No tracks, blood or a bullet holes.. it's like the cows just agreed to lay down and surrender .. in some cases these cows have were miles off the nearest road , which if it were people they would have walked by hundreds of other cows to choose the ones miles away .. this has been happening all over the world for a long time..documented cases go back hundreds of yrs ..
Now let's just assume it's aliens and they are monitoring thier science project and the effects of pollution/radiation in the environment ..maybe the radiation particles/fallout from decades of above ground tests some how manifest in the tounges and butts of living organisms that eat the particles ..
As much as the govt. Lies to the citizens about alot evertyhing possible....I think the few topics they just totally ignore and not even mention ...is what speaks volumes..