Ketosis is an important metabolic disease associated with the negative energy balance commonly experienced by dairy cows soon after calving, and such condition can have ramifications in the immune system of dairy cows in early lactation. The objective of this study was to evaluate blood neutrophil function under ketotic conditions in early lactation cows via an ex vivo LPS challenge. Fourteen Holstein dairy cows (n = 7/group) were monitored during the peripartal period. Blood BHB was measured with the Precision Xtra at 1, 3, 5, 7, 9, and 11 d postpartum. Cows were classified as subclinically ketotic (KET; > 1.4 mmol/L) or non-ketotic (NONKET; < 1.4 mmol/L). Blood samples were collected on d 5 postpartum for an ex vivo LPS challenge conducted at 0 (control), 0.01 (low dose), and 5 µg of LPS/mL (high dose) for 3.5h. Immediately after oxidative burst, neutrophil %, and selectin L were measured via flow cytometry. Additional blood on d 5 was collected for phagocytosis and neutrophil isolation for gene expression. The MIXED procedure of SAS was used to analyze the data. A priori contrasts statements were used to determine a linear effect based on the LPS challenge. As expected, a Group × Day (P < 0.01) was observed in BHB, where BHB increased at a greater rate in KET cows and was reflected in greater (P < 0.01) BHB in KET cows than NONKET. A trend (P = 0.06) for a Group × LPS interaction was observed in oxidative burst increasing linearly (P < 0.01) in NONKET cows as LPS was increased from 0 to 5 µg, while no change (P = 0.89) was observed in KET cows. Selectin L decreased linearly (P = 0.02) in NONKET cows while no change (P = 0.22) was observed in KET cows. Blood neutrophil concentration was not affected by either ketosis (P = 0.27) or LPS challenge (P = 0.31). These results suggest that neutrophils from cows undergoing a ketosis condition will have a lower ability to detect inflammation sites and lower killing capacity based on the lack of response in oxidative burst and selectin L, respectively when facing a further inflammatory or stress conditions.