Ok, I've seen this referenced many many times in reference to higher risk of genetic issues with rats especially. What to be totally honest I can't figure out is exactly what is defined as "high white". I have lots of hoodeds, I also have some with just the dark heads, and quite a few berks with white bellies, but some white going up further than their bellies as well. I also have PEW's, and a couple young ones I'm not sure what they are (maybe straight agouti?) with gray/brown/reddish fur with gray stomachs.
So when do they classify as high white, and do most breeders then cull them out?