Is this a common practice?

[JodanOrNoDan]

I always wondered what line breeding meant. I figured it would take a lot of time out of a breeding project depending on what your going for. What do you mean by genetically healthy?

If the potential mother or father is carrying an undesirable trait you would not line breed until the undesirable trait has been removed from the line. Lets pretend for a second that albinism is an undesirable trait. The trait does not manifest itself unless the animal carries two copies of the gene. So out crossing would be safer. Any inbreeding would increase the chance of the bad gene expressing itself. In a real world example, there are certain morphs know to have a high incidence of kinking. I would not line breed these animals because the heterozygous is safe but the homozygous is not.