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To investigate the influence of maternal Se supply and plane of nutrition on lamb morbidity, mortality, and passive transfer of IgG, pregnant ewe lambs were used in 2 experiments with 2 x 3 factorial treatment arrangements. Supplementation of Se began at breeding and was either adequate Se (ASe, 9.5 µg/kg of BW) or high Se (HSe, 81.8 µg/kg of BW) in Exp. 1 or ASe (11.5 µg/kg of BW) or HSe (77.0 µg/kg of BW) in Exp. 2. On d 50 or 40 of gestation for Exp. 1 or 2, respectively, ewes were assigned randomly to 1 of 3 nutritional planes: 60% (RES), 100% (CON), or 140% (HIGH) of NRC requirements. This resulted in the following treatments: ASe-RES; ASe-CON; ASe-HIGH; HSe-RES; HSe-CON; and HSe-HIGH. Upon parturition, lambs were separated from their dams and serum samples obtained. Lambs were fed artificial colostrum for the first 20 h and then placed on milk replacer and grain pellets until completion of the study (Exp. 1, 57 d; Exp. 2, 21 d). Twenty-four hours after parturition, lamb serum samples were collected for IgG analysis. All lambs were reared similarly and morbidity and mortality assessed. Main effects were considered significant when P = 0.05. In Exp. 1, there was a Se x plane of nutrition interaction (P = 0.01) for lamb morbidity from birth to weaning and for 24-h IgG concentration. Lambs from ASe-RES and HSe-HIGH ewes were treated more frequently (P < 0.01) for respiratory and gastrointestinal disease, and lambs from HSe-HIGH ewes had the lowest (P < 0.01) 24-h serum IgG concentration. In Exp. 1, lambs from HIGH ewes also had the greatest (P < 0.01) mortality rates from birth to weaning compared to lambs from CON and RES ewes. In Exp. 2, there was an effect (P < 0.01) of maternal plane of nutrition with lambs from RES ewes having increased 24-h IgG compared to lambs from CON and HIGH ewes. There was no effect of maternal Se supplementation on lamb 24-h IgG in Exp. 2; however, there was a Se x plane of nutrition interaction (P < 0.01) for morbidity. From birth to 21 d of age, lambs from ASe-CON ewes had reduced (P < 0.01) treatment days compared to lambs from any of the other treatment groups. There also tended (P = 0.08) to be an effect of maternal Se supplementation on lamb mortality with increased mortality observed in lambs from HSe ewes. Results from the studies show a restricted maternal plane of nutrition can increase lamb serum IgG. Selenium results were not consistent between the two experiments and may be due to differences in maternal Se. [ABSTRACT FROM AUTHOR]