inbred

[Tikall]

Line breeding is mother/father x son/daughter and is less likely to cause genetic issues if done responsibly (ie only a few generations before introducing new blood) whereas inbreeding is brother x sister and is more likely to cause issues if done repeatedly without introducing new genes.

What exactly do you mean? You said the same thing for both- that they are harmful after a few generations without new blood, and that is impossible to tell. You are waiting for deformities on the outside to become apparent, and that just isn't going to happen all of the time. Close inbreeding has shown to have harmful side effects time and time again, so why do it to balls too?

Also those are both examples of inbreeding. Line breeding is just a nicer word for a moderate form of inbreeding. Line breeding refers to crossing distantly related animals, and inbreeding in breeder terms is crossing sib x sib, offspring x parent, and other closely related animals. You are still increasing the frequency of the genes in a particular line which is still potentially very harmful. Why would you risk the long term genetic diversity and health of the animal to save your wallet a little bit when you're already spending so much on them? Technically with some morphs that only have one founder, or the lines are incompatible, inbreeding is unavoidable, but it's better to cross distantly related animals than closely related ones.