By Joe Fassler
Scientists can now tell us how much time dairy cows spend outside. Why that may improve accountability and transparency in the organic industry.
How much fresh grass did the “grass-fed” cows who make your milk eat? A team of scientists from Iowa State University’s Leopold Center for Sustainable Agriculture has found a new technique they say can determine exactly that. Their findings, reported in The Journal of Agricultural and Food Chemistry last month, suggest that fluorescence spectroscopy—a relatively cheap and simple form of light measurement—could be a way to assure shoppers about “grass-fed” claims in the supermarket. And it could prove to be an important tool for transparency in the organic dairy sector, where cows are required to spend time foraging outdoors—something critics allege doesn’t always happen.
To understand why this technique could prove to be transformative, it’s important to first address a simple question: Don’t all cows eat grass? You could be forgiven for thinking so. Anyone who takes a stroll down the dairy aisle at the local supermarket will be confronted by a range of jugs and cartons labeled “grass-fed,” or that feature illustrations of bovines grazing contentedly near the shade of old-timey barns. But the reality behind the marketing is not so simple. Though smaller herds often spend the warmer months outdoors, foraging the grass that makes up most of their diets, the vast majority of American milk comes from cows confined inside large, concrete-floored dairy barns. These cows are fed grass in the form of cut hay, as well as grain silage and crude protein (which can range widely, from soybean meal and day-old bread to red Skittles and chicken feathers). They don’t forage on pasture.
It’s in organic milk where things get tricky—where the matter of what cows eat, once an easy quiz for kindergarteners, becomes a question worthy of the hardest-nosed investigative journalists.
By law, cows that produce organic milk are required to have outdoor access. And not just token access. According to the National Organic Program’s “Access to Pasture” rule, organic dairy cows must spend at least 120 days each year outside; fresh, foraged grass must be a minimum of 30 percent of their diets. But there’s reason to believe that isn’t always happening.
Last May, The Washington Post’s Peter Whoriskey published an exposéalleging serious fraud at an organic dairy north of Greeley, Colorado. The Aurora Dairy’s 15,000-cow herd—huge, considering that the vast majority of organic dairies milk fewer than 100 cows—produces certified organic milk that ends up on shelves at Costco, Safeway, and Walmart, according to the article. But when the Post dropped in on eight different occasions over the course of 2016, something seemed off: Each time, Whoriskey wrote, the fields were empty. Satellite imagery seemed to confirm this account.
For its part, Aurora dismissed the Post’s visits as “drive-bys,” and suggested the cows just happened to be inside when the visits took place. But Whoriskey didn’t rely just on anecdotal evidence: the Postbrought receipts. By testing the fats in Aurora’s product, the paper found a nutritional profile that was much closer to conventional milk. That was an important finding because, in general, grass-fed milk tends to be higher in beneficial fats like conjugated lineolic acid and omega-3 fatty acids. Conventional milk is higher in omega-6 fats, which are more abundant in feed grains.
There’s still debate over whether grass-fed milk is healthier, though multiple studies have found that pasture grazing increases good fats in milk (see here and here). But if chemical differences in the milk produced by grass-fed and conventional dairy cattle are so apparent, why can’t the industry apply empirical standards to claims like “certified organic?”
One issue is that gas chromatography—the method of nutritional analysis the Post used to fact-check Aurora’s claims—is too cumbersome and time-consuming to be feasible at scale. It’s also expensive. According to Logan Peterman, an agricultural research manager at Organic Valley, the country’s largest organic dairy cooperative, it can cost as much as $100 per sample, a cost he says is financially prohibitive for most organic dairy farmers and processors.
Which is where the Iowa State study comes in.
Rather than analyze milk’s fat content, the Iowa State scientists used fluorescence spectroscopy—a method that can be thought of as a kind of molecular fingerprinting, one that involves beaming light at the product and measuring for luminescent signals in response. Unlike nutritional testing, which usually requires samples to be sent away to a lab, the results are instantly visible. (Spectroscoptic techniques are already being considered elsewhere in the food industry, including new methods for rapid E. coli detection and spotting fake oregano.)
“Spectroscopy is easy,” says Jacob Petrich, an ISU biochemist who co-authored the study. “There’s really no sample preparation involved. You just need to shine light on the sample, and there are signatures in the milk that you can see. There’s very little preparation to be done, and you get the answer almost immediately.”
Not all foods carry the kind of fluorescent markers spectroscopy can easily measure. But milk happens to contain a strong and readily detectable signal: lingering traces of chlorophyll that have been metabolized by the cow. Think back to freshman year biology—chlorophyll is the green pigment responsible for converting the sun’s light into energy, abundant in grass. When exposed to a certain frequency of light in cow’s milk, it returns a bright, easily detectable cue. This method takes the guesswork out of the grass question, according to the study—the scientists found they could instantly spot the differences between various types of milk.
When the researchers compared milk from a true grass-based dairy to samples from the grocery store, the chlorophyll content varied dramatically. Control samples were taken from Radiance Dairy, a small, pasture-based operation in Fairfield, Iowa, where cows forage 85 percent of their diets from fresh pasture during the grazing season—far more than the 30 percent required by law for organic producers. (Individual brands were anonymized in the study, and the co-authors wouldn’t tell me which specific ones they bought.)
Francis Thicke—Radiance’s owner, who was the Democratic Party’s candidate for Secretary of Agriculture in Iowa in 2010 and just finished serving a term on the National Organic Standards Board—tells me by phone that his cows don’t eat only grass. Given the state of modern cow genetics, he says, the animals do a little bit better with some grain, and that corn is a good way to lure them back into the barn at the end of the day. But his animals do spend the vast majority of their time outdoors, grazing.
And it shows in their milk. The concentration of chlorophyll metabolites in Radiance Dairy milk ranged from 0.13 to 0.11 micromolar, compared to only 0.09 to 0.07 micromolar in a range of organic milk the scientists bought from the supermarket—about 50 percent higher, on average. But the differences were even starker in store-bought conventional milks, which the study found ranged from .04 to a mere .01 micromolar, four to 10 times lower than Radiance Dairy’s milk.
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