Feral cow killing still takes place along the Mexican border but it is usually done by control officers. I know of one who carries a .458 Lott in his truck for bulls because of an unnerving experience with a bull that soaked up several hits... of I don't remember what. We were looking into hunting some down there but it is generally not something that is available to the average sport hunter. I'd be dubious of an "outfit" that specialized in "wild cow" hunts. Pretty scammy I'd think. I was raised on a ranch and over a twenty year period we had to put down two bulls that had gone rogue and could not be controlled. Our weapon of choice? A bolt action Marlin shotgun loaded with 1 ounce slugs. Not very glamorous. On both occasions we drove up in the truck, pulled out the shotgun and put a dollar sized hole in their foreheads at thirty yards as they stood there pawing the dirt glaring at us. Not exactly something for the adventure mags.