According to The Local, the agency stated in a press release that it considers the matter very serious from an animal protection standpoint and that three slaughter facilities have been reported on suspicion of breaching of animal welfare legislation.

"Scalding and plucking would subject a living chicken with feelings to unbearable pain," the agency wrote.

Thomas Jönsson, regional director of agency in northern Skåne, told the TT news agency that all four cases were uncovered in February of this year.

The reports are based on information from veterinarians which the agency has in place to monitor production at the three slaughter facilities.

Mr Jönsson argued that while thousands of chickens are slaughtered on a daily basis, such incidents are very unusual.

"I have not experienced anything like it before," he said.

He saw no reason why the four cases occurred during a single month. He furthermore explained that it is not connected to an increase in production at the slaughter houses concerned, nor to changes in procedures or equipment which may explain accumulation.

"It seems to be a mere coincidence," he said.

The slaughter houses concerned in the report are Lantmännen Kronfågel AB in Kristianstad, Lagerberg in Norjeby AB in Sölvesborg and Torsåsens Fågelprodukter AB in Falkenberg, where two incidents were reported.

The slaughter of chickens begins with the birds first being stunned with electricity in a water bath. They are then emptied of blood and, once dead, are then scalded and plucked.

If the birds are not completely emptied of blood then there is a risk that they regain consciousness and thus are scalded and plucked alive.

Mr Jönsson confirmed that the agency regards the reports as very serious and the prosecutor has been informed in accordance with the terms of the Animal Welfare Act.

Bjorn Elb at Torsåsens Fågelprodukter, said on Thursday that the responsible staff have been alerted after the reported incidents at the slaughter house.

"We have zero tolerance of this kind of thing," he said.

The plant slaughters an average of 42,000 chickens per day.

The firm has announced that staff monitoring the process in which animals are bled prior to scalding will now be rotated every 15 minutes.

"They are not allowed to stand for too long. This is one of the actions we have taken," said Mr Elb.