Not necessarily. I switched my six year old female to live after five years of f/t and then I've just recently switched her back to f/t again because my younger male can't quite handle a live one yet, he has difficulty killing them without getting nipped. But, the moral of it is that it's possible and sometimes very easy. I just waited two weeks between the last live rat and then went to f/t she took it like she hadn't eaten in months.