In the early 1980's (gettin' old and can't remember for sure which year) we were living in north east Wyoming. A rancher friend of ours asked us to come over to look at "something really weird".
We saw a mutilated calf. As in the other reports, eyeballs, viscera, lips all removed. Not jagged tears, like a predator would do, but removed with surgical precision. There was no evidence of blood, nor of a struggle. There were no flies, nor insects of any kind on the carcass. But there were many on a nearby dead jack rabbit. This was in the spring and there was tall grass around the carcass. It was not trampled in any way. It was almost as if the calf had been dropped there from above.
We called Game and Fish and the BLM. After inspecting the carcass, they were just as puzzled as we all were. No explanation.
planekt and I were chatting about this type of thing just this afternoon. The most recent incident (a fancy surgery) that I know of was on a ranch in Northern California, four months ago.
Here's some pics of the Bartons mutilated cattle.
http://www.earthfiles.com/news/news.cfm?ID=1038&category=Environment