Fistulated animals can leak gas out of the fistula, therefore the gas does not leave from the animal’s muzzle. Because of this, GreenFeed cannot measure the gases accurately for fistulated animals. The fistula attachment is a blanket that is manually placed over the fistula and collects leaked gases from the fistula and routes them into GreenFeed for quantitative measurement. Because the blanket must be manually placed over the animal, it must be confined in a tie-stall for use with the fistula attachment. The gas collected inside the blanket is then routed into GreenFeed for measurement of gas concentrations and flow rates to determine flux.