They were displaying the typical symptoms of being stoned: red eyes, wobbly gaits, and drowsy demeanors. But these weren’t people who had just frequented their local dispensary—they were cows.
In a new study, scientists report cattle that have eaten feed containing varying amounts of hemp seemed to get stoned like people do. The work may give regulators pause when considering whether the affordable, fast-growing crop is safe for livestock to eat. It also raises concerns about whether the active ingredient in marijuana can enter the human food supply through the milk of blazed bovines.
The behavioral effects documented in the new study are noteworthy, says Serkan Ates, an agronomist at Oregon State University, Corvallis, who has studied hemp consumption in cows, lambs, and chickens. “They found a much more profound effect on the animal’s behavior than what we’ve seen in any of our dairy-feeding studies.”
Derived from Cannabis sativa plants, hemp possesses a less potent concentration of the psychoactive compound tetrahydrocannabinol (THC) than marijuana-related varieties of cannabis. Instead, hemp flowers are loaded with cannabidiol (CBD), a chemical that has been linked to alleviating a slew of health issues such as anxiety, addiction, and insomnia. Additionally, hemp’s pliable fibers can be made into a variety of products such as clothing, shoes, paper, and biodegradable plastics.
The cultivation of hemp has exploded in recent years. However, the U.S. Food and Drug Administration has yet to approve feeding the now-widespread crop to cows because of concerns about THC entering the food supply.
To flesh out how hemp’s cannabinoids impact livestock, scientists at the German Federal Institute for Risk Assessment fed 10 lactating dairy cows differing amounts of hemp feed containing a range of cannabinoid concentrations. Over the course of the weekslong experiment, the researchers collected milk, blood, and fecal samples and paid close attention to the cattle’s behavior.
Dosage was key. Cattle that ate fermented feed formulated from whole hemp plants (which have a relatively lower concentration of cannabinoids) exhibited few noticeable changes from cows fed a normal corn-based diet. It was a different story for cows that consumed feed made from cannabinoid-rich hemp leaves, flowers, and seeds. By the scientists’ calculations, these cows consumed up to 86 times the amount of THC that’s required to get humans high. The animals’ breathing and heart rates slowed as they ate less and produced less milk.
The befuddled bovines also yawned more, produced more saliva and snot, and exhibited overactive tongues, the researchers report today in Nature Food. Some even exhibited reddening in their eye membranes and unsteady movements.
The unusual behaviors ceased a few days after the cattle stopped eating hemp. But the cannabinoids persisted in the cows’ milk, which contained elevated concentrations of THC, CBD, and other cannabinoids.
It remains unclear whether such milk would get human consumers high. “The study does not allow any conclusions to be drawn as to whether there is a health risk from consuming milk on the market,” says animal nutritionist and study co-author Robert Pieper.
If proved safe, hemp would be a welcome addition to farmers’ feedstock options, Ates says. Hemp is a cheap, widely available, and nutritious alternative to more popular feeds. Ates has found that spent hemp biomass, the byproduct of CBD oil extraction, is comparable to alfalfa in terms of nutrition. Because of the potential to pass on cannabinoids, “it may not be possible to feed this to high-yielding dairy cows,” Ates says. “But there is plenty of low-hanging fruit to explore, like feeding hemp to non–food-producing animals like heifers or young lambs.”
Even if it’s not used as a primary feedstock, hemp may have other uses for livestock. Earlier this year, Michael Kleinhenz, a veterinarian who studies beef consumption at Kansas State University, Manhattan, and colleagues found cows that ingested hemp—in smaller amounts than the new study—spent more time lying down and had noticeably lower stress levels. This makes hemp feed a potential tool to mellow out cattle during transportation, weaning, and other stressful situations, he says.
Jack Tamisiea is a freelance science journalist based in Washington, D.C., who covers the nexus of natural history and environmental science. In addition to Science, his work has appeared in The New York Times, Scientific American, National Geographic, and a variety of other science-focused publications. You can read more of his work on his website: https://jacktamisiea.com.
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