Supplementation with selenized yeast before parturition improves Se and antioxidant status of dairy cows during early lactation. Agricultural biofortification is a cost-effective method for selenium supplementation of beef cows and their offspring. In this study, we evaluated the effect of supplementing dairy cows with sodium-selenate fertilized alfalfa from 40 d prior parturition to 2 weeks postpartum on whole blood and milk level of Se and other trace minerals, immune competence, and performance. After blocking for breed, 12 dairy heifers (6 Holsteins and 6 Jerseys) fed ad libitum with a TMR based on grass silage (0.14 mg Se/kg DM) were randomly assigned to a TRT group supplemented with 1 kg DM/100 kg BW with alfalfa enriched with Se (3.2 mg/kg DM) or a CTR group supplemented with low Se alfalfa (0.4 mg/kg DM). Cows were monitored daily for health status, dry matter intake, activity, and milk yield and weekly for body weight and body condition score. Carrageenan skin test was performed throughout the experiment. Whole blood and milk were used to determine Se and other trace minerals by ICP-MS. White blood cells count and hematocrit were assessed. Phagocytosis and leukocytes differentials were measured by flow cytometer. Milk yield and components were measured at each milking using Afimilk system and samples were collected to assess milk composition by a DHIA lab. Data were analyzed by GLIMMIX of SAS with the fixed effect of treatment, breed, time and their interactions and cows as random effect. After 4 weeks into the trial, Se concentration in whole blood increased 2-fold (P < 0.0001) in TRT vs. CTR (210.4 vs. 105.9 ng/mL) that resulted in higher (P < 0.01) Se in milk (42.1 vs. 24.9 ng/mL). Milk yield was higher in TRT vs. CTR (20.2 vs. 18.2 kg/d, P < 0.05). No other differences were detected. Our preliminary results point out that agricultural Se biofortification of dairy cows during the close-up period is an effective and cost-efficient management tool to improve Se in blood and milk. Se supplementation improved milk yield but had not measurable effect on leukocytes profile and peripheral immune response in primiparous cows during the peripartum.