The Genetic Basis of Host Susceptibility to Bovine Respiratory Disease

There is growing interest in the selective breeding of livestock for enhanced disease resistance. Bovine respiratory disease (BRD) or pneumonia is the largest single natural cause of death in US beef and dairy cattle, and BRD resistance represents an obvious target for selective breeding programs. The heritability of disease resistance is  typically low, partly as a result of suboptimal diagnosis (i.e. not all sick animals are identified, healthy animals may be incorrectly diagnosed as ill, and some susceptible animals will appear resistant when in fact they have not been exposed). Additionally, the genetic basis of BRD susceptibility is likely complex and governed by the effects of multiple genes. This suggests a large number of case:control animals will be needed in datasets for disease susceptibility marker discovery. In 2011 AFRI funded a 5-year Coordinated Agricultural Project entitled “Integrated Program for BRD in Beef and Dairy Cattle”. The overarching research objective of this multi-institutional project is to use newly-available genomic tools to identify host genome regions associated with susceptibility to BRD. During the past year 2,000 dairy calves on a single large California facility were enrolled in a BRD case:control design study using an objective scoring system and  genotyped using a high-density bovine SNP chip. It is envisaged that analyses of these data and future studies will lead to the development of DNA tests to enable the selection of animals that are less susceptible to BRD which is is much-needed given growing concern regarding both animal welfare and use of antimicrobial therapeutics.