200 cows were found dead Friday on a farm in Portage County, Wisconsin. The dead cows had to be removed with semi-trucks. The rest of the farm has not been quarantined, as officials say no threat is posed toward humans or other animals, according the The AP.

The owner of the dead cows was working with a local veterinarian, who initially believed a virus such as infectious bovine rhinotracheitis (IBR) or bovine virus diarrhea (BVD) could be the culprit, according to The Wausau Daily Herald. WSAW News reports that more recent updates have suggested pneumonia as the cause of the mass cow deaths, though such widespread cases of pneumonia are rare. Tests are still underway to determine what is responsible. See WSAW's full video report here.

Though likely unrelated, many other incidents of mass animal deaths have been reported in the U.S. and around the world in the past month. Thousands of dead birds fell from the sky in Arkansas on New Year's Eve, following a massive fish kill just 100 miles away days earlier. In the week following, other mass bird deaths were reported in nearby Louisiana and Kentucky. Birds were also reported to fall dead from the sky in Italy and Sweden, and more recently similar incidents have been reported in California and Alabama.

Mass fish kills have also been reported in Chicago, Maryland, Brazil and New Zealand, along with 40,000 dead crabs that washed ashore on England beaches.

Many explanations have been offered for the various mass animal deaths, with everything from fireworks, semi-truck collisions, overeating and cold weather blamed for the birds' deaths. Cold weather has also been pinned to likely be the cause of many of the fish and crab deaths, as well. According to The AP, mass animal deaths are not all that uncommon.