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.
- Animals are kept in environments ranging from temperate to tropical, resulting in selection for different characteristics in different locations.
- Humans have selected animals for specific uses, e.g. cattle for draft purposes, meat and milk; poultry for eggs and meat, sheep for meat, wool and milk.
- Animals are often kept in large groups, leading to indirect selection for disease resistance and behaviour.
Reasons for Genetic Conservation
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
adaptive value.
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 provide an insurance policy against
- 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
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.
Necessary Steps 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.
