2017 ACVIM Forum Research Abstract Program

6-month old calves maintained higher ISF/plasma concentration ratios throughout the study period compared to that observed in 3-week old calves for both danofloxacin and tulathromycin. Nonlinear mixed effect modeling revealed age as a significant covariate in plasma concentration differences seen for calves administered tulathromycin but not for danofloxacin treated calves. Plasma protein binding was assessed in-vitro in individual dairy calves (n = 5) for 5 drugs, including danofloxacin and tulathromycin. No significant differences were seen in calves from the ages of 1, 7 and 21 days of age but trends toward changes in 8-week and 6-month old calves indicate the need to assess protein binding changes for future drug approvals in young calves.