I have read that around 100 years ago it was normal to have charcoal bits in feed for at least cows. I don't know what temperature the char was made at (which can make a difference) or if they inoculated it. However, it was considered beneficial for their guts and my recollection is that cows that got it were healthier and less likely to get sick than cows that didn't get it.
Then after the war, vitamins and antibiotics were cheap and the practice was abandoned.
I sprinkle biochar into my two duck runs. which usually also have some
chickens in with, and the
chickens certainly peck at it.
Dogs are scavengers, and are certainly known to eat things that *aren't* good for them. However, I suspect it isn't doing them any harm. I think I've even read in certain circumstances, humans ingesting it. It may be helping their gut biome.