The study evaluated the effects of supplements of Moringa oleifera leaf meal (MOLM) on blood biochemistry and growth of pre-weaned Holstein calves (n = 48). Four-day-old calves were blocked (based on order of birth and birth weight) and randomly allocated to three dietary treatments, namely M0: unsupplemented control, M30: supplemented with 8.33 g MOLM /100 kg bodyweight (BW), and M60: supplemented with 16.66 g MOLM /100 kg BW. The experiment ended when the calves were 42 days old. The MOLM was diluted in the milk of the morning feeding session. Feed intake, faecal score, and body temperature were recorded daily. Bodyweight and body measurements were taken weekly, and blood samples were collected at the same time. Starter dry matter intake (DMI) for the M60 group was higher than for M0 group with a significant week effect. Calves in M60 had higher final bodyweight and body measurements than M0 and M30. Similar trends were observed for superoxide dismutase (SOD), catalase (CAT), and serum antioxidant activity (SAOA). Immunoglobulin G (Ig) levels increased with the age of calves in both M30 and M60 groups, with the increase being progressively larger with the level of MOLM supplementation. Calves in the M60 group had fewer days of diarrhoea. Supplementation of MOLM supplied secondary metabolites and nutrients that improved feed utilization and later stimulated growth, increased enzymatic antioxidants, and reduced diarrhoeal incidence in pre-weaned calves. Dilution of MOLM by as little as 16.66 g/100 kg BW in the milk for dairy calves can be recommended.