Stephane Dahirel doesn't exactly say eat chicken and save the planet, but that is what he's hinting at as he opens a shed door on his intensive farm in Brittany, western France.

The 30,000 chickens inside will more than triple in size in less than a month and their meat will have a low carbon footprint.

"The objective is to produce the best meat possible, in the least amount of time, with the least amount of food," Dahirel said.

The two million snow-white chickens he produces every year — bred mostly for McDonald's nuggets — will reach their slaughter weight in less than half the time it takes on a traditional farm. 

At 20 days they already weigh one kilo (two pounds) — 20 times heavier than at birth. By the time they are slaughtered at 45 days, they will weigh over three kilos.

Chicken has the smallest carbon footprint of any meat, according to the UN's Food and Agricultural Organization (FAO), less than half the two kilos of CO2 produced for a kilo of pork, and 30 times less than that of beef.

While cows produce a lot of planet-warming methane, chickens emit very little. As much, in fact, as rice, the FAO says, or even less if they are intensively farmed.

Dahirel insisted that intensive farming is "the most efficient and rational system" for producing meat "from an economical and ecological perspective".

Animal welfare

But there are big drawbacks too. Despite the low emissions he claims for his chickens, producing the grain to feed them requires large amounts of land, synthetic fertilizers, and pesticides.

All have effects on biodiversity and water quality. Indeed green algae blooms on beaches in Dahirel's native Brittany — partly caused by intensive pork, poultry, and dairy production — have caused an environmental outcry and been linked to several deaths.

Intensive farming is also in the dock on animal well-being.