Breast milk is the best, there is no better alternative, if your work place is close by you can take a break every 3 - 4 hrs and feed the baby in between, if the work place has facilities to keep babies, that woul also be better, if these options are not available, you can express the breast milk before going to work, that can be stored in fridge and can be fed to the baby when you are away, expressing breast milk will you to continue secreting and forming more milk required for the baby atleast till 1 year of age, breast milk is the best for baby, second alternatives would be lactogen/ nan1