The animals' remains have since been analysed by the National Veterinary Institute (Statens veterinärmedicinska anstalt--SVA) which announced on Sunday that anthrax was responsible for their deaths.
Officials believe the cows were infected from dormant spores which rose to the surface following excavation work.
“In the air, the spores disappear, but in the ground they are more resistant. There they can lie for perhaps 50 or 100 years,” Lena Hult, a veterinary at the Swedish Board of Agriculture (Jordbruksverket), told the Svenska Dagbladet (SvD) newspaper.
In the 1950s, cows that died from anthrax in Sweden were simply buried on the farms where they died, meaning the disease may lay beneath the surface at many locations across the country.
In order to reduce the risk of additional outbreaks caused by building projects or excavation, the SVA is combing its archives for records dating back to 1916 and running up to the present day to learn which farms have been affected by anthrax in the past.
“After 1937, there was no reporting requirement, so it's going to be harder to find affected farms,” doctor and historian Bodil Persson, who has been hired by SVA to carry out the investigation, told the newspaper.
The last documented case of livestock being infected by anthrax in Sweden was in 2008 at a farm in Halland County in western Sweden.