The objective of this study was to apply a quantitative proteomic approach to investigate changes in the plasma proteome of normal and over-conditioned dairy cows during the transition period. We used an animal model with a targeted difference in body condition score (BCS) at calving. For this, multiparous Holstein cows were allocated to two groups 15 weeks before anticipated calving and were fed differently to reach either high (HBCS: 7.2 NEL MJ/kg dry matter (DM) or normal BCS (NBCS: 6.8 NEL MJ/kg DM) until dry-off. Thereafter, both groups were fed identical diets. The targeted BCS difference was sustained during the dry period (7 weeks before calving) and the subsequent 12 weeks of lactation. Plasma samples (n = 5) from d -49, +7, and +21 relative to parturition were used from both groups (each n = 5) for proteome profiling in aby applying quantitative Tandem Mass Tags (TMT) approach.