Why are thousands of cows with surgical-like incisions being found at specific sites only? The cattle's vital organs have not only been removed, but the bodies have also been drained of blood. After removing carcasses from farms, the cattle seem to be getting brought back and dumped on their left side.

Chuck Zukowski, 58, UFO hunter who has been on the search for 30 years, says that this is probably the work of aliens. 

He was earlier a microchip engineer, but switched to investigating over 1,000 paranormal incidents. He explains: "Since 1967, there have been over 10,000 cases reported across the US, and out of those no person has ever been caught or sent to jail. There are no tracks around the animals and they appear to have been dropped from a great height. There is no evidence of a predator attack or humans. The probability of aliens doing this is more than the probability of not, that's what I say. This is not old news either, it is happening right now."

But the first known incident happened two centuries ago, on April 21, 1897, Alexander Hamilton, a well-known statesman, narrated that he was woken at night by "loud humming noises" from his cattle yard. He went outside with two men and observed an "airship" in his yard.

"It consisted of a great cigar-shaped portion possibly 300 feet long, with a carriage underneath. The carriage was made of glass or some other transparent substance alternating with a narrow strip of some material. It was brilliantly lighted within and everything was plainly visible. It was occupied by six of the strangest beings I ever saw. They were jabbering together, but we could not understand a word they said. It seemed to pause and hover directly over a two -year old heifer, which was bawling and jumping, apparently fast in the fence. Going to her, we found  a cable about a half-inch in thickness made of some red material, fastened in a slip knot around her neck, one end passing up to the vessel, and the heifer tangled in the wire fence. We tried to get it off but could not, so we cut the wire loose and stood in amazement to see the ship, heifer and all, rise, slowly, disappearing in the northwest. Neighbor Thomas Link (four miles away) found the hide, legs, and head in his field the next day and no tracks in the soft ground, which mystified him."

The most recent case of mutilation was reported in Nevada on August 30. A couple of cows were found dead on their left side. Those who had been around reported that there were balls of light in the sky then. Later, they witnessed four helicopters with searchlights beaming on the spot, looking for "carnage".

Chuck Zukowski has an explanation that sounds quite ghastly. "It may be that their blood is being used to build alien-human hybrids. Or aliens may be monitoring the environment here because there have also been goats, sheep and dogs found too. About the helicopters, it appears the US Government has a secret investigation going on, there has been no trace of them afterwards. These cows are the ranchers' livelihoods and they are scared their families are going to get mutilated."

He denies that humans could be doing it, because most of the humans in the farms where the animals were found were pretty taken aback. His probes are being examined in a new book 'The 37th Parallel', which was released last week. 

Zukowski says: "Every animal is being taken from location A to location B and back to location A. Colorado law allows ranchers to shoot people who steal their cattle on their land. So to steal cows in the first place is brave but to take the carcasses back again? You just wouldn't do it."

It is also noted that a number of the UFO sightings and cattle mutilation cases across the US points to a highway being used by aliens on the 37th latitude or parallel. Zukowski explains: "I think there is a pattern, many of the mutilation cases happen on or near the 37th latitude or parallel and near water. It seems to be a highway which the aliens are using, from east to west. For some reason aliens like water, I think it may be for the hydrogen."

It is not just in the last few years either, Zukowski added. Even the native Indians refer to "star travellers". Spiritual sites, Chaco Canyon and Cahokia Mounds, have also been discovered on the same line of latitude. 

However, the sceptics have some explanations too. Chris O'Brien, researcher of cattle mutilations for two decades, disagrees with Zukowski.

"Why would some non-human intelligence come light years to the pastures of the planet to gather ingredients for lip and testicle stew?" he asked. "It just doesn't make sense."

He believes the killings are by some agency to prevent Bovine Spongiform Encephalopathy, or the "Mad Cow Disease". Another Colorado-based vet, Truman Smith, is convinced that it is the work of animal predators.

However, UFO supporters counter: "Predators don't drink 11 pounds of blood and leave the carcasses intact."