Conservation genetics in poultry breeding
Chicken and other poultry species contribute to humankind in many ways:
The excellent advances in poultry production during 20 th century are attributable to a large extent usage of population genetics principles and intensive selection and development of specialized populations of poultry. The breed base made available to scientists at the turn of 19 th century provided resources and opportunity to achieve many scientific advances during 20 th century. For continued genetic progress during 21 st century, it is very important to conserve the genetic reservoir of existing poultry populations which can respond to future research and production needs. The biological diversity of the planet is rapidly being depleted and is a global concern because of dangers of total extinction and/or endangered level of many flora and fauna. Poultry biodiversity is also declining at an alarming level globally and we may need to review the urgency of conserving poultry biodiversity because avian species are unique and different from other flora and fauna.
Why conserve Poultry biodiversity?
Poultry biodiversity refers to the genetic variants available within and among poultry species (chicken, turkey, quail, duck, goose, pheasant) distributed around the globe. Distinct indigenous varieties, native breeds, small scale traditional farms, fancy breeds maintained by hobbyists, stocks developed and maintained by government and research institutions and specialized populations developed by industry form the bulk of this genetic reservoir. The enormous potential of these valuable resources for contributing to food production, biotechnology and health of humankind remains largely untapped. These germplasm resources form the basis for future economic, scientific and socio cultural opportunities. Maintenance of the genetic potential of these resources at adequate levels requires systematic scientific application of conservation biology principles. Applied conservation genetics, which integrates population genetics and molecular biology, has attracted the attention of international scientific community recently. This emerging discipline would help identify, analyze and develop strategies to conserve existing biological diversity and variability and make them potentially available for future scientific progress.
Causes of decline in Poultry biodiversity:
Diminishing poultry biodiversity and genetic variation are caused by,
Experimental research populations:
Many specialized research populations of different species of poultry were developed by research organizations and universities from as early as 1930's. They include random-bred, inbred, long-term selected, mutant and cytogenic stocks and made valuable contribution to scientific application to enhance poultry production, vertebrate biology, human and animal health, etc. But, due to various reasons many of these stocks do not exist anymore. Between 1988 and 1998 alone USA has documented discontinuation of more than 200 experimental research populations of poultry. Probably in India, a parallel situation may exist but has not been documented. Changed priorities of organizations, researcher retirements, reduced funding and rising costs are cited as major reasons for such losses. The losses of biodiversity and untapped future potential in these cases is enormous and unknown.
The indigenous breeds consisting of locally adapted stocks evolved over millions of years get replaced by modern industrial stocks at a faster rate. The true genetic potentials and their value to food production and biotechnology are, as such, unknown. This is especially true for developing countries like India where, due to economic reasons small-scale poultry breeders and fanciers are not able to survive. Globally, FAO (2000) has listed 30 extinct chicken breeds in the recent past with many more in critical list .The total percentage of avian breeds at risk of being lost increased from 51 to 63% in a matter of 4 years indicating the alarming trend. USA has a system of periodic census inventories of genetic resources available with small and middle level poultry breeds having economic and historical significance through American Livestock Breeds Conservancy (ALBC). American Poultry Association also lists more than 150 breed standards. Indian database on the above model is very important.
Consolidation of primary breeding companies:
Due to thin profit margins and fierce competition the global poultry breeding companies witness many mergers, closures and takeovers. This has resulted in an overall decrease in total number of elite pure lines by these multinationals marketing breeding stocks globally. In egg layer stocks only five major poultry breeding companies supply almost all the eggers throughout the world. Six major primary breeders holding 35-40 pure lines control and supply 400 billion market broilers globally. These stocks are designed and genetically selected over many generations for economically important traits of growth, production, and reproduction. They also require specialized management, nutrition, and disease prevention and environment conditions for optimal performance to ensure profitability. Because of their uniform genotype they may not have adequate heterozygosity to sustain evolutionary genetic adaptations. Decisions about retention or termination of lines from programs are necessarily based on profitability and not genetic. As a result, these stocks have a restricted narrow genetic base.
Erosion of genetic potential:
As a result of intense genetic selection over many decades, there is loss of genetic variation in industrial stocks and many stocks may be nearing physiological plateau in the near future. Stocks with less genetic variability can not cope up with challenges like: newly emerging or reemerging diseases, environment conditions etc. Genetic diversity in industrial stocks is essential to afford future opportunities of selection for changed market/consumer preferences, products etc. This makes it imperative for primary poultry breeding companies to conserve all their bio-resources without dropping.
Conservation of Biodiversity by Molecular tools:
The modern day molecular tools provide highly efficient scientific levers to arrest the decline in biodiversity of the endangered poultry species. With the advent of various DNA profiling techniques, the endangered and threatened breeds of poultry can be efficiently evaluated for their genetic worth and be maintained without further erosion of genetic variability. The multi-locus DNA fingerprinting utilizing VNTR sequences (conserved across the various orders, genera and species of aves), provide the most economic and powerful way of analyzing their intra and inter-population genetic variability. Besides working as ultimate tools to determine the parentages and strain/ line identities, these tools can be used for greater application in conservation genetics. By DNA fingerprinting, it is possible to deduce the existing genetic relatedness and or distances between individuals & breeds and thereby estimate various population parameters like average heterozygousity in a given flock (even in absence of pedigree and quantitative information), coefficient of genetic differentiation (that reflects the components of total genetic variation attributable to intra and inter-population genetic variations) and above all, the indices for inbreeding (accumulated over generations) to any breeder stock. By judicious amalgamation of the DNA profiling tools, the job of arresting the fast-diminishing bio-diversity becomes much easier and a feasible task. With the release of the draft chicken genome map database by the NIH, USA, since March 2004, there is a plethora of DNA markers available to the molecular geneticists, which can be put to use for the conservation geneticist following suitable protocols. Among the most potential DNA markers are: microsatellites, unique RFLPs and SNPs, which can be efficiently used for the above, using the sequence info, freely accessible from the public domain databases. With such available genetic information in hand, custom-breeding programs can be designed, by the breeders, which could help-conserve any endangered breed in a scientific manner.
Systematic steps to arrest decline of poultry biodiversity:
Training: It is important to take urgent steps to generate trained human resources with knowledge of conservation biology especially genetics.
Education: Veterinary/animal husbandry curricula may incorporate conservation biology as one of core subjects.
Research: Studies encouraged at post graduate and doctorate levels to assess and compile database on biologically important indigenous varieties of chicken species.
Data: organization on the lines of American Livestock Breeds Conservancy (ALBC).
Standards: Compilation of Indian Poultry Breed Standards and Specifications like British Poultry Standards and American Standards of perfection.
Extension: Encourage local/fancy chicken breeding at their source locations
Coordination: Coordinate with zoological parks and wildlife personnel in assessing the genetic worth of avian/chicken species available with them and apply conservation genetics principles to maintain present levels of diversity
Participation: Encourage private sector pharmaceutical, biotechnology, bioinformatics firms to invest in conservation of valuable avian genetic resources of India.
There is an urgent need to evaluate the poultry biodiversity of India and to compile a viable data base for future potential applications in scientific and biotechnological applications of food production. To achieve this objective, trained human resources in the areas of conservation biology especially genetics are to be made available within a reasonable time. The latest emerging genetic tools like DNA profiling procedures are real boons for such purposes and should be employed to the advantage of conservation genetics. Active involvement of various agencies and poultry community is very essential.
Crawford,R.D. (1990),Poultry Breeding and Genetics, Elsevier, Amsterdam
Francham,R.,Ballou,J.D. and Briscoe,D.A. (2004),A Primer of Conservation Genetics, Cambridge University Press
Muir.W.M. and Aggrey, S.E. (2003) Poultry Genetics, Breeding and Biotechnology, CABI Publishing.
|Source : IPSACON-2005|