Saying ‘you are not a horse, you are not a cow’ in a headline is condescending and an attempt at mocking those who seek what they believe is alternative treatment.
Taking another countries problems out of context is why you are struggling with it's meaning. A few lost individuals have 'heard' Ivermectin can cure Covid and can't get prescribed it as they don't have worms, instead they turn to black market sales of horse and cow versions of the drug. Which are much larger doses and contain other ingredients not suitable for human consumption, they are then getting sick or dying because of this. The FDA is not mocking them in that statement, it is not mocking the dead or dying, it is making a clear statement that those drugs are not for humans, especially if you read the material on the site. I'm pretty sure the message is working in the US now, a few of the 'anti' protagonists have died from covid scarring the others into vaccination. As I said earlier the FDA statement is pretty much in line with sentiment and media coverage of the issue.