I can understand where you're coming from, but you may be best off just avoiding this subsection on the future. (Save you some heartache) Lots of people come for advice on how to get started or for help because this is the best way for them to feed their snakes. (Most do not actually feed the rats to the snakes live unless the snake would starve itself otherwise. Typically, the rats are pre-killed by the same method as the companies selling frozen rodents online, i.e. CO2)
I wouldn't say that inbreeding was definitely the cause of those tumors, though. Rats in captivity live longer than in the wild and, same as with humans expanding their life span, they begin developing otherwise unheard of health defects (i.e. tumors, mental diseases, etc.)
This is a large part of what makes rats such valuable test subjects for scientific research like working to cure cancers/tumors in both the rodents (though probably far beyond the cost a pet owner could or would pay when it is discovered) and later humans.
I grew up with hamsters and gerbils and currently have 4 gerbils (2 same-sex pairs), so I understand the sentimentality, but snakes have to eat too. Breeding my own is as much for lowering the cost of keeping snakes (I've got 15 snakes now) as it is to ensure that the food my snakes eat is high quality. I have the ability to ensure high care standards for the rats, high quality food, and safety from disease/parasites, etc while I have them and a quick/painless and humane death when it becomes necessary.
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