This study focused on assessing whether the inclusion of probiotics (B. subtilis) as feed additives during the preweaning stage can enhance the body weight and metabolic condition of neonatal calves. A total of 50 Holstein calves, all born on the same farm, were randomly divided into two homogeneous treatment groups after birth. The calves in the control group (CG) were fed a milk replacer (n = 25) (13 females and 12 males) and those in the B. subtilis-supplement-treated group (TG), (n = 25) (13 females and 12 males) were fed a milk replacer with 7.5 mL/calf/day of B. subtilis probiotic (complied with the manufacturer’s guidelines). The probiotic was administered 24 h post-birth, signifying the start of the experimental period. It took one month to collect the animals. Body weight was measured at birth for all animals. A local veterinarian, working on the farm, conducted daily health checks of the calves, recording health parameters and any antibiotic treatments. Blood samples were collected from each calf at birth and 30, 60, and 90 days by puncturing the jugular vein using 10 mL evacuated serum tubes before morning feeding. Significant differences in body weight were observed between the CG and the TG at 30, 60, and 90 days of age. At 30 days, the TG had a 4.11% higher average body weight than the CG (54.38 kg vs. 52.71 kg). At 60 days, the TG’s average weight was 3.75% higher (79.21 kg vs. 76.34 kg), and at 90 days, the TG had a 2.91% higher average weight (112.87 kg vs. 109.67 kg). At 30 days of age, the TG showed significantly lower AST activity, with a 41.12% decrease compared to the CG (51.02 IU/L vs. 72.00 IU/L). Conversely, GGT activity was significantly higher in the TG by 64.68% (40.64 IU/L vs. 14.35 IU/L). Phosphorus concentration at 30 days was also significantly higher in the TG by 9.36% (3.27 mmol/L vs. 2.99 mmol/L). Additionally, the TG had a significantly lower total protein concentration, with a 21.63% decrease at 30 days (46.32 g/L vs. 56.34 g/L) and a 20.28% decrease at 60 days (48.32 g/L vs. 58.12 g/L) compared to the CG. These findings indicate that dairy calves given conventional milk replacer along with a daily dose of 7.5 mL of B. subtilis probiotic experienced enhanced growth performance and a more favourable metabolic profile during the first 90 days of their lives.

: This study focused on assessing whether the inclusion of probiotics (B. subtilis) as feed additives during the preweaning stage can enhance the body weight and metabolic condition of neonatal calves. A total of 50 Holstein calves, all born on the same farm, were randomly divided into two homogeneous treatment groups after birth. The probiotic was administered 24 hours post-birth, signifying the start of the experimental period. The Control Group (CG), consisting of 25 calves, was fed with a milk replacer, while the Treatment Group (TG), also with 25 calves, received milk replacer supplemented with 7.5 mL/calf/day of B. subtilis probiotic, in accordance with the manufacturer's guidelines. It took one month to collect the animals. Body weight was measured at birth for all animals. A local veterinarian, working on the farm, conducted daily health checks of the calves, recording health parameters and any antibiotic treatments. Blood samples were collected from each calf at birth and again after 30 days by puncturing the jugular vein, using 10 mL evacuated serum tubes before morning feeding. Significant differences in body weight were observed at 30 days of age (p < 0.05). The CG's average body weight (BW) was 52.71 kg (±10.68), compared to 58.49 kg (±14.21) in the TG, a difference of 5.78 kg or an increase of 9.88%. Additionally, the TG exhibited significantly lower aspartate transaminase (AST) activity at 30 days of age (p < 0.001), with an average of 51.02 IU/L (±5.16) compared to 72.00 IU/L (±12.68) in the CG, a 41.12% decrease. The TG also had a significantly higher average phosphorus (P) concentration (p < 0.001) of 3.27 mmol/L (±0.22), a 9.36% increase over the CG's 2.99 mmol/L (±0.27). A significant increase in gamma-glutamyl transferase activity was observed in the TG compared to the CG (p < 0.001), with a 64.48% (or 26.29 IU/L) increase. The TG's average GGT activity was 40.64 IU/L (±22.43), while in the CG it was 14.35 IU/L (±3.45). Additionally, there was a significant 17.7% decrease (or 10.02 g/L) in total protein (TP) concentration in the TG compared to the CG, with the TG averaging 46.32 g/L (±17.43) and the CG 56.34 g/L (±9.81). Overall, dairy calves who were given conventional milk replacer along with a daily dose of 7.5 mL of B. subtilis probiotic experienced enhanced growth performance and a more favorable metabolic profile. Their body weight exhibited a 9.88% growth, but the activity of AST decreased by 41.12%, suggesting a decreased likelihood of liver damage. Additionally, their protein digestibility was 17.7% greater compared to the control group. In addition, B. subtilis had a positive impact on the overall concentration of phosphorus.