Newborn lambs depend on their dams for passive transfer of immunoglobulins, primarily IgG, for protection from harmful pathogens until their own immunological defenses have developed. Previous studies have suggested that supplementation with Se results in a modest increase in IgG concentration in serum of newborn calves and lambs. To evaluate the effect of the Se source and supplementation rate in ewes during pregnancy on passive transfer of IgG to their lambs, 210 Polypay, Suffolk, or Suffolk × Polypay cross ewes were divided into 7 treatment groups (n = 30 each) and drenched weekly with no Se, at the maximum FDA-allowed concentration with inorganic Na-selenite or organic Se-yeast (4.9 mg Se/wk), or with inorganic Na-selenite and organic Se-yeast at supranutritional concentrations (14.7 and 24.5 mg Se/wk). Ewe serum IgG concentrations were measured within 30 d of parturition, ewe colostrum and lamb serum IgG concentrations were measured at parturition before suckling, and lamb serum IgG concentrations were measured again at 48 h postnatal. Ewes receiving 24.5 mg Se/wk tended to have or had, independent of Se source, greater colostral IgG concentrations than ewes receiving 4.9 mg Se/wk overall (81.3 vs. 66.2 mg/mL; P = 0.08) and for Polypay ewes only (90.1 vs. 60.7 mg/mL; P = 0.03). Polypay ewes receiving Se-yeast at 24.5 mg Se/wk transferred a greater calculated total IgG amount to their lambs than Polypay ewes receiving Se-yeast at 4.9 mg Se/wk (15.5 vs. 11.6 g; P = 0.02), whereas the converse was true (interaction between Se source and dose concentration; P = 0.03) for Polypay ewes receiving inorganic Na-selenite at 24.5 mg Se/wk vs. Na-selenite at 4.9 mg/wk (11.6 vs. 15.7 g; P = 0.08). Our results suggest that supranutritional Se supplementation of Polypay ewes during pregnancy increases colostral IgG concentrations but that the optimal supplementation rate for IgG transfer from ewe to lamb may differ for Na-selenite and Se-yeast.