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1 The Need to Conserve Livestock Genetic Resources Selected varieties of plants and animals form the foundation of agriculture. Domesticated animals have provided people with food, fiber, transport, and-draft power for thousands of years, and during the past 200 years, they have been modified by selective breeding to serve better the changing needs of humanity. Genetic diversity within agricultural species is important as expanding hu- man populations seek to improve their standards of living and place greater demands on natural resources. New technologies that ma- nipulate animal physiology and environment have substantially en- hanced livestock production, particularly in the latter half of this century, to meet food and other economic demands. As a result of modern changes and improvements, however, the genetic diversity of some species may be declining. Symptomatic of that decline is the increased reliance on animals of a single breed or type for commercial production at the expense of other recognized types. If genetic diversity is significantly reduced, it may limit future options for improving livestock populations or for modifying them to meet unforeseeable needs. THE DEVELOPMENT OF ANIMAL AGRICULTURE Domestication of livestock began about 11,000 years ago, follow- ing the rise of grain cultivation (Hodges, 1990a; Willham, 1982~. As the security of plant-based food supplies increased, people adopted a more settled life-style in small communities. However, decreased 21
22 / Livestock mobility intensified hunting around the settlements and nearby ani- mals became scarce. Domesticated animals offered a dependable source of meat, skins, and bones; later, their value for other products and uses was recognized. Ruminants, such as cattle, goats, and sheep, were particularly beneficial because they ate forage plants that were unsuitable for human consumption. Goats and sheep were the first species to be domesticated for food, beginning about 11,000 years ago. Domestication of pigs and cattle followed and was complete by about 8,000 years ago. The earliest archeological traces of these domesticates are found in the Fertile Crescent, an area of southwest Asia between the Mediterra- nean Sea and the Persian Gulf. Horses were probably tamed about 6,400 years ago in central Eurasia; chickens were domesticated about 5,000 years ago in Southeast Asia; and buffalo were domesticated about 4,000 years ago in India and Southwest Asia. In the Americas, there is evidence of the taming of alpacas and llamas in the Andes Mountains up to 6,000 years ago and the domestication of turkeys in Central and South America about 2,000 years ago. (Reviews of the domestication of these and other animal species can be found in Clutton-Brock [1981i, Epstein [1969, 1971], Mason [1984], and Zeuner [1963~.) About 40 domesticated mammalian and avian species are widely recognized (Table 1-1~. However, only 6 mammalian species (buffalo, cattle, goats, horses, pigs, and sheep) and 4 avian species (chickens, ducks, geese, and turkeys3 are used extensively throughout the world because cultural preferences and use for them have developed. These species are classified as the major domesticates. (See Appendix A for an overview of the status of these species.) Although the other minor species are numerically less abundant on a global scale, they are nevertheless critically important to the people whose livelihoods are built around them (National Research Council, 1991~. The uses of the minor species depend primarily on their abilities to produce valued products in specific environmental niches and on the traditional or cultural patterns of use for their products in some societies. Species have developed marked physi- ological distinctions under different environmental conditions, and accordingly, some breeds are far better suited than others for produc- tion under specific conditions. Examples are guinea pigs, alpacas, llamas, and yaks in high altitudes; camels in desert regions; and musk oxen and reindeer in arctic tundra. In addition to genetic variation among species, genetic differ- ences are also found between types and breeds of a single species. For example, hair sheep are recognized for their superior ability to
The Need to Conserve Livestock Genetic Resources / 23 TABLE 1-1 Generic Distribution of Important Domesticated and Semidomesticated Mammals and Birds, by Order, Family, and Species Mammals Birds Lagomorpha Leporidae Rodentia Carnivora Oryctlagus cuniculus (rabbit) Muridae Rattus norvegicus (rat) Mus musculus (mouse) Caviidae Cavia porcellus (guinea pig) Canidae Canisfamiliaris (dog) Felidae Felis catus (cat) Proboscidae Elephantidae Elephas maximus (Asiatic elephant) Perissodactyla Equidae Equus caballus (horse) E. asinus (ass or donkey) Suidae Sus domesticus (swine) Camelidae Camelus bactrianus (Bactrian camel) C. dromedarius (Arabian camel) Lama pacos (alpaca) L. glama (llama) Cervidae Rangifer tarandus (reindeer) Bovidae Bos taurus (humpless, primarily temperate zones) B. indicus (humped, primarily tropical zones) B. grunr~iens (yak) Bibos sondaicus (banteng) B. frontalis (gayal) Bubalus bubalis (water buffalo) Ovibos moschatus (musk ox) Ovis aries (sheep) Capra hircus (goat) An s e riform es Anatidae Anas platyrhynchos (duck) Cairina moschata (muscovy duck) Anser anser (goose) Branta canadensis (Canada goose) Galliformes Phasianidae Gallus gallus (chicken) Coturnix coturnix (Japanese quail) Phasianus colchicus (ring-necked pheasant) Pavo cristatus (peafowl) Numididae Numida meleagris (guinea fowl) Meleagrididae Meleagris gallopavo (turkey) Columbiformes Columbidae Columba livia (pigeon) NOTE: Not covered in this report but also of value are certain reptiles (for example, crocodiles, turtles), insects (for example, silkworms, honeybees), fish and shellfish (for example, carp, salmon, crayfish), doves, red deer, and fur-bearing mammals.
24 / Livestock produce meat and milk in tropical and subtropical climates, while wool sheep are more suited to producing fiber needed by people in cooler regions. In cattle, the Bos indices breeds from the Indian sub- continent are generally better adapted to hot, humid climates than are the European Bos Taurus breeds, which, although genetically su A PROBLEM OF NOMENCLATURE Carolus Linnaeus, a Swedish botanist during the 1700s, developed a system of naming and classifying plants and animals. According to his system, cattle belong to the order Artiodactyla or even-toed hoofed mammals (ungulates), the family Bovidae, and the genus Bos. Domes- ticated cattle are usually classified into either the humped (Bos indicus) or humpless (Bos taurus) types. Most of the humpless cattle include ancestors of the European cattle and the majority of the cattle, which came from Europe, found in the temperate regions of North and South America. The humped cattle, usually called zebu, originated in Paki N'dama cattle (left page) are a humpless breed, Bos taurus, noted for relatively high production of meat and milk per unit body weight and its resistance to trypanosomiasis and other endemic diseases of West Africa. Credit: International Livestock Centerfor Africa. Zebu (right page)from
The Need to Conserve Livestock Genetic Resources / 25 perior for milk production and growth rate under temperate condi- tions, usually fail to produce adequately or to survive under tropical conditions (Cunningham and Syrstad, 1987~. However, some Bos taurus breeds that were established in West Africa and Latin America before the introduction of the Bos indices have successfully adapted. Stan and India and later spread into the tropical zones of Asia, Africa, Australia, Central and South America, the Caribbean, and the southern United States. The designation of cattle as two species appears to be inappropriate because B. indicus and B. taurus have the same chromosome number and interbreed readily; the crosses between them are fertile. However, because of historic origins, the types continue to be distinguished by their original species names. They also represent types that are widely divergent in their adaptation to various environments. The informa- tion that will come from genetic maps of B. indicus and B. taurus may one day help determine how closely related the various breeds are within these species. - _5 . it_ 1 I: lo. _ B~s Chad in equatorial Africa are Bos indicus cattle with pronounced humps and fleshy dewlaps that aid heat regulation in hot, humid climates. Credit: Food and Agriculture Organization of the United Nations.
26 / Livestock THE EFFECTS OF TECHNOLOGY ON GENETIC DIVERSITY Technological advances, such as artificial ~nsemmation, and changing practices, such as better disease control, in all areas of animal hus- bandry, including breeding and genetics, reproductive physiology, and nutrition, are contributing to the improved production capacities of modern livestock. However, these and other techniques have the potential to affect negatively the number and diversity of breeds and types in both developing and developed regions. Such techniques include in vitro fertilization and cryopreservation of semen (storage typically in liquid nitrogen at a temperature of -196°C). Many livestock species traditionally have been raised under ex- tensive farming conditions, that is, on the range or in fenced areas, often with minimal inputs for housing, labor, nutritional supplements, and veterinary care. Their survival has been challenged by diseases, parasites, and nutritional and climatic stresses over many centuries, allowing time for natural selection to create populations genetically adapted to local conditions. In developing countries, where livestock management practices and inputs have changed little, adaptation to the environment re _~ _:.~23~ ... Many village families in Botswana keep free-ranging pigs and poultry. These animals do not receive veterinary care and are fed only household scraps, but they provide meat and other products for the family and cash from sales. Credit: Elizabeth Henson, Cotswold Farm Park.
The Need to Conserve Livestock Genetic Resources / 27 mains critical. The N'Dama cattle of West Africa, for example, have developed specific resistance to trypanosomiasis, a parasitic disease spread by tsetse flies (Trail et al., 1989~. The cattle survive in an environment in which other, more recently introduced, breeds be- come unproductive and often die. Yet tremendous pressure to in- crease food production exists in these developing countries, and the highly productive breeds of livestock developed in the industrialized world may superficially appear ideal for use. The technology for sending germplasm to Africa exists, but the capacity to replicate the improved environmental conditions of the industrialized world does not. The result can be the introduction of unadapted livestock that survive poorly and do little to improve food production. Inputs and management technologies, such as climate control, are more common in developed countries and reduce the need for livestock to be adapted to the environment. Yet a breed's capacity to be adapted to new conditions, which requires genetic diversity, re- mains critical to meet future needs and to respond to future produc- tion changes. For example, beginning in the 1940s in developed countries, cages were adopted by chicken farmers to have cleaner eggs and to reduce cannibalism and feather pecking. The cage system was also a better alternative to land that could harbor the disease organisms contained in fowl droppings. Production and management advantages, such as automated feeding, watering, egg collection, and better feed conver- sion efficiency, led to further adaptation. However, a move to ban the use of cages in the European egg production industry was begun in the early 1980s in response to animal welfare concerns. The Coun- cil of Ministers of the European Community has established space and other minimum requirements for hens that will apply to all cages as of January 1, 1995; Switzerland has banned cages; and Sweden and the Netherlands may also ban cages (U.S. Department of Agriculture, 1991~. These changes may now require the development of poultry breeds better suited to cageless environments. Breecting and Improvement Technologies Increased production of milk, meat, eggs, and animal fiber has been based on extensive records of pedigree and performance, which are essential for accurately identifying superior individual animals. Systematic improvement of livestock. Copulations began in eiabteenth- century Europe. ~ ~ v v Livestock were bred, and the best animals were selected for breeding until a degree of uniformity was attained. Herdbooks were started to record pedigrees because of the reliance on ancestry.
28 / Livestock The science of population genetics, developed in the 1930s and 1940s by scientists in Europe and North America, has since been effectively applied to achieve substantial increases in animal production and productivity, primarily in developed countries. Progress has been greatest in dairy cattle, pigs, and poultry. Compared with 30 years ago, the average dairy cow in the United States produces over twice as much milk (U.S. Department of Agriculture, 1976, 1990), and fat thickness in Danish pigs had declined by half (Christensen et al., 19861. Today's broiler chickens mature in 6 weeks instead of 3 months (Cahaner and Siegel, 1986; Chambers et al., 1981~. The positive gains achieved through applying genetic theory to animal improvement do not necessarily reflect a strategy for coping with different goals that change with time. Instead, the emphasis is AN EXAMPLE OF BREED UNIQUENESS . ;_ North Ronaldsay sheep eat seaweed on Linga Holm, one of the Orkney Islands of Scotland. The island is owned by the Rare Breeds Survival Trust and run as a sanctuary for this breed. Credit: Howard Payton, Cotswold Farm Park. A much larger vari- ety of livestock breeds exists than is used in commercial agricultur- al operations. Thou- sands of years of adap- tation to region-specific environmental condi- tions and more recent domestication have cre- ated diverse and unique traits in many breeds, which today are rare or endangered. The poten- tial loss of rare or en- dangered breeds is of concern to livestock breeders, who may need their special character- istics to adapt commer- cial breeds to unforeseen needs, and to research- ers, who could study them and expand society's understanding of domestication, selection, genetics, and evolution. One such rare breed of sheep, indigenous to an island in the Orkney archipelago off the northeast coast of Scotland, has adapted to a unique
The Need to Conserve Livestock Genetic Resources / 29 on identifying selection objectives that represent current economic situations in the industry and on attempting to maximize rates of genetic change to achieve those objectives. This approach can also have a negative effect on maintaining genetic diversity. Superior animals are identified and, through re- productive technologies, can produce large numbers of progeny. Certain breeds are recognized for their superior performance and are more widely used and more rapidly improved. Breeds that are not eco- nomically competitive, or that are perceived as being less profitable, are less popular and are not maintained by producers. A 1982 survey in western Europe identified more than 700 distinct breeds of cattle, goats, horses, pigs, and sheep, about 240 of which were classified as endangered (Maijala et al., 1984~. set of severe environmental conditions and management practices. It serves as an example of a livestock breed with an exceptional physiolo- gy that merits preservation because its genetic characteristics cannot be found elsewhere. The North Ronaldsay sheep survive exclusively on a diet of seaweed on an island shoreline buffeted by the North Sea's cold winds and winter storms. They have fine bones, a naturally short tail, and a small body, one-third the size of sheep in commercial production. Character- istic of all primitive sheep breeds, the North Ronaldsay displays a wide range of wool color, from white to grey or blue-grey and occasionally brown or black. The islanders of North Ronaldsay erected a protective, circumscrib- ing seawall 160 years ago to prevent foraging sheep from damaging the iodine-rich seaweed surrounding the island. When the demand for cropland increased the sheep were placed outside the seawall, and sea- weed became their primary source of forage. Then, as now, islanders harvest the sheep for meat and wool. Excluded from all sources of grass forage, the North Ronaldsay sheep developed distinct foraging preference and behavior that set them apart from other breeds. To obtain all nutritional requirements from limited fresh water and abundant kelp beds along the shore, they have mas- tered the physiological challenge of handling elements, like sodium, present in excess in their environment as well as obtaining important trace elements, like copper. The copper concentration present in Laminaria, the most preferred kelp, is one-third the concentration found in terrestrial herbage. Other breeds found in Scotland, which normally feed on grass or hay, would (continued)
30 / Livestock Animal breeders have recognized that selection objectives change over time, but they have always assumed that sufficient genetic di- ~rersity would remain to permit changes In selection objectives. However, as technological advances improve the ability to select for particular genetic traits, the potential of losing related, unselected genes in- creases. Consequently, the capacity for an intensively selected trait to be further manipulated through selection and improvement may be compromised. . Reproductive Technologies Reproductive inefficiency, or the inability to produce regularly the optimum number of offspring, is a costly and economically limit die from lack of copper if fed Laminaria. However, the North Ronald- say sheep are so well adapted to the low concentration of copper present in Laminaria that higher copper levels are toxic to them. The North Ronaldsay sheep are also very salt tolerant. Foraging on seaweed directly from the sea subjects the sheep to high concentrations of sodium and other salts. With no source of fresh water for much of the year, their capacity to withstand saltwater is unique. The physio- logical or biochemical mechanism by which this adaptation is possible has yet to be studied and understood. These sheep have also adapted to the challenges of living and feed- ing on rocky island shores where the sea is a constant threat. While other sheep breeds have a diurnal feeding pattern, the beginning deter- mined by sunrise and the end sunset, the behavior of the North Ronaldsay sheep is linked to the tidal cycle. The sheep begin to feed about 3.5 hours after high tide when the beds of Laminaria are exposed. Feeding ends 4 hours later, shortly after low tide, when the tide begins to ad- vance and the likelihood of being stranded at sea increases. Until recently the entire population of North Ronaldsay sheep, about 3,000 individuals, existed exclusively on one island. The entire breed was at risk. Sudden environmental degradation, like a catastrophic oil spill in the North Sea, could destroy its food source and habitat. Dis- ease could decrease its number, thereby reducing the genetic diversity within the population. In 1973, a population of 150 North Ronaldsay sheep was established on the island of Linga Holm by the private, then newly formed Rare Breeds Survival Trust of Great Britain. This reserve sheep flock has now grown to 500 individuals. The physical environment of Linga Holm is similar to North Ronaldsay, but grass forage is available from
The Need to Conserve Livestock Genetic Resources / 31 ing problem for animal industries (Pond et al., 1980~. Reproduction is influenced by genetics, nutrition, disease, and environmental fac- tors, such as temperature arid pholoperiod. Each of these factors can be modified to enhance productivity and profit, but improvements can rarely be realized with only one modificahon. For example, highly prolific breeds of sheep and pigs exist, but their use in commercial production may be contingent on the ability to provide improved prenatal nutrition to the dam, increased attention to the offspring at birth, and supplemental postnatal nutrients to both offspring and dam. Highly productive dairy cows and layer hens usually require large amounts of feed to produce high levels of milk or eggs. Where the production environment is ideal, reproduction is lim- ited by physiology. The situation is particularly clear in cattle, which the interior of the island. The sheep still prefer Lamirtaria and other types of kelp. However, other groups, brought to farms in England and Scotland, that have less access to kelp may change their forage preference. Over time, the genotype and phenotype of these splinter populations may be expected to diverge from that of the original in response to new environmental conditions and management practices. Although not of great commercial value, the North Ronaldsay sheep possess other characteristics that may be of interest to local breeders. The ratio of weight to pelvic dimensions in this breed produces fewer problems during birthing compared with other breeds. Introduction of this trait to commercial sheep on the Orkney Islands may decrease ewe mortality. Commercial sheep introduced on these islands often die because of a lack of grass forage during winter storms. North Ronald- say ewes crossbred with commercial meat rams produce lambs that are able to finish on Laminaria to carcasses of commercial value. These characteristics may decrease losses and increase productivity for farm- ers in the Orkney Islands. The remarkable breed improvements realized in recent years were possible, in part, because of the enormous genetic variation developed over centuries of natural selection and husbandry practices. Further enhancement of commercial livestock may be necessary as environ- mental conditions change, market demand varies, or production mech- anisms are modified. Future study of salt tolerance and copper metab- olism may benefit from examining the rare, physiological model of the North Ronaldsay sheep. Preserving the unique qualities of this sheep and other diverse livestock breeds will ensure a wealth of genetic re- sources for future use in basic scientific research and the advancement of the agricultural sciences.
32 / Livestock normally produce one calf per cow each year but may calve less frequently. These low reproductive rates have a major limiting effect on production efficiency. They especially limit the effectiveness of selection programs by reducing the number of progeny that can be expected from an individual mating. To achieve an acceptable num- ber of births each year, many females must be bred. Advances in reproductive physiology and cryobiology have gen- erated the capability to produce large numbers of offspring from only a few parents. Techniques that have particular implications for ge- netic diversity include the capability to collect and cryopreserve germplasm, particularly spermatozoa and embryos, and the ability to manipulate the breeding of parental stocks through artificial insemi- nation or embryo transfer. Application of these technologies can increase diversity in a popula- tion through the introduction of new genes, but it may also narrow diversity where introduced spermatozoa, ova, or embryos overwhelm or replace local breeds. Semen can be collected from a single male, frozen, and later used to produce tens of thousands of progeny. Tech- niques for collecting, manipulating, and preserving oocytes, ova, and embryos, although more recent, are rapidly expanding. In cattle, up to a hundred offspring can be produced from a single female, and within a few years in vitro fertilization will likely increase the num- ber of possible offspring to thousands per cow. Techniques have also been developed to split individual embryos and to clone embryos by nuclear transplantation. Cryopreservation using liquid nitrogen per- mits long-term storage of gametes and embryos as well as shipment worldwide. As these techniques become increasingly cost-effective, they will be applied in more environments and production systems. Their effects on rates of population improvement have been and will in- creasingly be profound and favorable. Their potential negative im- pacts on genetic diversity and the potential for future genetic change have not been fully assessed, but they could be substantial and must be recognized in the design of breeding programs. Changes in Production Systems and Nutrition Technological and management advances in livestock production are far more widespread in developed countries than in developing countries. Particularly for dairy cattle and poultry, and to a lesser extent for pigs, industrialized systems of livestock production have been established. Stocks with very high genetic potential for specific traits are raised in high-input, carefully managed environments. Ad
The Need to Conserve Livestock Genetic Resources / 33 The Red Star People's Commune In Me People's Republic of China produces 10,000 ducks per monk for the nearby Beijing market. Credit: Food and Agriculture Organization of the United Na- tions. vances in the understanding of nutrient requirements to support high levels of production are rapidly implemented through supplemental feeding. Endemic diseases are controlled by regular programs of vaccination and antibiotic administration. Under these controlled con- ditions, genetic uniformity is an advantage because superior genotypes, under a stable, improved environment, will maximize production. The development of uniform stocks, however, increases vulner- ability to genetic disaster. For example, most of the world relies on the industrial stocks of a few multinational corporations for elms and broiler meat (Mason, 1984~. 1 ~ 0~ A particular disease may develop that could decimate these populations. A similar situation exists for com- mercial turkeys, which also experienced declining reproductive abili- ties as size and muscling increased. Artificial insemination is now universally used in the breeding of industrial stocks. Concurrently, the fertilizing ability of semen, number of eggs per female, and egg hatchability have declined (Mason, 1984~. The ramifications of this trend are considerable for developing countries and include the replacement of small, near-subsistence farming operations with larger enterprises that have greater access to feed
34 / Livestock and technology. A village economy based on diverse indigenous genetic types is not necessarily inferior to intensive production using highly uniform genetic types when market channels are poorly de- veloped and availability of the necessary inputs is limited. However, increased production must be achieved in conjunction with adequate marketing and distribution systems to ensure access to animal prod- ucts by all consumers. Management technologies and exotic livestock have been imported into many developing areas in response to demands for higher pro- duction levels. Entire production systems for chickens, including EXTENSIVE AND INTENSIVE PRODUCTION SYSTEMS Livestock are generally produced and managed in two distinct ways: extensive production, practiced for many thousands of years, and in- tensive production, in use for only the past few decades. Each system has its place in world agricultural production and must be evaluated in terms of its appropriateness for a given region's social, financial, and natural resources. Extensive systems are employed on small farms in subsistence pro- duction and on large farms that produce considerable quantities of animal products for market. Small extensive systems are primarily found in developing countries, while large extensive farms operating under range conditions may be present in both developed and devel- oping countries. Herd or flock size in small extensive systems is usual- ly significantly smaller than that of intensive or large extensive sys- tems, which can accommodate thousands of animals in a year. Intensive operations are found predominately in developed countries on special- ized, one- or two-product farms. Extensive and intensive production systems differ in many other respects as well. Typically, in small extensive production systems, ani- mals obtain forage and water on open pasture and are adapted to sur- vive on available nutrients and trace elements. Livestock in large ex- tensive operations may receive supplemental feeds, such as hay, in addition to range forage. Animals in intensive production systems are given water, fortified mixtures of feeds to enhance desired production characteristics, like increased carcass weight, and supplemental injec- tions of vitamins and trace elements as needed. Housing is also addressed in varying ways. Animals in extensive operations are more exposed to the elements. Housing in small exten- sive systems, if provided, is of natural materials, such as straw bedding (continued on page 36)
The Need to Conserve Livestock Genetic Resources / 35 management technology, genetic stocks, arid sometimes feed supplies, have beers successfully transferred. Production systems for pigs, in- cluding high-producing genetic lines, are also being transferred. For these species, the trend is to replace indigenous stocks and produc- tion methods completely. Purebred dairy cattle have been exported from temperate to tropical regions with varying degrees of success in drier areas but usually with disastrous results in the humid zone. The crossbreeding of indigenous stocks with imported ones, up to certain levels of exotic inheritance, have usually been successful (Cunningham and Syrstad, 1987~. However, this result largely de This commercialfeedlot contains beef cattle that can befed high-energyfeeds to increase their weight rapidly, an example of intensive production. In contrast, grass-fed cattle kept in pastures until they reach a desirable slaughter weight is an example of extensive production. Credit: Gordon W. Gahan, O1992 National Geographic Society.
36 / Livestock pends on the availability of adequate nutrition to support greater milk production and a structured breeding program to stabilize the optimum gene mix. The demand for greater rates of production and aggressive mar- keting practices on the part of exporters can lead to the introduction of unsuitable animals without scientific and technical information about their adaptability for the region. Management technologies (for example, climate control) and physical inputs (for example, high- quality feeds) are necessary to maintain productive exotic stocks. The long-term efficiency and sustainability, as well as the social and eco for ground cover and branches for makeshift corrals, collected from the immediate surroundings. Large extensive systems may provide wood- en or concrete shelters or paddocks. In intensive systems, high-capital investments are required for housing construction and equipment, which may include pens or cages in enclosed buildings with ventilators, ther- mostats to control temperature, heated floors, insulated roofs, and arti- ficial lighting. Animals in extensive production systems adapt to regional climate, temperature extremes, and seasonal variations in photoperiod, while animals kept in artificial, intensive production settings are kept in a managed or artificial environment. Some intensive production envi- ronments are deliberately manipulated to increase production. Layer chickens, for example, may be placed in a 26-hour light-dark cycle to optimize egg production. Little or no effort is made in extensive production systems to pro- vide preventative care or symptomatic treatment of disease or parasitic infection. The success of intensive production systems, however, de- pends on the provision of preventative inoculations and prompt veter- inary treatment of sick or diseased animals. The concentration of ani- mals in intensive systems requires rigorous sanitary measures to prevent the spread of disease. For example, wastes are removed regularly and animal living areas cleaned. The udders of dairy cattle in intensive systems are also given an antibacterial rinse after each milking to pre- vent the spread of infections of contagious pathogens. The genetic composition of the animals used in the production sys- tems is markedly different. Small extensive production systems may have relatively homogeneous (and often inbred) individuals within each production unit, but the number of production units (herds or flocks) may be large. Animals in different production units may represent
The Need to Conserve Livestock Genetic Resources / 37 nomic implications, of imported production systems must be closely examined. Improvements in livestock production can be explored and implemented as appropriate for a region, but until their relative values and costs are thoroughly understood, endangered indigenous stocks should be protected. Currently the survival of many indigenous populations is threat- ened by the introduction of animals from temperate areas. Indig- enous stocks are crossed with or, more important, replaced by im- ported animals. Under conditions of controlled and artificially enhanced reproduction, imported breeds can replace indigenous stocks at a rapid various indigenous breeds. Genetic differences among production units and periodic exchange of breeding animals maintain genetic diversity within the entire production system. Animals in intensive systems, by contrast, are genetically similar individuals from one or two commer- cial, highly productive breeds that are selectively mated according to a farmer's breeding program. Large extensive operations may have sev- eral breeds or only one or two. Exposure to disease, parasites and regional extremes of tempera- ture, humidity, and photoperiod has produced livestock capable of surviving and efficiently producing food and fiber from available resources, rela- tively unaided by humans. Animals in intensive production environ- ments are shielded from the extremes of the natural environment and protected from most diseases. If the artificial production environment were not maintained, animal productivity would decrease. A new dis- ease strain is likely to cause a higher infection and mortality rates in intensive production systems because animals live in closer proximity, in greater numbers, and have less genetic diversity. Advantages and disadvantages exist in both types of production systems. Extensive systems have the advantage of requiring less labor and capital investments. Native breeds used in extensive systems have lower rates of production than commercial breeds, but they are less vulnerable to disease and do not depend on costly production inputs and artificial environments to maintain production. Intensive systems generate greater quantities of food and fiber than extensive systems by maximizing the production capabilities of a few, highly productive an- imal breeds. Extensive systems represent an affordable way for farm- ers to produce food and fiber efficiently in areas where the high capital costs and input demands of intensive management practices would be prohibitive.
38 / Livestock rate. Generally, the relative merits of indigenous and imported stocks are only superficially weighed when crossbreeding or upgrading programs are being considered. Comparisons of performance should be made under the conditions in which the animals will be maintained. In many cases, a mixture of imported and indigenous genes will be required to produce suitable crossbreeds. However, indigenous stocks should be protected until the best crossbreeds can be determined. Until then, breed replacement runs the risk of losing genes for later adaptation. RATIONALES FOR CONSERVING LIVESTOCK GENETIC RESOURCES To some extent, the loss of less competitive livestock can be con- sidered a normal part of the livestock improvement process. Natural selection favors animals that are best suited to a particular environ- ment. The genetic composition of a species is thereby adjusted to new requirements over time. Artificial selection simply redirects and accelerates this process for the presumed benefit of society. Most dependent on genetic diversity are the ruminants, because they must adapt to a wide range of climatic conditions and nutrition levels, and because they must interact closely with their environment to forage for feed. They have acquired great diversity that could be reduced through the misapplication of new technologies for propagating and disseminating germplasm. A variety of unpredictable factors could change current demand for animal products and in turn alter animal production systems. For example, many of today's consumers demand leaner meat and less fat in their diets. Pigs that are high in fat, once prized for lard pro- duction, have been replaced by modern breeds and hybrids that meet current market and price structures based on lean yield (Alderson, 1990a). The chief reasons for conserving livestock genetic resources have economic, scientific, and cultural and historical bases. These factors are discussed below. Economic Reasons for Conservation The strongest basis for conservation is inherently practical: pre- served germplasm may contribute to future increases in the efficiency of livestock production. Production demands and conditions have changed in the past 50 years, and the ability of livestock producers to respond has been due in part to the ready availability of a wide
The Need to Conserve Livestock Genetic Resources / 39 The Pantenero swamp cattle of the Pantenal in Brazil are adapted to the extreme heat and humidity of the region. Credit: Elizabeth Henson, Cotswold Farm Park. range of genetic variation. In 1940, for example, 25 million cows in the United States produced 109.4 billion pounds of milk. In 1990, 10 million cows produced 148.3 billion pounds of milk (P. Vitaliano, National Milk Producers Federation, Arlington, Virginia, personal com- munication, June 1991~. Greater production efficiency was achieved mainly through improved feeds and the selection of breeding stock with higher capacity to produce fluid milk. The economic benefits of preservation relative to its costs are dif- ficult to assess without knowing the nature and degree of future change, which is not easily predicted. The development of pathogen strains that are resistant to specific antibiotics, for example, could require access to germplasm not available within a dominant breed. Deci- sions about what to preserve are difficult because the costs of main- taining breeding herds or populations are high. Smith (1984a), however, demonstrated that preservation programs based on cryopreservation have very low costs relative to the value of the livestock industry they are designed to protect. He estimated that the yearly costs for satisfactorily maintaining a breeding stock range from £3,000 ($4,000) for sheep or chickens to £12,000 ($16,000) for pigs. Although the costs to collect and place semen or embryos in cryogenic storage may also be high, they are incurred only once and
40 / Livestock yearly storage costs are low (Smith, 1984a,b). Smith (1984a) thus concludes that the use of cryopreservation is sound because of the large potential returns relative to the low continuing costs of mainte- nance. Insights into the molecular makeup of the genome advanced quickly in the 1980s. The foundation is being laid for mapping the genomes of all livestock species and for gaining a better understanding of gene action. Although an understanding of variation at the genomic level is only beginning to develop, molecular techniques offer tre- mendous promise for identifying and manipulating valuable genes for a marketable trait or a physiological function. Biotechnological advances may allow identification of individual genes that can have positive effects on production, adaptation, and disease resistance traits. The ability to find useful genes in otherwise undesirable stocks and to transfer these genes mechanically to improved stocks will aug- ment genetic diversity. This potential provides a powerful argument for maintaining currently uncompetitive stocks. Methodologies for studying the genome at the molecular level are not, as yet, being routinely applied to livestock populations, even in developed countries. Nevertheless, rapid progress is being made in techniques for gene mapping and for identifying associations be- tween specified segments of the DNA (deoxyribonucleic acid) and primary production traits. Application of these techniques to animal species will aid in dis- cerning and characterizing diversity among various populations, but it may have both positive and negative effects on maintaining diver- sity. Marker-assisted selection involves the use of molecular genetic information to supplement traditional performance information and, in some cases, can increase rates of genetic improvement. Unfortu- nately, marker-assisted selection also has the potential to increase genetic uniformity and could produce an additional decline in ge- netic diversity in highly selected populations. Documentation of endangered breeds in some developed coun- tries has been done by nongovernmental private interest groups, such as the Rare Breeds Survival Trust (RBST) in England and the Ameri- can Minor Breeds Conservancy (AMBC) in the United States (Alderson, 1990a). In other developed countries, such as France as well as the nations of Eastern Europe and the Commonwealth of Independent States, government programs have been established if. Hodges, con- sultant, Mittersill, Austria, personal communication, March 1992~. Generally, endangered breeds have lower profitability under prevail- ing production and marketing conditions; therefore, substantial in- vestment in their preservation by commercial interests is unlikely.
The Need to Conserve Livestock Genetic Resources / 41 Public support to preserve the unique and most endangered of these breeds may be required. Some breeds in developing countries have become extinct, but the extent of risk and the rate of decline to other indigenous breeds are known in only a few developing countries if. Hodges, consultant, Mittersill, Austria, personal communication, March 1992~. Economic arguments for preservation are more readily justi- fied for indigenous livestock that are not well characterized because of specific genes they may carry or their potential genetic contribu- tions. Scientific Rationale Diversity is the base on which genetic research depends. Pre- served genetic diversity can be of value to many scientific investiga- tions. Researchers may use genetic variants to clarify mechanisms of development and physiological controls, patterns of domestication and migration evolution and speciation, and other biological ques- tions. For example, the annual number of lambs per ewe vary greatly among sheep breeds. Certain sheep breeds from countries such as Australia, Bangladesh, China, Finland, Indonesia, Ireland, Poland, and the United Kingdom have high lambing rates. Through crossbreed- ing, they provide the means for genetically transforming ewe prolifi- cacy. In the Australian Booroola Merino, a single major gene pro- duces an increase in ovulation rate, but its operation is not completely understood and requires further study (Bindon and Piper, 1986; Tho- mas, 1991~. Special genetic stocks of livestock species are also essential re- search tools. For example, inbred lines of chickens developed at the University of California at Davis are used worldwide for research on immunology and disease resistance of chickens (Office of Technology Assessment, 1987~. Other beneficial uses of preserved germplasm will emerge as genome maps are created and as scientists learn to identify and manipulate specific genes involved in the mechanisms of growth, reproduction, and disease. Cultural and Historical Rationale Preservation programs can provide visual evidence of a nation's heritage. Just as historical qualities are valued in buildings and geo- graphic sites, the same regard can be extended to animal populations that are representative of antique or heirloom breeds or populations. In restorations of historic villages, for example, old (and often rare) breeds are desired for authenticity. Farm parks, in which a large
42 / Livestock number of endangered and unusual breeds are maintained for the public, have proved popular in England, where 12 farm parks are now operating in association with the REST. Similar programs have begun in other countries (Alderson, 1990a). Furthermore, some ani- mals are used for recreation and in animal shows, exhibits, and fairs. One of the poultry stocks identified by the AMBC as being en- dangered is Dominique chickens, perhaps the oldest of the chicken breeds in the United States and present as a barnyard chicken since colonial days. They have black and white feathers and a rose comb and are featured in American folk art, music, and literature. The few surviving today in hobbyist exhibition flocks are highly inbred and not very vigorous. Some livestock breeds characterize a way of life and provide spe- cific products in areas around the world. For example, six native cattle breeds of southern Spain are in serious danger of extinction- the fighting bull was derived from these cattle. Among the endan- gered breeds are the dual-purpose Berrenda breeds, used for meat production and as steers to assist in the handling of fighting bulls (Rodero et al., 1990~. Although the community value of a certain stock for its cultural heritage role is difficult to assess, its economic value is evident from the financial support provided by visitors to farm parks. Thus, live- stock can, arguably, be accorded the same consideration as other en- dangered reminders of national heritage. APPROACHES TO LIVESTOCK CONSERVATION Numerous reports agree on the need to develop national and international efforts to preserve and manage livestock genetic resources (Alderson, 1990a; Council for Agricultural Science and Technology, 1984; Food and Agriculture Organization, 1984a,b; Hodges, 1987; Of- fice of Technology Assessment, 1985, 1987; Smith, 1984b; Wiener, 1990~. However, the approaches to conservation differ widely within the livestock community. They hinge on different perspectives about the importance of traditional livestock breeds, including indigenous breeds, to long-term genetic improvement programs. These perceptions also vary between developed and developing countries. In general terms, these approaches can be divided between two broad categories: (1) utilizationist, the primary aim being immediate use of available genetic resources, and (2) preservationist, the pri- mary goal being long-term preservation of genetic resources for un- known future use. Proponents of both approaches recognize that conservation of genetic diversity is economically justified only to the
The Need to Conserve Livestock Genetic Resources / 43 Oxen are still used today for plowing rice paddies in Bangladesh. Credit: Steve Raymer, O1992 National Geographic Society. extent that the preserved germplasm can reasonably be expected to make a contribution to future livestock improvement programs. Both also recognize that preserving breeds that are not currently economi- cally viable has a place in livestock improvement systems. Differ- ences between the two approaches largely pertain to perspective and emphasis, but they are real and strongly influence the practices fa- vored for managing genetic resources. The use and definition of the terms utilizationist and preservationist are not perfect or exclusive. Rather, they serve to illustrate the diversity of approaches to genetic conser- vation of livestock. The Utilizationist's View The utilizationist gives the highest priority to using available ge- netic resources to improve current livestock populations. Increases in the rate and efficiency of livestock food and fiber production are paramount. Existing populations are crossbred in carefully planned programs to achieve new and potentially more valuable gene combi- nations. The loss of breeds as distinct identities is not generally viewed as a matter of concern, as long as the genes that make those breeds potentially useful are retained in commercial stocks. This approach also recognizes the fallibility of planners, produc
44 / Livestock ers, and scientists. Endangered stocks must be preserved during the period of evaluation, crossing, and progeny assessment, and adequate genetic diversity must be maintained within commercial stocks to allow responsiveness to future changes in selection goals. Stocks with documentable, unique biological characteristics must also be pre- served for future use. However, the utilizationists place no particu- lar priority on preserving stocks that have not contributed to improv- ing current populations or that have no documentable, unique biological characteristics that they foresee as having potential future importance. In a report on animal genetic resources conservation in the United States, the Council for Agricultural Science and Technology clearly presents the utilizationist's view. It states that two kinds of animal germplasm merit priority for preservation (Council for Agricultural Science and Technology, 1984~. They are the following: · Breeds threatened with deterioration or extinction that have either known superiority for one or more traits or genetic uniqueness that could be important in meeting unforeseen needs. · Stocks that are useful for research or potential commercial ex- ploitation because of unique genetic traits. The report further states, "priority in germplasm preservation should favor stocks of known superiority in specific traits over those that are merely different from genetic material that is widely accepted" (1984:29~. It indicates that special efforts to preserve rare livestock and poultry breeds may not be justified if they do not have identi- fied, potentially useful biological characters. The Preservationist's View The preservationist regards existing breeds as unique genetic en- tities representing genes and gene combinations that have evolved over considerable periods of time to fit unique environmental and production conditions. This approach emphasizes the value of pre- serving the widest possible spectrum of genetic diversity, because it is not possible to predict future needs. Breed preservation is re- garded as the most practical method of gene conservation. The cross- breeding of endangered breeds with more popular stocks is consid- ered to be a threat to the survival of endangered stocks. It is acceptable only when the identity of the original stock as a purebred line has been preserved. The cultural and historical importance of breeds is also given high priority. The preservationist's view recognizes the potential value of breeds to livestock development, but it places higher priority on preserving
The Need to Conserve Livestock Genetic Resources / 45 existing breeds. Future use of genetic resources in crossbreeding and selection programs at the commercial level remains the primary justi- fication for conservation, but the inability to predict future needs and, therefore, to choose which breeds are most worthy of preserva- tion remains central to the rationale for this perspective. The Cotswold Farm Park in England gives three reasons for sav- ing rare breeds that do not appear to meet today's production stan- dards. First, they are part of society's heritage. Second, their charac- teristics could make them ideal research subjects. Third, and most important, they provide livestock breeders with a broad pool of ge- netic diversity to meet unforeseen needs (Cotswold Farm Park, 1985~. The Committee's View The utilizationist emphasizes the characterization of existing breeds and the evaluation of the most promising as components (either purebreds or crosses) of current production systems. Only the most promising breeds or those that represent documentable biological extremes should be preserved. Improvement of existing populations should meet cur- rent and perceived future needs. The preservationist's view, by con- trast, calls for preserving the greatest possible number of breeds as purebreds. Crossing to form new populations should be accompa- nied by the protection of breed identity. The preservationist empha- sizes the inability to predict future needs and, therefore, to create a priority list of candidate breeds for preservation. Reconciliation of these two views must begin with the recogni- tion of their common goal: sustained long-term improvement of live- stock for use by an expanding global population. The main conflict is in how each view establishes priorities for conservation and how each assesses future livestock needs. Current human needs for food and fiber are pressing and will continue to increase. These needs must be met. The goal of this report is not to validate one position at the expense of the other, but to present a position that is acceptable to these divergent views for building coordinated efforts toward the common goal of conserving global livestock diversity. The committee agreed that one goal of genetic resource manage- ment programs must be to maximize rates of genetic improvement in commercial stocks. It also endorsed the view that some form of ge- netic resource conservation is an essential component of long-term livestock improvement programs. Differences of opinion existed within the committee on the amount of resources that should be devoted to breed preservation. It was agreed that preservation should, at a minimum, address breeds that are of (1) potential economic value, or are (2)
46 / Livestock endangered and represent types with documentable, unique biologi- cal characteristics. For a national program, this approach would en- courage maintenance of adapted indigenous types as pure lines while they are being compared with imported stocks and while their opti- mum role in breeding programs is being determined. It would also encourage long-term preservation of genetic extremes that could pro- vide material valuable in future commercial stocks. The establishment of priorities and the determination of which breeds or populations are to be preserved will depend on several considerations, including the resources available, national and inter- national needs, and the genetic similarity among available breeds and populations. Development of an understanding of population structures and genetic relationships among breeds or strains can aid the setting of priorities. The committee thus concluded that responsible management of livestock genetic resources involves aggressive programs of livestock improvement as well as strategic programs for conservation. RECOMMENDATIONS The development of comprehensive national and global strate- gies for preserving and using animal genetic resources will require the integration of livestock improvement programs and programs for conserving livestock genetic resources. To date, improvement pro- grams have taken precedence over conservation programs, largely because of the quicker and greater return to investment. Yet, a long- term approach to increasing global food resources demands that con- servation become an integral part of programs for animal improve- ment. Mechanisms must be put in place to ensure that genetic diversity of the major livestock species is maintained to support improvements in produc- tion efficiency and to Accommodate future changes in selection goals. Global human populations will continue to increase in the fore- seeable future. Global capacity for food production must, therefore, also increase. Most major livestock populations of developed coun- tries have been subject to intensive artificial selection for a period of less than 50 years. Scientists cannot predict what level of genetic diversity will be required to support genetic manipulations in live- stock populations over periods of many hundreds of years. Yet, ac- tion is required now to maintain genetic diversity, and it must be undertaken responsibly, regardless of current limitations in under- standing the basis of genetic diversity. These mechanisms for action
The Need to Conserve Livestock Genetic Resources / 47 could take many forms, depending on national and international needs and resources, but their common objective would be to conserve the livestock genetic resources essential to agriculture and society. Clear national and international policies are needed to prevent further losses of potentially important animal generic resources. Agricultural research policies have focused exclusively on live- stock improvement programs. They must recognize that conserva- tion is a vital part of these efforts. In developing countries, the re- sponsible handling of indigenous breeds must be given a high priority. Priority for preservation should be given to species, breeds, or popula- tions that are both at the greatest risk of loss and that appear to have potentialforfuture use in livestock improvement programs. In most countries the resources available to preserve animal ge- netic resources will be limited. In addition, not all animal species or particular breeds within a species will have a significant economic role in other countries. Preservation efforts must focus first on those species and breeds that are at risk and that have potential for contrib- uting to future economic or social development in the country. A1- though it may be desirable to save all endangered breeds, limited resources will necessitate the setting of priorities, based on perceived future economic contribution and biological uniqueness.
