Its not tractor lube...lol They give it to farm animals dude. It states USP on the bottle---you have to remember as of yet not a single thing we vape is labelled safe to vape by any entity.
PG, PEG and Glycerine has been used as an inhalant for many decades in Medicine and it's safety has been verified in numerous studies and via practical application over those decades. So that something we can be certain is safe to inhale.
And just because it's safe to eat (whether it's you or a farm animal), doesn't mean it's safe for you to vape and inhale it (See: Diacetyl). So it's not unreasonable for someone to want true Pharmaceutical grade components wherever possible.
USP Grade PG and VG are both approved by the FDA for use in most medical applications. So for our intents and purposes, anything marked USP can be considered Pharma Grade.
There is a higher standard that would be considered the "true" Pharma grade, but that true pharma grade stuff is
expensive. For example, USP grade VG, which is 99.7-99.8% pure, can be had for ~$20-40/gal, retail. True Pharma grade Glycerin, which is 99.999% pure, is around $700/gal. 0.299% isn't worth a $660 price premium for most people. Especially since that $700 bottle of Glycerin would become USP grade the second you opened the bottle outside a 0% humidity clean room as most of the 0.3% of "impurities" in USP grade is water and air molecules.
Flavoring though is always going to be the wild card. They are proprietary so it's hard to know what's in them as vendors can't give out their secrets. Plus in natural and organic flavorings, even the manufacturer couldn't tell you every compound contained in them. And even if we did know what was in them, most of the compounds haven't been tested for safety as inhalants.
But there's nothing wrong with trying to use the best ingredients possible. That's why I ask what brand of PG/VG I'm getting from vendors. There's nothing proprietary about PG/PEG/VG and all of it is manufactured by a small handful of companies, few of which sell direct to users so there's no legitimate reason for anyone to hold back that info from their customers. If they refuse to give you the exact brand name of the PG/VG they are selling, it's probably because they're using low grade stuff or are rebranding and marking up stuff from another vendor (or buy it from someone who does). If that happens, go somewhere else until you find someone who can and
will give you that info.
Once you have the brand info, you should be able to find a product sheet to see just how pure their stuff is and can decide how comfortable you are using it.