The Dutch safety board is starting an investigation into factory farm fires to establish why such large numbers of animals are being killed.

The board, which has been monitoring the fires for some time, will start by collecting information and then determine the parameters of the investigation.

According to animal rights lobby group Wakker Dier, there have been 12 factory farm fires this year, killing 174,000 birds and pigs. The biggest, involving 100,000 chickens, was in early July.

Last year 122,000 animals died in fires at factory farms in the Netherlands but the government said it would not force farmers to take further measures to prevent fires breaking out because of the cost of the investment.

The current measures do not include compulsory lightning conductors and sprinkler systems.