Why a Sheep THC Half-Life Cannot Set a Human Cannabis Detection Window
THC persisted in sheep plasma long after a high oral dose, but the resulting half-life cannot be used as a human cannabis clock. Ruminant physiology, dose, and study design all define the meaning of the measurement.
The plasma experiment
Stevens and colleagues characterized THC pharmacokinetics in eight Merino ewes after a high oral exposure. Plasma THC remained detectable in all eight at 216 hours and in three at 264 hours. The mean terminal half-life was approximately 31 hours, with substantial variation.
No tested THC metabolites were detected in plasma. This nondetection is bounded by the assay and experimental conditions; it does not prove that sheep produce no metabolites whatsoever.
Detection, absorption, and elimination differ
Observed peak times were delayed and variable. A terminal half-life describes the fitted late decline, rather than the time when exposure began, effects ended, or every molecule disappeared.
A separate two-animal pilot provided only an approximate oral-bioavailability estimate. The paper expressly notes that incomplete sampling limited that calculation. It should not be presented as a definitive species-wide absorption fraction.
Where the findings are useful
The work addresses ruminant handling of THC and questions relevant to hemp feed and residues. It differs from simply documenting signs of animal toxicity. Plasma persistence also is not interchangeable with a measured concentration in meat or another tissue.
Human interpretation requires human data matched to route, formulation, specimen, and use history. Neither the sheep’s delayed peak nor its fitted half-life validates a last-use estimate for a driver, a human impairment threshold, or a universal clearance interval.
Related reading: how route and timing affect cannabis evidence.
Primary research
Sarah A. Stevens; Scott H. Edwards; Glenys K. Noble; Colin J. Scrivener; Gaye L. Krebs; Christopher E. Petzel; Christopher D. May; Zi Xuan Tai; Bronwyn L. Blake; Kenneth C. Dods; Leon N. Warne. The Pharmacokinetics of Δ9-Tetrahydrocannabinol in Sheep. Animals : an Open Access Journal from MDPI (2024). DOI: 10.3390/ani14223328.
