Free-Range Chicken More Disease-Prone?

Jan. 23, 2009 -- In an effort to eat compassionately, many people choose free-range chickens and eggs -- assuming that the birds lived happy, high-quality lives before they became dinner. A free-range label, however, doesn't guarantee your poultry had a worry-free existence.

Swedish researchers have discovered that, if farmers aren't extremely careful, bacterial infections like E. coli can run rampant through free-range chicken flocks. The finding raises questions about what's best for both animals and people.

The study began when scientists at the National Veterinary Institute in Uppsala, Sweden, noticed a sudden spike in dead laying hens submitted for necropsies. They decided to investigate.

The researchers guessed the surge in deaths was linked to the way farmers were housing the birds. In Sweden, a new law bans the use of small laying cages and instead requires that chickens live more naturally -- with access to nests, perches, and piles of dust they can roll around in. This type of living is called a litter-based system. In a "free-range" litter-based system, the birds are also allowed to go outside.

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Most Swedish farmers made the switch from cages to litter-based housing between 2001 and 2004. Around the same time, more dead hens started showing up at the Institute.

To further investigate, veterinary pathologist Oddvar Fossum and colleagues analyzed the necropsies of 914 hens from 172 flocks. The researchers found that as many as 10 times more hens were submitted from litter-based and free-range setups than from caged systems during those years.

Compared to caged birds, free-ranging hens had more bacterial infections (the most common cause of death), more parasites, and more viruses. They were also more likely to become victims of violent pecking and cannibalistic attacks, the scientists reported this month in BioMed Central's open access journal Acta Veterinaria Scandinavica.