Also....
Pre-killed, simply means when you take possession of the balls prey or before it is feed to the ball, it is already killed, e.g. frozen.
I have never feed a ball an ASF rat but I have heard that some balls once have eaten a ASF may only prefer an ASF, me personally, I wouldn’t feed ASF unless you are sure you are always going to have a consistent supply or don’t have any other choice available to you. But then again I have also heard some balls easly switch from normal rats to ASF's and vice versa with out a problem.