Dairy calves are born without an active immune system, and therefore rely on good-quality, adequate volumes of colostrum to ensure the passive transfer of IgG. Despite this knowledge, poor colostrum management still occurs on farm, with one of the main reasons for failure of passive transfer being due to feeding colostrum more than 6h after birth. The objective of this study was to investigate how delaying the first colostrum feeding can impact the passive transfer of IgG, as well as bacterial colonization in the intestine of neonatal dairy calves. Twenty-seven male Holstein calves were randomly assigned to 1 of 3 treatments at birth: calves were fed colostrum before 1 h after birth (0 h, n = 9), at 6 h after birth (6 h, n = 9), or at 12 h after birth (12 h, n = 9). Calves were fed pooled colostrum at their respective feeding times at 7.5% of birth body weight, and fed milk replacer at 2.5% every 6 h thereafter. Blood samples were taken every 3 h using a jugular catheter. At 51 h of life, calves were euthanized and tissue and digesta of the distal jejunum, ileum, and colon were collected. QRT-PCR was performed using DNA extracted from tissue and digesta samples and the prevalence (% of total bacteria) of bacterial groups was determined. Calves fed colostrum at 0 h had significantly higher (P < 0.001) serum IgG concentrations (g/L; 24.77 ± 1.91) compared with 6-h (17.13 ± 0.91) or 12-h calves (16.88 ± 1.50), while no differences existed between 6-h and 12-h calves. In addition, 0h calves had a greater prevalence (P < 0.10) of Bifidobacteria (1.24 ± 0.64) and Lactobacillus (0.26 ± 0.08) attached to colon tissue compared with those fed at 12 h (0.12 ± 0.02 and 0.07 ± 0.02, respectively). In contrast, there were no differences (P > 0.05) in E. coli, Clostridium, and Fecalibacterium colonization among treatments in the digesta or tissue of the distal intestine. These findings suggest that feeding dairy calves colostrum immediately after birth can increase the passive transfer of IgG and the colonization of beneficial bacteria in the colon; both of which are hypothesized to assist in protecting the calf from enteric infections during the pre-weaning period.