Dairy cows fed a diet containing industrial hemp experienced several physical and behavioral changes, including increased yawning, salivation and unsteady movements, according to a study.
The authors of the study, which was published in the journal Nature Food, said the findings could have implications for human health as the popularity of industrial hemp products grows, although more research is needed to assess the risks.
Industrial hemp is a type of cannabis plant that is cultivated for a wide variety of uses, including textiles, paper, cosmetics, food, biofuel, biodegradable plastics, construction materials, food and animal feed.
One of the fastest-growing plants on Earth, hemp, which originated in Central Asia before spreading to the Mediterranean and other parts of the world, has been cultivated by humans for thousands of years.
Hemp is the same species of plant as Cannabis sativa, which is used to produce the drugs marijuana and hashish. But hemp has much lower levels of the cannabinoid delta-9-tetrahydrocannabinol (THC), the psychoactive substance responsible for the “high” effect of weed.
Hemp also contains other cannabinoids—a class of substances found in the cannabis plant—such as cannabidiol (CBD), which is not psychoactive like THC but can produce some pharmacological effects.
In the United States, hemp is legally defined as Cannabis sativa containing 0.3 percent or less of THC. Usually, hemp-derived products intended for consumption do not contain enough THC to create the “high” traditionally associated with marijuana.
The industrial hemp sector is growing rapidly, and several hemp-derived products have been launched in recent years, including animal feed. In 2018, the U.S. legalized the production of hemp as an agricultural commodity at the federal level, while removing it from the list of controlled substances, as part of the 2018 Farm Bill.
While hemp production was legalized with the passage of the bill, no hemp ingredients have yet been approved for use in pet or livestock animal feed in the United States by the Food and Drug Administration. But a handful of states allow the feeding of hemp to animals, and there is interest in developing these kinds of products.
Not all cannabinoids are psychoactive, but the proliferation of hemp products raises consumer safety issues because this class of substances interacts with the animal and human endocannabinoid system.
Some veterinary, feed industry and animal safety groups—such as the Association of American Feed Control Officials (AAFCO) and the American Veterinary Medical Association (AVMA)—have warned against feeding animals hemp products until research has demonstrated safety.
“It is our position that sufficient scientific research to support the safety and utility of hemp in animal feed must be completed prior to any federal or state approval,” the AAFCO, AVMA and several other co-signed organizations wrote in a letter to agriculture leaders and state policymakers this past February.
According to these groups, more research is needed to understand whether hemp ingredients are safe for animals when consumed frequently for extended periods of time. It is unclear if cannabinoids in industrial hemp can be transferred from animal feed into the resulting products—such as meat, milk or eggs—and whether this could pose any health risks for humans.
Amid the current interest in developing industrial hemp animal feed products, a team of German researchers decided to explore the issue by conducting a study on dairy cows.
The researchers analyzed the effects of giving feed containing industrial hemp to 10 milk-producing dairy cows. They used two different varieties of hemp in the experiment, both of which contained less than 0.2 percent THC—below the maximum legal level in the European Union—although one had a much higher concentration of cannabinoids overall.
The scientists then analyzed the milk, blood and feces of the cows while assessing other physiological factors and observing their behavior.
The team found that feeding the cows a diet containing up to 0.92 kilograms of industrial hemp with a very low cannabinoid concentration per animal per day had no noticeable effect on the livestock’s health.
But the results showed that cows fed a diet with 0.84 or 1.68 kilograms of a cannabinoid-rich variety of industrial hemp displayed behavioral and physical changes. These included increased yawning, salivation, unsteady movements, nasal secretions, pronounced tongue play and a reddening of the nictitating membrane—a transparent third eyelid present in some animals—as well as other effects.
“We observed significant changes in respiratory and heart rate as well as a reduction of feed intake and milk yield,” Robert Pieper, an author of the study who is with Berlin’s German Federal Institute for Risk Assessment, told Newsweek.
The researchers observed changes to feed intake and milk yield from the second day of exposure to the cannabinoid-rich industrial hemp. All changes observed disappeared within two days of discontinuing feeding with the hemp.
Analysis of the milk that the cows produced showed that a transfer of cannabinoids, including THC, from the hemp to the dairy product had occurred.
The researchers also found that this transfer had taken place to such an extent that the quantity of THC in the milk reached levels that could exceed the acute reference dose in some consumer groups if it was consumed by humans. The acute reference dose is the estimated amount of a substance that can be ingested in a 24-hour period without any identifiable health risks.
“Higher intake levels are undesired, since adverse effects may occur,” Pieper said. “These exposure levels may especially affect the central nervous system—for example, increased sedation, impaired working memory performance and mood alterations.”
Pieper said the effects experienced by the cows “were mostly likely attributable to the intake of high amounts of cannabinoids from industrial hemp in the ration.” However, the authors note that the effects cannot be traced to a specific cannabinoid or particular combinations of substances in the hemp.
According to the authors, the results of the study indicate that feeding industrial hemp—even with levels of less than 0.2 percent THC—in realistic rations to dairy cows has an influence on the physiology and behavior of these animals and could lead to THC concentrations in the milk that may pose a health risk for certain consumer groups. But the scientists said more research is needed to assess the impacts of these cannabinoids.
“The scientific study was designed to investigate the question of the extent to which a transition into cow’s milk can basically occur when industrial hemp is fed,” Pieper said. “The study does not allow any conclusions to be drawn as to whether there is a health risk from the consumption of milk on the market.”
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