (Figure 4) which was proposed as the basis of a research strategy for tropical latitudes, was that sugar cane could be the basis of an integrated farming system in which the juice expressed from the stalk in a simple 3-roll press could be used as the energy source for pigs while the residua fiber (bagasse) could be the feedstock for gasification to produce electricity The advantage seen in such a system was that the juice, composed of 100% digestible sugars, would create opportunities for using forages as the protein source, since the absence of fiber in the juice would facilitate the intake of protein-rich forages.

Figure 4. The model for integrated feed, fuel and biochar from sugar cane

The system depended on making efficient use of the bagasse as a source of energy by gasification. This was shown to be technically feasible in test drive in a Scania truck in Umea, Sweden. The vehicle had been fitted with a gasifier design to use would as the sole source of fuel, The wood was replaced by sugar cane bagasse(sourced from the University of Yucatan in Mexico). There was no loss of power in the truck engine during a 30 minute test drive in the streets of Umea. (Preston T R and Lindgren A 1980 unpublished date).

The technology was confirmed with a 4KW gasifier imported to Colombia from India in 2006 where it was shown that the residue after gasification of the sugar cane base was “biochar” a product with multiple uses as a sink for atmospheric carbon, as an additive in soils to enhance plant growth and as a “prebiotic” with multiple uses as an additive that enhances microbial activity in the digestive system in livestock. Biochar is a unique product and will become increasingly important via its role in soil improvement as well as its role as a “prebiotic” when added to the diets of livestock. Despite these multiple uses of sugar cane bagasse as a renewable source of energy ad prebiotic, the integrated “feed-energy” system has not passed beyond the research phase constrained by the competition from cheap oil.

However, the world is now facing a future in which by 2050 the use of fossil fuels must be discontinued completely in order to prevent the rise in ambient temperatures to no more than 1.5ºC in order to avoid catastrophic changes in the world climate (IPCC 2021). Thus the sun will eventually be the only source of energy, and gasification of biomass will increasingly become relevant as one of the means of using this free, abundant and non-contaminating energy from the sun. Th integrated “feed-fuel” hypothesis will become increasingly attractive as the world responds to the realities of a world without fossil fuel.

A basic feature of the original hypothesis was that in order to use efficiently the protein in forages the basic energy source should be low in fiber. There are a number of tropical feeds which satisfy this condition:

• The juice extracted from sugar cane stalks
• The sap from the flower of palm trees such as Borassus flabelius and Nypa fruticans
• The roots from cassava, taro and sweet potato
• The fruit of bananas and plantains
• The oil from fruits of the oil palm.

All these alternative energy feed sources can be managed as perennial crops with high biomass yields, and the sap, fruits and roots are readily consumed by livestock, especially pigs.

Genotype-environment interactions

There are two ways to proceed with the development of feedings systems for pigs that incorporate high levels of forages. The decision to follow one or the other of these systems will be determined by whether the available pig breeds have been selected for high rates of growth of lean tissue or whether they are the result of a process of natural selection against a background of scavenging / foraging as is the case when pigs are components of resource-poor farming systems that use negligible amounts of purchased feeds.

If the available pig breeds are those of high genetic merit for lean tissue growth, they must be fed highly nutritious diets. In this case the opportunity for incorporation of forages in the diet will be as sources of protein which will need to be balanced with energy sources that are very highly digestible. On the other hand, if the available pig breeds (Indigenous ecotypes) have not been selected for high growth rates, then there will be opportunities to have the diet composed entirely of forages. An example of the effect of this type of genetic-environment interactions is seen in the data reported by Duyet et al (2010; Figure 5). Yorkshire sows, the product of selection for growth and leanness, had lower rate of reproduction (measured as days from weaning to first estrus) than sows of the ‘indigenous’ Mong Cai breed (the product of natural selection in a nutritional environment dominated by freedom to forage for what was available).

Figure 5. Mean values for days from weaning to mating for Mong Cai (MC) and Yorkshire(Y) sows fed diets in which forages (L) represented 0, 50 or 100% of the supplementary protein (Duyet et al (2010)

Forages as the major source of protein

Research on livestock production from local feed resources was the focal point of a project initiated in Vietnam in 1992 supported by the Swedish International Development Agency. In 2001, the activities of the project were extended to include Cambodia and Laos. Research on forages as protein supplements for pigs was a major feature of this program.

The research began with studies on duckweed (Photo 4). This was followed by experiments with sweet potato vines, water spinach, cassava foliage, taro and bore.

The conclusions from this research were that duckweed (Lemna minor) showed promise as a replacement for conventional protein meals such as soybean and fish meal while the foliage of Sweet potato (Ipomoea batatas) and Taro (Colocasia esculenta) and bore could be fed as the sole diet.

Duckweed (Lemna spp.)

Duckweed initially attracted international attention as an alternative feed for fish (Skillicorn et al 1993; Leng et al 1995). Experiments in Vietnam showed that it could produce up to 10 tonnes of protein per ha per year in ponds fertilized with biodigester effluent (Rodriguez and Preston 1996a). It fits naturally into integrated farming systems where the manure from the livestock component is recycled through biodigesters to produce biogas for cooking and nutrient-rich effluent as fertilizer.

Duckweed was used in one of the first plants to be evaluate in diets in which all of the protein was derived from forage (Rodríguez and Preston 1996b). Young pigs of a local Vietnamese breed (Mong Cai) and crosses of Mong Cai with Large White, were given free access to sugar cane juice and increasing levels of fresh duckweed (protein content of 35% in dry matter), that had been fertilized with biodigester effluent (Photo 4). Nitrogen retention increased linearly according to the proportion of duckweed in the diet (Figure 6).

Photo 5. Duckweed (Lemna spp)

Figure 6. Relationship between N retention and proportion of duckweed consumed by Mong Cai and Mong Cai crossbred piglets offered a basal diet of sugar cane juice (Rodríguez and Preston 1996b)

On-farm results confirmed the potential benefits from the use of duckweed for growing pigs fed diets based on rice bran (Figure 7).

Figure 7. Supplements of fresh duckweed increased growth rates of pigs fed rice byproducts on farms in Central Vietnam (DuThanh Hang 1998)

Sweet potato (Ipomoea batatas)

A very comprehensive study on sweet potato vines (Photo 6) was done in Vietnam by An (2004).. He concluded that the best options in terms of leaf and stem production were a cutting interval of 20 days and a defoliation of 50% of the total branches. Defoliation reduced tuber production.

Photo 6. Sweet potato (Ipomoea batata) grown for forage (An 2004)

There appear to be considerable differences, depending on variety, in the content of crude protein and crude fiber in the dry matter of the foliage of sweet potato, the former ranging from 26.5 to 32.5 % in leaves and from 10.4 to 14.1 % in stems (Woolfe 1992; Ishida et al 2000; An 2004). For crude fiber the mean values were 11.1 and 20.7 % in leaves and stems, respectively (Woolfe 1992). It is therefore important to separate leaves from stems when the aim is to maximize the rate of inclusion of sweet potato foliage in pig diets. According to An (2004) there are no major differences in nutritive value between fresh, sun-dried or ensiled leaves. Adding synthetic lysine (L) to a basal diet of rice by-products supplemented with sweet potato leaves increased pig growth rates to a level which did not differ from that on the positive control diet containing fish meal and which were better than on the diet supplemented with groundnut cake (Figure 8).

Figure 8. Growth rates of pigs fed rice bran supplemented with fish meal (FM), groundnut cake (GC), or sweet potato leaves (SP) alone or complemented with synthetic lysine (SPL)

Water spinach (Ipomoea aquatica) and cassava (Manihot esculenta) leaves

Foliages from these two plants as protein supplements for pigs have been the subject of considerable research in Cambodia and Vietnam since the late 1990s.(Photo 7)

Water spinach

Water spinach grows equally well in the water or in soil. It is traditionally consumed by people in SE Asia and appears to be devoid of non-nutritional elements. Harvesting this plant from lagoons fertilized with wastewater from urban centers is an important source of income for poor people in Vietnam and Cambodia. An important feature of water spinach is its capacity to yield high levels of biomass when fertilized with effluent from biodigesters charged with pig manure (Kean Sophea and Preston 2001).

It was to be expected that water spinach, widely consumed as a vegetable by people in SE Asia, would also have high nutritive value for pigs.

Photo 7. Harvesting water spinach in the lagoon receiving wastewater from Phonm Penh city, Cambodia	Photo 8. Stems and leaves of water spinach for sale in the market

Following the concept of using a basal diet with a low content of fiber, a combination of broken rice and palm oil plus 3% dried fish was supplemented with water spinach at increasing levels to the point at which it supplied 46% of the diet dry matter and 74% of the dietary protein in diets for growing pigs (Table 1).

High values for digestibility of the dietary nitrogen and its biological value (% of digested N) confirm the excellent nutritive value of water spinach when fed as the major source of protein to pigs receiving low-fiber diets (Table 2).

Cassava (Manithot esculenta)

Cassava is traditionally managed as an annual plant for production of roots for human consumption or for industrial extraction of starch. However, if the plant is adequately fertilized it can be harvested for forage at successive 2 month intervals over a 2-year cycle with annual yields of the order of 7 tones protein/ha/year (Photo 9; Preston 1995).

Photo 9. Cassava (Manihot esculenta) in the backgound is the plant ready for harvest after 2 months growth; in the foreground is the regrowth 2 weeks after harvest

Many studies have evaluated the use of cassava leaves as partial replacement for soya bean meal and fish meals in conventional diets for pigs (see review by Bui Ngu Phuc 2006). However, the levels used rarely exceeded 15% in the diet DM, and the emphasis was mainly on methods of reducing the risk of cyanide toxicity from cyanogenic glucosides in the leaves. Sun-drying appeared to be more effective than ensiling in this respect (Bui Huy Nhu Phuc et al 1996). Despite this concern for cyanide toxicity, it is relevant to note that there appear to have been no reported deaths of pigs from this cause.

The uncertainly relating to possible risks of HCN toxicity led Du Thanh Hang and Preston (2005) to compare processing of the fresh cassava leaves by washing, chopping and washing, and feeding them to pigs of 25 kg live weight as supplements to a basal diet of cassava roots and rice bran. The cassava leaves were readily consumed providing 38% of the dietary DM and over 70% of the dietary protein with no effect of processing method on total DM intake, which ranged from 27 to 31 g/kg live weight. Levels of HCN were reduced slightly (16%) by washing, and substantially (82%) by wilting, resulting in intakes of HCN between 6.0 and 15 mg/kg live weight, levels considerably higher than the range of 1.4 to 4.4 mg/kg live weight, previously reported as safe to avoid toxicity (Getter and Baine 1938; Johnson and Ramond 1965; Butler 1973; Tewe1992).

Following on from these findings, Chhay Ty and Preston (2005a, b) compared fresh cassava foliage, cassava foliage mixed with equal parts of water spinach, or water spinach alone, as sources of supplementary protein in a low-protein, low-fiber basal diet of broken rice. Digestibility coefficients were highest when the water spinach was the only supplement and lowest with cassava foliage, with intermediate values for the mixed foliage (Figure 9). N retention was similar for water spinach and the mixed foliage with 30% lower values for the cassava foliage alone (Figure 10)

Figure 9. Mean values for apparent digestibility of dry matter, crude protein and crude fiber in pigs fed broken rice and foliage of cassava, water spinach or a mixture of the two	Figure 10. Mean values for N retention in pigs fed broken rice and foliage of cassava, water spinach or a mixture of the two

Growth rates followed the same pattern as for N retention, with indications of complementarity for the mixed foliage (Figure 11).

Figure 11. Growth rates of pigs (from 11 to 50 kg) fed broken rice supplemented with fresh cassava leaves (FC), water spinach (WS) or a mixture of the two (WS-FC (Chhay Ty and Preston 2005b)

Mulberry (Morus alba)

The leaves of the Mulberry tree (Photo 10) have long been used as substrate for growth of the larvae of the silkworm. It could therefore be expected that they would have potential as a protein source for pigs.

Photo 10. Mulberry (Morus alba)

Sun-dried mulberry leaves were studied as partial or complete replacement for rice bran and fish meal in a low-fiber basal diet of broken rice (Table 3; Phiny et al 2003). Nitrogen retention was improved as the proportion of mulberry leaf meal in the diet was increased (Table 4). It is clear from this experiment that mulberry leaf meal is an excellent protein source for growing pigs.

Bore/Giant Taro/New cocayam

The species is widely distributed in tropical South and Central America known locally as “ Bore” (photo 11-12.

“Bore” o “new cocayam” is a species of the Araceae family with very specific characteristics:

With two types of stems, one rhizomatous horizontally extended with roots that are fasciculate and the other aerial (pseudo stem) cylindrical where it accumulates starches and develops over the years that can reach up to 2 meters in height and weight from 10 to 15 kg.

There is still confusion between the different genres: Alocasia, Colocasia and Xanthosoma.

The research strategy that was used to optimize the use of “bore” New Cocoyam in pig diets is described in some detail as is exemplifies the approach that should be used when evaluating a new “forage” source for pig feeding.

Photo 11. Alocasia macrorhiza (Bore) cultivated on a farm in Colombia	Photo 12. Petioles and the corm make up a large proportion of the biomass of Bore

The appreciation of the potential role of “Bore” as a protein-rich forage for pigs was accidental. Initial attempts in the in Santander, Colombia (Preston and Rodríguez 2014) to grow and use cassava foliage as the protein-rich forage to accompany the energy from sugar cane juice proved to be a failure in that at 1500 msl the cassava plant would not survive the repeated harvesting that had proved successful at <20 msl in Vietnam and Cambodia (Preston 2001).

New Cocoyam was found growing wild in the humid natural forest area. Observations on the pigs offered the leaves of Bore showed it to be highly palatable and led to the experiment described by Rodríguez et al (2006) in which 50% of the protein normally supplied by soybean meal was replaced by fresh leaves of New Cocoyam with no reduction in pig performance rates compared with the control diet of 100% of the protein from soybean meal (Figure 12.).

Figure 12. Growth curves of pigs fed a basal diet of sugar cane juice supplemented with soybean meal or a 50: 50 mixtures (equal protein basis) of leaves of "New Cocoyam" and soybean meal

The experiment described by Rodríguez et al (2009a) aimed to explore the effects on parameters of apparent digestibility and N retention in young growing pigs of 100% replacement of the soybean protein by New Cocoyam leaves (Figure 13). In this trial the leaves were homogenized in a blender along with sugar cane juice to facilitate feeding and to avoid wastage in the metabolism cage. DM intakes were high (5% of live weight) and similar with substitution rates of soybean protein up to 53% and even with 100% substitution intakes were only reduced by some 7%.

Figure 13. A sugar cane juice basal diet makes it possible to vary the dietary protein component from 100% control protein (soybean meal) to 100% test foliage protein	Figure 14. When soybean protein is replaced by Cocoyam leaf protein, the increased losses in feces (lower digestibility) are compensated by decreased losses in the urine (better amino-acid balance)

As soybean protein is replaced by Cocoyam leaf protein, the increased losses in feces (lower digestibility) are compensated by decreased losses in the urine (superior biological value) (Figure 14). The implication therefore is that the nutritive value of the protein in Cocoyam leaves is constrained by its digestibility and not by the balance of amino acids. The same probably holds true, to varying degrees, for most other tree/shrub foliage.

From this research arises the generalization that the opportunity to utilize tree foliage as a protein source in pig diets will be determined principally by the digestibility of the protein, and that this in turn will be determined by the digestibility of the foliage dry matter.

Using the ensiled leaves as a protein source for growing pigs

The third experiment in this series (Rodríguez et al 2009b) aimed to determine the feasibility of using ensiled New Cocoyam leaves (ENCL), instead of the fresh leaves, as the only protein source to balance the sugar cane juice in the diet of young growing pigs. The experimental design was a production function with the independent variable being the level of crude protein in the range of 80 to 160 g crude protein per kg of diet DM. The levels recorded in the experiment varied slightly (87 to 149 g crude protein/kg DM) equivalent to a range in proportions of diet DM as ENCL of 46 to 67%.

The relationship between proportion of ENCL in the diet DM (X) and N retention (Y=g N/kg LW) was curvilinear with the maximum value of N retention being reached when the ENCL provided 66% of the diet DM, equivalent to a crude protein concentration of 13% in the diet DM. Intakes of DM were high on all diets with the maximum of 4.5% of LW with 55% of ENCL in the diet corresponding to a crude fibre content of 9% in the diet DM.

The experimental deign can be criticized in that the 8 different levels of ENCL were achieved by using the same 4 pigs in two consecutive periods such that there was no replication of any one chosen level. Nevertheless, the results were broadly in line with theoretical expectations. The pigs easily consumed the ensiled leaves at levels (66%) which were double those (35%) reported by Leterme et al (2005) who dried and ground the leaves of New Cocoyam prior to incorporating them in a diet based on maize. The maximum pig response, as measured by N retention, was achieved with 66% of the diet in the form of ENCL. At this point the crude fiber content had reached 9% which is within the range (7-10% according to Kass et al 1980) when pig growth rates begin to be depressed, as was observed in our experiment. In the experiment of Leterme et al (2005), the basal diet contained maize, soybean meal and rice hulls, thus with only 35% of New Cocoyam leaf meal in the diet, the overall fiber level was already 8% in DM, relatively close to the level of 9% fibre with 66% ENCL in a basal diet of sugar cane juice.

In the pig feeding system, in which the basal diet of sugar cane juice contains neither fiber nor protein, these two components have opposing influences on performance when foliage is used as the protein source. To achieve the level of protein necessary to optimize growth rates (about 13% in DM) results in reaching levels of fiber which act so as to reduce performance (eg: “the shielding effect on the plant cell contents by the indigestible cell walls, increased rates of passage of digesta as a result of its increased bulk and water-holding capacity, irritation of the gut wall mucosa by VFA produced in the hind-gut, possible presence of anti-nutritional factors, bulkiness, energy dilution and possibly heat stress” Ogle 2006. Thus, the digestibility of the fiber fraction, relative to the level of protein, will determine the degree to which the foliage can be incorporated in the diet.

Ensiling leaves and petioles of New Cocoyam Alocasia macrorrhiza

Practical experiences on a farm in Colombia led to the conclusion that daily harvesting and feeding of fresh New Cocoyam leaves was not convenient from the standpoint of: (i) appropriate management of the New Cocoyam plant - as leaf growth was dependent on climatic factors, which meant that daily harvesting did not always yield the required amounts of leaves, and often the leaves were harvested when they were still immature; and (ii) daily harvesting was time consuming and entailed inefficient use of labour and transport. This led to the decision to study the ensiling of the leaves which would permit harvesting of the leaves at the most appropriate stage of growth. From the physiological viewpoint, the leaves of New Cocoyam have similar growth cycles as leaves from banana plants, in that every 2 to 3 weeks new leaves emerge from the stem and grow until the point of senescence is reached usually some 3 to 4 weeks later. The work of harvesting and ensiling should thus be organized on a cycle of 20 to 25 days in accordance with the growth stage of the plants.

The studies described by Rodríguez and Preston (2009) were initiated in order to define the most appropriate method for ensiling the New Cocoyam foliage, as there were no references to be found in the literature on ways to process and store this foliage by ensiling. The first attempt followed conventional procedures using sugar cane juice as a substitute for molasses. The ensiled leaves produced by this process had all the required qualities of low pH, attractive colour and smell and absence of mould. The problem was the considerable effort needed to mix the cane juice with the macerated leaves and then to consolidate them in the plastic container. The other problem that arose was the disposal of the petioles. It was not convenient to leave them in the field as mulch, as this would have required transporting only the leaves – a difficult operation in sloping terrain which necessitated stacking the load in a structure mounted on the horse which is the traditional way of transporting sugar cane (Photo 13). Attempting to accommodate only the leaves in this structure proved to be highly inconvenient and inefficient.

Photo 13. Transporting bore in Colombia

The other option of feeding the petioles to the pigs proved to be feasible in that they were well accepted. It was also observed that ensiling the petioles, despite the high moisture content (>90%) was an effective way of conserving them. Furthermore, it was found there was no need to add additional fermentable sugars as the pH dropped to less than 4 within 48 hours. But again, the workload of separating the leaves from the petioles and macerating each of these components separately was time-consuming. Moreover, forcing the leaves into the chaff-cutter machine was difficult. By contrast, passing the intact foliage – leaf and petiole – into the ensiling machine was easy and rapid.

The logical next step was to ensile the combined leaf and petiole. This also produced excellent silage and has become the standard management system on the farm for processing New Cocoyam foliage. This procedure thus fulfilled all the requirements for producing a uniform and nutritious product, without the need for any additive.

The observation that the juice in the petiole was high in soluble sugars (4-5% in the juice = about 25% in the DM) explained the good results obtained by incorporating the petiole with the leaf in the silage. The negative consequence – a decrease in the protein content of the mixture (the petiole contains only 7 to 8% crude protein in DM) – was compensated by the more efficient use of the plant biomass (the petioles make up some 50% of the foliage DM). The other feature of the petiole in New Cocoyam is that, in contrast with many other forages, it is not heavily lignified as it is the water in the petiole which provides the main structural support for the leaves, in the same way that the pseudo-stem supports the leaves in the banana plant. Analysis of the leaves and petioles showed that the content of NDF was lower in the petioles (22.7% in DM) than in the leaves (37.8%). ADF values showed similar trends. The low content of structural carbohydrates in the petiole, together with the high content of soluble sugars, leads to the conclusion that the petiole can be considered as a potential energy source, as well as a convenient medium for facilitating the ensiling process.

Taro (Colocasia esculenta)

In SE Asia and the Pacific islands, Taro (Photo 14), often known as “Old Cocoyam”, plays a similar role as New Cocoyam in Latin-America. A series of research (Chhay Ty et al 2007, 2009, 2010; Du Thanh Hang and Preston 2009, 2010; Du Thanh Hang and Kien 2012; Du Thanh Hang and Binh 2013; Du Thanh Hang et al 2011) showed that the same advantages and constraints applied to Taro as to New Cocoyam when used as a protein source for pigs.

Photo 14. Taro (Colocasia esculenta) grown as feed for pigs in Vietnam

The research done by Du Thanh Hang and colleagues (Du Thanh Hang and Preston 2010; Du Thang Hang and Binh 2013; Du Thanh Hang et al 2011) emphasized the advantages of the ensiling process by showing that it reduced to minimal levels the concentration of oxalate salts that caused the itching on skin surfaces – one of the constraints to management and feeding of fresh Taro (the same applied to New Cocoyam). Ensiling was easier and eliminated the need for fuelwood required in the traditional method of boiling, or cooking with rice bran, the traditional method of control employed by smallholder farmers (Buntha et al 2008).

Local breeds fed Taro and Sweet potato forages

The results of the experiment carried out by Hai et al (2013) confirm the importance of the interaction between breed and nutrition when the aim is to promote maximum use of local feed resources. The treatments applied to “local” “Van Pa” sows were mixtures of ensiled taro foliage (leaves and stems) and ensiled sweet potato vines replacing 50% or all the fish meal in diets based on rice bran and cassava root meal. There were no major differences in reproductive performance among treatments nor in feed conversion (Tables 5 and 6). The small litter size for Van Pa sows (6 to 7) translates into less nutritional stress and therefore the opportunity to use diets of lower nutritional density.

In the study by Duyet et al (2010) the reduced time between weaning and first heat in Mong Cai compared with Large White (Yorkshire) sows when ensiled forage replaced fish and soybean meals can be ascribed to the ease with which the early-maturing native breed (Mong Cai) stored fat during pregnancy and later metabolized it during lactation.

In an on-farm study with Mong Cai gilts fed diets with up to 60% of the dry matter as ensiled Taro foliage, and varying amounts of water spinach, reproductive performance was excellent (Tables 7 -10). The rather high mortality of piglets to weaning was not related to diet and was more a function of the inadequate housing.

Positive results from feeding a mixture of ensiled taro foliage and sweet potato vines to replace fish meal in diets of indigenous Van Pa sows in Vietnam were reported by Tran Thanh Hai et al (2013). Reproductive performance and piglet growth were similar for the conventional diet and the experimental one with protein mainly from ensiled taro and sweet potato forages (Tables 11-12).

Biomass productivity of Bore and Taro

There were major advantages of establishing Bore suckers (emerging new shoots) than from buds (disks) taken from the stem (Rodríguez and Preston 2009). The predicted annual per ha yields, in acid soils of low fertility, of 14.5 and 1.90 tonnes of DM and crude protein, respectively, show that the plant is efficient in capturing solar energy.

Agronomic studies with Taro showed similar high productivities (Vivasane et al 2012), and of particular importance for integrated farming systems, a 50% increase in yield due to application of biochar the carry-over effect of which was maintained at least to the third harvest (Figure 15). Assuming the yield recorded at the third harvest would be maintained over a full year then the potential annual yield, with biodigester effluent fertilization, is of the order of 23 tonnes/ha of DM with 2.9 tonnes of protein.

Figure 15. Effect of soil amendment with biochar on predicted annual yield of Taro biomass fertilized with biodigester effluent (Vivasane et al 2012)

Ensiled Taro foliage as a compete feed for indigenous pigs in Vietnam

The high level of production of Taro foliage grown for the production of com (edible part of the stem stored below ground level) can be seen in Photos 15 and 16. Very higher yields of Taro foliage (27 tonnes/ha of DM and 4.2 tonnes/ha of protein) were also reported from the Central coastal region of Vietnam (Du Thang Hang and Kien 2012). In other words, at the time of harvesting the “corms” the associated foliage was a balanced diet (with 14% crude protein in the dry matter).

This hypothesis was tested by Tuan and Preston (2021) in an experiment in which ensiled Taro foliage was supplemented with cassava root meal as a source of entity (Figure 16). The results showed that there was no advantage in adding an energy rich feed in the form of cassava root meal. The growth rate of indigenous pigs increased an almost linear trend as the proportion of ensiled Taro foliage was increased.

Photo 15. A crop of Taro ready for harvest in the Mekong delta in Vietnam	Photo 16. Collecting leaves and petioles of Taro prior to ensiling them for feed to pigs

Figure 16. Growth rate of indigenous pigs increases as the proportion of ensiled Taro foliage increases (Tuan and Preston 2021)

Probiotics and Prebiotics

The terms “probiotics and prebiotics” arose from the decisions made by Health Authorities in a range of counties to forbid the use of antibiotics as growth promoters. Subsequent research followed two paths; one was to administer live microorganisms that would compete with pathogenic species. Lactobacilli and yeast were the basis of many experiments and were allotted the tern “probiotics” The other approach was to evaluate compounds that would create condition in the digestive tract that were unfavorable to colonization by pathogenic organisms and/or were supportive of mechanisms that would benefit the immune system of the host animal. Supplements that fell into this category of “health promoters “were designated as “prebiotics”. Our research with the category of compounds followed experiences in Lao PDR and Vietnam which showed health benefits in cattle fed bitter cassava foliage when they were supplemented with low levels (4% of diet DN) of “Brewers” grains (Phanthavong 2015, personal communication; Binh et al 2015). The hypothesis to explain this effect was that Brewers’ grains contained the residues from the yeast, used to produce the ethanol in beer”, undergo a final process of auto-hydrolysis in which the yeast cell wall is hydrolyzed to for simple carbohydrate molecules such as “bet-glucan” that are specific sources of energy for bacteria that produce volatile fatty acids; and that these compounds create an environment in the cecum and colon of the host animal that is unfavorable to pathogenic organisms.

It is a common practice in most Southeast Asian countries to make rice wine. The process is very simple (Figure 17) involving the fermentation of polished rice with yeast followed by distillation of the ethanol in simple equipment available on most small farms. The process leaves a residue (Photo 17) O known as “Hem” in Vietnam where it is commonly used to feed pigs.

Figure 17. Yeast fermentation of rice produces vine rice” a byproduct with properties prebiotic	Photo 17. Rice distillers’ byproduct in Laos to have to be used as a prebiotic for feeding to pigs (Sankhom et al 2017)

There were major benefits on reproductive performance of Mong Lath sows when they were supplemented with either “brewers’ grains” or with “rice distillers’ byproduct (Figures 18 and 19). The beneficial where effect were more pronounced when rice distiller’s byproduct was the source of the prebiotic as compared with brewers’ grains. In the case of rice distillers byproduct, the improvement in feed conversion in the overall production cycle was of the order of 100%; being superior to the benefits from the brewers´ grains where the overall improvement was abouts 30%.

Figure 18. Effect of brewers’ grains and rice wine byproduct on weight of piglets at weaning (Sivil et al 2019)	Figure 19. Effect of brewers’ grains and rice wine byproduct on the overall feed conversion of feed DM into litter weight at weaning (Sivil et al 2019)

Conclusions

Promoting research on feeding forages to pigs must be seen in the wider context of appropriate farming systems to provide both food and energy from renewable resources. A fundamental feature of this strategy is that the alternative feed and energy resources should be grown on the farm as this will: (i) directly benefit the poorer farmers, who have limited cash resources to purchase inputs from outside the farm; (ii) be an active response to the need to promote sustainable rural development as a response to pressures to increase employment opportunities; (iii) reduce the dependency on transport which almost certainly will have an increasing cost as renewable energy replaces “cheap” fossil fuel.

This review has shown that:

• All or part of the protein in diets for pigs can be supplied from the leaves from shrubs such as cassava and mulberry, from vegetables such as sweet potato and herbs such as Bor and Taro, and from water plants such as duckweed (Lemna spp) and water spinach (Ipomoea aquatica).
  
  
• All or part of the energy can be obtained from the juice in sugar cane, from the roots of cassava, from the petioles of Bore and Taro and from the fruit of the oil-palm.
  
  
• Forages can make a greater contribution to the diet of pigs: (i) during the reproduction phase compared with growth and finishing; and (ii) when native “indigenous” breeds are used as compared with breeds genetically selected for high growth rates and lean carcasses.
  
  
• The use of vegetative protein sources is facilitated when they are accompanied by energy sources that are low in both fiber and protein. A low content of fiber in the energy source creates "space" in the digestive tract of the pig for fiber present in the leaves of forages. Thus, there is potential for a natural synergism between sources of energy and protein in tropical latitudes.
  
  
• When energy sources low in protein (eg: sugar cane juice, cassava roots, sweet potato tubers, or banana fruit and palm oil) are combined with leaves which normally have well balanced arrays of amino acids, it is possible to reduce the overall level of protein in the diet since the amino acid array in such a combination of feeds will more closely approximate to that in the "ideal" protein (See Wang and Fuller 1989).
  
  
• Preliminary experiments suggest that the above ground foliage of Taro and probably of Bore can be a complete diet at least for indigenous breeds such as the Mong Cai in Vietnam and the Moo Lath in Laos.
  
  
• Much of the research with protein-rich forages has been done with conventional sources of energy (ie: maize and rice bran). As these feeds are imbalanced in essential amino acids, the potential to use high levels of protein-rich foliages is compromised. It is strongly recommended that future research in this area should be with herbariums plants that combine both energy (in the petiole) and protein (the leaves).
  
  
• Recent research in Vietnam (Tuan and Preston 2021) indicates that ensiled Taro foliage (leaf and petiole ) can provide all the energy and protein needed for growth of indigenous pigs.

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