it happened to one of my Russell pups at 8 months old,Im not saying it will happen to yours but my dog never killed a rat again it would just yap at um,my mum has the dog now,
and yet my Pats were killing rats at 4month old and getting bit never bothered them at all,it just shows you how not all dogs progress the same and how some,even thought they come
from a working background never make the grade even as ratters
I wish you atb with yours mate