Chasing the Genetics of Ascites in Broilers

Our research group has been pursuing the genetics of ascites in broilers for many years.  Ascites, a form of pulmonary arteriole hypertension, is a collection of adverse changes in a broiler chicken including high venous pressure, accumulation of fluids in the body cavity, and cardiac hypertrophy, resulting from the reduced ability for oxygen to be supplied to the organs. These events result in either processing plant condemnation or death from heart and lung failure. Losses in the poultry industry vary but have been estimated at $10-100 million/year. We have employed low and medium density SNP-based genome wide association studies (GWAS) in multiple generations of experimental lines selected based on ascites phenotype.  Earlier GWAS analysis identified regions on chromosome 9, but further analyses have yet to demonstrate these regions as generally applicable in commercial lines.  Multigenerational GWAS identified regions on chromosome 2 and Z.  Further analyses reveal that only the GgaZ region is reliably associated with ascites in our experimental line.  Review of our results suggest there are no major genes for ascites in our experimental lines, despite an ability to rapidly select for or against ascites phenotype and a relatively high estimated heritability.  Alternatives for moving forward on dissecting ascites susceptibility will be discussed.