Livestock (1993) / Chapter Skim
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1 The Need to Conserve Livestock Genetic Resources
1 The Need to Conserve Livestock Genetic Resources
Pages 21-48
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From page 21... ...
Genetic diversity within agricultural species is important as expanding human populations seek to improve their standards of living and place greater demands on natural resources. New technologies that manipulate animal physiology and environment have substantially enhanced livestock production, particularly in the latter half of this century, to meet food and other economic demands.
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From page 22... ...
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 Mediterranean Sea and the Persian Gulf.
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From page 23... ...
Cervidae Rangifer tarandus (reindeer) Bovidae Bos taurus (humpless, primarily temperate zones)
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From page 24... ...
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.
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From page 25... ...
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.
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From page 26... ...
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~ ...
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From page 27... ...
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, remains critical to meet future needs and to respond to future production changes.
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From page 28... ...
;_ 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.
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From page 29... ...
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.
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From page 30... ...
Disease 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.
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From page 31... ...
Future study of salt tolerance and copper metabolism 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 resources for future use in basic scientific research and the advancement of the agricultural sciences.
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From page 32... ...
Their potential negative impacts 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.
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From page 33... ...
A similar situation exists for commercial turkeys, which also experienced declining reproductive abilities as size and muscling increased. Artificial insemination is now universally used in the breeding of industrial stocks.
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From page 34... ...
Livestock in large extensive 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 injections of vitamins and trace elements as needed.
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From page 35... ...
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.
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From page 36... ...
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 environments are deliberately manipulated to increase production.
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From page 37... ...
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.
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From page 38... ...
RATIONALES FOR CONSERVING LIVESTOCK GENETIC RESOURCES To some extent, the loss of less competitive livestock can be considered a normal part of the livestock improvement process. Natural selection favors animals that are best suited to a particular environment.
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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.
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From page 40... ...
Unfortunately, marker-assisted selection also has the potential to increase genetic uniformity and could produce an additional decline in genetic diversity in highly selected populations. Documentation of endangered breeds in some developed countries has been done by nongovernmental private interest groups, such as the Rare Breeds Survival Trust (RBST)
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From page 41... ...
In the Australian Booroola Merino, a single major gene produces an increase in ovulation rate, but its operation is not completely understood and requires further study (Bindon and Piper, 1986; Thomas, 1991~. Special genetic stocks of livestock species are also essential research tools.
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From page 42... ...
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; Office of Technology Assessment, 1985, 1987; Smith, 1984b; Wiener, 1990~. However, the approaches to conservation differ widely within the livestock community.
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From page 43... ...
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 economically viable has a place in livestock improvement systems.
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From page 44... ...
The Preservationist's View The preservationist regards existing breeds as unique genetic entities 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 preserving the widest possible spectrum of genetic diversity, because it is not possible to predict future needs.
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From page 45... ...
Second, their characteristics could make them ideal research subjects. Third, and most important, they provide livestock breeders with a broad pool of genetic diversity to meet unforeseen needs (Cotswold Farm Park, 1985~.
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From page 46... ...
RECOMMENDATIONS The development of comprehensive national and global strategies 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 programs have taken precedence over conservation programs, largely because of the quicker and greater return to investment.
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From page 47... ...
In developing countries, the responsible handling of indigenous breeds must be given a high priority. Priority for preservation should be given to species, breeds, or populations that are both at the greatest risk of loss and that appear to have potentialforfuture use in livestock improvement programs.
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