from 2010 to 2013, McD's helped to finance, through the Coalition of Sustainable Egg Supply, a groundbreaking study on hen housing. Conducted by 18 leading researchers at Michigan State University, the University of California, Iowa State and the U.S. Department of Agriculture, it compared the impact of the three most-used housing systems:

• Standard battery cages, in which four to eight birds each have about 67 square inches (the size of a magazine cover) of living space;
• “Furnished” or “enriched” cages, which have about twice as much space, plus separate areas for nesting and perching;
• Cage-free, often known as free-run, in which birds are loose in an open barn, but not allowed outside (free range means the birds get to go outside when the weather co-operates).

All three systems were rated based on a variety of factors, including food safety, animal health and well-being, environment, worker health and safety, and food affordability.

When it came to freedom and the ability for birds to express natural behaviours, a cage-free environment, not surprisingly, provides the most benefits. And yet, contrary to popular opinion, it also has the greatest negative impact in every category. On animal health and well-being, the environment, worker health and safety, and food affordability, cage-free had the most severe consequences.

For example, 12 per cent of cage-free hens die prematurely – about double the rate of those in cage systems – often from issues that cages were originally introduced to prevent: bone injuries, excessive pecking – and cannibalism.

The last of those is caused by a variety of factors, but “once cannibalization starts, it spreads throughout the flock, because birds copy each other’s behaviour,” says Joy Mench, a professor of animal science at UC Davis, and a lead researcher on the study. “If a bird is in a conventional [battery cage] system and there’s only six birds, it doesn’t go very far. But if it’s in an aviary where you have lots of birds, you can get this very rapid spread of cannibalization.”

The study also raised concerns about hygiene, air quality and health, of both hens and workers. With cages, manure drops through the wire floor, collected safely away from both the bird and eggs. But when birds are free to roam, it can be difficult to control where the eggs and manure end up. Meanwhile, material for dust-bathing – bits of straw or sawdust that the birds roll around in to “clean” themselves of parasites – is also kicked up into the air, resulting in dust levels between eight and 10 times that of caged systems.

In most categories, problems with furnished cages were less severe than they were with either battery or cage-free systems.
https://www.theglobeandmail.com/news...ticle29797385/