CHAPTER 13
BREEDING LIVESTOCK TOR THE FUTURE

by

J.C. Bowman
Director
Centre for Agricultural Strategy
University of Reading
2 Earley Gate
Reading, RG6 2AU
England

Summary

The purpose of livestock breeding is to produce animals with traits which are different from those of animals now used for agriculture. Whatever the objective the breeder will have to form some view about the future structure and requirements of agriculture in 10-20 years in order to determine what changes in livestock performance may be desirable and for which to select.

The future is difficult to predict. A range of possible futures different from the present can be portrayed. Such scenarios give some indication of the requirements for animals in the future. The response of livestock breeders must be to maintain or even increase the range of variability available in domesticated stock. They must also look for ways of increasing the flexibility of their ability to make changes in the types of animals used in agriculture in response to changes in production and market requirements.

Flexibility is much greater if several or preferably many breeds with different charact­eristics are readily available. Such breeds and crosses between them can be substituted for the contemporary breed as circumstances change. Far greater genetic change per unit time can be achieved by breed or crossbred substitution than by within—population selection. The ability to substitute will be enhanced as techniques for genetic storage and multiplication are developed and improved.

In future, with the increase in real cost of some inputs, particularly feed, it may prove more rewarding to concentrate selection on improving the efficiency of production of prime products rather than on their yield alone.

13.1 Introduction

The purpose of livestock breeding is to produce animals with traits which are different from those of animals now available to farmers for the production of livestock products. In particular, the livestock breeder is attempting to provide animals which improve the efficiency of converting inputs to outputs. Specifically the purpose may be to inorease body growth or milk production or egg production per animal, or per unit time, or per unit of feed. It might also be to increase the carrying or pulling capacity of a draught animal. The range of possible objective which the animal breeder may adopt as selection criteria is very considerable. Apart from the obvious ones which are mentioned above, there are others which are not easy to adopt in practice but which nevertheless might make an important contribution to improving livestock production efficiency. Examples of these sort of criteria include the changes in temperament of the animal so that it is easy to handle and, because it more placid it consumes less feed energy. A similar example is that of the whole range of traits related to resistance to disease and tolerance to changes in the climate.

Whatever the objective that has been established as the selection criterion, the breeder will have had to have formed some view about the future structure and requirements of agriculture in order to determine what changes in livestock performance may be desirable, and for which to select. It cannot be stressed too strongly that many selection programmes in progress today have been established with objectives which relate to present physical and economic circumstances. Such selection programmes are probably a complete waste of time and resources for it is almost certain that the circumstances which will prevail when the selected livestock are produced and made available to the commercial animal producer, will be very different from those which prevail today. The livestook breeder must be weaned from the notion that the best guess as to what tomorrow will be like is a reflection of today.

For most of the farm species with which we now deal, and with the reproduction techniques now available, the breeder will need an impression of likely future circumstances of pro­duction and marketing at ten and perhaps twenty years on. From past experience it would be most unwise to assume that the circumstances of agriculture will remain as they are now, by the time the effects of selection have been achieved. The animals with new performance characteristics may prove to be unsuitable to the changed methods of production and market requirements. Herein lies a major problem for the livestock breeder. It is notoriously difficult, indeed almost impossible, to predict the future even in the short—term, so that the breeder may have to be prepared to produce animals suitable for a range of likely pro­duction and market circumstances. As a consequence, the livestock breeder must try to include a substantial element of flexibility into his operations. Selection objectives must be applied so that unpredicted changes in circumstances can be responded to by changing quickly and easily the type of animal used. ThuB, it seems that the conservation of a wide range of genetic variation coupled with the development of a capability to reproduce and multiply quickly and cheaply desirable types of animals, are far more important to the future of animal production than the development of ever more sophisticated forms of within-popul-ation selection.

13.2 Forecasting and the future

It is quite salutary when contemplating the future to consider the past. Animal pro­duction during the last forty years has changed in many ways. Forty years ago the world had a very much smaller population. The pressure on land use was very much less; fossil energy and timber were in comparatively plentiful supply and relatively cheap. Several techniques such as artificial insemination and carcass appraisal of live animals were still very much in their infancy. The application over the past forty years of a very substantial worldwide programme of animal production research, development and extension coupled with a considerable improvement in the ability of farmers to manage livestock, have caused sub­stantial changes not only in the methods of production but also in the performanoe per animal, and in the output per unit of land and other resources. Yields per animal and conversion of feed into animal product have risen on average by between 1 and 3% per year. Not only has production changed but also consumption and the products which the market now requires are different in quality and quantity from those required forty years ago. As part of this enormous evolution of animal production in the world there has been a substan­tial reduction in the variation in the animals available and used for production purposes. The worldwide spread of Freisian/Holstein cows, of Leghorn hens and of Merino sheep, is impressive; but it has also hidden the substantial loss of genetic variation caused by the extinction of many local breeds which have been unable to compete. We shall return to this point later in the paper.

Against the picture of forty years of substantial change in animal production it seems extremely curious that so many livestock breeders assume that the future for which they are breeding their stock will be the same as today. Indeed the evidence suggests that the change of circumstances has been getting faster. Even if we assume that the rate of change will remain the same, we can gain some indication of the prospect over the next twenty years to 2000 A3). Some of the likely changes are already apparent whilst about others there can only be guesses. Predicting tne future is not a worthwhile activity but as has been indicated earlier in this paper it is essential for the livestock breeder to have some appreciation of the future circumstances in which his 'improved' stock will be used by farmers. It is therefore worthwhile to indicate some of the likely changes in input availability and relative cost, changes in the legal and climatic circumstances affecting animal production, as well as potential changes in consumption of animal products which may take place over the next twenty years. This sort of futures consideration leads to the establishment of possible future scenarios for animal production. Such scenarios (Cole et al., 1978} Norse, 1979) should be an essential requirement in establishing selection pro­grammes.

It is not the intention here to write specific scenarios relating to animal production for the year 2000 AD. However, it is the intention to point to some of the changes in important circumstances which may take place. This is done to emphasize the point that flexibility in the availability of animal genetic resources is an essential requirement for the future of animal production.

13.3 Change of circumstances

13.3.1 Economic growth

Economic growth depends partly on non-quantifiable factors including confidence and political constraints upon trade, but some conclusions must be drawn as economic growth has a major impact upon the future path of world evolution. A technique for handling this problem is to postulate a range of growth rates and deduce their implications for other factors. In the same way, alternative scenarios of world development can be contructed from sets of assumptions about political change, particularly as evinced by country group­ings within common markets and blocs. One very important consequence of such groupings is the resultant pattern of world trade. All groups are interdependent for flows of industrial goods, agricultural produce, energy and technical know-how, so their economic growth rates should be related to some extent. Nevertheless, as the level of wealth per head in the developed countries is so much greater than that found in the poorer countries, this latter group must experience much faster growth of GNP per head than the developed countries if the gap between the two is to be reduced. Thus the context of world economic growth can be characterized by the size of this gap: improved worldwide distribution of wealth or deteriorating distribution.

13.3.2 Food trade

At present about one-tenth of total world food production enters world markets. Wheat, accounting for 16% of the total value of food trade, is the major commodity. Most of world food trade is carried on between the developed nations: the EEC, Japan and USSR import more food than all the poor countries and North America, Australia and New Zealand are major suppliers.

FAO has calculated that during the period 1970-1972, 81$ of the world's people lived in countries which were at least 95% self-sufficient in food energy. (The degree of self-sufficiency of a country is, of course, partly determined by its capacity to import: as incomes rise,food may be imported in forms not previously consumed.) The FAO has also made projections for the world food trade over the next 20 years, by extrapolating existing trends (FAO, 1979). A marked trend towards decreasing food energy self—sufficiency is identified as the world's import requirement doubles.

The FAO has suggested that if food production in the developing- nations is stimxilated �to provide a larger share of developed—country consumption, then the foreign exchange generated in the poor countries may be used to pay for the goods of the industrialized world - goods which may be intended for agricultural production or for industrialization. By contrast and at the same time, the dependence of the developing world upon developed country agricultural produce is also expected to increase by the end of this century. If present trend continue, developing country self-sufficiency for cereals will fall from 92% (in 1975) to 80% by 2000; for livestock the predicted fall is from 102% to 76%; and for milk products from 91% to 71$. In the past the developed countries have restricted their production of various products below feasible levels, so there is scope, technically, for improved developed-country food production for export to the poorer countries. To achieve the desired balance of food trade, the FAO suggests that increased agricultural production in the poor countries must be accompanied by restraint in the rich countries with respect to those goods which compete with the developing world produce (e.g. rice), whilst production of those goods which are likely to fall into shortest supply is stepped up (e.g. livestock, milk products).

In order to explore world prospects for food trade and availability by 2000, the FAO study compared the results of trend projections with those of 'normative' projections, based on rates of GNP growth thought to be a feasible maximum for the developing regions. The rates of growth in agricultural output used in the two sections of the study were consequently as shown in Table 13.1.

Table 13.1

Growth rates of gross agricultural production: trend and normative scenarios

Source: FAO, 1979

These growth rates could be met by a continuation of extension of the agricultural area (only half of the world's cultivable land is currently used) by increasing yields, by wider use of existing techniques where applicable, and by the introduction of new technologies and new cropping patterns. If these growth rates for agricultural production are achieved, they would go a long way towards improving the ability of the developing world to provide a larger proportion of its food needs. (Nevertheless, more intensive agriculture might simultaneously increase the developing world's dependence on other countries for the supply of fuels and chemical inputs). Surpluses would exist for some tropical products but large deficits would still exist for cereals and milk products, with falls of 10%. and 13% respect­ively below total requirements by 2000, assuming the 'normative' scenario. Meat production would be approximately in balance with consumption (FAO, 1979). If these growth rates are not achieved, then there will be additional pressures upon population levels and upon the developed countries to provide more food either by aid or trade. In addition, the nutritional value of developing country diets could be expected to fall.

13.3.3 Population

The UN has projected a total world population of about 6.3 billion by 2000 (Atkinson, 1977). This assumes a slightly reduced overall ieveloping-country population growth rate (2.3% as compared with 2.6% in the period 1963-1975) though the African population growth rate is expected to continue to rise, showing a rate of 3.0% for the 1980-2000 period, as compared with 2.6% over the years 1963-1975. Of the world's present 4.3 billion inhabitants, 70% now live in the developing countries; by 2000, this proportion will have increased to about 80%. The developing world will be the origin of 90% of the 2 billion extra population (Campbell, 1979). Another significant change will be seen in the age structure of populations  which will move in different directions in the two sets of countries. Whereas the population of the developed world will, as a result of only 10% increase by 2000, show a trend towards older populations, the population pyramids of the developing countries will have even wider bases than now: the youngest age groups will he the largest. Young populations require more food, and food preferences are not the same as those of older populations. Changing age structures means that both developing and developed worlds will have larger proportions of 'non-active' populations than at present. In the developed world, as one consequence of new industrial technology, there is a reduction in working hours. Some of the increased 'leisure' time may be devoted to home food production.

13.3.4 Incomes and spending power

As incomes rise in developed countries, a very small amount is spent on extra food, as satiety has largely been reached. Instead, the types of food eaten tend to change: the same amount of food energy is obtained from a diet which contains more protein and more fats. In developing countries on the other hand, some increase in food energy intake is likely to result from higher incomes, but as before, there will also be a trend towards consuming more expensive foods further along the food chain, notably animal products. The average income elasticity of demand for food energy of animal origin averaged for all dev­eloping countries is O.58, which may be compared with an elasticity of 0.22 for all food energy in developing countries or 0.24 for food energy of animal origin in the developed countries. There is some likelihood, however, that these trends will change in future: there is already evidence that the populations of developed countries are tending to move away from animal proteins and fats towards a greater proportion of food energy of vegetable origin. This is in response partly to the cost of meat and animal fats, but also to indications that the consumption of high levels of animal products can lead to health problems. Trends showing lower animal product consumption also relate to antipathy to animal production from animal welfare groups. If this trend away from animal foods becomes general, it could have considerable importance for world food regimes: the efficiency of conversion of solar energy to human food would be improved as an intermediate conversion process is removed from the chain: moreover, part of the grain now consumed by livestock would be released for human consumption, thus reducing competition between animals and humans for food. Livestock production would probably continue, nevertheless, at least in situations where difficult climates and topography, or the nature of available feedstuffs, make animals the only feasible product.

13.3.5 Energy

World availability of energy from fossil fuel may be quite different by 2000. Like population, the rate of economic growth will tend to increase energy consumption, most noticeably in the developing countries where consumption is now relatively low. Assuming that consumption of fossil fuels proceeds more or less unchecked, oil and gas are expected to run out by around 2020, though coal supplies will continue to be available for at least a century after that (World Energy Conference, 1978). Thus oil and gas will still be in quite plentiful supply (unless consumption suddenly increases sharply) though the effect of increasing costs may have started to change the pattern of oil consumption - in which case we may expect that it will be the non-industrialized, poor countries which will have most difficulty in paying for oil and, at the same time, most difficulty in funding the development of alternative power sources (sun, wind, nuclear). Thus, around 2000 it seems likely that the developed world will still be able to use energy-intensive methods of food production, but the developing countries (where energy input is now low, so increased inputs would give greater gains than in energy-intensive agriculture) the level of inputs of energy-associated inputs such as fertilizers, machinery and irrigation, will remain low, largely limited by cost.

The general energy picture by 2000 is one of declining energy availability, if not of severe scarcity. It seems inevitable that an increasing number of energy conservation measures will be introduced - measures to improve the efficiency of insulation and power conversion and to control the amount of oil used in non-essential or non-productive ways. Over the period 1954-1980 there has been an annual improvement (reduction) in energy demand of industry by 1.6-2.0%, as a result of conservation measures. If a rate of only 1.4% were maintained until 2000, this would mean a 30% reduction (on present forecasts) in energy demanded by that time (World Energy Conference, 1978). Conservation strategies will be of three types: technical improvement to give greater efficiency of conversion and use; the substitution of new resources (e.g. hydrogen) for declining resources and also changes in lifestyle. Price rises will undoubtedly a major strategy to hasten the acceptance of conservation.

One effect of increasing fossil energy costs is the development of fuels and other chemical feedstocks from crops and biological by-products. Fuel and feedstock cropping using sugar cane, cassava, sorghum and other cereals as well as tree crops, is being pursued in many countries. There are two important consequences for animal production. First the competition for the use of hetter quality arahle land for crops to provide human food, fuels and chemical feedstocks rather than animal feed will intensify. Second, biotechnological methods of deriving fuels and feedstocks from crops will leave substantial quantities of residues (such as the high protein residue from gasohol production from cereals in the USA), which may be suitable for animal feeding.

Research is also underway to produce high yielding short rotation tree crops which could make a substantial contribution to energy and fibre requirements. Tree crops which produce good fibre yields whilst also permitting access to livestock (as in New Zealand) would have the important advantage of reducing competition for land between fuelwood production and agriculture.

13.3.6 Climate

An additional factor which may affect the world's food supply position is the possibility of climatic change. In recent years there have been many occurrences of extreme weather conditions of all kinds (drought, flood, extreme temperatures, etc.) and this has often been interpreted as evidence of a climatic change in process. There is no consensus, however, about the direction in which this change is taking place. In fact, extreme conditions in one part of the world have often been offset by 'opposite' conditions in another region: so prediction of a trend of climatic change is not necessarily appropriate. For agriculture, of course, the effects of extreme conditions cannot be 'offset' against conditions in other regions in the same way as can meteredogical data. Crops will be lost if the average conditions of a region change greatly in any direction, as the crop planted at a site is one which is thought to be best suited to the environmental conditions of that area. Agricult­ural investigation in recent times has concentrated on determining ever more closely the climatic and microclimatic parameters to which a crop is suited and on breeding crops for specific conditions. The 20-year period 1950 to 1970 was a time of what is now seen as unusually stable weather conditions, and it was a period of much plant and animal hreeding. The varieties developed then are unlikely to he ideally suited to more variahle weather conditions. Obviously, species breeding will prohahly continue and new strains better suited to fluctuating weather regimes will probably be developed after a delay. However, species developed to show adaptability to a wide range of climates will often have lower potential yields than those which have been bred to take advantage of well-defined conditions of light, moisture and temperature. Once appropriate species have been bred, the overall significance for food production of changing climates may be quite slight, although regional differences could be very great. For example, if world temperatures were to rise (and world climate zones thus effectively moved northwards) some areas where cold now limits production might improve their output; conversely, regions close to the Equator might suffer more markedly from temperature and moisture stress, as a result of which their productivity per hectare would fall (Lansford, 1975; Lamb, 1977).

13.4 Consequence for animal production

It is quite clear that circumstances affecting animal production will change substantially over the next twenty years but in which direction is not clear. Changes in population, income and world trade patterns all seem to indicate the need for an expansion of animal production to meet an increased demand as outlined by FA0 (1979). However, changes in food preferences caused by changes in relative prices of foods, by changes in the range of foods on offer, including processed vegetable protein with the appearance of animal products, and by social and welfare attitudes to animal products may lead to little if any increase in animal product consumption in total.

Similarly, the predominant changes in animal production methods in recent years have been toward more animals per unit land and per unit labour and with substantial capital invest­ment in buildings and equipment. The production and processing of animal feed has been highly specialized with feed carried to the animal. Will such trends continue or will animal pro­ducers respond to high energy prices and more labour being available by turning to new forms of extensive production? Animal production might be altered to make use of marginal land areas (in competition with trees and water catchment) which are otherwise unsuitable for food production, and to make use of fuel, chemical feedstock and food processing by-products which cannot be consumed directly by humans.

So far there has been little mention of the changes occurring in the food processing industry. Of particular relevance here are the developments in separating milk into its constituent parts and reassembling them in a variety of ways to form conventional and new food products. The processing animal carcasses is being developed so that the less valuable parts can be used in the production of higher value products. These changes may lead to different requirements from processors for the type of animal and animal products purchased from farmers. However, such changes may also lead to less consumer discrimination between genuine animal products and vegetable products masquerading as animal products. The con­sumer will then buy the cheaper vegetable based product.

It is argued that whilst some forms of animal production may decline, the ruminant serves a valuable function of converting crops and residues of no direct food value to man into prime quality protein foods. Even this argument may be of little consequence if bio­technology is developed to carry out the rumen function "in vitro". The animal still retains the advantage in the grazing situation of collecting its own feed from a potentially wide area and from land which may be unsuitable for mechanized crop harvesting. All these considerations point to the development of extensive forms of animal production and on land not suitable for other purposes.

13.5 Meeting market requirements

It is perhaps obvious but nevertheless very important to stress that the prime purpose of animal production is to meet market requirements - the main products for which the prices paid cover the production costs. In past years there has been a tendency to develop and select animals which have had a higher yield of by-products which have incurred a cost in disposal. In future with the increase in real costs of some inputs, particularly feed, it may prove more rewarding to concentrate selection on improving the efficiency of pro­duction of prime products rather than on the yield of prime products (the numerator in the efficiency ratio) alone.

13.6 The genetic response of the future

Whilst much of the research and development effort in animal genetics has been devoted to selection within populations, there has also been much selection between populations (breeds) associated with a careless, indeed wilful, reduction in breeds. The history of domestication is a record of deliberate and savage destruction of genetic variation. How much more flexible could be our response to the future if only the wild populations of cattle and horses still existed. From this history we must learn the lesson that it is essential to conserve the variation now available even if some of the variants are not of immediate commercial significance.

The challenge before us is to develop the means of responding to changes in production and marketing. Though the slow but steady response of 1—2% per year achievable from within population selection has proved valuable in chickens and to a lesser extent in cattle and pigs, this form of genetic improvement alone does not provide the flexibility needed for the future. Flexibility is much greater if several or preferably many breeds with different characteristics are readily available. Such breeds and crosses between them can be substit­uted for the contemporary breed as circumstances change. Par greater genetic change per unit time can be achieved by breed or crossbreed substitution than by within population selection. The ability to substitute will be enhanced as techniques for genetic storage and multipli­cation are developed and improved. Resources devoted to improving these techniques would be better spent than on within-population selection in its present form.

For the future, certain selection objectives need to be examined. These include twinning in cattle, increased appetite in most species, changes in body and tissue composition in meat animals and ability to cope with varied and low quality diets in all farm species. There are exceptional individuals, close to the biological ceiling, in most large populations and these need to be sought out and multiplied using new techniques.

The choice of species which have been domesticated and used for agriculture seems to have been a somewhat haphazard affair. The resources devoted to new domestication have been minimal. The domestication of a presently wild species may well prove less expensive and a quicker response to market needs than trying to convert a domesticated population by within-population selection.

13.7 Conclusion

The future is difficult to predict. A range of possible futures different from the present can be portrayed. Such scenarios give some indication of the requirements for animals in the future. The response of livestock breeders must be to maintain or even increase the range of variability available in domesticated stock. They must also look for ways of increasing the flexibility of their ability to make changes in the types of animals used in agriculture in response to changes in production and market requirements.

13.8 References

Atkinson, L.J. (1977) World population growth: analysis and new projection of the United Nations. United States Department of Agriculture, Foreign Agricultural Economics Report No. 129.

Campbell, K.O. (1979) Food for the future. Lincoln & London: University of Nebraska Press.

Cole, S., Gershuny, J. and Miles, I. (1978) Scenarios of world development. Futures, 10, 3-20.

FAO (1979) Agriculture: toward 2000. Conference Paper C79/24. Rome: PA0.

Lamb, H.H. (1977) Climate and the outlook for society. Optima, 27, 1-17.

Lansford, H. (1975) Weather watchers. Nature, 256, 688-690.

Norse, D. (1979) Scenario analysis in interfutures. Futures, 11, 412-422.

World Energy Conference (1978) World energy: looking ahead to 2020. IPC Scientific & Techological Press.

La sélection animale pour l'avenir
Résumé

Introduction. La sélection animale a pour but de produire des bêtes dont les carac-tères sont différents de ceux du b*tail actuellement utilisé dans 1'agriculture. II peut s'agir d'une manière plus sp*cifique d'accroítre le gain de poids, la production de lait ou d'oeufs par animal ou par unité de temps ou d'alimentation, ou encore d'augmenter la capacité d'une bête de somme ou de trait. Quel que soit 1'objectif, le sélectionneur devra avoir son opinion quant à la structure et aux besoins future de 1'agriculture afin de déterminer les modifications souhaitables des performances du bétail qu'il faudra réaliser par selection. Pour la plupart des animaux domestiques et compte tenu des techniques de reproduction actuellement dieponibles, le sélectionneur devra pouvoir se faire une idée des circonstances probables de la production et de la commercialisation au moins 10 à 20 ans à 1'avance. A en juger d'après 1'expérience, il serait peu sage de tabler sur l'hypothèse que les circonstances entourant l'agriculture resteront les mêmes qu'aujourd'hui. D'ici à ce que les effets de la selection aient pu 8tre obtenus les animaux offrant des aptitudes nouvelles risquent de ne pas convenir aux métthodes de production et aux nouveaux besoins du marché et c'est en cela que résidel'un des principaux problèmes auxquels est confronté le sélectionneur. II est notoirement difficile de préaire I'avenir même à court terme, si bien que le sélectionneur devra peut-être se préparer à produire des animaux adaptìs à toute une gamme de conditions particuliàres en matière de production et de marché. Aussi doit-il s'efforcer d'inclure dans son programme une certaine souplesse. Les objectifs de la sélection doivent être appliqués à tout prix de telle sorte qu'il soit possible, en modifiant le type d'animal utilisé, de faire face rapidement et sans difficulté à des changements de circonstances imprévus.

Les prévisions et I'avenir. S'agissant d'envisager I'avenir, il est tout à fait salutaire d'étudier le passé.La production animale a changé de bien des façons depuis une quarantaine d'ann*es. Non seulement les rendements par animal et la transformation des aliments en produit animal se sont accrus de 1 à 3 pourcent par an, mais de plus les types d'animaux utilisés sont beaucoup moins variés. Les méthodes de production et les produits mis sur le marché ont eux aussi évolué. En supposant que le rythme d'évolution ne ralentisse pas, on peut avoir une indication des perspectives pour les 20 prochaines années jusqu'à 1'an 2000. Certains des ohangements probables sont déjà manifestes, tandis que d'autres relévent d'estimations. L'èvolution du coût relatif des combustibles fossiles, joints à l'énvolution de la microteohnologie, influeront de plusieurs façons sur la production animale. Dans les économies développées, ces changements pourront avoir pour effets directs une réduction de l'équipement et des bâtiments et une augmentation de la main-d'oeuvre. II se peut qu'il y ait aussi des effets moins directs dans le monde entier par suite de la plus grande poussée s'exerçant sur l'utilisation des terres en vue de remplacer l'élevage par les cultures vivriràs et la production de matériaux et de combustibles. Peut-être le bétail sera-t-il do plus en plus nourri avec les sous-produits de cultures vivrlères, étant integré dans des systèmes d'agriculture autonomes où les apports on combustibles fossiles et en minéraux seront minimaux.

Le régime alimentaire des populations du monde entier évolue en accusant dea tendances très différentes selon qu''il s'agit de pays d«veloppés ou de pays sous-développés. Bar ailleurs, il existe dans certains pays tout "un mouvement visant à modifier les normes en matiere d'èlevage et les produits fournis par les industries agroalimentaires. On ne peut préaire I'avenir avec exactitude mais il est possible en revanche d'*tablir une série de scénarios auxquels correspondra vraisemblablement 1'évolution future. On peut conclure de tout ce qui précède que le changement sera la norme et qu'il est fort peu probable qu'un seul type d'animal par espèce devienne universel.

Fatre face aux besoins du marché. Même si c'est évident, il importe néenmoins de souligner que la production animale a pour but essential de répondre aux besoins du marché, le prix payé pour les produits de base devant couvrir le coût de production. Au cours des années passées, on a eu tendance à produire et à sélectionner des animaux offrant un rendement plus élevé de produits de base, mais aussi un rendement plus élevé de sous-produits dont l'écoulement a entraîné des défenses. A l'avenir, eu égard à 1'augmentation du coût réel de certains facteurs de production, en particulier 1'alimentation, il sera peut-être plus valable de centrer la sélection sur 1'amèlioration de la rentabilité des produits de base plutôt qu'uniquement sur leur rendement (le numérateur dans le taux de rentabilité).

la réponge génétique pour l'avenir. Bien qu'une grande partie de 1'effort de recherche et de développement en gétique animale ait été consacré à la sélection au sein des popula­tions, il y a eu égaleraent un important travail de sélection entre populations (races) associé à une réduction déplorable, et parfois voulue, du norabre dee races. D'ailleurs l'histcire de la domestication révèle une destruction délibérée et sauvage de la variation génétique. Avec combien plus de souplesse pourrions-nous faire face à l'avenir si seulement les populations sauvages de bovins et d'équidés existaient encore i L'enseignement qu'on peut tirer de cette histoire, c'est qu'il est indispensable de conserver la variation encore existante, même si certaines des variantee ne semblent pas dans 1'immédiat présenter de 1'importance sur le plan commercial.

Le défi auquel nous devons faire face, c'est de trouver le moyen de répondre aux changements qui interviennent dans la production et la commercialisation. Bien que la pro­gression lente taais constante de 1 à 2 pourcent par an que permet de réaliser la sélection au sein d'une population se soit révélée valable pour la volaille et, à un degré moindre pour les bovins at les porcins, cette forme d'amélioration génétique ne peut à elle seule assurer la souplesse néceosaire pour 'avenir. la souplesse sera d'autant plus grande que l'on disposera aiséraent de omhreuses races dotées de caractéristiqu.es différentes. Ces races et les produits issus de leurs croisenients pourront se substituer à la race du moment à mesure que les circonstances évoluent. Le remplacement d'une race par une autre ou d'un produit de croisement par un autre permet, bien mieux que la sélection au sein d'une population d'obtenir une modification génértique plus forte par unité de temps. Cette possibilité de'substitution 3era renforcée à mesure que seront raises au point et améliorées les techniques de stockage et de multiplication génétiques. II serait plus rentable de consacrer les res-sources à l¹amélioration de ces techniques qu'à la sélection au sein d'une population telle qu'elle s'effectue à 1'heure actuelle.

Il convient d'examiner certains objectifs de sélection pour l'avenir, notamment lc généllité chez les bovins, 1'accroiseement de l'appétit chez la plupart des espèces, la modification de la morphologic et de la composition des tissus chess les animaux de boucherie enfin 1*aptitude à accepter des régimes alimentaires variés et de qualité médiocre pour toutes les espèes domestiques. la plupart des populations à effectifs noobreux comprennent des sujets exceptionnels, proches du plafond biologique, et il y a lieu de les rechercher et d'en assurer la multiplication au moyen de techniques nouvelles.

Il samble que les espèces ont été domestiquées et utilisées en agriculture aient été choisies d' une manière assez fortuite. On n'a consacré que dee ressources minimes à la domestication de nouvelles espèces. Or, il se peut que la domestication d'une espèce actuellement sauvage se révèle moins coûiteuse et réonde plus rapidement aux besoins du marché que la transformation d'un cheptel domestique par sélection au sein d'une population.

Conclusion. II est difficile de préaire l'avenir, mais on peut envisager toute une gamme de posiblitiés qui diffèrent du preéent. De tels scénaris qui seront néceseaires pour l'avenir. Les sélectionneurs de bétail devront réagir en maintenant, voire en élargissant, l'éventail de variabilité' existant chez le cheptel domestique.Ils dovident e'galement rechercher les moyens de pouvoir modifier avec plus de souplesse les types d'animaux utilisés dans 1'agriculture pour faire face à évolution des besoins en matière de production et de commercialisation.

La crìa de ganado para el futuro
Resumen

Introducoión. La crìa de ganado tiene por objeto producir animales da caraotaraa diferentes da loa animalaa qua se utilizan actualmente an la agricultura. Concretamente, al objetivo conaiate an incrementar el crecimiento corporal, aumantar la producóin da lecha o de huavos por animal o por unidad de tiampo o da pianso, o aumantar quizá la capacidad da carga o tracción da un animal de tiro. Cualquiera qua sea el objetivo, el criador tendrá que babersa formado una idea sobre la satruotura y las naoasidadas futuras da la agricultura para podar determiner qua cambios puadan ear daaaables an el randimiento y conformación del ganado y con qua fines conviene seleccionar. En lo que se refiere a la mayor parte de los animales agrlcolaa y oon las técnicas de reproduccióo ahora disponibles, al oriador habrá da taner también una idea da cualaa sarán probablemente las cireunstanoias futuraa de producción y comercialiaación, por lo menos dentro de dies y quizá da veinte anoa. A juzgar por la experiencia del pasado sarìa de lo más aventurado suponer que las circuna-tancias da la agricultura permanecerán tal y como son an la actualidad. Para el momento en que se hayan logrado los efectos de la selección, los animalaa con nuevas características da randimiento puadan resultar inadacuados para los nuevos métodos da producción y las nacesidades del mercado. Este punto constituye un problema fundamental para al ganetista. Como es a todas luces diflcil predecir el futuro aún a oorto plazo, conviene que el oriador esté praparado para producir animales aptos para una saria de cirounstancias probables da producción y mercado. Por ello, el criador debe tratar da incluir un elemento sustancial da flaxibilidad an su programa. Cuaste lo que cueste habrán de aplicarse los objetivos da selección de manera que puadan afrontarse los cambios impravistos de situación nodificado con rapidas y facllidad el tipo de animal empleado.

La previsión y al futuro. Al imaginar el futuro es muy saludable tener en cuenta el pasado. En los últimos 40 amos, la producción ganadera ha cambiado en muchos aspectos. Ho sólo han aumantado los rendimientos por animal y la transformación del pienso en producto animal antra al uno y el tres por ciento anuales, sino que los tipos de animales empleados son mucho manos variados. También ban cambiado los métodos de producción y los productos del mercado. El hecho miamo da suponerggugjjel ritmo de cambio no disminuirá ofrace ya una indicación de las parspaotivas de los/que median de aquí al año 2000. Algunos de los cambios probables son ya evidente otros só1o pueden conjeturarse. El cambio del costo relativo del com­bustible fósil, unido a las innovaoiones en el campo de la microtecnología afectará a la producción ganadera de formas diversas. Los efectos directos sobre las economías desarrolladas pueden sar antra otros una reducción de la maquinaria y edificios y un aumento de la mano de obra. Efectos manos directos para el mundo pueden surgir de una mayor presión sobre la utilisación de la tierra con miras a obtener cultivos alimentarios, Matarialas y oombustible an vas da ganado. El ganado podrá alimentarae cada vas más da subproduotos da otros cultivos alimanticioB y former parte de sistemas agrícolas de auto-auflciencia donda los insumos da combustibles fósiles a inorgánicoa saan mínimos.

La ingestión dietética da loa pueblos del mundo está cambiando con arreglo a tandenciaa muy diversas, que se manifiestan en países desarrollados y an desarrollo. Taunbién existan en ciartos países fuartas movimiantos tendentes a modificar las normas ralativas a una sootacnia acaptable y a la elaboración de los diversos productos animales disponibles. El futuro no puede predecirsa, pero es posible representarse lo que sobre poco más o manos va a suceder probable­mente an los tiempos futuros. La conclusión da todo allo as que el cambio es la norma y que resulta muy improbable que un tipo de animal por especie vaya a sar universalmante adecuado u óptimo.

Satisfacoión de los requisitos del meroado. Aunque es cosa bisn sabida, no •atari da mis insistir an qua la finalidad principal da la produooión animal satiafaoer loa raquisi-toa dal mercado, da suerte y manera qua al precio pagado par los prinoipales productos cubra loa cost os da producción. En años pracadantas, sa ha tandido a dasarrollar y salaocionar animales qua tianan ua alto rendimiento da productos da primera calidad, paro también subproductos cuya oolocaoión o vanta ha resultado bastante oostoaa. £s posibla qua, an lo porvsnir, al aumanto da los costos raalas da oiartos insumos, especialmente da los piensos, hega que rasulta más ramunarativo oonoantrar la selección an la mejora da la aficacia da la producción da productos da primera calidad y no solamente en el randimiento de dichos productos (el numerador de la relación de eficacia).

la respuesta genética para el futuro. Aunqua buena parte de loa traba job de investigación y mejora en materia zoogenética se han dedicado a la selección dentro de las poblaciones, sa ha operado también una selección entre poblaciones (rasas), asociadas a una reducción de las rasas, sea por abandono, sea incluso de propio intento. La historia de la domesticación com-tituye un testimonio de destrucciói deliberada y salvaje de la variación genética. 'Cuánto más flexible podría ser nuestra respuesta al futuro si existieran aún las poblaciones salvajes de ganado vaouno y caballarl De esta historia nemos de aprender una lección, y as que resulta esencial conservar la variedad ahora disponible, incluso si algunas de las variantes no tianan una importancia comercial inmediata.

El desafío a que hemos de hacer frante consiste en desarrollar los medios para res-ponder a los cambios en materia de producción y oomeroialización. Aunque la respuesta lenta pero oonstante del 1-2 por ciento al año, que puede lograrse mediante el sistema de la selección interna de la población, ha resultado valioso an las aves de corral y en manor grado para el ganado vacuno y para el porcino, esta forma de mejora genétioa por sí sola no ofrece la flexibilidad que el futuro requiere. La flexibilidad es mucho mayor si se dispone ya de diversas o, preferentemente de muchas razas con diferentes caracterlstioas. Dales rasas y los crusamientos entre ellas pueden reemplazar a la raza contemporánea al cambiar las cix— ounstancias. Hediante la sustitución de razas o los cruzamiantos puede lograrse un cambio genétioo mucho mayor por unidad de tiempo que mediante la selección interna de las poblaciones. La aptitud para sustituir mejorará a medida que se desarrollen y perfeccionen las técnicas de conservaoión y multiplicación genética. Entonces será preferible que los recursos dedicados a mejorar estas técnicas/aestinen a la selección interna de las poblaciones, en su forma actual.

Para el futuro deberán examinarse ciertcs objetivos de seleooión. Estos objetivos incluyen los partos de gemelos en el ganado bovino, un aumento del apetito en la mayor parte de las espeoies, cambios en la oomposioión del cuerpo del tejido de la came de los animales y aptitud para hacer frante a dietas variadas y de baja calidad en todas las especies que se utilizan en agricultura. £n la mayor parte de las poblaciones grandes existen ejemplares exoepcionales, cercanos al límit biológ±co óptimo, que deberán busoarse y multiplicarse empleando nuevas técnicas.

La eleoción de especies domesticadas y utilizadas con fines agrícolas parece haberse dejado elgo al azar. Los recursos dedicados a nuevas domesticaciones han sido mínimos. La domesticaoión de las especies salvajes actuales puede muy bien resultar una respuesta menos oostosa y más rápida a las neoesidades del mercado, que el intento de convertir una población domestioada mediante la selección interna de la poblacion.

Conclusión. Sa difloil de premer el futuro. Cabe representarse o Iwmglnar diversidad de futuras situaoiones distintas de la actual. Tales esoenarios dan ciertas indicaoiones sobre las futuras neoesidades en materia de animales. La respuesta de los genetistas debe con­sistir en aantener e incluso aumantar la gama de variedades disponibles en las poblaciones domesticadas. También deben busoar los medios de acreoentar su capacidad de introducir en los tipos de animales empleados en la agricultura, los cambios que las nuevas neoesidades de la produooión y del meroado impongaa.