I have read most of the thread and feel the need to comment. I work for the FDA. I deal with food, not drugs.
All drugs go through the same approval process. Foreign companies get inspections from FDA too. Every week there are tons of trips to places like China and India. People from my office have gone on these trips to do the inspections. I have gone overseas for food inspections.
Warning Letters are just that, a warning. It does not mean they cannot produce. But depending on the way things are written they may not be able to produce until the issue is fixed.
As far as supplements, CFR 21 part 111 covers the regulations for supplements. A lot of companies are still not following the regs. They are getting punished too. I am not sure about animal supplements as I have not come across them in my work.
Labeling claims are a big deal. The wording can make it a drug or not. Ingredients can make it a drug or not. Some ingredients are drugs no matter what. We find a lot of unapproved drugs in products coming in from other countries.
Inspection happen on a routine basis. I am not sure about the drug companies but firms are scheduled based on risk and inspection history.
We are trying our best to make all food, drugs, devices, etc safe for humans and animals. It is hard with all the red tape we deal with because of the laws made years ago.
With the new FSMA rules (food safety modernization act), we will see more regulations just for animal feeds and such.
I am not on the forum much so if you ask a question I may not see it for a while. I hope I helped answer some questions.