The objective of this study was to evaluate the effects of dietary supplementation with bacteriophage and β-mannanase on health and growth performance in calves. Thirty-six pre-weaning male Holstein calves were randomly allocated to one of four dietary treatments: no supplementation, 0.1% β-mannanase, 0.1% bacteriophage, and both 0.1% bacteriophage and β-mannanase supplementation in a starter. The experiment lasted from 2 weeks before weaning to 8 weeks after weaning. Twenty-two calves survived to the end of the experiment. No interaction was observed between the two methods of supplementation. A 1-kg increase in initial BW resulted in a 1.41-fold increase in the odds ratio of survival (p < 0.01). The bacteriophage supplementation tended to increase the odds ratio of survival (p = 0.09). The number of Escherichia coli in feces significantly decreased one week after weaning. β-mannanase supplementation increased the concentrates intake (p < 0.01) and tended to increase the final BW (p = 0.08). Analysis of repeated measures indicated β-mannanase supplementation increased weekly body weight gain (p = 0.018). We conclude that bacteriophage supplementation may have a positive effect on calf survival rate, while β-mannanase supplementation may increase the growth rate and intake of a starter in calves.