Hard to believe it isn't widespread in the industry.
When challenged, you mention 4 vets you know. You say they've all at least experimented with animal drugs. What portion of the 4 said that was a reason for them to become vets? What portion did more than "at least experiment"? Do either of those represent a majority share of your sample? TBH, I think you would have phrased it differently if they did...
What is it about this small sample which is still influenced by your location, social class, education, etc that makes it representative of all vets?
Just wanted to note the wide gulf between your original reply and where you retreated.
also, ketamine has been shown to help with depression. could be that people are self-medicating.