Newborn calves are immunodeficient. Colostrum provides them immunity, but it also can be a potential source of pathogen microorganism such as Mycobacterium avium ssp. paratuberculosis (Johne’s disease), Mycoplasma spp., Escherichia coli, and Salmonella spp.
It has become a common practice to feed non-saleable milk to dairy calves. Non-saleable milk accounts for 1–4% of the total milk produced in the farm and this includes milk from antibiotic-treated cows along with colostrum from fresh cows and milk containing high somatic-cell-counts.