Exogenous supplements to enhance passive immunity can be given orally provided the neonate is less than 24 h old, or by intravenous injection after that time. Findings from studies described in this dissertation support the fact that passive immunity can be enhanced through both methods. In the first study, foals were offered a colostrum supplement at 10 and 12 h of age providing 24--30 g of IgG. Treated and control foals were allowed to nurse their dams ad libitum. Immunoglobulin G concentrations and rate of IgG absorption were not different between treated and control foals. In the second study, a concentrated oral product for foals was studied that provided 72 g of IgG. Supplement treated foals were muzzled to prevent nursing from their dam through 12 h of age. Treated foals had higher IgG concentrations compared to control foals at 5 h and 48 h of age, and IgG concentrations were not different between the two groups at any other time period measured. Forty calves were utilized in the third study to examine the efficacy of providing newborn calves with colostrum supplements or replacers designed to provide 150 g of IgG. A second concentrated plasma fraction that contained elevated concentrations of IGF-1 and TGF-beta was also added to two treatment groups. Feeding 150 g of IgG at 1 h of age was superior to feeding 150 g of IgG split in two doses 7 h apart. All calves that received 150 g of IgG in one dose had plasma IgG concentrations above the recommended concentration of 10 g/L. Addition of elevated growth factors decreased plasma IgG concentration. The final two studies examined intravenous use of concentrated bovine plasma (IVIG). Initial IgG concentration appears to influence response to IVIG in that calves with lower initial plasma IgG concentrations have a larger increase in plasma IgG concentration after IVIG infusion. The second IVIG study was designed to characterize reactions to IVIG, and to determine if reactions were related to rapid infusion of large molecular weight molecules. Reactions were not caused by infusion of large molecular weight molecules, or by histamine release.