Ceftiofur is the most commonly used antimicrobial in lactating dairy cows. Recently, there has been an increase in the number of violative residues of ceftiofur in the tissues of cull dairy cows. This was the first project in a series of projects we will be completing aimed at characterizing the pharmacokinetics of ceftiofur in disease challenged animals. The results of this study indicate that diseased animals have lower plasma concentrations and altered pharmacokinetics compared to healthy animals. Future work will investigate the influence of altered pharmacokinetics on the presence of violative residues.