CHAMPAIGN, Ill. — From the first days of the recent recall of 550 million eggs from two Iowa farms, one issue about large-scale agriculture has been clear: When something goes wrong on a big farm, it's going to be a big problem.

It's a point even some supporters of industrialized farming acknowledge.

"If you have something go wrong, it'll generally go wrong through a million and a half birds," said Arnold Riebli, one of the owners of Sunrise Farms near Petaluma, Calif., which has more than a million laying hens.

The issue has received more attention since two huge Iowa farms acknowledged some of their eggs were contaminated with salmonella and ordered the recall. As many as 1,500 people have become ill in the outbreak, the largest blamed on a single strain of salmonella.

There are 434 mega-farms, each with at least 100,000 laying hens, that supplied more than three-quarters of the nation's eggs in 2007, the year of the U.S. Department of Agriculture's most recent Census of Agriculture.

Large-scale production is widely credited with keeping consumer food prices low. When adjusted for inflation, the price of a dozen eggs is less now than in 1980, an average of $1.44 compared to $2.05, according to the U.S. Department of Commerce.