7. Future prospects for meat and milk from grass-based systems

by
I.A. Wright1

Abstract

There are three key drivers that are likely to affect the production of meat and milk from grass-based systems in the next 20 years. These are: (i) a general increase in global demand for milk and meat; (ii) concern about the environmental impact of agricultural practices; and (iii) an increasing concern by consumers about food quality, including food safety and animal welfare, especially in the developed world. The global demand for animal products is projected to increase considerably, driven mainly by population growth, economic growth and urbanization in China and Southeast Asia. The environmental impacts of grazing systems vary considerably depending on the climatic conditions, but are likely to be an increasingly important factor. Food quality, food safety and animal welfare will also probably continue to be an important aspect in the market for milk and meat in developed countries, providing an opportunity for producers of meat and milk from grass-based systems.

Introduction

Grassland-based meat and milk production systems account for a large proportion of both the global land area and of the production of meat and milk. Approximately 60 percent of the world’s pasture land (just less than half the world’s usable surface) is classified as grazing land (de Haan, Steinfeld and Blackburn, 1997). In addition, grassland plays an important part in many mixed agricultural systems, providing a break in rotational cropping systems and providing feed to livestock in systems in which the diet comprises both crop residues or by-products and grazed or conserved grass.

The annual production of meat and milk products from grazing systemsand mixed farming systems is shown in Table 7.1. Only about 9% of global meat production comes from grazing systems (defined by de Haan, Steinfeld and Blackburn (1997) as systems based almost exclusively on pasture with little or no integration with crops, mainly based on native pasture). Mixed farming systems account for 54% of meat production and 90% of milk production. A considerable proportion of the feed consumed by livestock in these mixed systems will be from grazed and stall fed pasture.

However, these global figures hide a huge range in the importance of grassland-based systems in different regions and countries. In temperate regions, grass-based systems of milk production predominate. For example, in New Zealand, virtually all dairy production is based on grassland, with over 90 percent of the total nutrient requirements coming from grazing (Hodgson, 1990). In the European Union, over 95 percent of milk production is based on grassland (Plate 7.1), often managed relatively intensively. Even although the level of supplementary feeding may be relatively high in dairy systems, grazed or conserved grass still accounts for 50–70 percent of the nutrient requirements of the cows, and 75–100 percent of requirements in most beef and sheep systems can be met from grazed or conserved grass.

Many of the world’s arid and semi-arid rangelands are grazed by domestic livestock, and although the stocking density may be relatively low, animals provide livelihoods for pastoralists and are often central to their cultural heritage.

Compared with other sources of fodder for meat and milk production, grass, especially grazed grass, can provide a cheap source of feed (Table 7.2). The costs of grazed grass are generally about half of those of conserved hay or silage. In addition, the support-energy requirements for harvesting and storing conserved grass, especially as silage, are often considerable (Wilkins, 1990).

While the above gives an indication as to the current state of meat and milk production from grasslands, the objective of this chapter is to look forward and to try to analyse future prospects. There are a number of recent trends and developments that might give some pointers as to future trends. Observers and commentators have identified three important drivers that are likely to have a bearing on the production of meat and milk from grass in the next 20 years. These are:

  1. A general increase in global demand for milk and meat.
  2. Concern about the environmental impact of agricultural practices.
  3. An increasing concern by consumers about food quality, including food safety and animal welfare, especially in the developed world.
Plate 7.1 Dairying on perennial white clover-ryegrass pastures in Scotland
[Photograph by John Frame]

Table 7.1 Total world meat production (‘000 tonne) from grazing systems

Region

Beef

Sheep and goat meat

Milk


Sub-Saharan Africa

1 380

 390

 9 827

Asia

 765

 656

 308

Central and South America

5 652

 231

13 553

West Asia and North Africa

 88

  237

 1 191

Eastern Europe and CIS

 n/a

 n/a

 n/a

OECD and other developed

4 396

1 466

 17 647


Note: n/a = not available.
Source: de Haan, Steinfeld and Blackburn, 1997.

Table 7.2 Costs of different ruminant feeds


Feed

Cost (US$ tonne-1)


Grazed grass

36–56

Maize silage

48–60

Alfalfa haylage

70–100


Source: Hlukik and Smith, 1988

Changing global demand for animal products

There is a huge range in the amount of meat consumed by the population in different regions in the world. Meat consumption in the developed world is much higher than in developing countries. In the early 1990s, the per capita consumption of meat in the developed world was 78 kg, with higher amounts in the United States of America and lower amounts in Europe. In developing countries of Asia, 18 kg of meat was consumed per capita, while in Latin America consumption was 46 kg. In sub-Saharan Africa, the equivalent figure was only 9 kg (Delgado et al., 1999).

Milk consumption per capita in Latin America is higher than in other developing countries: four times higher than in Africa and three times higher than in developing countries in Asia. However, even in Latin America, milk consumption per capita is about 40 percent less than in developed countries.

Per capita consumption in developed countries is likely to be relatively static over the next 20 years. The levels of consumption in developed countries are already relatively high and so the scope for further increases is limited. However, per capita consumption of meat and milk is forecast to increase considerably over the next 20 years in developing countries since demand for meat tends to increase more rapidly than disposable income (Ahmed and Gruhn, 1995). Thus, as countries become richer, meat consumption tends to increase quickly. The rate of increase in per capita income is much higher in some developing regions, e.g. China and Southeast Asia with rates of economic growth of 6–9 percent, whereas in developed countries economic growth rarely exceeds 3 percent and is often less. Urbanization is also thought to be a key factor in driving up demand for livestock products. The urban population in developing countries is growing at 3.5 percent per annum, compared with only 0.75 percent in developed countries, which are already highly urbanized (United Nations, 1995).

A further important factor is that changes in per capita consumption in the developing world are likely to have a much greater global impact than changes in the developed world. This is because, first, the developing countries have a much greater proportion of the world’s population (about 77 percent in the 1990s), and, second, they have much higher rates of population growth (1.9 percent per annum, versus 0.4 percent in developed countries).

The International Food Policy Research Institute has developed a global food model (IMPACT; Delgado et al., 1999) and used it to predict the growth in demand for a range of foodstuffs in different regions of the world. Delgado et al., (1999) have produced estimates in the demand for different livestock products up to the year 2020. They predict considerable increases in demand for livestock products as a consequence of population growth, economic growth, higher income per capita and increased urbanization. Much of this increased demand is predicted to take place in China and Southeast Asia, where levels of economic growth are high. The IMPACT model predicts that in China, for example, meat consumption will reach 63 kg per capita, approaching the current consumption in developed countries. Total world meat production is predicted to increase by 63 percent by 2020 compared with the early 1990s. China alone is projected to account for almost 30 percent of global supply (including pig and poultry meat).

While much of the increased demand will be for white meat (pig meat and poultry), there will also be a considerable increase in the growth in demand for milk and beef (Table 7.3). Although the demand for beef will remain relatively constant up until 2020 in the developed world, there is predicted to be a doubling of beef production and a 2.5-fold increase in milk demand between 1993 and 2020. A number of assumptions are built into the IMPACT model, including the continued growth of the economies of developing countries, especially in Asia, and the continued supply of relatively cheap fossil fuel. Given the known levels of global fossil fuel reserves, this seems a reasonable assumption, at least over the twenty-year time period for the projections.

While there are a number of assumptions built into the IMPACT model and the absolute increases in consumption that are predicted might be questioned, there does appear to be considerable evidence to support the view that the global demand and production for meat and milk is likely to increase in the next 20 years. A major factor that will affect whether the predicted increases in demand can be satisfied will be the ability of the natural resources to support them, in the light of the increased demand that will be placed on those natural resources, upon which the production systems depend to cope with the environmental pressures that such an increased demand will place upon them.

Table 7.3 Projected trends in production of selected livestock products


Region/Product Projected annual growth in production

Total production (million tonne)

(1993–2020)

1993

2020


Developed world

 Beef

0.6

 35

38

 Milk

0.4

348

371

Developing world

 Beef

2.6

 22

44

 Milk

3.2

164

401


Environmental impact of grazing livestock production

Types of grazing system

The form of the environmental impact of grazing livestock is determined to a large extent by the environmental conditions in which the grazing system is located, and especially the climatic conditions. From an environmental perspective, de Haan, Steinfeld and Blackburn, (1997) classified grazing systems into a number of broad types, including:

  • arid grazing systems;
  • semi-arid grazing systems;
  • subhumid tropical grazing systems;
  • temperate grazing systems; and
  • mixed farming systems.

Grazing systems are defined as livestock systems in which more than 90 percent of the dry matter fed to the animals comes from rangelands, pastures, annual forages and purchased fodder. In terms of total production, these grazing systems supply only 9 percent of global meat production. Livestock provide the sole source of income for 20 million pastoral families.

There are also mixed systems in which crop and livestock production are much more closely linked. In many cases, the contribution of grazed or conserved fodder from grassland is limited.

Arid and semi-arid grazing systems

Arid grazing systems have been defined as having an average growing season of less than 75 days, with rainfall limiting production. Semi-arid areas have a growing season of 75–180 days, with less variability in rainfall than in arid areas. Examples of these areas include parts of the Sahel and central Asia. These ecosystems are often important habitats for a range of plant and animal species and there is competition for resources between domestic animals and wildlife, although sometimes occupying different niches.

The higher rainfall in the semi-arid regions means that the grazing pressure on these resources can be considerable. The greater concentration of water points in semi-arid zones can also lead to high levels of local degradation. Historically, it was thought that many of these arid and semi-arid rangelands were “degraded” and that significant desertification had taken place. UNEP (1992), for example, suggested that about 20 percent of the world's rangelands had been degraded, and Gilmanov (1996) estimated that about one-third of the rangelands in the Former Soviet Union were degraded. More recently, there has been considerable debate as to both the definition and extent of degradation and desertification (e.g. Skarpe, 2000). Studies that have taken a long time frame (decades rather than years) suggest that many of the observed changes are climatic-driven rather than due to the effects of grazing livestock. The expansion of the Sahara desert in the 1970s and 1980s was probably a result of climatic changes rather than due to the impact of human activity.

The concept of degradation has also been questioned. The idea of degradation emerged from rangeland science in North America, based on the assumption that rangeland vegetation moved through a series of states to a climax in the absence of grazing, i.e. Clemensian succession. Degradation was then considered as the extent to which the rangeland differed from this climax state. This model still dominates much rangeland management policy, especially in the United States of America. In ecology, this model has given way to the concept that rangelands can exist in a range of stable states depending on weather conditions and management regimes. The “state and transition model” (Westoby, Walker and Noy-Meir, 1989) implies that there is no longer a simple state against which “degradation” can be measured. Rather the implication is that the desired state can only be defined in relation to a particular set of management objectives.

Behnke and Scoones (1993) argued that the condition of arid and semi-arid rangelands where there is considerable variation in rainfall is climatically driven rather than driven by grazing pressure, i.e. the “non-equilibrium model”. However, recently Illius and O’Connor (1999) have questioned the view that rangeland systems can be conveniently classified as “equilibrium” or “non-equilibrium” and consider that there is a range of coupling mechanisms of plant and animal dynamics. Certainly Fernandez-Giminez and Allen-Diaz (1999) found that neither of these two models fitted data collected from Mongolia. Nevertheless, there are undoubted examples of degradation of arid rangelands in certain areas caused by grazing pressure, notably around settlements and water points where the vegetation can be completely absent as a consequence of pressure from grazing livestock.

Thus there needs to be a reassessment of the environmental impacts of livestock grazing on arid and semi-arid rangelands. In practical terms this is proving difficult, as currently the state and transitional model and the non-equilibrium models do not provide any conceptual basis for the development of monitoring techniques. Recently Stolte et al. (2004) have tested a field methodology for assessing temperate rangeland condition that is based on both a consideration of a desired state and a sound understanding of the interaction between the vegetation and the grazing herbivores. Whether such as approach is more generally applicable remains to be seen.

Sub-humid tropical grazing systems

In these zones, vegetation growth, stimulated by rainfall normally lasts for six to nine months, sometimes in two separate periods with one or two dry seasons. In the sub-humid tropics, the wetter climate leads to a range of diseases being endemic (e.g. river blindness, African sleeping sickness, tick-borne diseases, and tsetse fly, which spreads trypanosomiasis), which can limit the exploitation of the resources. With progress in tsetse and tick control, and with better medicinal treatment against animal diseases, many pastoralists from the semi-arid regions of Africa are entering wetter areas during the dry season to find grass regrowth, either after savannah burning or in the wet lowlands. Eradica tion or control programmes for tsetse fly in Zimbabwe and Cameroon, for example, have opened up new pasture areas to pastoralists. The main environmental issues in relation to grazing of these areas are the change in vegetation, especially bush encroachment, the dissemination of invasive plants, the long-term consequences of the bushfires on open pastures, and the consequences for wildlife.

Temperate grazing systems

Temperate grazing systems, based on natural permanent pastures, account for 13 percent of the world’s pasture lands (de Haan, Steinfeld and Blackburn, 1997), mainly in China, northern United States of America and South America. Much of these temperate rangelands appear to be in a relatively healthy state (USDA, 1988), as domestic livestock have replaced the wild herbivores under which these ecosystems have evolved. However, there are areas of the world where the pressure from domestic livestock may be high, such as parts of the western United States of America, the Former Soviet Union, China and Mongolia. Zhong (1993) suggested that 40 percent of Inner Mongolia’s rangelands were degraded.

In extensive grazing systems in Europe there is concern about the impact that grazing by domestic livestock has had on the biodiversity of what are often relatively fragile habitats. Thus, grazing by sheep and the replacement of natural vegetation with sown species has reduced the area of heather (Calluna vulgaris) in many part of upland Britain (Mowle and Bell, 1995).

Mixed farming systems

Mixed farming systems occur in both the developed and developing world. They supply over 90 percent of the world’s milk, 70 percent of the sheep and goat meat, and approximately 35 percent of the beef. They have the potential to be the most integrated of the livestock systems because of the opportunities for the efficient use of resources and in particular the integration of cropping and livestock systems to maintain soil fertility and biodiversity, better use of wastes and the opportunities for intensification of production without resorting to high levels of external inputs. However in developing countries with high population growth (e.g. the Sahel, Ethiopia, Nepal, Bangladesh) there is increased pressure on the pasture component of the system, with pasture land being converted to cropping, with a resultant increase in stocking rate on the remaining pasture. In the developed world, mixed systems usually entail pasture, grazed by ruminant livestock as part of a crop rotation, or the integration of the use of areas of natural pasture with cropping land. In the past few decades the levels of external inputs, especially fertilizers, has increased dramatically. Between the 1960s and 1990s, the amount of nitrogen fertilizer used by agriculture in the United Kingdom rose from about one-third of a million tonnes to over one-and-one-half million tonnes. While by 1986 some grassland was receiving over 300 kg N ha-1, over half was receiving less than 100 kg ha-1 (Wilkins, 2000). However, nutrient surpluses have had a major impact on surface and groundwater, resulting in particular in high levels of nitrate in drinking water and eutrophication of surface waters. This has led to a series of nutrient control measures being applied to farms in some parts of the European Union and the United States of America. As mixed farming systems have become more intensive, with higher stocking densities and reliance on sown pasture with fewer plant species, biodiversity has probably decreased.


Food quality, food safety and animal welfare

In many developed countries, consumers are becoming increasingly aware of issues such as the quality and safety of food, as well as of the conditions under which animals are kept for food production. The impact that food safety can have on consumer confidence in products and on consumption was dramatically illustrated in the United Kingdom in 1996, when the British Government announced that there was a possibility that new variant Creutzfeldt Jacob Disease (CJD) in humans could be linked to Bovine Spongiform Encephalopathy (BSE). Beef consumption in the United Kingdom fell by 16 percent in 1996 compared with 1995 (Figure 7.1) and in the European Union by 10 percent, although by 1998 consumption levels in the United Kingdom had recovered. A recent survey of Irish consumers showed that 64 percent were concerned about beef. Concerns included freshness of food, BSE/CJD, antibiotic residues, hygiene standards and bacteria (Riordan, Cowan and McCarthy, 2002).

In developed countries, where consumers have high levels of disposable income, many are increasingly concerned about the conditions under which animals are kept for food production. Legislation often provides for a minimum standard of animal welfare that is considered by society as being acceptable.

Figure 7.1 Beef consumption in the United Kingdom, 1992 to 1998.
Source: Eurostat, Luxembourg

p>Most concern has been expressed about intensive production methods for pigs and poultry, where animals are kept indoors at high stocking densities. At the same time, animal products that are produced from grass-based systems are seen as being more ‘natural’ by consumers, and to pose fewer welfare problems for the animals concerned.

Nutritive value of meat and milk from grass

The importance of animal products in the human diet has long been recognized. Much of the research on animal production in the early half of the twentieth century was stimulated by the need to increase the amount of animal protein in the diet of a mainly urban, industrialized population, with diseases such as rickets being prevalent in children in many of the industrialized towns in Britain, for example.

In the latter part of the twentieth century many human health problems, such as cardiovascular disease, have been linked to an overconsumption of fats, especially saturated fats, mainly derived from animal products such as meat and milk. Official government advice in many developed countries has been to reduce saturated fat intake, and considerable progress has been made through breeding and nutrition programmes in reducing the fat content in meat from cattle and sheep. In the 1960s, typical fat contents for beef and lamb as sold retail were 25 and 31 percent respectively, while by 2000 the equivalent figures were 5 and 8 percent.

The fatty acid composition of ruminant products has become the focus of considerable research attention in recent years, because of the link between saturated fat consumption and cardiovascular disease. The UK Department of Health, for example, has recommended a reduction in the intake of saturated fats and an increase in the intake of unsaturated fatty acids, especially the omega-3 polyunsaturated fatty acids (n-3 PUFA). These are known to be beneficial, especially in protecting against heart disease. It is recommended that the ratio of polyunsaturated to saturated fatty acids (P:S) in the human diet should be about 0.4 and that there should be an increase of the relative intake of n-3 compared with n-6 PUFA (Department of Health, 1994).

The fatty acid composition of beef is partly determined by the animals’ diet. Grass is rich in α-linolenic acid and recent research has shown that the fatty acid composition of beef from cattle which have been fed on a grass diet differs from that in cattle fed in concentrates (Table 7.4). In particular, the grass-fed animals had a higher concentration of α-linolenic acid (C18 : 3 n-3) and its n-3 long chain derivatives, while concentrate feeding resulted in higher amounts of linoleic acid (C18 : 2 n-6) and long-chain derivatives.

Meat and milk from ruminants also represents a major source of conjugated linoleic acids (CLA) in the human diet, which have a number of health promoting benefits such as anti-carcinogenic activity, anti-artherogenic activity, the ability to reduce the catabolic effect of immune stimulation, enhanced growth promotion and reduction in body fat (Banni and Martin, 1998). Recently, it has been shown that there is a positive relationship between the concentration of CLA in milk and the proportion of fresh forage in the diet of dairy cows (Ward et al., 2003).

Recent research in Kenya has shown, for the first time using a controlled feeding intervention study, a link between meat and milk intake in children and a range of physical and behavioural measurements (Global Livestock CRSP, 2001). Children of 6 to 9 years of age were supplemented with meat or milk and a range of measures of cognitive function, physical measurements, physical activity and behaviour were monitored. Supplementation with meat promoted cognitive function, leadership behaviour and initiative, as well as physical activity and improved biochemical micronutrient status of iron, zinc, vitamin A, vitamin B12 and riboflavin, while supplementation with milk promoted linear growth and vitamin A, vitamin B12 and riboflavin status. This study highlights the importance of animal products in the diet of children, not only for physical development, but also in psychological development. These findings could have far-reaching consequences for development in developing countries, since learning capacity and the development of human potential may be being stifled by a lack of animal foods in the diet.

Thus in both the developed and developing world, the role of meat and milk in the human diet may receive more attention in the future. In the developed world there may be considerable health benefits from the inclusion in the human diet of meat and milk from cattle reared on grass. However, the extent to which this may significantly and practically improve human health remains to be determined, but may become an important factor in the promotion of meat from grass-based systems in the future. In developing countries there is clearly benefit from inclusion of animal products in situations where the diet is sub-optimal.

Table 7.4 Effect of diet on fatty acid composition (mg g-1 muscle) of longissimus dorsi muscle from cattle fed grass or concentrates.

Fatty acid


P-value

Diet

 

Grass

Concentrates

 

C16 : 0

6.98

4.88

0.01

C18 : 0

4.56

2.79

0.001

C18 : 1 n-9

10.1

6.22

0.001

C18 : 2 n-6

0.65

1.62

0.001

C18 : 3 n-3

0.33

0.10

0.001

C20 : 4 n-6

0.21

0.44

0.001

C20 : 5 n-3

0.13

0.004

0.001

C22 : 6 n-3

0.02

0.01

0.001


Total

28.6

21.7

0.01

Technological Developments

Genetic improvement of livestock

Considerable research and development effort has been devoted to genetic improvement in livestock in past decades. There have been some spectacular improvements in some production traits, but these, in the main, have been when animals have been kept in relatively intensive systems, such as in the pig and dairy cow sectors in developed countries. Pittroff, Cartwright and Kothmann (2002) have argued that in extensive systems, as exemplified by much of the world’s grazing land, the opportunity for genetic improvement is much limited. Hammond (1947) stated that, in general, variability in quantitative characters is greatest under good nutritional conditions. Many grazing systems offer relatively low levels of nutrition, and animals may undergo annual cycles of weight gain and loss. In such circumstances, rates of reproduction are often limited by nutrition. Attempts to improve productive traits, such as milk yield or growth rate, may exacerbate the low levels of reproduction because of negative phenotypic correlations between these productive traits and reproductive traits, even although there may be no genetic correlation (Baptist and Carles, 1989). Thus, attempts to increase traits such as milk yield or growth rate in environments that offer relatively low levels of nutrition usually result in reduced reproductive success. Reproductive traits usually have low levels of heritability, and so attempts to improve them genetically are usually limited.

A further complicating factor is the variability in the environment in many grazed systems, even within a single location. Intra- and inter-annual variations in climate result in variability in the level of nutrition. The genetic ranking of animals that have been selected in one environment often changes in another, less favourable environment. Even at a single site, the effect of genotype ´ environment interactions can be important (Wright et al., 1994).

There may be cases where genetic selection for disease resistance may be important, and could yield important benefits, but the interaction with other production traits will always need to be considered (Vagenas et al., 2002).

It is not clear at this stage what role transgenics may play in the future. There is considerable public resistance to the introduction of transgenic crops, especially in Europe. Research on transgenic livestock has, to date, mainly been focused on the production of animals with the ability to express novel proteins in their milk for pharmaceutical use. Whether transgenic livestock will be acceptable in the food chain has yet to be tested, but given the limitations to genetic improvement in extensive grazing systems, discussed above, it is unlikely that transgenic technology in livestock will have an impact on the production of meat and milk from grassland in the next couple of decades.

Genetic improvement of plants

Advances in plant breeding have the potential to both increase productivity and improve the environmental impact of grassland-based systems. The development of varieties of grass with higher water soluble carbohydrate concentrations, for example, can lead to a better ratio of nitrogen and energy yielding compounds in the rumen. This can result in higher levels of production, increased efficiency of nitrogen use and reduced nitrogen excretion (Miller et al., 2001). Transgenic technology could play an important part in the future, by allowing the introduction of genes into forage plants that confer traits that make them more suitable for harsh environments. The introduction of genes that enhance drought tolerance or cold tolerance (Thomas, 1997) could potentially have beneficial implications for livestock production from grassland.

Animal nutrition

One of the keys to the more efficient and sustainable production of meat and milk from grass-based systems is a better understanding of the nutritional resources available to grazing animals. While much is known about the way in which ruminants utilize nutrients for conversion to meat and milk, based on several decades of research (e.g. NRC, 1996; ARC, 1980), there are large gaps in our knowledge of the nutritional value of much of the world's grazing resources, especially tropical forages. Although conceptual models of diet selection have been developed (O'Reagain and Schwarz 1995), in practical terms it is extremely difficult to predict both the quantity and the composition of the diet that grazing animals will select when faced with a complex array of plants. This lack of understanding and predictive ability represents a major limitation to the development of more efficient grazing systems. For temperate systems, based on relatively simple monocultures of ryegrass or simple mixtures of a few plant species, some progress has been made in the past two decades in understanding these complex plant-animal relationships, leading to the development of predictive models, but for much of the rest of the world’s grasslands, such predictive models do not exist.

Grazing management

The increasing global demand for meat and milk, environmental concerns about the sustainability of intensive production systems and, in the western world at least, issues of food quality, safety and animal welfare are increasingly having an impact on the buying patterns of consumers. These factors, coupled with the fact that grass is a relatively cheap source of feed for ruminants and that grassland-based systems are seen as being environmentally sustainable and ‘welfare friendly’, suggest that there is considerable scope for the continuing production of meat and milk from grass-based systems. However, there is a real challenge to develop production systems that maximize the utilization of grass per unit of animal product, commensurate with sound environmental practice. This necessitates developing grazing management systems that maximize the use of grass and forage in the diet of animals.

The main aim of grazing management is to convert forage resources to animal products such as meat and milk, in the most efficient way possible. To achieve this, it is necessary to supply the animals with high quantities of high quality forage to ensure acceptable levels of animal performance. It is also important to ensure that the herbage is utilized effectively, with low levels of wastage. All this must be done within the context of sustainable farming systems, to ensure that the grazing resources are maintained and that the management practices to not have unacceptable deleterious impacts on the environment, in terms of soil, water, air and wildlife habitats.

At one level there are few management options available to managers for the management of grazing systems. The basic factors that can be altered by grazing management are (i) the species of livestock, (ii) the timing or seasonality of grazing, and (iii) the grazing pressure. The distribution of animals on grasslands is often quoted as an important factor, but as pointed out by Walker and Hodgkinson (1999), it can be affected by the three factors already mentioned. In practice, there are a multitude of ways in which these three principle factors can be manipulated, and grazing research has focused on how their manipulation affects both plants and animals.

In temperate regions, grassland systems are usually part of a mixed grassland-arable rotation or based on permanent pasture. The grass species, especially those used in sown swards, usually have relatively high nutrient contents, especially if they are grazed before the formation of seed heads (Frame, 1992). For example, if perennial ryegrass is defoliated regularly, the sward can be maintained in a vegetative state by continuous grazing, with a high dry matter digestibility. However, growth is often limited by low temperatures in winter and may often cease for six months or more in winter. In such situations the aim of grassland management is to maximize the utilization of grazed grass in summer, while ensuring sufficient grass can be conserved as hay or fodder to feed the herd or flock in winter.

The level of performance achieved by grazing livestock is primarily a consequence of their daily level of herbage intake. Efficient grazing systems should, therefore, aim to maximize the intake of grass by grazing cattle. In temperate swards, of relatively high digestibility, intake is not constrained by the digestibility of the diet and it is the three-dimensional structure of the sward canopy that determines the size of a grazing bite, and therefore, to a large extent, daily intake. The sward structural characteristics that determine bite size have been the subject of considerable research effort, and factors such as the bulk density of the grazed horizon, leaf-to-stem ratio, green leaf mass and the height of the pseudostem have all been implicated in determining bite size (Rook, 2000). However, many of these variables are highly correlated in a temperate sward, and they are often correlated with sward height. Sward height is therefore a simple measure that is related to daily herbage intake. When cattle grazed continuously on a perennial ryegrass dominated sward, maximum daily intake of herbage was achieved at a sward height of about 10–11 cm (Figure 7.2). At heights of below 10–11 cm, intake is progressively reduced (Wright, 1988), and this is reflected in the liveweight gain of the animals. Maximum liveweight gain of continuously grazing beef cows and growing/finishing cattle occur at sward heights of 8–10 cm. Above that height, liveweight gain decreases because of the reduction in the digestibility of the herbage, especially in late summer (Wright and Whyte, 1989; Swift et al., 1989). For sheep, the maximum intake on perennial ryegrass dominated swards is around 4–6 cm (Figure 7.3).

Figure 7.2 The herbage intake of beef cows continuously grazing swards of different height.
Source: From Wright, 1988.

Table 7.5 Target sward heights (cm) for cattle and sheep grazing perennial ryegrass-dominated pasture.


 

Continuous stocking

Rotational grazing

 

Early summer

Late summer

(post grazing height)


Dairy cows

7-8

10-12

8-10

Growing/finishing cattle and beef cows

7-8

10-12

7-10

Sheep

4-6

6-8

-



Source: From Mayne et al., 2000

Figure 7.3 The herbage intake of ewes grazing swards of different heights.
Source: From Penning et al., 1991.

This sward height information has been used to develop target sward height profiles for dairy cows (Mayne, Wright and Fisher, 2000), beef cattle (Wright, 1988) and sheep (Maxwell and Treacher, 1987) (Table 7.5). In spring, beef cattle should be turned out to pasture before sward height reaches 8 cm. If turnout is delayed until sward height is over 8 cm, it can be difficult to control sward height thereafter, because of high rates of herbage growth. In spring and early summer it is important to keep the sward surface height of continuously grazed swards to 7–8 cm because above that height there is increased development of flower heads in grass and this leads to a reduction in the digestibility and feeding value of the grass. Once the risk of seed head development has passed, then sward height can be allowed to increase to 10–12 cm in late summer. The same heights are recommended for mixed grass/white clover swards, although the clover component may benefit from a rest period followed by a conservation cut.

In New Zealand, mixed grass/white clover (Trifolium repens) swards have been central to the development of the pastoral agricultural industry. As concern grows about the impact of nutrient surpluses on surface water and groundwater, there is increased interest in the use of legumes in pasture in areas that have in recent decades relied on the application of high levels of nitrogen fertilizer Mixed grass/white clover swards are becoming more common, and offer considerable potential. In the United Kingdom, up to 280 kg nitrogen ha-1 year-1 can be fixed by white clover in a mixed grass/white clover sward (Cowling, 1982), although a more usual figure might be 200 kg, and mixed grass/white clover swards with about 30 percent white clover can produce the same amount of herbage as all-grass swards receiving 200 kg nitrogen fertilizer ha-1 year-1 (Morrison, 1981). Incorporation of white clover into a sward can improve the nutritive value of the pasture, with increased intake and nutrient supply, especially protein (Ulyatt, et al., 1980). Levels of animal performance are generally higher on grass/white clover swards than on all-grass swards (Davies and Hopkins, 1996) and Clark and Jans (1995) suggested that for each 10 percent increase in white clover in the sward, milk yield from dairy cows increases by 0.30–0.45 kg per day. Management systems based on mixed grass/white clover swards are being developed for environments where white clover is at the limit of its environmental range (Sibbald et al., 2002) and mixed grass/legume systems will probably play a more important role in temperate grassland systems in the future. Several other legumes, such as red clover (Trifolium pratense) and birdsfoot trefoil (Lotus corniculatis) are currently being studied (Wilkins and Jones, 2000). Alfalfa (Medicago sativa) already plays a very important role as a source of conserved forage in many parts of the world.

The level of production of meat and milk from the arid grazing systems of the world is severely limited by climatic conditions. The levels of production rarely exceed that which can support subsistence levels, and the main grazing management tool is mobility of herd or flocks in response to the high spatial and temporal variability in rainfall. Herders move their animals, following water and pasture resources.

In semi-arid grazing systems, the level of biomass production is higher, although the stocking density is still relatively low. Traditionally, these areas have been grazed extensively by nomadic pastoralists, producing a range of meat, milk and fibre products, moving their animals seasonally. Where sedentarization of the population has occurred, this has often led ultimately to an increase in the stocking rate, sometimes stimulated by the ability to produce fodder for feeding during the dry season and an increase in the grazing pressure to the extent that the rangeland resources have become locally degraded.

The benefits of mobility in semi-arid grazing systems have been dramatically illustrated in Central Asia. In Kazakhstan, forced sedenterization of the nomads in the 1930s during collectivization in the Soviet Union led initially to a massive decline in animal numbers, due to starvation, as the animals were not moved to the traditional winter grazing areas. Gradually a form of centrally-organized flock mobility was re-introduced, with each collective having access to large areas of seasonally grazed pastures. At the break up of the Soviet Union sheep numbers collapsed in those countries where agriculture was p rivatized in the early 1990s, e.g. Kazakhstan (Behnke, 2003). Farmers did not have the resources to move their flocks to the traditional seasonal grazing areas and so most animals spent all year grazing around the villages, putting considerable pressure on the vegetation within 5–10 km of the village. Recently, larger farmers have started to become mobile and to move their flocks seasonally. These farmers have the resources, e.g. a truck and the ability to pay hired labour, to move their flocks of 300 or more. The benefits of doing so are twofold. The flocks that move seasonally incur much lower winter feed costs than those that stay around the village all year (US$ 0.24 compared with US$ 0.78 per sheep). The sheep in the mobile flocks also gain weight over winter (+3.7 kg) compared with a weight loss (-10.8 kg) in the non-mobile flocks (Kerven et al. 2003). These differences demonstrate dramatically the benefits, from a production efficiency perspective, of flock mobility in these semi-arid systems.

Conservation of forage

Forage conservation will continue to play an important role in meat and milk production in some parts of the world to overcome seasonal shortages of feed supply. Forage can be conserved as hay, where weather conditions are such that the probability of rain occurring is relatively low. In higher rainfall areas, advances in silage-making technology in the past few decades have allowed a huge increase in the amount of silage made.  For example, in the United Kingdom from 1970 to 1994, the amount of conserved fodder produced doubled from 8.2 to 16.3 million tonnes of dry matter .with a sixfold increase in the amount of silage produced and a halving of the amount of hay made (Wilkinson, Wadephul and Hill, 1996). In Western Europe, about 70 percent of the fodder conserved is in the form of silage (Wilkins and Stark, 1992).

Recent advances in silage technology have included (i) the development of machinery, including mower design, conditioning and chopping equipment, and for producing big bale silage; (ii) the development of a range of chemical and biological additives to enhance and encourage fermentation; (iii) enhancement of silo design to reduce aerobic fermentation and effluent losses; and (iv) feeding technologies to reduce secondary fermentation.

While the costs per hectare of producing hay tend to be lower than for silage, the cost per unit of dry matter of fodder are similar because of higher yields of silage, related in part to lower field losses (Wilkins, 1990).

Future developments in silage making technology are likely to include the development of more effective inoculants, possibly by genetic engineering to produce lactic acid bacteria that can use a wider range of substrates, including cellulose. It may also be possible to breed varieties of grass that are particularly suited for ensiling, with, for example, a higher sugar content and lower protein degradation (Merry, Jones and Theodorou, 2000). 


Organic meat and milk production

In developed countries, where many consumers have high levels of disposable income, consumer concerns about food safety and quality and the environment have led to an increase in the production of organic or ‘biological’ farming. A simple definition of organic farming has eluded practitioners, commentators and scientists. As pointed out by Lampkin (1990), organic farming has often been defined by stating what it is not, but, as he points out, definitions such as ‘farming without chemicals’ misses out several key characteristics that are of fundamental importance. The most comprehensive definition of organic farming is provided by the guidelines to which producers have to adhere to qualify as ‘organic farming’. Internationally, standards for organic farming are set by the International Federation of Organic Agriculture Movements. These standards are then interpreted by certifying authorities in different countries, taking account of local conditions and customs. Thus the precise standards may vary. For ruminant livestock production, the key standards are that no soluble mineral fertilizers can be used, animals may not be treated routinely with drugs, and there must be a minimum level of forage in the diet. The proportion of organic meat and milk sold in developed countries is increasing, partly due to an increase in the demand, but also in some cases partly due to financial incentives from governments to persuade farmers to convert production systems from conventional to organic because of the environmental benefits. The proportion of organic meat and milk production varies hugely in different countries, and although the market is increasing, it is not clear to what extent it will continue to do so.

The level of individual animal performance achieved in organic meat and milk systems is comparable to that in conventional systems, but the stocking rates are generally about 80 percent of those of conventional systems (Wright, Zervas and Louloudis, 2002). Thus because of the lower output per hectare, to be financially competitive with conventional systems the price for organic products must be higher than that for conventional products. For example, Figure 7.4 shows that for a beef production system in the United Kingdom, the price of organically produced beef must be at least 23% more than that of conventionally produced beef if the gross margins are to be comparable. While such premiums can be obtained, it is not clear if these can be sustained in the long term. While the price of organic milk in the United Kingdom is approximately 60 percent higher than conventional milk, the market may have reached saturation, as it is increasingly difficult for new organic producers to find a market.

Thus, while extensive production of meat and milk from extensive grassland systems are amongst the easiest to convert to organic production, because the levels of input have traditionally been relatively low, the long-term prospects for organic systems are not clear. As there is continued pressure to ensure that all livestock systems, and agriculture in general, develop in a way that has minimal environmental impact, the difference between organic and conventional systems may become less and so the growth in demand for organic products may slow.

Conclusions

There is considerable opportunity for producers of meat and milk to benefit from a number of future developments. In the developed world there is a real prospect that milk and meat, particularly from grassland-based systems, will increasingly be seen as an important component of a healthy human diet. Although this is not likely to result in significant increases in consumption, it may result in a stabilization of consumption. The projected increase in global demand potentially could result in opportunities for producers in developing countries. Whether they can take advantage of these opportunities will depend on a number of factors. These include the degree to which trade in meat and milk is liberalized and the extent to which markets are opened up. While there is a general move towards the reduction and removal of import tariffs, there may be a number of non-tariff barriers that prevent trade in agricultural products. These include sanitary standards, animal health and welfare requirements, and product quality and traceability (Holden, 2002). The increasing concerns about the environmental impact and animal welfare standards of intensive livestock production systems may provide increasing opportunities for the marketing of animal products from grass-based systems, which are seen by consumers as being more benign environmentally and offering a higher standard of animal welfare.

Figure 7.4  The effect of organic price premium on the gross margin from beef production.
Source: From Wright, Zervas and Louloudis, 2002.

References

ARC [Agricultural Research Council].  1980.  The nutrient requirements of ruminant livestock. Slough, UK: Commonwealth Agricultural Bureaux.

Ahmed, R. & Gruhn, P.  1995.  Selected issues in the supply of and demand for red meat and poultry products in developing countries. In: R.T Wilson (ed). Supply of livestock products to rapidly expanding urban populations. Proceedings of the joint FAO/WAAO/KAAS symposium, Hoam Faculty Club, Seoul National University, Seoul, Korea, 16-20 May 1995. FAO, Rome.

Banni, S. & Martin, J.C.  1998.  Conjugated linoleic acid and metabolites. pp. 261–302, in: J.L. Sebedio and W. Christie (eds). Trans fatty acids in human nutrition. Dundee, UK: The Oily Press.

Baptist, R. & Carles, A.B.  1989. How can litter size affect wool production with zero genetic and phenotypic correlations? pp. 124–130, in: Proceedings of the Small Ruminant Collaborative Research Project Workshop. Nairobi. VII,

Behnke, R.H.  2003.  Reconfiguring property rights and land use in pastoral Kazakstan. In: C. Kerven and S. Akiner (eds). Prospects for Pastoralism in Kazakstan and Turkmenistan: From State Flocks to Private Farms. Routledge Press (in press).

Behnke, R.H. & Scoones, I.  1993.  Rethinking rangeland ecology: Implications for rangeland management in Africa. pp. 1–30, in: R.H. Behnke, I. Scoones and C. Kerven (eds). Rangeland Ecology at Disequilibrium. London: Overseas Development Institute.

Clark, D.A. & Jans, F.  1995.  High forage use in sustainable dairy systems. pp. 497–526, in: M. Journet, E. Grenet, M.-H. Farce, M. Theriez and C. Demarquilly (eds). Recent Developments in the Nutrition of Herbivores. Proceedings of the VIth International Symposium on the Nutrition of Herbivores. Paris: INRA Editions.

Cowling, D.W.  1982.  Biological nitrogen fixation and grassland production in the United Kingdom. Philosophical Transactions of the Royal Society of London, Series B, 296: 397–404.

de Haan, C. Steinfeld, H. & Blackburn, H.  1997.  Livestock and the environment. Finding a balance. European Commission Directorate General for Development.

Delgado, C., Rosegrant, M., Steinfeld, H., Ehui, S. & Courbois, C.  1999.  Livestock to 2020: the Next Food Revolution. IFPRI Food, Agriculture and the Environment Discussion Paper, No. 28. International Food Policy Research Institute, Washington DC.

Davies, D.A. & Hopkins, A.  1996.  Production benefits of legumes in grassland. pp. 234–246, in: D. Younie (ed). Legumes in Sustainable Farming Systems. British Grassland Society Occasional Symposium No. 30.

Department of Health.  1994.  Nutritional aspects of cardiovascular disease. Report on health and social subjects, No. 46. London: HMSO.

Enser, M., Hallet, K.G., Hewitt, B., Fursey, G.A.J., Wood, J.D. & Harrington, G.  1998.  Fatty acid content and composition of UK beef and lamb muscle in relation to production system and implications for human nutrition. Meat Science, 49: 323–341.

Fernandez-Giminez, M.E. & Allen-Diaz, B.  1999.  Testing non-equilibrium models of rangeland vegetation dynamics in Mongolia. Journal of Applied Ecology, 36: 871–885.

Frame, J.  1992.  Feeding value of grass. pp. 146–160, in: Improved Grassland Management. Ipswich, UK: Farming Press.

Gilmanov, T.G.  1995.  The state of rangeland resources in the newly independent states of the former USSR. pp. 10–13 (Vol. 2), in: N.E. West (ed). Rangelands in a Sustainable Biosphere. Proceedings of the Fifth International Rangeland Congress. Denver CO: Society for Range Management.

Global Livestock CRSP.  2001.  Role of animal source foods to improve diet quality and growth and cognitive development in Kenyan school children. pp. 77–90, in: Global Livestock CRSP Annual Report 2001. Davis CA: University of California.

Hammond, J.  1947.  Animal breeding in relation to nutrition and environmental conditions. Biological Review of the Cambridge Philosophical Society, 22: 195–213.

Hlukik, J.G. & Smith, T.R.  1988.  Economics of pasture systems. Proceedings: Pasture in the Northeast Region of the United States. NRAES-36. Cornell University, Ithaca, New York.

Hodgson, J.  1990.  Grazing Management: Science into Practice. Harlow, UK: Longman.

Holden, S.  2002.  How do trade regimes make livestock producers vulnerable? pp. 7–8, in: Responding to the Increasing Global Demand for Animal Products. Penicuik, UK: British Society of Animal Science.

Illius, A.W & O’Connor, T.G.  1999.  When is grazing a major determinant of rangeland condition and productivity? pp. 474–476, in: D. Eldridge and D. Freudenberger (eds). People of the Rangelands. Building the Future. Proceedings of the VI International Rangeland Congress. Townsville, Australia, 19–23 July 1999.

Kerven, C., Alimaev, I., Behnke, R., Davidson, G., Franchois, L., Malmakov, N., Mathijis, E., Smailov, A. Temirbekov, S. & Wright, I.  2003.  Retraction and expansion of flock mobility in Central Asia: Costs and Consequences. pp. 543–556, in: Rangeland in the New Millennium. Proceedings of VII International Rangeland Congress. Durban, South Africa, 28 July–1 August 2003.

Lampkin, N.  1990.  Organic Farming. Ipswich, UK: Farming Press.

Mayne, C.S., Wright, I.A. & Fisher, G.E.  2000.  Grassland management under grazing and animal response. . pp. 247–291, in: A. Hopkins (ed). Grass, its Production and Utilization. 3rd ed. Oxford, UK: Blackwell Science.

Maxwell, T.J. & Treacher, T.T.  1987.  Decision rules for grassland management. pp. 67–78, in: G.E. Pollot (ed). Efficient sheep production from grassland. British Grassland Society Occasional Symposium, No. 21.

Merry, R.J., Jones, R. & Theodorou, M.K.  2000.  The conservation of grass.  pp. 196–228, in:  A. Hopkins (ed). Grass, its Production and Utilization. 3rd ed.. Oxford, UK: Blackwell Science.

Miller, L.A., Moorby, J.M., Davies, D.R., Humphreys, M.O., Scollan, N.D., Macrae, J.C. & Theodorou, M. K.  2001.  Grass and Forage Science, 56: 383–394.

Morrison, J.  1981.  The potential of legumes for forage production. pp. 1.1–1.9, in: Legumes and Fertilizers in Grassland Systems. British Grassland Society, Winter Meeting 1981.

Mowle, A. & Bell, M.  1995.  Rural policy factors and land use change. pp. 165–182, in: M.B. Usher and D.B.A Thompson (eds). Ecological Change in the Uplands. Special Publication No. 7 of the British Ecological Society. Oxford, UK: Blackwell Scientific Publications.

NRC (National Research Council).  1996.  Nutrient requirements of beef cattle. 7th edition (revised). Washington DC: National Academy Press.

Nolan, A.J., Hope I. & Scott, R.  2002.  Rapid assessment of grazing and trampling impacts on upland habitats.  In: The Macaulay Institute Annual Report 2001.  Macaulay Institute, Aberdeen, United Kingdom.

O'Reagain, P.J. & Schwartz, J.  1995.  Dietary selection and foraging strategies of animals on rangeland. Coping with spatial and temporal variability. In: M. Journet, E. Grenet, M.-H. Farce, M. Theriez and C. Demarquilly (eds). Recent Development in the Nutrition of Herbivores. Proceedings of the VIth International Symposium on the Nutrition of Herbivores. Paris: INRA Editions.

Penning. P.D., Parsons, A.J., Orr, R.J. & Treacher, T.T.  1991.  Intake and behaviour of responses by sheep to changes in sward characteristics under continuous grazing. Grass and Forage Science, 46: 15–28.

Pittroff, W., Cartwright, T.C. & Kothmann, M.M.  2002.  Perspectives for livestock on grazinglands. Archivos Latinoamericanos de Producción Animal, 10: 133–143.

Riordan, N., Cowan, C. & McCarthy, M.  2002.  Safety of Irish beef – concerns, awareness and knowledge of Irish consumers. Journal of Food Safety, 22: 1–15.

Rook, A.J.  2000.  Principles of foraging and grazing behaviour. pp. 229–246, in: A. Hopkins (ed). Grass, its production and utilisation. Oxford, UK: Blackwell Science.

Sibbald, A.R., Maxwell, T.J., Dalziel, A.J.I. & Agnew, R.D.M.  2002.  The implications of controlling grazed sward height for the operation and productivity of upland sheep systems in the UK. 5. The effect of stocking rate and reduced levels of nitrogen fertilizer. Grass and Forage Science, 57: 33–47.

Stolte, A.M., Nolan, A.J., Brewer, M.J., Duff, E.I, Elston, D.A. & Henderson, D.J.  2004.  Rapid assessment of grazing and trampling impacts over large areas of rangeland; a sampling approach. Biological Conservation (in press).

Skarpe, C.  2000.  Desertification, no-change or alternative states: Can we trust simple models of livestock impact in dry rangelands? Applied Vegetation Science, 3: 261–268.

Swift, G., Lowman, B.G., Scott, N.A., Peebles, K., Nelson, D.R. & Hunter, E.A.  1989.  Control of sward surface height and the growth of set-stocked finishing cattle. Research and Development in Agriculture, 6: 91–97.

Thomas, H.  1997.  Plants for all seasons. IGER Innovations. Institute of Grassland and Environmental Research, Aberystwyth, UK.

Ulyatt, M.J., Beever, D.E., Thomson, D.J., Evans, R.T. & Haines, M.J.  1980.  Measurement of nutrient supply as pasture. Proceedings of the Nutrition Society, 39: 67A.

United Nations.  1995.  World Urbanization Prospects: the 1994 Revision. United Nations, New York.

UNEP [United Nations Environment Programme].  1992.  Status of Desertification and Implementation of the United Nations Plan of Action to Combat Desertification. UNEP, Nairobi.

USDA [United States Department of Agriculture].  1988.  Second RCA Appraisal: Soil, water and related resources on non-federal land in the US. Analysis of condition and trends. Natural Resource Conservation Service, Washington DC.

Vagenas, D., Jackson, F., Russel, A.J.F., Merchant, M., Wright, I.A. & Bishop, S.C.  2002.  Genetic control of resistance to gastro-intestinal parasites in crossbred cashmere goats: responses to selection, genetic parameters and relationships with production traits. Animal Science,
74: 199–208.

Walker, J.W. & Hodgkinson, K.C.  1999.  Grazing management: new technologies for old problems. pp. 424–430, in: D. Eldridge and D. Freudenberger (eds). Proceedings of the VI International Rangeland Congress. Townsville, Australia, 19–23 July 1999.

Ward, A.T., Wittenberg, K.M., Froebe, H.M., Przybylski, R. & Malcolmson, L.  2003.  Fresh forage and solin supplementation on conjugated linoleic acid levels in plasma and milk. Journal of Dairy Science, 86: 1742–1750.

Westoby, M., Walker, B. and Noy-Meir, I.  1989.  Opportunistic management for rangelands not at equilibrium. Journal of Range Management, 42: 131–138.

Wilkins, R.J.  1990. Grass utilisation for animal production. pp. 22–34 (Vol. 1), in: Soil-Grassland-Animal Relationships. Proceedings 13th General Meeting of the European Grassland Federation. Banska Bystica, June 1990.

Wilkins, R.J.  2000.  Grassland in the twentieth century. IGER Innovations. Institute for Grassland and Environmental Research, Aberystwyth, United Kingdom.

Wilkins, R.J. & Stark, B.A.  1992 Silage in Western Europe. Second Edition. Canterbury, UK: Chalcombe Publications.

Wilkins, R.J. & Jones, R.  2000.  Alternative home-grown protein sources for ruminants in the United KingdomAnimal Feed Science and Technology, 85: 23–32.

Wilkinson, J.M., Wadephul, F. & Hill, J.  1996.  Silage in Europe. Lincoln, UK: Chalcombe Publications.

Wright, I. A.  1988.  Suckler beef production. pp. 51–64, in: J. Frame (ed). Efficient Beef Production from Grassland. British Grassland Society Occasional Symposium, No. 22.

Wright, I.A., Jones, J.R., Maxwell, T.J., Russel, A.J.F. & Hunter, E.A. 1994. The effect of genotype ´ environment interactions on biological efficiency in beef cows. Animal Production,
58: 197–207.

Wright, I.A. & Whyte, T.K.  1989.  Effects of sward height on the performance of continuously stocked spring-calving beef cows and their calves. Grass and Forage Science, 44: 259–266.

Wright, I. A., Zervas, G. & Louloudis, L.  2002.  The development of sustainable farming systems and the challenges that face producers in the EU. pp. 27–37, in: I. Kyriazakis and G. Zervas (eds). Organic Meat and Milk from Ruminants. EAAP Publication, No. 106. Wageningen, The Netherlands: Wageningen Academic Publishers.

Zhong, M.  1993.  Inner Mongolia grassland resources and its management. In: Proceedings of International Symposium on Grassland Research. Huhehot, China.


1Macaulay Institute, Craigiebuckler, Aberdeen, AB15 8QH, Scotland, United Kingdom