They have qualified the amount gases from farm animals can irritate the human respiratory system. It is curious that they have decided to qualify farm animals now, when humans have been farming for thousands of years. Still many humans live in a bubble known as civilization, where all farm produce is processed and packaged, so the closest they get to a farm is the organic grocery section of the supermarket. With all of the artificial noxious chemicals introduced into the environment over the past few hundred years, I'd say farm animals are the least of our worries. particularly when many animals these days are born into and never leave a processing plant unless they're pre-packaged.