The efficacy of a whey protein concentrate was evaluated as a colostrum substitute or supplement in two experiments using four groups of 29 calves. In Experiment 1, calves were fed either 2 L of pooled colostrum (group 1) or 500 g of whey protein concentrate (group 2). A mean total of 123.6 and 17.7 g of Ig was fed to calves in groups 1 and 2, respectively. Mean serum IgG, total protein, and globulin concentrations and Ig antibody activities to Escherichia coli K99 and rotavirus were significantly higher for calves in group 1 at 24 to 36 h and at 3 wk of age. Weight gain from birth to 3 wk of age was significantly lower for calves in group 2. The incidence of diarrhea was high but not different between treatments. The mortality rate (0 to 3 wk) was significantly higher for calves in group 2 (27.6%) than for calves in group 1 (3.4%). In Experiment 2, calves were fed either 2 L of pooled colostrum (group 3) or a solution of 1 L of pooled colostrum plus 500 g of whey protein concentrate (group 4). A mean total of 117.2 and 69.1 g of Ig was fed to calves in groups 3 and 4, respectively. Absorption rate of IgG was significantly lower for calves in group 4. Mean serum IgG, total protein, and globulin concentrations and Ig antibody activities to E. coli K99 and rotavirus were significantly higher for calves in group 3 at 24 to 36 h and at 3 wk of age. Mortality rate, BW gain, and incidence of diarrhea did not differ significantly between groups.