Researcher follows dairy cow carbon footprint from barn to field

Research may help create whole-farm decision models producers can use to predict outcome of various management practices.

April 5, 2018

4 Min Read
Researcher follows dairy cow carbon footprint from barn to field
Michel Wattiaux examines the contents of a cow’s stomach.University of Wisconsin-Madison

University of Wisconsin-Madison dairy scientist Michel Wattiaux sometimes approaches his research like a cop at a traffic stop, using a breath analyzer to check cows for problematic products of fermentation.

Last spring, Wattiaux began using a specialized device to measure the methane being exhaled or belched by a group of Holsteins and Jerseys. It was the first step in an ongoing study by dairy scientists, engineers and agronomists to see how a cow’s breed and forage consumption affect the greenhouse gases (GHGs) generated by her gut and her manure, according to an announcement from the university.

GHGs, which collect in the atmosphere and trap the sun’s radiation, are a big issue for the dairy industry. Methane is a concern because it’s particularly potent, trapping about 30 times as much radiation as carbon dioxide does. A cow generates a lot of methane in her rumen, where microbes are fermenting up to 200 lb. of plant material. Also worrisome is nitrous oxide, another potent GHG that is emitted from manure during storage and after it’s spread in the field, the university said.

The U.S. dairy industry has set a goal of reducing its GHG emissions 25% by 2020, and University of Wisconsin-Madison researchers are helping identify strategies to accomplish that.

Breath samples were the first in a sequence of experiments designed to measure GHG emissions at three critical points: from the cow’s breath, from her manure during storage and from the field where her manure is spread. The researchers are looking at how three variables — the breed of cow, the type of silage fed and relative levels of forage in the diet — affect GHG emissions at each point.

While versions of each of these experiments have been done on a stand-alone basis on the University of Wisconsin-Madison campus, Wattiaux said this is the first time the three have been integrated so that emissions originating from a cow and her manure can be tracked from barn to manure storage to field.

“This is the first time where we do the nutrition part, the manure storage part and the field application part sequentially and then put it all together to give the Wisconsin dairy industry a solid number for how much methane and nitrous oxide come out of their farms depending on the breed, the kind of diet and the amount of forage in the diet,” Wattiaux said.

For the first experiment, which began in June and ran for four months, researchers fed 24 Holsteins and Jerseys a ration that included either alfalfa silage or corn silage -- the two primary forages fed on Wisconsin dairy farms -- along with some grain. Some cows were fed high levels of forage relative to grain, while others got less silage and more grain. Researchers periodically sampled each cow’s exhaled breath using the GreenFeed system, an analytical tool designed to determine daily methane emission.

“It drops a bit of sweet feed to entice her to stick her nose up to it,” Wattiaux explained. “The equipment sucks the air in, measures airflow, measures the concentration of methane and then estimates the amount of methane.”

In the second experiment, the manure from the cows was collected and held in barrels for two months to simulate manure storage on a dairy farm. Graduate student Elias Uddin collaborated with biological systems engineering professor Rebecca Larson to measure emissions of both methane and nitrous oxide from each barrel for 60 days.

The third experiment began at the end of October to simulate the post-harvest manure spreading typical of many Wisconsin farms. Researchers applied the stored manure to 24 field plots at the university's Arlington Agricultural Research Station. Under the supervision of agronomists Greg Sandford and Randy Jackson, a team of students began monitoring emissions from the plots last fall and will resume the activity this spring.

Wattiaux said he believes that the findings from this research will be useful to scientists who create whole-farm decision models that producers use to predict the outcome of various management practices. He likens it to software such as Wisconsin’s SnapPlus, which farmers use to minimize soil and nutrient loss from their fields.

“I think we’re going the same direction with this research. A model might calculate a tolerable level of (GHG) emissions and provide information on how to stay below that total by adopting new techniques in the field, new techniques in storage and new techniques in feeding,” Wattiaux concluded.

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