Treatment with granulocyte colony stimulating factor (G-CSF) has been shown to increase neutrophil count and function in transition cows. In this study we tested the hypothesis that cows with high or low body condition score (BCS) may have different response in peripheral blood leukocyte populations count after the treatment with pegbovigrastim (recombinant bovine G-CSF). Twenty-six Simmental cows were randomly allocated to one of 2 treatment groups, homogeneous for parity: pegbovigrastim (PEG; 14 cows) or saline control (CTR; 12 cows) injections. Within each treatment group, cows were divided in 2 subgroups according to a 5-point scale precalving BCS: BCS ≤3.5 (LowBCS; 7 PEG and 6 CTR cows) and BCS ≥3.75 (HighBCS; 7 PEG and 6 CTR cows). Cows received s.c. injections approximately 7 d before (1st) and within 24 h from calving (2nd). Blood samples collected at −7, 0, 1, and 3 d relative to calving (time) were used to determine the complete blood count using an Advia 2120 Hematology Analyzer (Siemens Healthcare Diagnostics inc., Deerfield, IL). The data were analyzed using a MIXED model procedure of SAS (Ver. 9.3) with fixed effects of treatment, BCS, time, and their interactions, and cow was the random effect. Overall, PEG-treated cows resulted in significantly higher neutrophil, basophil, and monocyte counts. These differences were also observed during time from calving onwards. LowBCS cows resulted in a tendency for higher neutrophil, basophil, and lymphocytes count compared with HighBCS cows. Furthermore, a BCS x treatment interaction was observed for neutrophil due to significantly higher count in PEG-LowBCS compared with PEG-HighBCS, while no differences were detected in CTR cows. These results shed light on the pegbovigrastim response in cows with different BCS. Simmental cows with BCS 3.5 or lower before calving experienced a greater responsiveness to pegbovigrastim treatment. However, further studies are required for the understanding mechanism of G-CSF response associated with the degree of adiposity around parturition.