When dairy cows ate spent hemp biomass, THC transferred to milk at levels exceeding safe human intake thresholds, but became undetectable after 12 days of hemp withdrawal.
Agricultural regulators, dairy farmers, and food safety researchers.
THC became undetectable in milk after 12 days of hemp withdrawal from cow diets
What the researchers found
Less than 1% of cannabinoids from spent hemp biomass transferred to cow milk, but THC levels in milk still exceeded the acute reference dose of 1 ug/kg body weight for human consumers. THC accumulated heavily in adipose tissue and remained detectable there 30 days after withdrawal. CBD and CBDA were detectable in plasma 90 days after hemp withdrawal (post-calving). Milk THC became undetectable after 12 days of hemp withdrawal.
Why it matters
Spent hemp biomass has excellent nutritional value as livestock feed but is banned in most countries due to THC concerns. This study quantifies the actual risk and identifies a practical withdrawal period that eliminates consumer exposure.
The numbers in context
Less than 1% cannabinoid transfer to milk. THC in milk exceeded acute reference dose of 1 ug/kg BW during feeding. THC undetectable in milk after 12 days withdrawal. THC detectable in adipose tissue 30 days after withdrawal. CBD/CBDA detectable in plasma 90 days after withdrawal.
How the study worked
Dairy cows fed spent hemp biomass (cannabinoid extraction byproduct). Cannabinoids measured in milk, blood, and tissues using UHPLC-MS/MS at multiple timepoints during feeding and after withdrawal.
What this study cannot tell us
Small number of animals typical for dairy feeding studies. THC accumulation in adipose tissue raises questions about meat safety. 90-day CBD persistence in plasma is unexplained. Specific SHB composition may vary between sources.
How to read the evidence
Well-designed feeding study with precise analytical methods, but small sample size typical of dairy research.
When this study was published
2025 publication.
The bigger picture
The data suggests a path to safe use of hemp byproducts in dairy farming: a two-week withdrawal period before milking eliminates THC risk to consumers. This could unlock a significant feed resource currently going to waste.
Questions still open
- Is a 30-day withdrawal sufficient for meat safety given adipose THC accumulation?
- Why do CBD and CBDA persist in plasma for 90 days after hemp withdrawal?
Read the original research
Cannabinoid Distribution and Clearance in Feeding Spent Hemp Biomass to Dairy Cows and the Potential Exposure to Δ9-THC by Consuming Milk.
Journal of agricultural and food chemistry, 73(22), 13934-13948
Citation
Irawan, Agung; Nosal, Daniel G; Muchiri, Ruth N; van Breemen, Richard B; Ates, Serkan; Cruickshank, Jenifer; Ranches, Juliana; Estill, Charles T; Thibodeau, Alyssa; Bionaz, Massimo. (2025). Cannabinoid Distribution and Clearance in Feeding Spent Hemp Biomass to Dairy Cows and the Potential Exposure to Δ9-THC by Consuming Milk.. Journal of agricultural and food chemistry, 73(22), 13934-13948. https://doi.org/10.1021/acs.jafc.5c02827
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