The problem with this theory is that the mutilations are too wide-spread, span 30 years, and would require a large amount of resources to execute. However, the way in which the animal died is inconsistent with how a predator would kill it. The drainage and absence of blood would be impossible for a predator to do. The absence of tracks, the mysterious nature of the act, and the coinciding UFO reports preceding mutilations suggest this is a sinister plan performed by aliens. Along with UFO sightings, black helicopters are also present before mutilations.
Conspiracy theorists believe the government is conducting top secret chemical warfare experiments.
The weakness of this theory is that the government would have access to their own stock of cattle and would not necessarily need to use random cattle belonging to civilians. Also, the phenomena is too global to be conducted by any one government. The craft generates its own gravitational field, causing it to move forward at a perpetual down-hill motion. Interestingly enough, the millions of eyewitness descriptions of the behaviour of UFOs, support this theory. There are reports of crashed or downed alien craft worldwide.