To the best of my knowledge, no-one has ever explained HOW they remove the thyroid hormone content. One company said they defatted the thyroid and that removed the hormone. Unfortunately for them, every description of producing desiccated thyroid starts off with defatting the thyroids.
The companies usually then go on about how their product contains desiccated thyroid obtained from somewhere or other (most often, New Zealand grass-fed cattle). And nothing nasty is added, nothing done to the powder. So where does the thyroid hormone go?
In the very early days of desiccated thyroid, Armour Laboratories (and others) put a lot of work into things like measuring hormone content through the year (it varies quite a lot), measuring biological effect (using laboratory animals to assay the potency), trying bovine and porcine sources, etc. But these companies who say there is no hormone content surely don't bother with all that - because there isn't any? So if there is any hormone content, doesn't it make sense that the amount won't be properly controlled? (Of course, if they controlled the hormone content, they surely couldn't then claim there isn't any!)
There is a pile of poo here. I don't like it, and never have. I don't trust the "supplement" companies any more than the straight pharmaceutical companies. (Actually, apparently, quite a bit of the supplement market is supplied with ingredients and product by the mainstream pharmaceutical companies.)
I make an exception for Thyro Gold which, although sneaking under the FDA radar, does more or less explain itself.