4. Environmental Aspects

The interaction of livestock and fish, either as specialized or integrated activities, and the environment can be considered in two ways (1) how the environment impacts on opportunities for livestock and fish production and (2) how livestock and fish production impact on the environment. Impacts can be positive or negative in both directions (Figure 12); in this section we explain how integration tends to enhance positive and minimize negative impacts.

Clearly both fish and livestock production are strongly influenced by, and affect, their agroecology. Aquaculture, by nature of the aquatic environment, is often integral to, and difficult to separate from, surrounding natural and human habitats such as rivers, lakes, reservoirs and coastal areas. Aquaculture has closer proximity to ‘wild’ organisms than animal husbandry that may threaten (through disease transfer, parasitism or predation) or support (through supply of seed or feed) aquaculture (Edwards, 1997). The key reliance on water leads to an enhanced vulnerability to pollutants and contaminants moving with water in and out of aquaculture systems because of the fluid medium.

Impacts on the environment of livestock considered alone, aquaculture alone or both together have both a local and global significance. There are two major interrelated problems facing developing countries and their relationship with the wider world. Sustaining poor peoples’ livelihoods directly, and indirectly, through enhanced agricultural productivity and, at the same time, ensuring that local and global environments are safeguarded. How nutrients are used, and recycled, in food production is of major importance to meeting these challenges. Water, and how food production affects its availability for other uses, is of major significance, not only to the sustainability of local communities but also to broader geopolitical stability. Irrigation systems that promise increases in arable crop yields and cultured fish production, typically undermine important riverine and flood-plain fisheries that may be fundamental to the food security needs of the poor. The integration of livestock and fish production may contribute to stabilising nutrient and water use, allowing increasing demands to be satisfied.

FIGURE 12

The two-way interaction between aquaculture and the environment involves numerous factors which range from positive to negative in their impact.

Source: Modified from FAO (1997a)

More resource-intensive, livestock and fish farming will have increasingly negative impacts on the global environment. These include the effects on global warming to which they directly and indirectly contribute. Fossil fuel use that is the major underlying cause of greenhouse gas production, supports much of the current food grain and concentrate production that underpins the culture of livestock and carnivorous fish species. The impact of increasing demand for concentrate feed on arable systems and the world’s natural stocks of fish to support growth in intensive livestock and fish production could be reduced if integrated farming became more widespread.

Local development of productive integrated systems can also contribute positively to the maintenance of biodiversity. There are two important aspects; reducing impacts on natural resources and adding value to local strains and varieties. Maintaining the genetic diversity of both wild and cultured animals and plants is critical for longer-term sustainability of both small-holder and large-scale commercial food production.

4.1 Nutrients

Intensive recycling of nutrients was critical to support dense rural populations, such as traditionally occurred in much of Eastern Asia (King, 1911). Urbanization and industrialization of agriculture have led to de-linking of nutrient recycling and production to produce food, or in the words of Borgstrom (1973): ‘the breach in the flow of mineral nutrients’. The flow of nutrients entering urban centres as food via processing and distribution systems has become unidirectional - a development that has been accelerated by sewerage systems that channel human wastes away from densely populated city centres (Vallentyne, 1974). Alternative fertilizers, firstly guano and later industrially manufactured fertilizers, began to free farmers from dependence on local nutrient recycling.

A serious geographical imbalance in nutrient distribution now exists; large amounts of nutrients are imported into industrial regions that then spend large amounts of money to avoid eutrophication. In contrast developing areas, which sometimes are the original source of the nutrients, are becoming nutrient-depleted. Cropping cassava on fragile tropical soils for export as low-cost livestock feed ingredients for developed countries is both unsustainable on a local scale and, through deforestation and erosion, has much broader adverse environmental impacts. Intense exploitation of fish stocks to produce fish meal has major implications for the integrity of marine ecosystems. The international trade in commodities has driven many of these practices, but many poorer peoples’ livelihoods are now dependent on them.

Aquatic systems have been used for nutrient disposal, both intentional and accidental since the beginnings of human settlement. Removal of the mainly organic wastes of people settled around waterways and waterbodies was convenient and, initially, left few traces. As the nutrient load increases however, water quality deteriorates with a number of obvious effects. The silting up and nutrient enrichment of community reservoirs and dams causes as many problems to communities around them as the disposal of sewage in industrialized countries. Shallow community water bodies commonly become choked with unmanaged macrophyte vegetation or waterways become plankton-rich and, if organic loads are unchecked, hyper-eutrophic and eventually anaerobic. Both types of plants can be the basis for nutrient recovery if used within managed systems and examples exist of both traditional and modern systems. Aquatic macrophytes can remove nutrients and have been important components in integrated farms in China and Northern Viet Nam to feed both pigs and herbivorous fish. Planktonbased aquaculture is the basis of semi-intensive production of filter feeding fish.

4.1.1 NUTRIENT RECYCLING IN AGROECOSYSTEMS

Agroecosystems differ from natural, unmanaged ecosystems in their larger and more rapid turnover of nutrients. Such systems producing food or fibre are therefore more open for nutrient transport across boundaries (Frissel, 1977; Tivy, 1987). Moreover, the level of nutrient inputs used can define the intensity of farming. Modeling of nutrient cycling is well established for conventional agriculture (Figure 13) but analysis of agroecosystems involving crops, livestock and fish is recent. Understanding how a pond stocked with fish affects fluxes of nutrients through the farm can be critical to developing more efficient and less polluting agriculture, animal husbandry and aquaculture.

Extensive agriculture, such as unimproved pastoral systems, relies on the natural or little modified soil nutrient reservoir, and has low yields of biomass and nutrients (<20 kg N ha^-1). In contrast, specialized intensive agriculture requires large nutrient imports but shows high productivity. Nitrogen outputs of intensive grass production can exceed 400 kg N ha^-1 (Frissel, 1977). Feedlot livestock can greatly exceed these values because high-density livestock are fed concentrates.

Mixed farming is generally intermediate between these two extremes, receiving low to moderate inputs from outside. The close relationship between wastes from livestock used for fertilization of crops, and use of N-fixing plants both reduce the need for N imports, and improve nutrient efficiency. Farming systems in which long-lived organisms such as perennial crops and large livestock are important components are more like self-sustaining natural cycles with increased system biomass and reduced primary productivity/ biomass ratios (Dalsgaard et al., 1995).

FIGURE 13

Nutrient cycles for an agroecosystem involving crops, fish and livestock. The crops, livestock and soil pathways, for which the major linkages are brown arrows, are reproduced unmodified from Tivy (1987). The fishpond, its major linkages with crops and livestock (dark green arrows), other inputs and outputs have been added here. Nutrient recycling within and between the fishpond water and mud are omitted for clarity. In some traditional Asian systems, human (household) excreta is an important additional input to crops and fishponds and kitchen waste the livestock and fishponds.

Source: Edwards (1993)

However, even a simplistic analysis of nutrient fluxes can indicate that mixed or integrated farming systems can be far from a closed ecological cycle. Imports of pig and human food into the seemingly tightly managed agroecosystems in Southern China were required to support the large nutrient exports of commodities such as silk, fish and sugar (Edwards, 1993) and a similar situation exists in Northern Viet Nam (Box 4.A).

A key factor in estimating overall system efficiency is not only the harvestable yield from a given level of input, but the practicality and yield from organisms raised on recycled nutrients in the waste. The relative ‘leakiness’ of nutrients from agroecosystems, as run-off and leaching and percolation into subsoil, and ultimately aquifers is also relevant. Decomposition of livestock manures spread on field crops and leaching of nutrients is a major environmental problem, even in developing countries where nutrients are limiting (see Box 4.B). Intensive specialized livestock production tends to lead to a greater waste of nutrients. In the Netherlands, 52 percent of pig manure, 60 percent of manure of fattening calves and 80 percent of chicken manure is wasted (Harrison, 1992).

FIGURE 14

Nutrient flows among village subsystems and between village and outside systems.

Source: Le and Rambo (1993)

4.1.2 NUTRIENT EFFICIENCY IN LIVESTOCK

Relative efficiencies of livestock

The role of livestock in supporting human populations, and their relative efficiency in terms of using land and food resources, are highly specific to the human and agro-ecology of the region. Whereas monogastrics (pigs and poultry) may compete for cereals, pulses and concentrates suitable for direct human consumption, ruminants may utilize plant production unsuitable for direct human food. Livestock can have important roles in improving total efficiency of conversion through use of by-products unsuitable for, or wastes from, direct human consumption. Spedding (1984) observed how monogastric and ruminant feed development could be synergistic. Extraction of energy/protein-dense food from herbage crops for pigs and poultry, leaving residues with value for ruminants, is one option. A good example of this is the use of sugar cane juice in pig feeds in Viet Nam (Preston, 1990). Another strategy is the biological processing of fibrous wastes in which earthworms or dipterous larvae are used to concentrate high-quality, microbial protein from decomposing animal and vegetable waste.

Any comparison of livestock in terms of nutrient efficiency is problematic. Protein conversion values, or protein to energy ratios have been used but any meaningful comparison is difficult because different animals can use different quality feeds. Thus, although poultry yield most protein per unit of gross energy fed compared to a range of other animals, the feeds used contain a higher proportion of metabolisable energy (ME), usually in the form of more expensive feeds. Efficiency expressed as protein conversion or protein per unit of energy consumed (g protein/MJ of ME) of single animals indicates that eggs, milk, milk plus beef, poultry and pig production are high and breeding animals low. But any animal production requires breeding animals and thus consideration of nutrient efficiency has to be made on the basis of populations rather than single animals. A high reproductive rate and low turnover of breeding animals improves overall efficiency. Highly productive pigs and poultry have low overhead feed costs for breeding animals compared to larger animals. Selection for earlier age at first breeding, reduced length of and improved regularity of a breeding cycle, greater fecundity and improved early survival of the young, all theoretically improve reproductive efficiency. In practice they may be counteractive or incur such high support costs as to be impractical. It is also known that separation of males and females and use of different diets and management can enhance feed utilization, but may not be practical.

Approaches to improve efficiency

Different approaches are known to improve overall efficiency of nutrient use in ruminants and monogastrics. Replacement of traditional sources of protein with non-protein N is one approach useful for ruminants. Use of micro-nutrient blocks for animals consuming poor-quality diets, and use of by-pass protein can all increase the efficiency of protein use. Development of diets with improved amino acid balance and optimal relationships between micro-nutrients has improved the nutrient efficiency of monogastrics.

Modern livestock systems can produce relatively less waste but it is often more nutrientrich than from traditional systems. Certain practices influence the amounts of N and P (Box 4.B).

4.1.3 NUTRIENT EFFICIENCY IN AQUACULTURE

A comparison of intensive and semi-intensive aquaculture reveals that conversion efficiencies are greater for fish fed formulated diets (21-53 percent for N, 11-28 percent P) than fish raised in ponds receiving livestock manure or inorganic fertilizer (5-25 percent and 5-11 percent respectively) (Edwards, 1993). However, these differences reflect a fertilized system in which phytoplankton is produced; and are far from a 90 percent decline in efficiency expected from an extra step in the food chain. The values reflect the high degree of nutrient recycling that occurs in food webs in fertilized ponds and, particularly in polycultures, how efficiently they are exploited.

Developments in intensive salmonid production are towards ‘low pollution’ diets in which highly refined processing of food ingredients produces more highly digestible, low P diets. These have resulted in declines in measured P effluents, despite rising production. However this has been achieved largely through use of greater amounts of fishmeal, with associated environmental impacts. Additionally, the level of soluble, excreted nutrients. (kg fish produced^-1) have probably increased with the use of such diets.

4.1.4 NUTRIENT RELATIONSHIPS IN LIVESTOCK- FISH SYSTEMS

Integration of livestock and fish production can improve the overall efficiency of nutrient use in the system and reduce the level of effluents. Relative inefficiencies in nutrient use by livestock can be compensated for by recycling in fish production. Efficiency of nutrient recovery declines as input levels increase, a clear case of diminishing marginal returns (Table 4.1). There are also differences in efficiency of nutrient transfer between wastes collected from different livestock systems. Both fish yield and N recovery were considerably poorer for ruminants fed poor-quality diets than feedlot ducks fed complete feeds. Such information is useful for estimation of opportunity costs of livestock-fish systems (Chapter 7).

Wastes are often composed of fractions of different value to fish culture. The mixing of feed with manure for example can improve its value and nutrient recovery of the overall waste. Ad libitum feeding of ducks resulted in an estimated 10 percent of the feed being wasted and directly available to the fish in the case above. In ducks, species, sex and type of feed were all found to significantly affect feeding efficiency and the amount of waste feed ‘lost’ to direct consumption by fish in integrated systems (Naing, 1990).

TABLE 4.1

Efficiency of N recovery in livestock-waste fertilized earthen ponds (200 m-2) stocked with Nile tilapia.

Source: AIT (1986)

4.2 Significance of Livestock and Fish Production in the Global Environment

Livestock and fish production impact on the wider environment in a variety of ways. The resources used to feed, maintain, process and distribute livestock and fish products are considerable. However, intensified production of both livestock and fish must occur if natural habitats are to be preserved (de Haan et al., 1997).

Intensification of livestock based on known technologies adapted to local situations could reduce impacts on the remaining natural environment (Murgueitio, 1990). While intensive livestock production is a major source of pollution, degradation of range lands and soil erosion in developing countries is associated with increased numbers of ruminants that are often extensively managed and of low productivity (Steinfeld et al., 1997). Extensively managed ruminants have been identified as a major factor in both tropical deforestation and increase in greenhouse gases. These claims are particularly important given the growth in livestock production, which at 4.5 percent year^-1, is higher than for agricultural production as a whole.

4.2.1 GLOBAL WARMING

Agriculture has been implicated as a major cause of global warming that is leading to adverse changes in the world’s environment. These include rising sea-levels that are likely to particularly affect densely populated flood-plains in Asia, communities that are also most dependent on cultured freshwater fish. This dependence is set to increase substantially, and the poorest are most at risk (Harrison, 1992).

Carbon dioxide, nitrous oxide and methane are the main ‘greenhouse gases’ linked directly and indirectly to livestock production. Permanent carbon release is mainly related to use of fossil fuels and deforestation, for which intensive animal husbandry and extensive ruminant production, respectively, are important. Nitrous oxides are associated with production and use of N-fertilized pasture and arable crop-based feeding.

Livestock and manure management contribute about 16 percent of total annual production of methane (de Haan et al., 1997) and unproductive ruminants contribute especially to emissions (Leng, 1991). A larger fraction of feed is used for maintenance in low productivity animals, resulting in a higher level of methane produced per unit of product. Also, lower quality feeds with poorer digestibility have higher emissions per unit of feed intake. Intensifying livestock production could therefore have impacts on both global warming and livestock productivity. More than 80 percent of methane from livestock arises from digestive fermentation and the balance is linked to manure management. Manure handled dry produces little methane, but feedlots, which produce large amounts of liquid manure, are the main contributors. Pigs and poultry cannot digest fibrous feeds and have relatively low fermentation emissions; the rapid increase in the numbers of these monogastrics compared to grazing animals on a world-wide basis is one reason for the stagnant methane emissions from livestock, despite growing numbers (de Haan et al., 1997). Improved productivity is also believed to contribute to stability of methane emissions related to digestion.

The recycling of methane after controlled collection and digestion is attractive, particularly for large pig and dairy operations with high energy requirements but has been less attractive for smallholders. Lower cost systems based on low-cost polyethylene tubing have also been promoted in the Mekong Delta, Viet Nam (Herrera, 1996). Farmers raising fish, however, prefer to use fresh pig manure directly and biogas slurry is rarely used to fertilize ponds (Bui, 1996). The disposal, with or without intermediate fermentation in a biodigester, of feedlot livestock wastes in aerobic fishponds would reduce methane and CO2 emissions considerably.

Expansion of fertilized aquatic systems stocked with grazing fish has greater capacity for sequestering carbon dioxide than even wellmanaged terrestrial pasture, as aquatic productivity may be most limited by carbon in otherwise fertile systems. Flooded rice fields of Asia have been identified as another major source of methane. The stocking of rice fields with fish that graze the soil-water boundary in ricefields ensures that it remains aerobic, with methane production correspondingly reduced.

4.2.2 WATER USE

Water is a renewable resource but its availability, if considered as the amount per person per year, is limited. Increasing water scarcity is undermining food security and becoming the cause of local and international conflicts (Falkenmark, 1999). Whereas water consumption of livestock is related mainly to the amounts required to produce their feed or fodder (Pimentel et al., 1997), the water used for holding fish during production needs to be considered in aquaculture (Beveridge and Phillips, 1993). Levels of seepage, evaporation and recycling of water in fish culture systems are therefore important criteria, as is the value of water after its use for fish production.

Water use efficiencies of livestock are dependent on both the type of feed given and the efficiencies of conversion. Intensively fattened beef dependent on irrigated crops is therefore water hungry. In contrast, poultry as efficient converters of diets mainly consisting of rain-fed cereals (sorghum, maize and wheat), can be produced using much less water.

The integration of livestock and fish production can reduce the amount of water used per unit of animal protein, compared to separate, stand alone production of poultry and fish in ponds (Table 4.2). This is basically because the amount of water required to produce feed for fish is eliminated. In more intensive systems, however, water can be used more efficiently if the fish are fed and raised at higher densities, and water is filtered and recycled.

A direct comparison of the efficiency of water use in different livestock and aquaculture systems is not realistic in other ways. The construction and siting of fishponds in watersheds to collect and store water that otherwise would be unavailable contributes to increasing the amount of available water for the whole farming system i.e. fish, livestock and crop components. The capital costs for any single component might be too high whereas the integrated use of the water ‘spares’ this initial cost, and reduces risk (Chapter 9). Moreover integrating livestock waste with semi-intensive fish production may increase the ‘value’ of the water since its nutrient level, and hence value for irrigation, will be increased when used locally in agriculture (Little and Muir, 1987; Pullin and Prein, 1994).

The potential and constraints to the integration of livestock and fish are reviewed by system in Table 4.3. Open ponds within diverse farming systems offer most potential for significant interaction. Water shortages have been an important motivation for closer spatial integration between livestock, fish and crop production in parts of Asia (Box 4.D).

Intensive fish production, especially in cages and raceways, tends to be highly consumptive of water (Table 4.2), degrading the value of large amounts of water required by other consumers. Regulators in the industrialized world view intensive aquaculture as a polluter of multipurpose water resources and tend to limit its size and distribution. Eutrophic water enriched by wastes from intensive aquaculture or livestock production requires extra treatment costs prior to distribution and use.

4.2.3 BIODIVERSITY

The case has been made for intensification of livestock production to safeguard remaining areas of wildlife habitat and, indirectly, biodiversity (de Haan et al., 1997). The expansion of fish culture, closely integrated with this intensified livestock production may also reap specific benefits in terms of protection of aquatic habitats. Exploitation of wild fish stocks has contributed towards collapse or impoverishment of native fauna but this is often based on industrial fishing to produce fish meal for feeding intensively raised livestock and fish. Low cost farmed fish can reduce these pressures, and the accompanying environmental degradation, by providing the market with alternative supplies, perhaps to a point where natural stocks can recover although this is probably unrealistic due to growing population pressure and different players catching and culturing fish.

TABLE 4.2

Water consumption of fish production integrated with livestock or as a stand-alone enterprise

^a seepage, evaporation; ^b livestock alone

TABLE 4.3

Potentials and constraints to integration of livestock with fish by system

The drainage or conversion of wetlands for aquaculture is a common strategy that risks losses to both biodiversity and the livelihoods of the poor (Chapter 7). Culture systems that depend on modification, rather than wholesale change of natural habitats and use indigenous species need greater attention in this respect.

The use of indigenous fish in culture may result in conservation of endangered species. There has been relatively little development of polycultures based on indigenous fish but experience in Java, where combinations of several indigenous carps and gouramis are traditionally cultured, suggests this is a promising strategy. Moreover, most fish eating cultures that have relied on natural stocks are familiar with consuming fish of a variety of species and size. One constraint is that many highly valued indigenous species are carnivorous and not good primary culture candidates. They may be useful, however, as components of semi-intensive systems that add value to polycultures mainly comprised of low value herbivorous fish. Stocking a variety of indigenous, carnivorous fish along with snakeskin gourami (Trichogaster pectoralis) is now a well-developed system in Thailand. The need for more diversity was market-driven and favoured use of indigenous and exotic species raised together to suit local needs (Yoonpundh, 1977). Production was enhanced using livestock manures and the system has emerged as an alternative strategy to high-risk intensification based on monoculture. It also allows resource-poor farmers to raise species with which they are familiar, and which are of high value.

Combinations of wildlife and livestock are now recognized for their value in increasing biodiversity and incomes for the people dependent on them such as pastoralists and ranchers (Steinfeld et al., 1997). The survival of wild aquatic species and their habitats, may also be more assured if they can be utilized within extensive and semi-intensive culture systems.

Integrated fish culture protects biodiversity in more indirect ways. Increased demand for feed concentrates creates significant pressures on the environment and aquatic habitats in particular through high rates of water extraction and the deterioration in quality that often occurs. Large quantities of both surface and ground water are used to irrigate cereal and oil crops that comprise most concentrates, and contamination of water run-off and drainage with agrochemicals typically occurs. When concentrates are used in semi-intensive systems, more fish can be produced per unit feed than intensive systems in which natural food is unimportant.

4.2.4 USE OF FISHERIES TO SUPPORT LIVESTOCK AND FISH PRODUCTION

Integration of livestock and fish is highly efficient if the fish species raised are herbivorous or omnivorous. The production of carnivorous fish has implications for equitable use of resources (see Chapter 7) since the small trash fish required to either feed them directly (as in certain catfish and snakehead systems in Southeast Asia) or indirectly for fishmeal production can be eaten directly by the poor.

Intensive aquaculture of carnivorous species uses a rapidly increasing proportion of the limited global supply of fishmeal as fish inputs are two to four times the volume of fish outputs in the production of farmed salmon and shrimp (Naylor et al., 1998). Although the amount of fishmeal used in livestock diets has declined recently, particularly for grower and finishing feeds of monogastrics, livestock remains the major user at about 75 percent of global production.

Cultured fish may be used increasingly to supply fresh fish and fishmeal needs. Production costs for waste-fed herbivorous fish are now similar to the price paid by manufacturers of valued added products such as pet foods for quality trash fish. Market pressures may also stimulate the emergence and acceptability of waste-fed fish for these purposes as consumers are becoming increasingly aware of environmental issues.

The use of small quantities of cultured fish to balance carbohydrate-rich on-farm diets for livestock has been suggested (Chapter 9).

4.2.5 IMPACTS OF LIVESTOCK SYSTEMS ON FISH PRODUCTION

Water pollution caused by residues and purposeful disposal of chemicals used in livestock production is typically highly harmful to fish and other aquatic organisms. Poor fish growth and survival in a system based on goat wastes from animals dosed prophylatically with anti-helminths has been reported in experimental systems (Mohsinuzzaman, 1992). Water pollution from agrochemicals to control livestock disease vectors such as ticks and tetse fly can negatively affect fish if inappropriate drainage or discharge is used.

In temperate climates, attention has been drawn to the negative impacts of grazing animals on riparian systems, around which they are often concentrated, through their consumption of vegetation cover and resulting run-off. Increased nitrate and phosphate levels affect plant communities, silt deposition and flow dynamics of surface waters. Aquaculture integrated within the farming system, especially of less tolerant species, can act as a bio-indicator of environmental health.