INDUSTRIAL hemp forage containing very low levels of the psychoactive cannabinoid THC has scope for use in some types of sheep, an AgriFutures Australia project has found.

AgriFutures Australia emerging industries senior manager Dr Olivia Reynolds said Phase 2 of the ‘Opening the gates to hemp-grazed livestock in Australia Project investigated the nutritional value and cannabinoid pathways in sheep fed hemp at its flowering stage.

“The project was designed to evaluate the nutritional benefits of hemp foliage as a green feed for ruminants during summer and to study the metabolism, storage, excretion and remobilisation of cannabinoids (THC and cannabidiol) in sheep.

“While this study suggests that hemp forage as a finishing diet is unlikely to be practical for sheep destined for the meat market, there is scope for its use in other animal groups, such as breeding ewes, growing animals or animals that are not, or do not produce, food products, such as sheep grown for wool production,” she said.

“The findings from the project will pointedly contribute to the development of an industry code of practice for feeding industrial hemp forage to ruminants, and will inform a future FSANZ application for setting a maximum THC level in meat.”

Dr Reynolds said the considerable biomass output of industrial hemp is a noteworthy asset.

“A promising development within this sector is the potential use of hemp as a summer crop, presenting a new option for summer grazing and rotational cropping for livestock producers in hemp-growing regions of Australia.

“However, to fully realise this potential, comprehensive data is needed to inform national regulators in establishing maximum residue limits for cannabinoids in meat products,” she said.

Under Australian regulations, THC cannot be present in animal products unless Food Standards Australia and New Zealand (FSANZ) has established a safe allowable level (a ‘maximum level’), and the residue does not exceed this threshold. To date, FSANZ has not set a maximum level for THC in animal products, largely due to a paucity of relevant data.

The project concluded that sheep consuming hemp in the form and at the level described in this study (0.01% and 0.25% THC in forage hemp) were safe for the human food market within a two-month withholding period; however, their consumption remains constrained by a lack of an acceptable residue limit.

It is unclear how long an adequate withholding period should be if tolerance levels remain at zero detection, suggesting longer term clearance studies will be needed if meat safety regulations are not updated, the project report said.

Key findings from the study were:

• Hemp hay (harvested at the flowering stage) was found to be a nutritionally suitable feed for ruminants, and when incorporated (at 42pc) into a pelleted diet, had no adverse effects on feed intake, apparent nutrient digestibility, rumen function or the gastrointestinal microbiome.
• Feeding hemp hay for less than one month resulted in deposition of ∆9 -THC in subcutaneous fat, which was still detectable up to 140 days post-exposure in sheep, which did not lose weight. High cannabinoid concentration (87.5 mg Δ9 -THC/kg BW, representing ruminant daily intake of a 0.25pc hemp crop) was detrimental to animal production as a consequence of reduced feed intake. Even a relatively low concentration (18 mg Δ9 -THC/kg BW, representing ruminant daily intake of a 0.05pc hemp crop) could be detrimental to animal production due to the potential adverse effects on rumen microbial activity.
• Oral administration of CBD had no apparent effect on either feed intake or animal health.
• The (plasma) elimination half-life of Δ9 -THC in the sheep was 31.4 hours (± 23.9), while that of CBD was 13.3 hours (± 4.4). The elimination half-lives of the CBD metabolites 7 hydroxy CBD and 7 carboxy CBD were 21 hours (± 6.04) and 34.8 hours, respectively. The long elimination half-lives of Δ9 -THC and the CBD metabolites 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.
• Somewhere between 0.01pc and 0.25pc THC in a forage hemp crop is the upper safe limit for sheep to graze without compromising productivity or welfare.
• Two months of sheep consuming clean (hemp-free) feed will not guarantee their tissues are clear of cannabinoids after consuming a pelleted 42pc hemp diet for up to 21 days.
• Hemp provides an off-season green forage option for livestock but only if careful management strategies are implemented and maximum residue limits for cannabinoids in edible tissues are set. Source – AgriFutures Australia.