Air quality researchers in California's San Joaquin Valley got an unexpected surprise recently when they accidentally discovered that what comes out of cows may not deserve nearly as much blame for the area's high ozone levels as it's been getting.

Instead, a bigger culprit may be what goes into them.

"Feed sources might be more important than all of the things we've been caring about in the past," said Michael Kleeman, a professor in the University of California, Davis Department of Civil & Environmental Engineering. Kleeman heads a team of researchers who for four years has been studying ozone levels in the valley as it struggles to meet federally-mandated reductions. Significant control measures have been implemented, yet ozone levels remain largely unchanged.

Over the years, blame has shifted from one end of cows to the other, then to uncovered manure lagoons. Now, according to Kleeman's team, a bigger "smoking gun" for harmful air emissions is fermenting silage. Specifically, silage that is not stored in air-tight bags.

Action on the researcher's findings appeared to have been taken very seriously. Associated Press reports that the executive director of the San Joaquin Valley Air Pollution Control District is planning to ask its board in June to require dairies to bag their silage.