Steps in the evaluation of industrial hemp biomass as a feed for livestock.

The suitability of industrial hemp biomass as a feed for ruminant animals destined for the food chain is largely unknown. A ‘maximum’ level for the cannabinoids contained in industrial hemp is yet to be set for foods of animal origin (meat, milk, eggs) by Food Standards Australia and New Zealand due to a lack of data. To be a viable option for ruminants, the feed needs to be palatable, not adversely affect the animal or their microbiome, and cannot result in detectable residues in body tissues and organs at the time of slaughter.
When either industrial hemp stubble or hay (cut near flowering) was incorporated (at 56% and 42%, respectively) in pelleted diets and fed to sheep, there were no adverse effects on nutrient digestibility or animal production. However, Δ9-THC residues remained in the subcutaneous fat of some sheep for more than four months. The cannabinoid concentrations in their diets were very low – but would the results be the same if the cannabinoid concentrations were higher (considering the industrial hemp crops can ‘legally’ contain up to 1% THC)? Further, were the positive effects (or alternatively the lack of adverse effects) due to the cannabinoids or other plant secondary metabolites in industrial hemp?
Using both in vitro and in vivo methodologies, we now know there are not only changes in the composition of the microbial population, but that the cannabinoids can adversely affect microbial activity, suggesting other plant secondary metabolites – and not the cannabinoids – accounted for the lack of adverse effects in the earlier studies when industrial hemp pelleted diets were fed to sheep
It is important to understand the pharmacokinetics of Δ9-THC and cannabidiol (CBD), the two main cannabinoids in industrial hemp, in ruminants. We now know that the elimination half-life (in plasma) of Δ9-THC (39.5 hours) is significantly longer than that of CBD (14.3 hours). The long elimination half-life of Δ9-THC further supports that residues will be present for an extended period post-feeding, reducing the likelihood of imposing a practical withholding period for animals involved in the human food chain.
Importantly, we found that an oral dose of 87.5 mg Δ9-THC/kg bodyweight (representing intake of a 0.25% industrial hemp crop) caused intoxication in sheep. We believe that somewhere between 0.01% and 0.25% total THC in a forage industrial hemp crop is the upper safe limit for sheep to graze without compromising productivity or welfare.