Inbreeding is not in and of itself a bad thing. Line breeding is just one of the names to call it.
What happens with inbreeding is that bad genes become isolated, which is when you see things like birth defects, developmental problems, etc. However, most people see the birth defects and blame inbreeding, and then outcross like crazy believing that it was the inbreeding that resulted in the defects.
The inbreeding showed you the bad genes that animal was carrying, and by outcrossing you are perpetuating those bad genes by masking them under the good traits in other lines. However, if one knows the cause for the bad genes to show, and works to eliminate them by either no longer breeding that line OR (as I think most breeders here would prefer) working to eliminate the problem through careful selective breeding.
Inbreeding is a great tool for establishing and maintaining a quality line of animals that reproduces itself successfully.
~jenny
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"Polysyllabism in no way insures that what you're saying is actually worth being heard." - Blake (an e-friend of mine)
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