Transcript Lecture 3b Why Conserve Farm Animal Genetic

Farm Animal Genetic Resource
conservation
What, why and how
Reasons for genetic conservation
1. We need to keep potentially useful genes
and gene combinations
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.
3 Examples
Example1
• Non-intensive agricultural production systems
may not want genes for prolificacy, such as the
Booroola gene in sheep which increases the
number of lambs per mating. Hyper-prolific
lines of sheep and swine are of value in
modern production systems.
Example2
• Porcine stress syndrome in swine can lead to
undesirable quality in the pork, but the
condition has been associated with faster
growth. DNA tests now allow us to select
directly against the allele linked with this
condition.
Example3
• DNA tests have now been developed and
commercialized to allow selecting beef cattle
directly for meat tenderness, using the
calpastatin gene. Frequency of this gene varies
among breeds.
2 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.
3 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.
4 To provide an insurance policy
against
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climate change
spread of disease, especially in monocultures
changing availability of feedstuffs
social change, such as issues of animal welfare and
environmental sustainability
• selection errors: a widely used sire may spread a
genetic disease throughout a population before the
problem is identified
5 For cultural reasons
Human history is closely linked to agricultural practices and
use of particular breeds. 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.
6 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.
For Research
• 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 for 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.
Goals for conservation
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.
Steps necessary for conservation
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
• Individuals
Commercial animal industry
The commercial industry must emphasize
traits of economic value now and in the shortterm future. Industrial breeders keep genetic
stocks as necessary to satisfy that need.
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
• Breed organizations, and private producers
obtain funding and provide resources and
information on conservation of animal genetic
resources. Membership includes farmers,
scientists, breed associations and commodity
organizations.
Government
Limited funding is available from national
governments for conservation. Agriculture
research stations and many universities keep
stocks of livestock breeds, but today these
stocks are minimal.
FAO
• 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.
Conferences
• 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.