This study examined the impact of maternal direct-fed microbial supplementation on transfer of passive immunity and development of active immunity in dairy calves from birth to weaning. Primiparous (n = 10) and multiparous (n = 11) cows were blocked by parity and body weight and fed a close-up TMR before calving. The dams’ TMR was either not supplemented (CTRL; n = 11) or supplemented with a commercial direct-fed microbial (DFM; n = 10). Within 4 h of birth, bull calves (n = 12) and heifer calves (n = 10) were fed 4L of maternal colostrum. Blood serum was collected from Holstein bull calves (n = 12) and heifer calves (n = 10) at 0, 24, and 72 h and then weekly until weaning. Also, calves were weighed at birth and weekly until weaning. Data were analyzed in SAS with fixed effect of treatment and, where appropriate, repeated effect of week. Average daily gain (ADG) did not differ between CTRL and DFM (1.34 ± 0.06 vs. 1.44 ± 0.07 kg/d, respectively; P = 0.29) or between bulls and heifers (1.33 ± 0.06 vs. 1.45 ± 0.07 kg/d, respectively; P = 0.20). Serum IgG concentrations at birth were not different between CTRL and DFM (1753 ± 290 vs. 2325 ± 372 mg/dL, respectively; P = 0.95). At 24 h, IgG peaked for CTRL and DFM (1562 ± 666 vs. 2176 ± 744 mg/dL, respectively; P > 0.74) and then subsided, at 72 h, for both CTRL and DFM (514 ± 666 vs. 855 ± 744, respectively; P = 0.43). Serum IgG concentrations increased for both CTRL and DFM between wk 4 (1681 ± 666 vs. 2813 ± 744 mg/dL, respectively; P = 0.43) and wk 7 (2636 ± 666 vs. 2653 ± 744 mg/dL, respectively; P = 0.43). These data suggest feeding a direct-fed microbial to dams may not impact passive transfer of immunity or weight gains in young calves. Also, calf endogenous IgG production appears to exceed maternal IgG denaturation between 4 and 7 weeks of age.