All cats play with their food.
I confess to not having read this entire thread, so I apologize if I missed what I was looking for. However, I searched the entire forum for the word cougar, as well as the big cat's names in other parts of the continent, puma, panther, and mountain lion, as well as its scientific name Felis concolor. No find, at least not in this area.
I'm amazed that you've written five pages about this "phenomenon" and nobody appears to have asked, "Hey, do you think it might have been cougars?" The most wily, stealthy and eccentric predator in North America? The only one that hunts like a cat and plays with its food because it IS a cat? (Again, if you managed to conduct that conversation without using the word cougar, I'm sorry.)
These "mutilations" have not been limited to cattle. Goat, sheep and llama breeders in the Wild West have had the same problem. This rather large community of stockmen decided not to wait 150 years for the invention of Warp Drive so the Vulcans can help them figure out which race of aliens was attacking their livestock.
They did what herding folk have been doing for thousands of years: they got some big tough livestock guard dogs from Turkey. The Anatolian, a 4,000 year old breed that weights 120 pounds, with the speed and agility of a greyhound on steroids combined with the teeth and ferocity of a mastiff.
They traveled to the nearest mutilation scene, set out some goats as bait, and sat far downwind with their dogs. The dogs heard the commotion first and went galloping off. The ranchers found them encircling the mountain lion, who had been caught feasting on an udder that had been removed from the goat with nearly surgical precision.
A few more episodes with the same conclusion and it was the end of the mystery. It was all cougars. Humans have kindly provided them with such an inexhaustible food supply, that they kill the animal just to eat what they consider to be the tastiest bits and leave the rest for the coyotes.
This is some tremendous irony. Before the Europeans arrived with their guns, the cougars' favorite but most difficult prey was bison. Hard to catch, even harder to kill, but oh so tasty. Then you know what the white folks did. Slaughtered entire herds of bison, took the livers, and left 500 tons of beef that even the coyotes couldn't eat up. We killed off their best food supply, just to eat our favorite parts.
So what are the cougars doing now? Killing off our food supply, just to eat their favorite parts. Who says there's no justice?
Of course the Anatolians have changed the balance, running cougars off and killing the ones who stayed to fight. (Like I said, they're tough. In Africa they breed them a bit bigger and they protect the cattle from lions.) Only the rich corporate ranchers whose ranches are too big for a pack of dogs to cover have to worry, but at least they know it isn't aliens they're up against.
The Anatolian was just accredited by the AKC. If you want to see one watch the Westminster Dog Show on USA, I think it's next week. He will be in the "Working Breeds" category. You'll understand why there aren't as many "cattle mutilations" as there used to be.
If the same thing is happening in South America, well they have two playful cats: mountain lions and jaguars. They need to get themselves some guardian dogs.