Why must I give baby pigs iron shots within the first 3-4 days of birth?

Sows’ milk does not contain enough iron for baby pigs. Iron must be given to pigs within their first 3 or 4 days to prevent anemia. Pigs can be supplied with iron by giving them clean sod (not from a hog lot), iron injections (iron dextran in the ham or heavy neck muscle), or iron compounds mixed with other minerals which pigs can eat.