S1037: Integrative Functional and Physiological Genomics of Poultry
Statement of Issues and Justification
Importance of research and potential consequences Genetic selection for economically important traits has often been at the expense of others such as reproductive efficiency, metabolic disorders and immunological fitness. Limited information is available to describe the genetic inter-relationships or interaction of genes and their subsequent effects on traits. Therefore, it is the purpose of this project to develop co-operative research to define physiological, biochemical and gene expression consequences to genetic selection in poultry using both selected and commercial lines. Archaeological evidence for domestication of fowl dates to approximately 2000 BC in the Indus valley (India). Almost 4000 years later, the chicken accounts for nearly 75% of major domesticated animals in the world, with 2003 US population of over 300 billion. This increase is inextricably linked to the unprecedented increase in per capita consumption of poultry during the same time. By 2003, Americans consumed in excess of 110 lb. of poultry per capitaof which >90 lb. were chicken alone. The modern broiler-type chicken attains a 5.5 lb. body weight in 40-42 days of age with an overall feed efficiency of less than 1.9. Approximately 85-90% of this change in growth has been attributed to selection for growth, and has been achieved by reducing the market age to the same body weight by one day per year. With continued progress for further-processed products there has been a shift in market age to slaughter. This has resulted in the re-emergences of physiological and metabolic syndromes. The normal process of growth involves the simultaneous deposition of bone, muscles, and fat; each exhibiting an individual pattern of development. Selection for body weight has altered two phenomena that impact these processes. One is progenesis, which reflects the acceleration of development as defined by precocious sexual maturity. The other is neoteny, which is the retarded development of specific tissues and/or organs. Progenesis and neoteny have very different roles during selection for growth. Selection at the point of inflection leaves some characters in their juvenile state, while accelerating others. For example, there is a relatively larger increase in the proportion of muscle mass in chickens selected for high body weight as compared to late selection. Overall these alterations in developmental timing, called heterochrony, can occur via changes in gene expression and/or changes in the allometric relationships among physiological and metabolic sub-systems themselves. Difficulties in determining the underlying physiological and metabolic systems responsible for this distortion have been two fold. First, there has been an inability to define the non-linear dynamics of the growth process in relation to other physiological systems. In part, this has been due to the absence of animal model systems to compare and contrast the different developmental periods of growth. The second has been the limited application of appropriate molecular, physiological and/or biochemical tools to identify changes in genetic and physiological processes underlying growth. Domestication, genetic improvement and controlled reproduction have come with a cost. The broiler industry has seen increases in the incidence of obesity, skeletal problems, juvenile mortality, disease resistance, ascites, maladaptation to stress, metabolic disorders and inability to utilize phytate phosphorus. Reduced reproductive performance in the guise of erratic ovulation and defective egg syndrome has become common place among broiler-breeder hens. Recent reports suggest that the ability of the broiler-breeder male to fertilize eggs is declining at a rate of 0.5% per generation. Curiously, a major challenge to the poultry in and animal agriculture is the propagation of the idea that traditional selection parameters coupled with production practices are the direct cause of decrease animal fitness and welfare. The negative relationship between genetic selection and fitness has been surmised from the temporal congruence of the two events in both industrial and experimental settings. This conclusion is reinforced by current industry practices that recommend the restriction of early growth. However, data from the S289 Project have consistently distinguished between shared environmental and/or spurious correlations. The focus of this project is to investigate the underlying changes in physiological, cellular and biochemical mechanisms associated with genetic improvement of economically important traits in poultry.Consequences if research is not done: The lack of understanding of the underlying physiological, cellular and biochemical mechanisms associated with genetic improvement would mean that there would be no remedy or solutions for the current problems associated with poultry breeding as enumerated in the previous section.
Need as indicated by stakeholders (Poultry breeding Industry) The prospect for genetic improvement continues to be encouraging. From poultry breeding industrys perspective, the limits of selection for growth rate and egg production may be on the horizon and industry will place increased emphasis on new sources of genetic variation, and appropriate biomarkers for the genetic improvement of fitness and welfare related traits. The upcoming transition period will be extremely important, and rate at which these changes can be adopted for commercial uses would influence the long-term economic sustainability of poultry as a viable source of food. A major effort to understand the physiological, cellular and biochemical mechanisms underlying genetic changes in poultry requires a wide range of expertise, which cannot be found in any single experimental station. Members of S289 group have primary expertise in genetics (quantitative, molecular/physiological), physiology, endocrinology and nutrition. While independent studies are conducted at the stations where primary genetic stocks are generated and maintained; it is the overall diversity of training and interest and consequential collaboration between stations that makes it possible to complete the objectives of this proposal. The chicken sequence is now available and this will change ways of conducting poultry research. Researchers can take advantages of the chicken genome and expressed sequences, microarrays and high-throughput genotyping that has been established (TX) and is available for all collaborators in the proposed projects. Interaction among project scientists would lead to the successful understanding of genetic mechanisms underlying growth, reproduction and fitness.
Multi-state Effort The S289 and its predecessor S233 Projects have a strong history of interaction as evidenced by the many multi-authored publications, sharing of methods and genetic resources including semen, hatching eggs, DNA and/or RNA sequences. This project directly addresses a national initiative in the area of Genetic Resources, Development and Manipulation . Several disciplines and co-operative investigations are encompassed within the proposed research. However, the distinguishing feature of this project is its emphasis on a systems approach to the elucidation of molecular, biochemical and physiological changes as impacted by genetic selection. Only collaborative efforts between geneticists, physiologists, nutritionists, immunologists make this possible. No one experiment station possesses the expertise to maintain and select genetic lines while conducting the molecular, physiological and biochemical assays necessary to meet the objectives of this proposal.
Technical feasibility of research Member stations have maintained models representing the major species of poultry (turkey, chicken, quail and guinea fowl) that will enable scientists to identify appropriate cellular, physiological and molecular mechanisms underlying genetic improvement in growth. Collaborative efforts are planned between stations housing and generating the primary genetic stocks and the remaining institutions. This multi-station effort is needed to better understand the consequences of direct selection for growth, immunological response and disease resistance on correlated traits such nutrient utilization, reproductive efficiency, metabolic and environmental stress. Genetically divergent poultry lines are an important resource for understanding the molecular basis of many economically important traits. Biochemical, physiological and molecular genetic tools will be used to determine the cellular effects of genetic selection.
Impact and benefit Benefits of this research include a) basic information about selected lines for use by poultry breeders and b) elucidation of biochemical, physiological and cellular pathways affected by selection for economically important traits. This creates an opportunity to transfer scientific knowledge from specific studies involving the chicken to other less widely-studied poultry species including turkey, quail and guinea fowl.
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