Viral infection in newly received feedlot cattle can lead to oxidative stress. As a constituent of glutathione peroxidase, Se plays a vital antioxidant role. Our objective was to evaluate effects of Se source on the performance and health of calves challenged with infectious bovine rhinotracheitis virus (IBRV; Exp. 1) or in field conditions (Exp. 2). In Exp. 1, twenty-four Holstein steers (initial BW = 170 ± 0.6 kg) were given either 1) no supplemental Se (control), 2) 1 mg/steer daily of Se from Se-yeast, or 3) 5 mg/steer daily of Se from sodium selenite. Treatments were fed for 28 d before steers were inoculated with IBRV (d 0) and were continued 21 d after the challenge. Treatments did not affect BW or DMI (P > 0.20) from 7 d before through 21 d after the challenge. Supplemental Se (P = 0.02) increased IBRV titer values on d 21. The IBRV challenge induced a febrile response; however, there were no treatment differences (P > 0.10) in rectal temperature. Total red and white blood cell counts, percentage of white blood cell types, and hemoglobin concentrations did not differ (P = 0.11) among the 3 treatments. In Exp. 2, newly received, crossbred heifers (4 pens/treatment) were fed the same treatments as in Exp. 1, except selenite was supplied at 1 mg/heifer dailyfor 28 d. No treatment differences (P > 0.10) were observed for performance or health during Exp. 2. Results help to define the effects of Se supplementation and source on the immune response to viral infections in cattle.