We have utilised genome sequencing and multilocus sequence typing to gain an unprecedented knowledge of the evolution of Streptococcus equi and its close relative Streptococcus zooepidemicus. We have exploited this information to generate defined deletion strains and identify some of the mechanisms underlying the ability of S. equi to cause disease (eg. superantigens and equibactin). We have translated this knowledge into industry-leading quantitative PCR (qPCR) and indirect enzyme linked immunosorbent assay (iELISA) diagnostic tests for the prevention of strangles. We have also developed a Welsh mountain pony infection system that is performed according to Good Clinical Practice, which has been utilised to quantify the importance of lipoproteins and a putative protein maturase to virulence in this natural host and to determine the safety and efficacy of commercial and developmental strangles vaccines.