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Sorry, I intended to also make a quick comment regarding the pig with polycystic kidneys.  The point was never really made that while the condition is "pathologic"  the reason the carcass does not require condemnation is that the etiology is genetic / inherited rather than an infectious process that would be harmful if allowed in the food chain.  Obviously the kidney is removed but the remainder of the pig is used as it would be normally.  To the best of my knowledge, polycystic kidney disease is genetic / inherited in all species in which it occurs including humans and cats (Persians for those of you about to take boards) and, while the condition does result in renal failure, it is usually fairly slow in progression.  Both humans and cats can be successfully treated with a kidney transplant.  Can't Spell said that disease is not seen in pigs but I imagine that is simply because of the typically short lifespan of the pigs she sees...