problem is with xylazine you want to reverse as soon as possible
with ketamine you NEED to let the drug wear off before reversing the xylazine, too soon and you get a violent reversal. Not good.
I've used ketamine 3-4 times on deer we were performing surgery on for extended time, no problems with reversal.
I have seen a fawn killed with ketamine used by a dog/cat vet who read on internet to use it. Ugly, ugly, death.