Cows are being kept inside 'bio-bubbles' so scientists can measure gas emissions.
The University of California project will be used to help write the state's first air quality regulations for dairies.
Cows are placed inside the bio-bubbles where monitors measure the gases that they emit.
It's been estimated that an average herd of cows causes more pollution than a car.
But researcher Frank Mitloehner believes the problem may have been over-estimated.