LSIRD NAPLIO CONFERENCE PAPERS

Identifying biological constraints acting on livestock systems in marginal areas

I A Wright

Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen, AB15 8QH, United Kingdom

Summary

There is a huge diversity of livestock systems in marginal areas, producing milk, meat, wool and hides from a large number of breeds of cattle, sheep and goats. Those systems all, however, rely to a large extent on pasture resources to supply most of the feed. Because of the seasonality of pasture growth in marginal areas both the quantity and quality of herbage available can limit the level of nutrition to livestock. In northern Europe pasture production ceases in winter due to low temperatures, while in southern Europe high temperature and lack of rainfall limit pasture growth in summer. Variability of rainfall between years is also a major problem in Mediterranean areas. In many marginal areas soil conditions are such as to limit the supply of nutrients to plants. In winter in northern Europe and in summer in southern Europe the nutritive value of herbage available ( in terms of energy and protein) is generally very low and often insufficient to provide animals with even maintenance levels of intake. Often animals have to browse shrubs, which tend to have a low digestibility and a low protein content. In addition many contain secondary plant compounds such as tannins which impair digestion. The low levels of nutrition generally limit the physiological processes of reproduction, lactation and growth, well below the potential achievable by the animals. Management systems have developed which try to overcome some of these difficulties. For example, the annual reproductive cycle in breeding animals is usually manipulated to ensure the time of maximum feed requirements coincides with maximum pasture production, and supplementary feeding can be provided to increase the level of nutrition. Nevertheless the levels of animal performance and total output from livestock systems in the marginal areas of Europe fall considerably below that of comparable systems in more favoured areas.

Introduction

There is no strict definition of marginal areas. However for the purposes of this paper it is assumed that as far as the EU is concerned, marginal areas equate roughly with those areas which have been classified as 'less favoured' by the European Commission in the Less Favoured Areas Directive (EEC, 1975). Briefly, the less favoured areas are those where there are limited possible land uses because of altitude, short growing season, steep slopes, infertile soils and low productivity. These areas are mainly suitable for livestock farming and farming is necessary to protect the countryside. The extent of Less Favoured areas in the twelve EC countries in 1992 is shown in Figure 1.

In the marginal areas there is a huge diversity of livestock systems producing milk, meat, wool and hides from a staggering number of breeds of cattle, sheep and goats. There are however several key features which many of the systems have in common which can be summarised as follows:

1. Most systems depend on pasture resources to supply the majority of feed resources.

2. Pasture production is seasonal.

3. Both the quantity and quality of herbage can limit the nutrient intake of animals.

This paper identifies the main constraints on animal performance and output from livestock systems in marginal areas. It considers the factors which constrain pasture production and quality, how the performance of animals can be limited by nutrition and how some of the limitations can be overcome.

Constraints on plant production

Temperature

Below 5oC the growth of grass species is negligible, and for practical purposes it can be assumed that the number of days that the temperature is above 6oC represents the length of the growing season. Thus in northern Europe there is little grass growth in winter, with the length of the growing season becoming shorter as latitude increases. Figure 2 shows a typical pattern of grass growth in Britain, with growth commencing in March and ending in October. Although the length of the growing season may become shorter further north, the daily rates of growth during summer can be higher because of the greater daylength during the growing season.

Temperature is also influenced by altitude. Research in northern Europe at altitudes of 150 to 680 m above sea level has shown how the annual dry matter yield of grass was decreased by 2% for each 30m rise in altitude (Hunter and Grant, 1971), although the effect did depend on the season. In spring, when temperature was limiting, yields were decreased by 5%, for each 30m rise in altitude, while in autumn the decrease was only 1.8% and in summer the highest yields often occurred at the highest or intermediate levels because of moisture deficits at lower altitudes.

Small changes in the duration of the growing season have been achieved by the breeding of grasses which initiate growth earlier in spring (Davies et al., 1989; Table 1), but the growing season has been altered by only a week or two, although even this can have significant impacts on animal performance.

Table 1. Annual lamb output from an early growing and a standard perennial ryegrass cultivar. (From Davies et al., 19)89

Rainfall

In many marginal areas of Europe pasture growth is limited not by temperature, but by rainfall. In northern and in western Europe, rainfall tends to be relatively uniformly distributed through the year, but in Mediterranean regions, not only is annual rainfall lower, especially in the Eastern Mediterranean, but 70-80% of rainfall occurs during autumn and winter. The lack of rainfall in summer, coupled with the high temperatures which lead to a high potential rate of evapotranspiration leads to summer droughts, which results in a cessation of pasture growth in summer (Figure 3). Another common feature of Mediterranean areas is the variability of rainfall, which in turn results in large inter-annual variation in pasture dry matter production. Table 2 shows the variation in dry matter production from pasture associated with rainfall at three sites in Basilicata in Southern Italy. Over a three year period pasture production varied by 375% at Stigliano, 68% at Bella and 50% at LiFoy associated with differences in rainfall. These data also show how the variation in rainfall has a greater effect in areas where the climate is drier (Stigliano).

Table 2. Variations in annual pasture production in relation to rainfall in Basilicata in Southern Italy (From Fedele et al., 1988).

Soils

The most important soil factor affecting plant production is probably acidity, which also affects nutrient supply (Floate, 1977). In many marginal areas soils are acidic because of the combined effects of the parent material and leaching of anions due to high rainfall. Low pH can be a major cause of slow rates of decomposition of organic matter in soils and hence may limit the cycling of nutrients. Application of lime alone has resulted in pasture dry matter yield increasing from 2000 to 6000 kg dry matter per hectare.

While the application of fertilizers (nitrogen, phosphorus and potassium) in either mineral or organic form can have large effects on plant production the specific response will depend on the particular circumstances relating to soil type, climate and plant species, and may or may not provide an economic response.

In areas of high rainfall and on poorly drained soils with a high clay or silt content it may be difficult to utilize pastures in spring and autumn because of damage caused by the treading and poaching of soils by grazing animals, and the length of the grazing season may be more limited by these factors than by the duration of plant growth.

Animal intake and diet composition

The cessation of pasture growth during part of the year because of either low temperatures or lack of moisture creates an imbalance between the pattern supply of nutrients from pasture and the requirements of livestock, with the carrying capacity of the pasture being much higher during the periods of active growth. Whilst the effects of limited plant growth can be overcome in some cases by ensuring that stocking rates are sufficiently low to allow a build up of herbage for animals to eat during periods of little or no growth, the nutritive value of pasture in winter or during dry periods is usually low. Figure 4 shows the variation in organic matter digestibility of the diet selected over the year by hill sheep grazing indigenous grassland in Scotland. The organic matter digestibility of the diet drops below 0.50 in late winter because of a high proportion of dead material in the diet, and, although it rises to above 0.70 in May, June and part of July, it falls again in autumn. A similar situation occurs in Mediterranean countries, where there is a decline in organic matter digestibility and crude protein content in summer.

In many areas, the vegetation consists not only of grasses and forbs, but there can be a substantial amount of shrub species in the vegetation communities. Shrubs may be better adapted to withstand periods of drought. For example over 2 million ha of land in the Mediterranean region is covered by woody shrubs. In many regions the Kermes oak (Quercus coccifera) is the dominant species. It occupies 0.8 million ha in Greece (Liacos et al., 1980). Figure 5a shows the proportion of browse and grass plus forbes in the diet of goats grazing paddocks with a ground cover of 62% Kermes oak and 20% grasses and forbs. The proportion of browse in the diet declines dramatically in spring and early summer, and then increases again to over 70% by August. These changes in composition result in associated changes in the quality of the diet. The high proportion of browse is associated with low diet organic matter digestibility (OMD) for much of the year (Figure 5b), and only from March to July does OMD reach values of more than 0.50. Similarly the crude protein content is less than 100g/kg DM when the proportion of browse in the diet is high (Figure 5c). The low digestibility of browse is due to the high degree of lignification in these woody species. However many woody plants also contain high concentrations of secondary plant compounds such as tannins which reduce rumen microbial activity. The total tannin content of Kermes oak, for example, is 123-213 g/kg depending on the physiological stage. Such high levels impose severe nutritional penalties on animals consuming these plants.

As well as digestibility constraints which limit the energy supply to animals, there are often limitations on the supply of protein to the animals. A 30kg goat requires approximately 80g of crude protein per kg of dry matter intake. As shown in Figure 5c, the diet selected when grazing a Kermes oak-dominated community can supply little more than maintenance for much of the year, and is insufficient to support pregnancy or lactation.

The level of nutrition is the major determinant of animal performance. If animals are to be productive, either for meat or milk production, then the food supply must be sufficient to sustain the physiological processes of reproduction, lactation and growth as appropriate.

Reproduction

Generally the rate of reproductive performance in ruminants increases as general levels of nutrition increases. In ruminants the probability of a female being barren reduces as the level of body condition and feed intake increases and in sheep and goats, which have the ability to produce more than one offspring per litter, the probability of multiple births increases, although at high levels of body condition lambing rate decreases (Tables 3 and 4). Thus in traditional British hill sheep systems only a small proportion of ewes produce twins and lambing rates are often less than 1.0, while the same breeds might produce 1.6-1.8 lambs per ewe in lowland environments. Nutrition affects reproductive rate by influencing both the ovulation rate and incidence of embryo mortality.

Table 3. Effect of body condition on lambing rate in North County Cheviot sheep (From Gunn, 1983)

Table 4. Effects of direction of change of live-weight at mating on lambing rate in Border Leicester x Scottish Blackface ewes
(From Gunn and Maxwell, 1978).

Once pregnancy is well established, sheep goats and cattle will sustain foetal growth in periods of undernourishment by mobilizing body reserves of energy (stored principally as fat) and to a lesser degree protein (Russel et al., 1968). In some cases animals can become so thin as to jeopardise their own changes of survival, especially in harsh weather conditions.

Lactation

Level of milk production, whether for human consumption or for consumption by offspring, is very sensitive to level of nutrition. However, although lower levels of nutrition result in reduced milk production to some degree, as in pregnancy, lactating animals mobilise body energy and protein to provide nutrients for milk synthesis. The degree to which this occurs depends on the genotype of the animal - females with a high genetic potential for milk yield have a greater propensity to mobilise body reserves to maintain lactation (Table 5).

Table 5. Live-weight change and milk yield in beef cows with a high (Hereford x Friesian) or low (Blue-Grey) milk yield potential (Wright, Russel and Hunter, 1986).

Growth

In addition to reproductive rate and lactational performance being restricted in environments where there are nutritional limitations, clearly the growth rate of young animals is affected, either by level of milk intake in suckling animals, or by the quantity and quality of solid food consumed.

Systems of production

Systems of animal production have evolved in marginal areas in ways which try to overcome some of the limitations imposed by the environment. There are two basic ways in which this can be approached, which are not mutually exclusive. The first is to choose an animal species and genotype which is adapted to the environment and the second is to manage the system in such a way as to modify the environment.

Choice of species and genotype

Smaller animal species, such as sheep and goats, have smaller mouths compared to cattle, and therefore tend to have the ability to be more selective in choosing their diet. Therefore in a plant community where the quality of the food on offer is generally low, smaller animals have an ability to select a better quality diet (Gordon and Illius, 1988). Thus sheep tend to select a diet with a higher digestibility than cattle and can achieve therefore a higher digestible organic matter or metabolisable energy intake (Hodgson and Eadie, 1986). In addition to being less selective, cattle are at a greater disadvantage than sheep when vegetation is scarce and the sward is short. Figure 6 shows how the intake of herbage, relative to the maximum achievable, declines more rapidly in cattle as sward height becomes shorter. These differences explain in part why systems of sheep and goat production tend to have developed in the regions with the poorest quality and quantity of vegetation. In addition, because goats are predominantly browsers, they are better adapted to areas with shrub vegetation.

In addition to selecting the most appropriate species, choice of breed can be equally important. Generally smaller less productive breeds are better adapted to harsher conditions. Attempts to introduce more productive animals into animal production systems without also altering the management system have often failed because the level of nutrition has not been able to support the more productive breeds. Data from Leon Province, Spain shows how a local breed of sheep, the Churra, produces only 90 1 of milk per lactation, while a more productive breed, the Assaf, introduced from Israel, produces 150 1. However the larger and more productive Assaf based has a much lower reproductive rate in these conditions and the result is that the difference between breeds in the amount of milk produced per ewe on the farm is much less than that produced per lactation (Table 6).

Table 6. Production from Churra and Assaf ewes in Leon Province, Spain (A.R. Mantecon, unpublished data)

Modification of the environment

In addition to selecting the appropriate species and breed, management can be used to alter the environment, particularly the nutritional environment. This can be achieved by improving the quality of pasture by grazing control, application of fertilizer or even replacing natural pasture by reseeding with improved plant species. Supplementary feeding can be provided to animals at times of the year when the quantity or quality of pasture is insufficient to support the required level of performance. The ultimate change in the environment can be achieved by removing the animals from the grazing resource and either housing them or moving them to another area, as happens in transhumance systems.

An illustration of the impact of modifying the nutritional environment is provided by the introduction of what became known as the 'two-pasture system' into traditional hill sheep systems in the UK. Figure 4 shows the severe nutritional limitations to production in traditional hill sheep systems because of the low levels of pasture growth, the short growing season and the poor quality of the diet except for a few months in early summer. It was identified that the most severe limitations imposed by nutrition were a) before mating, which limited reproductive rate, b) in late pregnancy when feed requirements were high and lamb birth weight was restricted and therefore lamb mortality was high and c) during lactation when there was a high demand for milk production, which was not being met and therefore ewes were producing low milk yields, lamb growth rate was low and ewes were becoming thin which reduced ovulation rate at the next mating. The stocking rate was limited by the carrying capacity of the pasture in winter (Cunningham and Russel, 1979).

These limitations could be overcome by reseeding a proportion of the hill and using that improved pasture during lactation and before mating. Supplementary feeding was provided in late pregnancy. Figure 7 shows how there was a marked improvement in the quality of the diet under the improved system.

The consequences of increasing the level of nutrition to the sheep and of increasing the level of utilization of pasture was to increase the stock carrying capacity. In the example shown in Table 7, this resulted in an increase in the number of ewes which could be carried from 387 to 683. Individual animal performance increased, with weaning rate increasing from 0.91 to 1.10. The combined effect of increased ewe numbers and increased weaning rates led to a 246% increase in total weight of lambs weaned.

Table 7. Comparison of performance of traditional and two-pasture hill sheep systems in Scotland, UK
(Armstrong, Eadie and Maxwell, 1986).

Comparison of systems

Although some of the constraints which were highlighted earlier in this paper can be overcome to a limited extent, the levels of biological performance which can be achieved from livestock systems in marginal areas tend to be considerably lower than those from comparable systems in lowland areas. Table 8 shows the performance of a sample of beef cow herds in lowland, upland and hill areas of the UK. Although reproductive rate does not vary to any great extent, upland, and especially hill farms, need to provide considerably more feed in winter, and the stocking rates are considerably lower, reflecting the longer duration of the winter feeding period and the lower rate of pasture production.

Table 8. Performance of lowland, upland and hill beef cow herds in the UK (Meat and Livestock Commission, 1994)

Conclusions

The problem of seasonality of pasture production in marginal areas causes major nutritional constraints on animal production systems. The effects of some of those constraints can be reduced by the appropriate choice of species and breed and by using a range of management strategies to improve the level of nutrition. There are, however, limits to the extent to which this can be done, from both an economic and environmental perspective. Compared to lowland areas, marginal areas will always be at a disadvantage. Therefore if livestock systems are to survive in these areas, ways must be found to ensure that these systems generate as much economic activity as possible.

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