FARM
ANIMAL GENETIC D.L. Patterson Copies of this pamphlet may be obtained from Canadian Farm
Animal Genetic January 2003 |
Background
Phenotypic characteristics (appearance) are often used to divide animals into species, and there is great diversity across species. However there may be limited genetic variation within any given species. Domestication of animals has led to the development of specific breeds, in the process increasing the within species variation.
Intensification of Agriculture
As agriculture has moved from small production systems to large commercial systems farm animal genetic diversity has declined. Selection goals and production environments are now very similar throughout the developed world. We are very efficient at changing the genetic diversity of populations.
For example:
The result? Modern animal industry now uses only a few breeds of any species. Of the many breeds once commonly seen on farms, many have declined greatly in numbers and others have disappeared completely.
Reasons for Genetic Conservation
If we have the best why are we concerned about preserving genetic diversity?
We need to keep potentially
useful genes and gene combinations
The ‘best’
is defined by industrial production of a small number of products in a developed
world. We are only now beginning to understand the complexity of genes and how
they interact to produce the phenotype. We risk losing genes of value.
For example:
To take advantage of heterosis
(hybrid vigour)
Heterosis is the increase
above the average of the parent stocks obtained by crossing genetically diverse
breeds. Crossbreeding is practiced widely in swine, sheep, and beef production.
If only a few breeds are kept the opportunity to develop good crosses is lost.
To overcome selection plateaus
A selection plateau occurs
when genetic variation is lost; no further change is possible because animals
are genetically alike. If genetic variation exists in other breeds, crosses
can be made to overcome this.
To provide an insurance policy against
For cultural reasons
Our history is closely
linked to agricultural practices and use of particular breeds. The vache Canadienne
and the poule Chantecler are associated with French Canadian culture. The Newfoundland
pony developed in response to a harsh environment and is now recognized as a
Heritage breed by Newfoundland and Labrador. The Canadian horse has been recently
recognized by Parliament as the national horse of Canada. Poultry breeds such
as the Barred Plymouth Rock and heavy horse breeds such as the Percheron and
Clydesdale were common on farms. These breeds are now used on ‘living
history’ parks or ‘living museums’, both important in education
and tourism.
For research
Control (unselected)
lines are used to measure genetic progress in selection. Identification of specific
genes, which regulate traits such as product quality and health, is made easier
by comparing very different groups.
Economic evaluation of breeding programs now includes sociological aspects,
as part of a focus on sustainable rural development. Research into the role
of minor breeds in such production systems is needed.
Goals of conservation
To keep genetic variation as gene combinations, in a form that is easily recovered
Live animals may be appropriate for some situations. Cryopreservation of sperm, ova or embryos is possible in many species and new tissue culture technologies show promise.
To keep specific genes
As gene sequences linked
to specific traits are identified and defined we will be able to save those
DNA portions of interest.
Steps necessary for conservation
Inventory
Definition of a breed
as endangered depends on factors such as the number of breeding males and females,
overall numbers, number of sub-populations, and trends in population size. It
is thus important to monitor numbers and change in numbers on an on-going basis.
Evaluation
Stocks must be characterized
for phenotype and genotype, using new technology as appropriate. Gene mapping
approaches such as testing for single nucleotide polymorphisms (SNP’s)
help to track ancestry and to determine the genetic distance of one group from
another. Phenotypic performance evaluation must be standardized, and carried
out in the environment in which the stocks might be used.
Choice
Choice of breeds for
conservation must include cultural reasons, potential value and threat of extinction.
New mathematical techniques and economic theories assist in assessing risk of
loss and potential benefits.
Saving pure breeds preserves that breed’s characteristics and makes a readily identifiable animal. Crossing several breeds to produce composites has the advantage of saving the genetic material from all while reducing upkeep costs. However the total genotype of each breed is lost.
Preservation
Populations can be saved
as live animals. This is expensive and unless the breed can be used for production
is not likely to succeed. Development of niche marketing schemes emphasizing
the traits of a particular breed can be successful. Linking breed maintenance
with tourism and education (farm visits) can be useful.
Cryopreservation: Semen, ova, and preferably embryos can be frozen. This is successful for cattle, but is unfortunately difficult for some species. For those species where cryopreservation is routinely practiced a national centre for monitoring and maintaining frozen genetic resources is needed.
DNA collection: The potential exists to use DNA and cloning to re-develop breeds, but the technology is still new and costs are high. Whether kept as live animals or as frozen material, more than one location is needed. Natural disasters, accidents, and changes in financial resources can result in instant loss of a stock.
Who is involved?
Commercial animal industry
The commercial industry
must emphasize traits of economic value now and in the short-term future. Industrial
breeders keep genetic stocks as necessary to satisfy that need. Increased globalization
and vertical integration of companies puts such genetic reserves at risk in
Canada and around the world.
Individuals
Private producers keep
stocks of minor breeds, as a hobby or as part of a farm enterprise. Emphasis
may be on phenotype and small populations may lead to reduced genetic diversity.
Stocks are subject to loss as a producer’s situation changes.
Conservation groups
The Canadian Farm Animal
Genetic Resources Foundation works with government, universities and research
centers, rare breed organizations, and private producers to obtain funding and
provide resources and information on conservation of animal genetic resources.
Membership includes farmers, scientists, breed associations and commodity organizations.
Rare Breeds Canada is an organization of producers and others interested in conservation of minor breeds of livestock. Information on management methods, breeds at risk, and exchange of genetic material is facilitated through meetings, a newsletter and a web site. The group works closely with other national groups such as the American Livestock Breeds Conservancy. Rare Breeds International is the umbrella organization for these groups around the world.
Government
Limited funding is available
from federal and provincial governments at present in Canada. At one time federal
agriculture research stations and many universities kept stocks of livestock
breeds, but today these stocks are minimal. Provincial governments may assist
via museums and farm parks. During the mid 1990’s Agriculture and Agri-food
Canada provided resources to develop an inventory of animal genetic resources
and to develop criteria and set priorities for conservation. Domestic breeds
are recognized as a genetic resource by the United Nations Convention on Biological
Diversity (1992) to which Canada is a signatory.
International
The United Nations Food
and Agriculture Organization (FAO) plays a major role in assisting individual
countries with conservation programs and provides a forum for international
consultation and planning. Their publications and website provide information
on methods and resources. At present countries around the world are developing
reports on the current status
of their genetic resources, for integration into a World Report by 2006. A draft
of Canada’s report was submitted to the federal government in September
2002.
The United States has established a National Animal Germplasm program. Activities include a central storage system for genetic material and a database to track resources.
Conferences such as the World Congress on Genetics Applied to Livestock Production provide a forum for scientists involved with genetic diversity. Whenever possible, funding is made available to allow scientists from developing countries to attend.
Further Reading and Resources