Abstract: [Objective] To investigate the effects of dietary supplementation with different concentrations of Parabacteroides distasonis F4 on growth performance,body measurements,and digestive metabolism in pre-weaning Holstein heifer calves. [Method] Thirty-six healthy Holstein heifer calves aged 3~6 days were randomly divided into three groups：control group（CON）administered 20 mL of saline daily;low-dose group （PDL） administered 2×10⁹ CFU of F4 bacterial solution daily;high-dose group （PDH） administered 2×10¹⁰ CFU of F4 bacterial solution daily. All treatments were administered before morning feeding. The experiment lasted 70 days,with growth performance and body size indicators of the calves measured at 35 and 70 days,and digestive and metabolic experiments conducted one week before weaning. [Result] Compared with CON,no significant differences were observed in dry matter intake （DMI） and average daily gain （ADG） in the treatment groups,although numerically,both PDL and PDH showed higher values than CON. For body measurements,no significant differences were detected in any indicators,but numerical increases were noted in the treatment groups. The digestion and metabolism trial revealed no significant differences in apparent digestibility of nutrients among groups;however,numerically,the apparent digestibility of dry matter （DM）,ether extract （EE）,and neutral detergent fiber （NDF） was higher in the treatment groups than in CON. [Conclusion] Parabacteroides distasonis F4 may improve nutrient digestion and absorption in suckling Holstein heifer calves,thereby promoting growth. This study provided a preliminary reference for the application of microbial agents in young ruminants.

Key words: Parabacteroides distasonis F4, Holstein heifer calves, growth performance, body measurements, digestive metabolism