Nearly 46 billion such chickens are reared in the world every year, 5.5 billion of them in the EU.

The EU has no specific laws governing the broiler trade, which is regulated under a general law on protecting animals for farming purposes.

But the European Commission, the EU's executive arm, says it will propose a broiler law this spring.

"There is legislation on laying hens at the moment but nothing specific on chickens reared for meat, so there's a gap to fill," a Commission official told Reuters.

"This (law) would bring improvements through technical and management changes," he said, declining to give further details.

Industry sources say it will set out rules for ventilation inside the mostly windowless sheds, as well as hygiene standards for the ammonia-ridden litter that piles up on the floors.

It also will tackle stocking density: how many birds may be packed into a specific area. These vary widely across the EU, ranging from around 30 kg of bird weight per square metre to more than 40 kg.

Industry sources said the Commission was likely to recommend 30 kg as a base standard but with leeway to raise this level to around 38 kg if welfare standards were met in other areas.

"If standards are good on ventilation, litter and other areas, then the stocking density would be able to rise. Those seem to be the conditions," said an official at one member state livestock authority based in Brussels.

"They (Commission) have suggested several times that the most generous stocking density will be 30 kg per square metre. It's a compromise with the economic demands of the industry," said Dil Peeling at lobby group Eurogroup for Animal Welfare.

While Sweden and Denmark have strict laws governing the broiler industry, most EU countries have none. A few, like Britain, have guidelines that are not legally binding.