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Hemp-Fed Cows Get ‘High’, Study Finds

By Alexander Beadle

Published: Dec 05, 2022   
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Dairy cows that eat a cannabinoid-rich form of silage made from industrial hemp seem to feel the high, a new study from the German Federal Institute for Risk Assessment (BfR) suggests.

The study, published recently in Nature Food, examined cows given animal feed supplemented with either a low or high dose of cannabinoid-rich hemp silage. The researchers found that animals given the higher dosage became visibly more tired and had lower heart rates and respiratory rates compared to measurements taken at the start of the experiment.

The researchers also detected a significant amount of cannabinoids in the milk the cows produced. Concerningly, the THC levels detected were high enough that a person consuming an average amount of milk and dairy products may, in some scenarios, exceed the dose recommended by the European Food Safety Authority (EFSA) as the limit for safe consumption.

However, current data are insufficient to make any conclusive statements about whether cannabinoid-rich animal feed may pose a significant risk to consumers, the researchers say.

Cow health declines after switch to high-cannabinoid hemp feed

For a six-day adaptation period at the beginning of the study, ten dairy cows had their usual corn silage partially altered to contain amounts of silage made from hemp. This hemp silage was made from whole-plant hemp, and so contained very low levels of cannabinoids overall.

The researchers then began to feed the cows a diet of corn silage mixed with a more potent hemp silage made only from hemp leaves, flowers, and seeds. One group of five cows was given around 840 grams of this cannabinoid-rich hemp silage per day in their feed, while the other five cows received a higher dose of around 1,680 grams.

The researchers observed no changes in the cows during the adjustment period. However, both groups of cows began to exhibit unusual behavior after consuming the cannabinoid-rich silage mix. For example, the cows tended to eat less feed overall, and as a result produced less milk. The respiratory rates and heart rates of the animals also fell significantly within hours of consuming the more potent feed mix, to the point where some animals would have met the classifications for developing bradypnea or bradycardia.

Both groups began to visibly yawn more often, exhibited other signs of sleepiness, and some animals’ eyes became redder. Cows from the higher dosage group were also occasionally seen walking in unsteady gates or standing for too long in unusual postures.

All these changes disappeared within two days of the feeding experiment ending, which would appear to confirm that the effects were due to the cannabinoid-rich hemp silage. However, which cannabinoids are responsible for these effects is less certain. THC is the most likely culprit. However, the researchers also note that cannabinoids such as CBD are also sometimes associated with somnolence.

Cannabinoids ingested from hemp can make it into cows’ milk

By the end of the adaptation period and throughout the exposure period, the researchers reported finding measurable levels of the cannabinoids THC, tetrahydrocannabinolic acid (THCA), tetrahydrocannabivarin (THCV), CBD, cannabinol (CBN), and cannabidivarin (CBDV) in the cows’ milk. Concentrations of up to 316 micrograms of THC and 1,174 micrograms of CBD per kilogram of milk were detected.

“Our study also shows that even a small addition of hemp silage to the daily ration of dairy cows leads to the detection of cannabinoids in the milk, including Δ9-THC,” study author and BfR feed expert Dr. Robert Pieper, said in a statement. “The impairments in animal health are apparently due to the cannabinoid concentration in the silage, which in turn depends on many factors.”

However, only a small fraction of the cannabinoids present in the animals’ feed actually ended up in the milk. Using toxicokinetic modeling, the researchers determined that most cannabinoids were actually eliminated in the animals’ urine or through other transformations in the gastrointestinal tract. Another 20-35% of the total cannabinoid concentrations ingested were excreted in feces, which the researchers say demonstrates a high bioavailability of the compounds in cows.

From their toxicokinetic models, the researchers estimate that the transfer rate of cannabinoids from silage to milk is around 0.2% for THC and 0.11% for CBD. The cannabinoid with the highest transfer rate was THCV at 0.56%, but given the low prevalence of THCV in hemp the researchers say that this is unlikely to result in high levels of THCV in milk. Similarly, while the transfer rates of CBD and THC are roughly equivalent in magnitude, CBD is actually found in higher amounts in hemp and so more CBD is likely to be found in milk samples.

Are consumers at risk?

After assessing the levels of cannabinoids present in the cows’ milk, the researchers were interested in comparing these to relevant consumer safety standards. The acute reference dose (ARfD) is a concept in toxicology used to define the dose of a chemical that can be ingested over a short period of time without appreciable health risks to the consumer. For THC in milk, the ARfD set by the European Food Safety Authority (EFSA) is one microgram per kilo of body weight.

Using this standard, plus an estimate of average consumption for milk and dairy products, the researchers estimated that the mean and maximum THC concentration found in milk from the cows in the low dosage group would still lead to the ARfD being exceeded by up to 14-fold for young consumers aged under 18. Based on the THC concentrations found in the high dosage group, this limit could be exceeded up to 120-fold across all population groups.

What this means in terms of risk is still unclear, the researchers say. Processing could have additional effects on the cannabinoid content of milk products, for example. Similar ARfD values for other cannabinoids in milk have also not yet been determined, likely due to a lack of relevant health and safety data. Further research is still needed before the size and scale of any consumer risks can be concretely established.


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