Polyunsaturated fatty acids have been observed to reduce inflammatory response. The adaptation of neonatal calves to an extrauterine environment is commonly associated with inflammatory-like conditions. Thus, our objective was to evaluate the effects of supplementing flax oil on immune function reflected in the profiles of systemic blood biomarkers and mRNA in polymorphonuclear leukocytes (PMNL). Thirty-six Holstein dairy calves housed in individual hutches were used in a randomized complete block design from birth until 12 wk of age. A subset of 16 calves (n = 8/trt) was used for immune function analysis. Treatments were control (CON) with no supplement or 80 g/d of flax oil (FLAX) with the milk. Calves were fed 2.8 L/d of pasteurized milk 2 × /d during wk 1 to 5. Starter pellets and water were fed ad libitum. Blood samples were taken at 1, 7, and 14 d of age for biomarker profiling of metabolism, oxidative stress, and inflammation as well as PMNL isolation. RNA was extracted from isolated PMNL, and concentration and viability were assessed through flow cytometry (Attune NxT; Invitrogen). Target genes evaluated in PMNL function involved inflammation, cellular receptors, and oxidative stress. Data were analyzed using the MIXED procedure of SAS. There was a significant (P = 0.04) diet by time (D × T) interaction in the mRNA expression of SELL (L-Selectin), a cell surface receptor, where an upregulation (P = 0.03) of SELL in FLAX calves at 7 d of age was observed. A trend (P = 0.14) for a D × T effect was observed in IL1B (interleukin 1β), an inflammatory cytokine, which resulted in a trend (P = 0.06) for lower expression of IL1B in FLAX calves at 7 d of age. The overall MPO (myeloperoxidase) mRNA expression tended (P = 0.07) to be upregulated in FLAX calves, which is commonly associated with PMNL activity. Results suggest that early life supplementation of flax oil to neonatal calves may benefit their transition into an extrauterine environment not only by mediating the inflammatory response, but enhancing the PMNL ability to detect potential infection sites through cell receptors such L-selectin.