.223 can be downloaded to 22LR velocities with the right powder. People shoot subsonic ammo through suppressed rifles all the time, and a subsonic load is just a reduced power load. It generally takes a smaller amount of powder, and you'll be using a shotgun or handgun type of powder with a relatively faster burn rate, like Blue Dot or the like. Do a google search for .223 remington and blue dot powder and you'll find lots of info. Hodgdon's webside lists data for several subsonic loads.
That said, I have shot lots of coyotes with a .223, and damage to the pelts was generally very minimal. The 40 grain Hornady V-max bullets I've used will generally not leave much in the way of an exit wound. The 55 grain Sierra Gamekings I carry with me most of the time will exit, but the exit wound generally isn't very big.