Another vote for the .22LR. I've dispatched a fair few cattle over the years, and a properly placed .22 will drop them like you cut the strings on a puppet. The diagram on this previously posted page (http://www.cdfa.ca.gov/ahfss/Livestock_ID/Euthanasia.html) shows the correct shot placement as described and demonstrated to me by my veterinarian, and I've never had any reason to doubt its effectiveness. As is stated there, perpendicular to the skull and aligned down the spine. You'll probably have to wait for the animal to angle its head correctly for these conditions to occur, so be patient.