No, it’s not a St. Patrick’s day joke, and has nothing to do with the actual color of the eggs.

But, Iowa State University researchers played a key role in a recently completed comprehensive study of egg production systems intended to study ways to improve animal health and efficiency and to reduce environmental impact.

Iowa is the nation’s top producer of eggs and was at the center of a 2010 health scare involving salmonella and the recall of more than a half-billion eggs from DeCoster operations.

Hongwei Xin, a distinguished professor of agricultural and biosystems engineering and director ISU’s  Egg Industry Center, said the study compared conventional egg production, which features six laying hens to a cage, with two alternative models.

One alternative approach, an enriched colony system, has approximately 60 birds in a large enclosure with access to perches, nest boxes and scratch pads. In the second system, an aviary,  hundreds of hens are allowed to roam freely in a large space for much of the day.  

Pressure has grown in recent years on egg producers to move away from conventional production methods due to animal welfare concerns, said Xin, who holds the Iowa Egg Council endowed professorship.

California’s Proposition 2, which went into effect on Jan. 1, requires egg producers to provide hens a minimum space of 116 square inches, an increase of 73 percent from current industry standards. Producers that don’t comply with the California law can’t sell shell eggs in the state.

Xin said there are tradeoffs. The aviary system, for instance, creates the potential for increased environmental impacts. Xin said his group found that the conventional and enriched colony systems had similar effects on indoor air quality. The aviary system resulted in higher dust levels and emissions. That’s because chicken manure can easily land on the floor of an aviary as the birds have so much space in which to move. The manure dries out and turns to dust, which is then kicked around by the roaming birds, Xin said.