The goal of this research is to determine the evolutionary history and functional significance of genetic diversity in current livestock breeds. This is underpinning the development of bespoke genotyping tools for the cattle breeding industry and leading to fine mapping the impact of variation on cellular immune function. As a consequence, differential immune responses during pathogen challenge can be traced back to genomic variation. A deeper understanding of this unique immune variation has the potential to improve disease resistance and vaccine efficacy in these key food producing animals.