The bovine corpses stunned the ranchers who found them. The animals’ ears, eyes, udders, anuses, sex organs and tongues had routinely been removed, seemingly with a sharp, clean instrument. Their carcasses had been drained of blood. No tracks or footprints were found in the immediate vicinity—nor were any of the usual opportunistic scavengers.

Between April and October of 1975, nearly 200 cases of cattle mutilation were reported in the state of Colorado alone. Far from being mere tabloid fodder, it had become a nationally recognized issue: That year, the Colorado Associated Press voted it the state’s number one story. Colorado’s then-senator Floyd Haskell asked the Federal Bureau of Investigation to get involved.

Throughout the 1970s, cases had continued to mount throughout the American heartland. And in 1979—after thousands of reported cattle mutilations, causing millions of dollars of livestock losses—the FBI finally opened an investigation into a series of cases that had reportedly taken place on New Mexico’s Indian lands. Pressure came, in part, from a heated public symposium on the subject that had been convened by that state’s science-minded U.S. senator, Harrison Schmitt, who had a Ph.D. in geology from Harvard and had walked on the moon as an Apollo 17 astronaut.

Ultimately, the FBI’s inquiry poured cold water on the idea that something strange was afoot. On January 15, 1980, the Bureau closed the investigation, putting out a statement saying that, “none of the reported cases has involved what appear to be mutilations by other than common predators.”

Locals sharply disagreed.

“I've been around cattle all my life and I can sure tell whether it's been done by coyote or a sharp instrument,” Sheriff George A. Yarnell of Elbert County, a rural area south of Denver, told The New York Times in the fall of 1975.

Mysterious livestock mutilations weren’t confined to the 1970s, or to the United States. Similar cases involving sheep, cows or horses have been reported as far back as the early 17th century and as recently as 2019. The ‘70s cases, however, brought the most widespread attention.

Broadly speaking, the debate about cattle mutilation falls into two camps: those who see the mutilations as unexplained phenomena, and those who see them as normal cattle deaths, repackaged as something mysterious or paranormal.

For those in the unexplained camp, opinions have diverged about the possible explanation. Some law enforcement communities opined that the animals were being mutilated by people in strange, quasi-religious rituals. In 1980, the Royal Canadian Mounted Police blamed the mutilations on an unidentified cult. The Department of Criminal Investigations in Iowa, meanwhile, asserted that the mutilations were being conducted by Satanists.

Reports within the affected ranching communities indicated that the mutilations regularly coincided with the sighting of mysterious unmarked helicopters. Some ranchers who suffered the worst losses believed the federal government had performed the mutilations—for an assortment of reasons, including the testing of biological weaponry. Animosity for the government proved so heated that the Nebraska National Guard ordered their helicopters to cruise at 2,000 feet (rather than the regular 1,000-foot altitude), for their safety, since panicky ranchers had begun shooting at helicopters.

Others have blamed unidentified earthbound creatures. At Skinwalker Ranch, a property in northeastern Utah whose numerous paranormal activities were the subject of the book Hunt for the Skinwalker: Science Confronts the Unexplained at a Remote Ranch in Utah, rancher Terry Sherman lost several heads of cattle to mutilation after buying the 512-acre property in 1996. Those mutilations coincided with several strange encounters: In one, Sherman saw a wolf-like creature three times the size of a normal wolf that was impervious to rifle fire; in another, a researcher saw an odd humanoid creature with piercing yellow eyes spying on him from a tree. Other cases have happened since on the property.

Still, others tie the mutilations to possible extraterrestrial visitors. Filmmaker, science reporter and Stanford-educated author Linda Moulton Howe has looked at more than 1,000 animal mutilation cases, winning an Emmy award for those efforts with her 1980 documentary A Strange Harvest. In her 1989 follow-up book, An Alien Harvest: Further Evidence Linking Animal Mutilations and Human Abductions to Alien Life Forms, Howe ultimately concluded—after researching hundreds of cases—that extraterrestrials were likely involved.

One particularly compelling case linking animal mutilation and aliens involved "Lady," a horse found dead and partially skinned at a ranch in Alamosa, Colorado in September 1967. Within 24 hours of the incident, in which the animal’s brain, lungs, heart and thyroid were cleanly cut out, local superior court judge Charles Bennett witnessed three orange rings in the sky, flying in a triangular formation at incredible speeds. Two sheriff's deputies, meanwhile, reported being followed around by a floating orange globe.

Some medical experts offer much more mundane explanations for animal mutilations. Veterinary pathologists point to the fact that scavengers tend to eat the soft tissue of a dead animal first, which might explain the missing external organs commonly described on the dead bovine. Bloodlessness, meanwhile, might be attributed to livor mortis: When an animal dies, the heart stops and the blood stops circulating, thus settling the blood via gravity, creating a “bloodless” effect in some surface parts of a carcass.

In Washington County, Arkansas in 1979, the sheriff’s department conducted an experiment: It placed a dead cow in a field for 48 hours and found it looked a lot like the ostensibly mutilated ones. Bacterial bloating had caused its skin to tear in an incision-like manner similar to what had been described in some ranchers’ reports. Maggots and blowflies, meanwhile, had cleaned out the animal’s organs.

Agricultural historian Michael Goleman theorizes that the ’70s reports of cattle mutilation likely provided a way for independent, small-scale ranchers to express both their economic anxiety and their resentment for government interference in agricultural life.

According to Goleman, unexplained cattle death has always been a part of ranching—cattle deaths were no higher year-to-year during the time of the reported mutilations than before or after. But most mutilation reports emerged at a time when the cattle industry was reeling. In the 1970s, the U.S. government sent a lot of grain to food-insecure nations, driving up the domestic price of cattle feed. At that same time, President Richard Nixon intermittently froze the price of beef (and other meat) domestically, to combat inflation. Cattle ranchers found themselves in a squeeze, and in a 1975 Senate agriculture committee hearing, the president of the American National Cattlemen’s Association said the industry had suffered “operating losses of $5 billion, plus a reduction in inventory value of $20 billion.”

As evidence for his argument, Goleman points out that the alleged ’70s mutilations occurred most frequently in states like Colorado and New Mexico, which had a higher percentage of small ranches most vulnerable to those governmental policies. Texas, meanwhile, reported considerably less of the phenomenon, despite having by far the most cattle in the country.

Because the mutilations were concentrated both geographically and over time, Goleman says, paranormal activity seems a less likely explanation than a case of mass hysteria.