You can make use of the same login/email address in all the administrations/herds but it's possible to make a login per herd but there is a small catch. You can use a different email address and make an account with that email address during the start-up in Myagrovision. Keep in mind that the account you do your first login in Myagrovision is the admin account for that administration/ herd. You have to ask yourself the question if you want to have multiple accounts to have admin rights or just one for your operation.