I agree that this, and a lot of similar products are crap, and targeting naïve pet owners that just want the best for their animals. Your vitamin E theory is unlikely, but not without merit. The Fluker's website does not reveal how much Vitamin E is in the bottle. Not that this matters, because there is no regulatory body for such products and there could be zero to asinine proportions of vitamin in any given batch produced. Nonetheless, using a drop, or 1/2 cc (10 drops), whichever it is, in a liter or two of bath water is unlikely to cause toxicity. Vitamin E is indeed fat soluble and can cause toxicity because of it, but it is a compound essential to the body which means there are physiological methods for it's use and regulation. As per the blood panel, vitamin E levels can be tested, but are not on a routine blood panel.

A gross necropsy (sounds like what was done) can be done on a frozen/thawed carcass but in itself is rather unrevealing. It can see visual changes to organs, masses, larger parasites, foreign bodies etc. The freezing causes cellular lysis, which means that histopathology is fruitless. Freezing also reduces the chance of pathogen isolation, but not always. We often freeze cultures and plasma in case future testing is warranted.

And because it was mentioned, Guinea pigs are the only known animals in addition to primates (including us of course) that cannot produce their own vitamin C, making it an essential vitamin. Lacking it causes scurvy, an utterly painful demise. Vitamin C in the water... another one of those crap products. It should be offered in a variety of methods, most reliably via daily tablet form (Oxbow products), but also in supplemented pellets (an unessential dietary component), and in my opinion, ideally from fresh vegetables like bell peppers.

Ian