Genetic and Functional Genomic Approaches to Improve Production and Quality of Pork

NON-TECHNICAL SUMMARY: The National Pork Board 2008 Plan of Work describes five critical issues facing pork producers. Desired outcomes and tactics to achieve them are listed for each critical issue. Issue #1 is "The competitive advantage for US pork". A desired outcome is science-based industry solutions for animal care and well-being, swine health, pork production, environmental management and food safety. Genetic solutions are given high priority. These include discovery of genetic factors that contribute to pig responses to disease with initial focus on Porcine Reproductive and Respiratory Syndrome (PRRS) and Porcine Circovirus Associated Disease (PCVAD) resistance and tolerance, development of new genetic technologies and outreach strategies to impact complex economically important traits including maternal efficiency, nutrient utilization, and disease resistance, and research to provide producers with information and technologies to enhance lifetime productivity of breeding females through improved production and longevity and reduced mortality. Research on sow longevity should focus on economically important production traits including gilt development, genetics/adaptability, nutrition, reproductive physiology, and management of breeding females. <p>This project uses these tactics to address NPB Issue #1. PRRS, caused by the PRRS virus (PRRSV), and PCVAD, caused by PCV Type 2, are the two most economically important swine diseases in the US. PRRS alone causes annual losses in excess of $600 million. Economic costs of PCVAD, a wasting condition from which pigs rarely recover, have not been documented. Secondary pathogens, along with PCV2, trigger the disease and its incidence in certain parts of the US is high, affecting 15 to 40% of pigs in some herds. Vaccines for PRRS exist but have not been broadly effective. Recently, a vaccine for PCV2 was developed. However, it is expensive to produce and supplies are limited. Annual sow replacement rates greater than 50 % and death losses of 10-15% are common in US herds. Whereas genetic selection for increased prolificacy has been effective, it appears it has also resulted in shorter productive life of sows. These losses are not only important economically, but they cause great welfare concerns. This project has two main focuses. One is on genetics of resistance/tolerance to PRRSV and PCV2 viruses. The second is on genetic and genetic by nutrition interaction effects on sow productivity and longevity. Improved disease resistance will enhance production efficiency, animal welfare, and producer and consumer acceptance of pork and reduce the need for antibiotics. Reducing sow losses will improve production efficiency and reduce welfare concerns. Because of the complex and multi-faceted nature of both disease and sow longevity research, no single institution has sufficient resources and facilities to address them independently. Therefore, a coordinated and integrated effort among experiment stations is crucial.

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APPROACH: Specific aims at NE are to determine genetic parameters for variation in responses to pathogens affecting pigs, to identify genes responsible for variation in resistance to pathogens, and to develop a comprehensive database with information on animal genetics, immune traits, disease symptoms, and environmental parameters. A central database is an important component to determine the degree of genetic, environmental, and genetic by environmental variation on pig health and responses to infectious organisms, to identify host genes and proteins that are critical to pig health and disease resistance, and to develop improved methods to select for resistance and prevent or manage disease.Data will be used to describe disease intensity, symptoms, duration, pathology, and morbidity/mortality, assess responses to routine vaccinations; define factors associated with disease resistance/susceptibility, identify specific pathogenic variants, develop models to predict disease incidence and disease loads from genetic and environmental information, estimate heritabilities of susceptibility to diseases and genetic relationships with production traits, and identify genes involved in disease resistance. NE will focus on both objectives, but specifically on genetic resistance to PRRSV, genetic resistance to PCV2 virus, genetics of sow longevity. Specific objectives are: PRRSV - test hypotheses about genetic selection for resistance to PRRSV. The working hypotheses are that high pre-infection serum levels of interleukin-8 are associated with PRRSV-resistant pigs, and following infection, low expression of interferon-gamma in cDNA and in serum are associated with resistance. PRRSV infection experiments will be conducted and data submitted to a central database for genetic parameter estimation, SNP association studies, and development of application in applied programs. Improved methods to control expression of Porcine Circovirus type2 diseases (PCVAD) will be developed. The relationship between level of antibodies for Porcine Circovirus Type 2 and amount of PCV2 genomic copy with the onset of Postweaning Multisystemic Wasting Syndrome will be determined. A database to determine other factors, including host genetic variation, related to severity of PMWS will be developed. Gilt development strategies as a means to improve sow longevity and lifetime production of females of prolific maternal lines that differ in rate of lean growth will be developed. The long-term aims are to offer swine producers management strategies to enhance sow welfare, to estimate genetic parameters for longevity, and to contribute tissue and data to a central database for association of SNP with longevity.