There was an article that I read not long ago and don't remember where it was, but they have found out that a calf builds a lot more immunity from early vaccinations than they once thought. They used to say don't vacc. anything under 2 months or if you did re vacc. later to build immunity. It all depends on if you are having a problem that you need to get a jump on. You know even if you don't get but 90% immunity from the early shots and it corrects or prevents a problem so what. It gets them to weaning where they will get another. I use alpha 7 MB at 12 hours and have for years.