most genetic defects are killed off, pretty dam fast, works to hard for genetic defects!!!
but things like undershot is a genetic defects in some peoples eyes, not to me
one of the main problems with line/inbreeding is loss of size, weak teeth and you have to breed very tight ,
then you need new blood ..and your problems now start ,when you try to find the new blood
the trick is to get the new blood on the go long before you need it that way you can work it see how
it goes ,and if good enough, breed the hybred stuff back into the line slowly JMO