MODESTO, Calif. -- Some experts say cows -- not cars -- are causing most of the dirty air in the San Joaquin Valley.

A citizen group recently filed a lawsuit claiming air district leaders aren't doing enough to control cow pollution in the area, but this week an appeals court sided with the air district.

The San Joaquin Valley Air Pollution Control District wouldn't comment on the lawsuit.

Cow patties -- in pollution terms -- is a volatile organic compound. Farmers said they are doing all they can to cut down on the pollution by flushing often -- as much as every six hours.

"It is a learning process and we are finding out that what we thought was a problem wasn't and what we didn't think was a problem was," dairy farmer Ray Souza said.

What's also been determined is that the silage, the cow's feed, produces more pollution than the cows. But when it's covered up with plastic, it is no longer a problem.

Unfortunately, the regulations may be responsible for many smaller dairy farms moving to other states as the rules become even more stringent.

California leads the nation in milk production, and the San Joaquin Valley is the largest milk-producing region in the world.

Reported by: Rich Ibarra
Web produced by: Laura Johnson