addition, the number of IgA-producing plasma cells were greater in both ileum (2.55 ± 0.40 cells/mm 2 ) and colon (3.03 ± 0.40 cells/mm 2 ) tissues for SCB calves compared with control (respectively 1.00 ± 0.40 and 0.60 ± 0.42 cells/mm 2 ). Endogenous IgA production in the gut of SCB calves was enhanced, which could make them less prone to pathogen intrusion. In addition, SCB calves had higher Lactobacillus and tended to have higher Faecalibacterium prausnitzii in the jejunum compared with control calves, which suggests that SCB supplementation during early-life gut colonization may have a positive effect in newborn calves. Direct SCB supplementation or the cross-talk between SCB and bacteria may be responsible for stimulating IgA production and may play a key role in shaping early colonization in the gut of newborn calves.