Hens that play together, lay together

Socialism can be a good idea, at least when it comes to egg-laying hens, say researchers at Purdue University.

William Muir, an animal science professor at Purdue’s campus in Lafayette, Indiana, has found that focusing on the number of eggs produced by a group is more beneficial than breeding the most productive individual birds.

“We chose the productivity of the pen as our unit of selection and said the individual is not important …. It has a lot of connotations of socialism,” said Muir, with a laugh.

Muir, who has been studying the idea of selecting the best group rather than the best individual hens for more than 30 years, has focused his recent research on breeding less aggressive hens.

Working in collaboration with Heng-wei Cheng, a biologist at Purdue, Muir has demonstrated that it’s possible to breed gentle hens, by selecting groups that produce the most eggs.

“We don’t even look at (the hen’s) behaviour. We just want to know how many eggs they produce. And if they’re nice to each other, they produce more eggs,” said Muir.

“That’s the beauty of the system. We select based on productivity … except we’ve changed the unit of selection.”

When housed in communal cages, hens can be aggressive and peck and kill other birds with their beaks.

After selecting a line based on the number of eggs produced as a group, Muir and Cheng compared the aggression in that pen to the violence in a commercial line of hens, bred for individual production.

The Purdue researchers found the “kindler, gentler line” had a 20 percent mortality rate in the communal cages, compared to 89 percent for the commercial line of hens.

Cheng’s role in the research was to determine why certain hens are violent and others are not.

He determined that the levels of dopamine, a brain neurotransmitter, might be lower in the less aggressive hens.

“Aggression is regulated by the dopaminergic system but other systems, such as serotonergic system, (are) also involved in controlling aggression and cannibalism in chickens,” said Cheng in an e-mail. The kind, gentle birds were selected from a group of 12 per cage, he added.

Muir’s latest research is part of his lifetime of work on group selection of egg laying hens, which began with a simple question during his graduate school days in the 1970s.

“Can genetic selection make things worse? In other words, is it possible that positive selection can take you in a reverse direction?” Muir said.

Selection programs typically focus on breeding productive individuals, but Muir believes the survival of the fittest model has unintended consequences.

“If I’m selecting for increased (individual) productivity, (but) that production occurs as a result of fighting and getting a greater share of the resource, then it’s possible that the productivity of a flock can decline.”

Instead, it’s better to breed for the production of a group of birds, an approach also called multi-level selection, Muir said.

One of his previous studies, published in Poultry Science in 1996, showed that his gentle hens produced 237 eggs per hen housed in a communal cage, compared to a control group that produced 91 eggs per hen.

Fewer penned birds

His research is timely, Muir noted, because egg producers are shifting away from individual hen cages in response to public pressure over animal welfare concerns.

Californians, for example, voted in favour of Proposition 2 during last fall’s presidential election, which will ban battery cages across the state in 2015.

The European Union will ban battery cages in 2012 and a ban on beak trimming in the EU will likely follow, Muir noted.

The problem though, he said, is that EU egg producers are finding the transition to floor pens difficult without beak trimming because of the aggression of the hens.

Muir is hopeful that his research into gentle birds will reduce the violence in the pens.

“With this group selection, we can hopefully eliminate the practice (of beak trimming) because it … is considered to be not too animal friendly.”

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