Immunological factors from maternal colostrum, especially antigen-specific IgG, modulates the gut microbiota colonization, which results in health or unhealth gut in the early of life. Escherichia coli (E.coli) is the most spread specie of bacteria in the dairy system production, which is the gut pioneer invader in the early of life and can induce mucosal and systemic inflammatory response called Coli sepsis. To understand the relationship between gut microbiota and immune system, this observational study followed the intestinal colonization by E. coli and the dynamic of total IgG and antibody recognizing E. coli in newborn Holstein calves submitted to a gold standard colostrum management. It was selected twenty Holstein dams, producing adequate quantity of good quality colostrum having uncomplicated deliveries and their healthy female offspring. Calves were scored daily for diarrhea. Blood and fecal samples were collected on D1 (before colostrum intake), D3, D7, D14 and D28. E. coli, their virulence and quantity were assayed by conventional PCR and qPCR, respectively. Serum IgG quantity and E. coli binding antibody titers were measured using ELISA. Peak diarrhea was observed on D12. Circulating IgG and E. coli binding antibodies were not detected before colostrum intake (D0). These sharply increased on D3. These antibodies declined in the subsequent samples. The total number of bacteria (16S rRNA) in the feces did not change from D1 to D14, however, its increased between D14 and D28.The number of E. coli was lowest in meconium on D1, but sharply increased D3-D7, then decreased from D14-D28. The stable toxin (ST) virulence factor was frequently identified in the E. coli isolated from calves’ fecal samples. E. coli K99 was not identified in the fecal samples thought the neonatal period. The gut was colonized by E. coli early in life; however, a decreasing number of E. coli were observed in response to passive transfer of immunity.

This work was supported by the São Paulo State Research Support Foundation (FAPESP) for the financial grant support [Process 2016/16748-2] and scientific initiation scholarship (BpB) [Process 2018/00744-3].