1 182 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 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 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
2 183 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-population selection 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
3 184 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 Change of circumstances 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 Pood 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 , 81$ of the world's people lived in countries which were at least 95% self-sufficient in food energy. (The degree of selfsufficiency 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
4 185 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 Table 13.1 Growth rates of gross agricultural production: trend and normative scenarios Trend scenario Normative scenario developing countries Africa Par East Latin America Near East 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 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 ) though the African population growth rate is expected to continue to rise, showing a rate of 3.0% for the period, as compared with 2.6% over the years 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.
5 186 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 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 Energy World availability of energy from fossil fuel may be quite different by 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 energyassociated 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 there has been an annual improvement (reduction) in energy
6 187 demand of industry by %, 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 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) 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
7 188 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 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 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
8 189 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 withinpopulation selection 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 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 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, FAO (1979) Agriculture: toward Conference Paper C79/24. Rome: PA0. Lamb, H.H. (1977) Climate and the outlook for society. Optima, 27, Lansford, H. (1975) Weather watchers. Nature, 256, Norse, D. (1979) Scenario analysis in interfutures. Futures, 11, World Energy Conference (1978) World energy: looking ahead to IPC Scientific & Techological Press.
9 190 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 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 sousdéveloppés. 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.
10 191 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 l 1 amélioration de ces techniques qu'à la sélection au sein d'une population telle qu'elle s'effectue à 1'heure actuelle. Ilconvient 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.
11 192 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 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.
12 193 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 comtituye 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. 1 desafío a que hemos de hacer frante consist* en deb&rrollar los medios para responder 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.
13 194 CHAPTER 14 ADAPTATION OF LIVESTOCK TO THEIR ENVIRONMENT by J.M. Rendel CSIRO Division of Animal Production P.O. Box 184, North Ryde, N.S.W., 2113 AUSTRALIA Summary There are severe environments, such as the wet tropics, where special adaptations to local conditions are necessary for animals to survive and produce successfully. There are four broad classes of adaptation which are desirable: to the local climate, to local diseases, to disease which depends for its success on special relationships between a virus or viroid and the genotype of the host, and, to methods of husbandry and types of production which have their own special requirements Where a local breed and its crosses are the only ones to survive, the local breeds will be preserved. There is danger in localities in which highly improved breeds can survive that they will predominate and push other breeds out of existence. A breed which becomes monotypic is an open invitation to a specialized disease to evolve and wipe out large sections of the breed. The problem facing us is one of preserving nascent breeds, based on highly productive ones or on crosses, from being swamped by highly productive breeds before they have had time to adapt and improve Introduction It is generally recognized that the number of breeds has been shrinking rapidly in all major domesticated species. There are a number of reasons for this. One important reason, which has a bearing on adaptation of animals to their conditions of life, is the increasing independence of animal husbandry from foraging on native pastures and browses. With the introduction of improved pastures, supplementary feeding, housing and veterinary services the environments of the world have come closer together, and highly productive breeds, bred in most cases for maximum production by the individual, can be of use whenever feed and perhaps housing is available. Highly productive breeds have tended to sweep across the world with an accompanying rise in productivity which is hard to partition between the influence of the productive breed on the one hand and the improved methods of management that go with it on the other, From time to time, where the need to be able to cope with local climates and diseases exists, the improvements expected from introduction of productive breads have not been forthcoming. The failiires have then been approached from two sides. Eradicate tsetse fly or introduce resistance to trypanosomes. Provide shade or breed for heat tolerance. Adapt the breed to the environment or the environment to the breed. The environments to which breeds have to be adapted will include the system of production in which the animal is expected to perform. Some breeds have shown themselves to be remarkably adaptable. The White Leghorn chicken and indeed other breeds of chicken have spread to all corners of the world. Their capacity to do so seems likely to be due to uniformity of husbandry conditions. The Merino sheep which thrive near the snowline in New Zealand and in near desert conditions in Australia as well as in Russia and China where they are often housed for most of the year are limited mainly by their failure to reproduce in very high temperatures, their susceptibility to fleece rot in wet climates and their dependence on reasonably short pastures. Although breeds like the Merino are widespread, it has been difficult to show that they have become adapted in any special way to their new environments, at least in recent times. The
14 195 environments inhabitated by the Merino in Australia are varied as to temperature, vegetation, mineral deficiencies and humidity and breeds might have been expected to have become adapted to habitats of characteristic kinds. It has been demonstrated (Dunlop, 1962, 1963) this has not happened in five major strains of the Australian Merino. Three environments were chosen - The New England Tablelands, deficient in sulphur, lying between 2,000 and 3,000 feet with inches of rainfall and cold in winter; the plains of Deniliquin, which are low-lying and hot and can be irrigated; and the dry, hot inland of south Queensland near Cunamulla where sheep graze mainly Mitchel grass dependent on a variable rainfall of about 12 inches. No important gene environment interactions in wool production were found between these five strains. There was a slight tendency for fine wools to do better at Armidale. No important interactions were found for fitness characters either, once more fine wools had a slight tendency to breed and survive better at Armidale. Dunlop points out that this does not mean that interactions between gene and environment do not exist, but that if they do they have not been used in establishing these strains. He suggests the strong variation from year to year at any one station in rainfall in particular may operate against selection in one direction. Adaptation to local conditions will not be automatic unless the breeding system and climate are such that natural selection in the local habitat can play a part. Though in the past introduced species such as creole and criollo cattle have adapted over the course of 200 years or so to a highly adverse environment, when there is strong selection for production and little pressure on adaptation the evidence of adaptation is not there. Experimental flocks in which rams instead of strains could be compared after selection in different environments were then set up to see if gene environment interaction with respect to production characters were in fact present. Latest results suggest that interactions with respect to production do exist. To date, the Merino breeders have not made use of these interactions; perhaps because most of the studs are in similar environments; perhaps because the strains have been adapted more to particular uses (fine, medium and strong wool growers) than to local conditions, perhaps as Dunlop suggests because variability is a characteristic of looal conditions. Since the production of wool by an individual sheep has doubled over the past generations in the Merino flock, it may well be that the decision, assuming it was a decision, to concentrate on production per head in this rather versatile breed was the correct one. Pigs and horses are two other species which seem to have been developed for special uses rather than for particular environments. In these two species, the intensity of management and housing may well be responsible for absence of major local adaptations. The number of breeds of cattle in temperate climates has reduced drastically in the recent past suggesting that adaptation has a minor role within temperate regions, but attempts to introduce the predominant temperate breeds into the tropics and subtropics were far from satisfactory in the early part of this centery. Some degree of adaptation to hot climates has been found necessary in all but the most elaborate systems of management. Even where production of imported breeds has been better than that of local breeds, survival has not, and herd replacement without regular "breeding has been a problem. It is in the cross between the temperate and the locally adapted animal and the strains extracted from the cross that the extra productivity of the temperate animals can really make itself felt in the most severe environments. In general, improvement of breeds, despite some notable exceptions where attention is paid to economy of gain, has concentrated on increasing the total production by the individual animal. The great success of this exercise in the more favoured environments has swamped advantages coming from adaptation to other particular environments except where environments are extreme and has resulted in highly productive breeds from one environment spreading to another. The tendency for high productive ability to swamp adaptation to local conditions has been reinforced by improved husbandry. In order to consider how adaptation to local conditions bears on the conservation of animal genotypes, it is necessary to include productivity in the picture. Adaptation to
15 196 local climate and disease often takes place in ways that are inimical to productivity. In addition, local husbandry practices are expected to set an optimum level to feed consumption and the amount used for maintenance and production, which have to be balanced for maximum profitability. These interactions are most easily expressed with reference to this equation: A=G + O + P + ' S + H A is appetite and measures what the animal eats as total digestible nutritents, G is what it costs to grow the animal to the point at which it becomes a productive machine. Once the animal is grown, G disappears. G and P are interchangeable when it is meat animal one is concerned with. 0 is the cost of operating and repairing the machine, P is the cost of production of meat, milk, eggs, etc. S is the surplus of A over G P and is usually laid down as fat, H is the heat generated by the whole operation which in cold climates suffices to keep the animal warm. It is not difficult to dissipate a surplus in cold climates. In hot climates, the surplus is not only bigger for the same intake of feed since there is less required to keep warm, but hard to dissipate. Where high quality feed is fed ad lib the animal's appetite A determines how much is eaten. Appetite is closely related to basal metabolic rate. Selection for production on ad lib feeding results in animals with large appetites, a large production machine and a high maintenance requirement. The breed relies for efficiency on the large amounts that a single individual can process. If S is small it is because P is large as also is 0. Since 0, though it varies with A, is to some extent independent of it, efficiency is also dependent on A being able to saturate 0 and P without increasing S. It also depends on successful disposal of H. Where A is limited, efficiency comes from a proper balance of 0 and P. Ideally, 0 and P must divide A exactly between them. If 0 is too high, P must suffer. Falconer's classic experiment with mice is an example. Peed may be limiting both because it is sparse and takes time to collect and because it is of very low quality and takes space to accommodate during digestion. One would not expect an animal selected for very high production on unlimited supplies to produce economically when fed a restricting diet. The elimination of heat is not a problem in temperate climates, but in hot ones it is. If heat production and absorption become more than can be eliminated animals lower their feed intake. This is expected to reduce efficiency of highly productive animals dependent on maximum feeding. Although when a highly productive breed is introduced into a new environment, there should be an advantage in it becoming adapted to local husbandry conditions, it can have an advantage over breeds that are adapted to live in the new environment if these have not been adapted to produce at a high rate as well as to live and breed. Although the introduced breed may not be fed at the optimum rate, because it is developed to produce, it may still outproduce the local breeds. This should not be taken to signify that adaptation is not important. When the dispersal of heat becomes difficult as it does in hot and particularly hot, humid climates, something has to be done about heat load. It appears that it is genetically easier to reduce basal metabolic rate and appetite and hence heat production than to increase the efficiency of active cooling. Animals that live in hot climates and those that have been selected in them certainly have lowered basal metabolic rates. Selection for production in these conditions has led to a lowered 0. That is to say, where appetite is restricted to conserve heat production, maximum production comes from the right 0, not a large 0. Unfortunately, seasons are not uniform, so in grazing conditions, selection for production will favour a different 0 one year from that in the next for two reasons: partly because temperatures differ and partly because the quality and quantity of grazing is different. A lower 0 also preserves an animal against a shortage of nutrients in climates with variable rainfall providing an unreliable feed supply. A good protein reserve moreover has been shown to favour an animal's power to resist disease. Elevated body temperatures in cattle have been shown to reduce an animal's capacity to
16 197 resist disease by damaging their immune mechanism in some way. They "become unable to mount a secondary response to an antigen and so never develop a proper immunity to diseases to which adapted animals rapidly 'become immune. Levels of hormones in the blood fall, cholesterol levels fall, the blood picture changes, tissue wastage takes place as shown by raised creatinine levels. It has been shown that reproductive rate is directly proportional, within unadapted "breeds of "beef cattle, to the extent to which body temperature is raised. So quite apart from the energy relations between feed intake, basal metabolic rate, production and heat dissipation, it is essential that an animal not protected from heat be able to keep its body temperature within physiological limits. It is quite clear that there are environments which require adaptation. Heat combined with humidity form one set of environments. Altitude might be another, though whether areas of extreme altitude are very large from the animal husbandry point of view is questionable. Grazing as against grain feeding is another contrast. It may prove desirable to subdivide the environment further with respect to temperature. Environments in which animals have to use intake over and above that required for 0, G and P to keep warm may form another group. Apart from general defence mechanisms against disease mechanisms of the kind that break down when animals cease to be able to maintain body temperature between normal physiological limits - there are two sorts of disease resistance from the geneticist's point of view. The first is polygenically determined, seems to have been established by selection and is against local diseases. Familiar examples are the resistance to the tick, Boophilus microplus, present in Indian cattle but not in European cattle. The multi-host ticks of Africa are a different problem. Some sheep are more resistant to intestinal parasites than others. Harayana cattle are resistant to Anaplasmosis, European cattle are not. N'Dama cattle are resistant to trypanosomes. The most impressive demonstration of this phenomenon of resistance to local disease was the disastrous result of the spread of European diseases to human populations which had never been exposed before when Europeans began to travel all over the world and the contrast between relatively low mortality of Europeans infected with bubonic plague which flourished in Europe between 600 and 1700 AD. by comparison with the almost one hundred percent mortality that followed its first introduction into East India in the 19th century. One of the best documented accounts of the acquisition of resistance to a virus disease is that of the resistance of the Australian rabbit population to myxomatosis. After 27 years, the resistance is nothing like as strong as the resistance of the sylvalagus rabbit to myxoma virus but it is clear that the Australian rabbit population has come to terms with the virus and will not be exterminated by it, whereas when first introduced mortality was of the order of 99%. Local diseases, particularly in the tropics, have proved a major drain on both survival and productivity. Adaptation to these is obviously an advantage and in some cases a necessity. It is not easy to make an estimate of the effect of adaptation on production. It is meaningless to do so without some measure of the degree of the environmental stress. Some examples from the work by CSIRO at Belmont are given here Temperature The degree of stress in this case is measured by rectal temperature. The effect of raised rectal temperatures on the number of calves born to 100 cows which have been mated for 7 weeks can then be expressed as the regression of calving per cent on rectal temperature measured in C. In a herd of Hereford/Shorthorns, rectal temperatures lay between 38.5 C and 40.5 C. The rate of calving fell 20% for each rise in rectal temperature of 1 C so the total effect of rectal temperature differences was 40%, calving rates being directly related to temperature and running from 30% to 70%. The advantage of the Brahman X and Africander X is not in its reaction to raised rectal temperature but in the far more severe conditions required to raise it. Rate of gain was also shown to fall with increased rectal temperature. Animals of 180 kg liveweight gained weight at a rate which fell 0.37 kg/day for each rise of 1 C in rectal temperature. Rate of gain lay between the limits of 0.37 kg/day and 1.11 kg/day.
17 Infectious disease B.I.K. ('bovine infectious keratitis) is an infection against which Zebu cross cattle are far more resistant in the tropics than Bos taurus» They are less often and less severely attacked. Calves of different ages from 3-15 months were scored for infection with B.I.K. and weighed. Presence or absence of infection was the indication of stress. The weights of those animals infected and those not infected at time of weighing give some idea of the effect of this disease. Again Brahman cross and Africander cross gain from not being infected, not from reacting less to the infection. Breed % of animals infected Age Affected Weight (kg) Not-affected Diff Hereford/ mths Shorthorn mths mths AX mths mths mths BX mths Tick infestation mths mths Brahman and Africanders are resistant to infestation which they throw off to a much greater extent than Bos taurus. The degree of stress is taken to be the number of female ticks that reach the last instar and attain mature size. This is counted on one side and expressed as a total tick load by multiplying by 2. HS had 176 ticks, AX 60 and BX 54. When initial weights were 167, 193 and 198 kg respectively, it was found that over 27 weeks the rate of gain was reduced by 0.23 kg a tick a year when animals of the same breed were compared (regression of rate of gain on tick numbers within breeds). When the difference between breeds was compared ticks accounted for 0.28 kg/tick/year. Estimates have been made by other people and vary from 0.3 kg/tick/year to over 1 kg/tick/year. The effect is not independent of rate of gain. When feed is good, the effect of the tick is reduced. Worm infestations have been found to have little or no effect on Braham X and to account in one trial for some 25% - 40% of the differenpe in growth between BX and HS. The second class of diseases are those which depend on the relationship between the pathogen and the host, often one gene being responsible for the difference between resistance and susceptibility. In the absence of a favourable relationship between the two, the pathogen will not grow. Of course the pathogen can adapt to the host it it is able to mutate. The influenza A. virus is an example. Strains adapted to humans or dog kidney cells or the chorio-allantois of the chick readily infect their own cell type, but not any other. However, populations from one can adapt, presumably by mutation and selection, to an alternative host cell. Extensive studies of this sort of resistance have been made in mice where large numbers of pure lines make the study of this phenomenon easier to analyse. I have listed a small sample of 8 cases reported in the recent literature. The
18 199 danger of this relationship between a single gene and a pathogen is that if a breed becomes too monotypic, it runs the risk that a pathogen will become adapted to it and sweep through the whole breed. This is of much greater danger in plants grown from selfed stocks or clones than it is in animals. An effective breeding population of five hundred should have sufficient genetic variation in it to shelter some individuals that will be resistant where others are susceptible. But one can always be unlucky and even in animals the possibility, since it exists, should be guarded against. Leucosis in European dairy cows may turn out to be an example. Breeds of livestock should stem from a population whose effective breeding size is not reduced below 500. Preferably it should be much larger. The relationship between the effective population size of the seed stock and the size of the total commercial population is also important, since the latter simply multiplies up the former and what might be a small occurrence in the seed stock might magnify into a major disaster in a section of the commercial population coming from the sensitive section of the seed stock. Diseases, resistance and susceptibility which depends on a single gene. Mice Virus induced diabetes Rous sarcoma Rickettsia tsutsugamushi Friend Leucemia virus Herpes simplex V-2 Salmonella typhunurium Chickens Rous sarcoma, various strains Pigs Pathogenic E. coli Sheep Scrapie In summary the animal breeder has four different sorts of tasks ahead of him. 1. Even in the best of husbandry conditions, in which selection for maximum production is still increasing total production by the individual animal, economy of production can only be achieved by a nice balance between appetite, maintenance and production. When there is any limitation on feed, this balance becomes increasingly important. 2. In severe climates, the energy balance between production and maintenance must take account of the heat balance between the animal and its environment which is also important for the proper function of the animal as a whole. 3. There are local diseases to which local livestock must be resistant. 4. In all environments, one must avoid allowing a population to become a happy hunting ground for pathogens whose attack depends on the presence of the right allele at one or two loci. As far as 1. and 2. are concerned, having settled on the foundation stock to be used, there seems only one way to go about adaptation and that is to select for optimal production in the conditions of husbandry and climate that are going to prevail. Selecting for economy of gain does mean paying attention to feed intake as well as output of product and it is not going to be easy, so it will probably be done on a small scale in the first instance. In 2. and 3. the choice of foundation animals is likely to be a cross. It is true that Creole and criollo cattle introduced into the tropics from Europe have eventually adapted and one could start with locally adapted cattle and select for production. Mahadevan has set out the arguments against this course. It is also possible to select in productive breeds for adaptation to climate and disease. It is the time scale that will influence
19 200 the choice in favour of a cross "between a productive and an adapted breed. The time scale on which changes can be made is still measured in terms of the generation interval. If we take 10 generations as a reasonable average time taken to make a significant change (the exact number depends partly on gene frequencies and partly on your idea of what is a significant change) then it will take 10 years to modify a chicken population and 50 to modify a dairy cattle one. Since the constructive breeding will be done in a few small populations, time must he added for spreading the results to the population at large. Even modern techniques with the present organization of livestock breeding can often take a long time. There are obvious advantages in making crosses between breeds that complement each other. Adequate adaptation to temperature can be achieved by one cross in cattle. To put it another way, it would take at least ten generations probably more, to achieve the heat tolerance of a Braham x Hereford cross by selecting in a pure bred Hereford herd. Much the same can be said of tick resistance What can be done by selection in beef cattle in 10 years Conditions of low stress Gains in kilo/day in Conditions of high stress Unselected control O Selected Brahman X 0.55 The table shows what has been done by selecting in a herd of Bos taurus for rate of gain at pasture in a severe environment. Notice that in the absence of stress, when worms and ticks are removed and the animals stalled in the shade and given good quality feed ad libitum, the selected animals grow more slowly than the unselected controls. On the other hand, when at grazing under stress, the reverse is true, but ten years of selection leaves the selected group when at stress far behind the Braham cross. Adaptation, if that is the right term, to 4. is a population structure. matter of maintaining a suitable In the light of the four tasks outlined, preservation of genetic resources in breeds of livestock embraces much more than the preservations of locally adapted breeds in areas where diseases of a virulent kind and severe climates make the maintenance of a population introduced from outside the region difficult. Since there are still many areas in which the production of adapted animals is low and since it is still true to say that the main source of highly productive animals is in the favoured environments it will be of advantage to introduce these into the severe environments to lift production. Since it is much quicker to adapt them to the severe environment by crossing them to local adapted breeds than to select in either the adapted breed for production or in the productive breed for adaptation, it will be highly desirable to make certain for several decades to come that local adapted breeds in difficult environments are preserved, so that the crosses can be made. But we need to go further than this. It is also necessary to preserve the nascent locally adapted breeds with improved production from being swamped by highly productive but unadapted genotypes. I think this is going to be a quite general requirement in all environments, not only in the more difficult ones. Once the present phase of animal improvement which has concentrated to date on maximum output by an individual begins to look for maximum production from a given resource of feed instead, the importance of adaptation to local management, climate and disease will increase. Since these adaptations will be important parameters in maximising feed utilization, it will be necessary to preserve nascent breeds from being swamped by huge monotypic enterprises in more favoured environments. Sooner or later we shall have to regenerate genetic diversity in the form of new breeds to replace many that have been lost and I think we are concerned with more than the preservation of existing
20 201 potentially valuable genotypes. We should be trying to preserve the possibility of genetic diversity and the possibility of developing it for the best use of local conditions. Once animals with very high oonversion rates are common place, and they are rapidly becoming commoner as methods of selection devised by the animal scientists become more widely used, further advances towards economic production can only come from adapting breeds to local conditions of husbandry, climate and disease, a proposition which is already true for the severe environments of the world. Local adaptation is equally necessary for local disease, local management and local climates. So long as there are or seem to be large economic advantages in importing breeds or genotypes from favoured areas where production is very high or from breeds developed on a large scale by the best methods of selection for high production under particular systems of management, it is going to be impossible to reduce the trend towards monotypic species. The only possibility of preserving the opportunity of genetic diversity, and specialization for local conditions, is through institutions such as colleges of agriculture and governmental research organizations. When it comes to diseases which depend on a special genetic relationship between the host and the pathogen, a relationship which may be determined by one or two gene loci, I find it difficult to assess to what extent monotypic breeds are at risk. Clearly the clone is the most exposed population. But if in a sexually reproducing breed a large number of progeny always stem from one sire there is a chance of having a large fraction of a population susceptible, to a disease depending on a single gene difference should the disease ever arise. I do not think there is any way of protecting oneself against introductions of diseases from other species such as the introduction of myxomatosis into the oryctolagus rabbit or for that matter green monkeys disease into the human species. However, plant breeders have run into difficulties with diseases in which single genes determine susceptibility or resistance and I believe animal breeders should look more closely at the problem. It is one which I do not feel competent to say more about than that it is possibly there. It is my opinion that at present the most urgent need to preserve existing adapted genotypes and the opportunity for genetic diversity and specialization is in those places in which environments are most exacting, environments in which it is already known that the highly productive breeds cannot thrive. In other areas, the danger is that the trend towards monotypic species will lead to monotypic methods of production References Frisch, J.E. and Vercoe, J.E Australian Journal of Agricultural Research. 20: Vercoe, J.E. and Frisch, J.E Australian Journal of Agricultural Research. 21: Frisch, J.E EAAP publication 14: Animal production 21: Proceedings of the Australian Society of Animal Production. Falconer, D.S. and Latyszowski, M Journal of Genetics 51: Turner, H.G. Chapter in "Introduction to Environmental Physiology". Editor A.B. Slebodzinski. Panstwowe Wzdawnictwo Nankowe, Warsaw. Dunlop, A.A Australian Journal of Agricultural Research 13: Australian Journal of Agricultural Research 14:
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