Why You Shouldn’t Feed Pot to Your Cows

Marijuana is all the rage, and now a new study quantifies the level of THC in hemp from which cow milk will start to be affected

Ruth Schuster
Ruth Schuster
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Credit: Artwork: Anastasia Shub / Krivos
Ruth Schuster
Ruth Schuster

Rats. There goes the dream of having a marijuana farm and feeding cows with “ugly” plants. Feeding hemp containing active cannabinoids from a certain level makes the animals high, and the substances reach their milk, a new study has found.

Put otherwise, the study published Monday in Nature Food by Bettina Wagner of the German Federal Institute for Risk Assessment, Pietro Gerletti of the Chemical and Veterinary Analytical Institute Münsterland-Emscher-Lippe, and colleagues, quantifies the point from which active substances in hemp may affect the milk the cows produce.

Well, stone the crows. Who would have thought that serving supper with tangible traces of psychoactive substances such as delta-9-tetrahydrocannabinol (THC) to cows would have a different effect than green grass?

It is true that the study was small, involving just 10 Holstein Friesians fed with industrial hemp silage. Yum. Asked how just 10 cows can represent the effect of eating hemp on bovine behavior and production, Sonja Schäche of the German Federal Institute for Risk Assessment elaborates that in compliance with strict regulations and ethics regarding animal experiments, they had to calculate how many animals of the breed they need to answer the scientific question. “We came up with a total of 10 cows,” she says.

Why would anybody feed hemp to herbivores? Is hay passé? Because revised marijuana farming regulations created a boom; it’s a “cheap, ecological and versatile” crop. And in today’s financially stressed world, who wouldn’t want a cheap, ecological and versatile source of nourishment for one’s livestock?

Not so long ago, researching cannabinoids had been verboten: nowadays it’s practically de rigueur. Thus, one rationale behind the study is that the hemp industry has been exploding, resulting in a slew of novel hemp-derived products – from drinks to oils to organic hemp socks.

Are farmers actually feeding hemp to livestock? That isn’t clear: The norm is maize and grass, Schäche says, but the plant is out there, and there was precious little information on the science of feeding industrial hemp to cows and what that may do to ensuing dairy products.

Many don’t realize it but hemp may contain cannabinoids, some of which have psychoactive effects. Under amended European Union rules, industrial hemp may contain up to 0.3 percent THC. But that begs the consumer-safety question: what happens if Bessie eats it?

Actually there had been little research on cannabinoids in milk if cows are fed hemp; not to mention, analytical techniques often couldn’t distinguish psychoactive THC from its non-psychoactive precursor, delta-9-tetrahydrocannabinolic acid (THCA).

Hence the study of dairy cows given hemp containing less than 0.2 percent THC (asked why 0.2 percent and not 0.3 percent, Schäche explains that when they designed the experiment, the threshold was 0.2 percent). Then the researchers ran analyses of the cows’ milk, blood plasma, faeces and behavior.

Here are the results. Feeding a cow up to 0.92 kilograms of industrial hemp per day had no discernible effect on the animal if the cannabinoid concentration was very low and the feed was made from whole plants. Well and good.

But feeding the cows 0.84 to 1.68 kilograms of cannabinoid-rich hemp made from leaves, flowers and seeds had a noticeable effect. The cows eyes turned red. They yawned, salivated, their tongues lolled, their heartbeats slowed and they staggered around when they moved at all, the team reports. Their noses ran.

Meaning, these cows were baked. All of them. Schäche points out that some were more resistant/affected than others. That was on the first day.

This is the only kind of grass cows should be enjoying.Credit: Mark Baker /AP

On the second day of being fed THC-rich hemp, the cows began eating less (anti-munchies? Well, different species may react in different ways) and yielded less milk, too, the team reports. And yes, the THC reached their milk to a degree that could affect a person.

Were persons given the milk of cows high on hemp? No, they were not. It’s statistics, and drinking that milk could theoretically have had effects on the central nervous system such as feeling logy, impaired working memory performance and mood alterations, Schäche explains.

The cows’ milk yield was reduced possibly not because they were stoned but because when eating fat-rich, THC-high silage, they ate smaller amounts and also seem to have drunk less water, the team surmises.

The changes disappeared within two days of discontinuing cannabinoid feeding, the team writes.

The team does elaborate that substituting hemp silage for corn silage changed the nutritional composition of the cows’ diet, but the “major difference” was in cannabinoid concentrations.

For the sake of caution, the team stresses that industrial hemp’s effect on the cows cannot be traced to a specific cannabinoid. Duly noted. But feeding even small amounts of cannabis leaves, seeds and flowers to cows clearly has an effect, and this is why you shouldn’t feed your stash to your cow.

Are farmers at large actually feeding hemp to cows? We don’t know. But this bore urgent testing because industrial hemp is fashionable and because of the paucity of information on hemp consumption by farm animals and milk yields.

Its effect on goats and sheep hasn’t been tested. That day may come. All the study was designed to do was see whether the milk of cows fed on hemp may contain narcotics. Yes, it may. The rest is inference.

“From our study, we could possibly derive a THC content in the feed at which feeding can be classified as safe or unsafe with regard to delta-9 THC content in milk as relates to the acute reference dose in humans,” Schäche sums up. “It is more difficult to derive concentrations that would not lead to clinical signs in the cows.”

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