Opening the gates to hemp-grazed livestock in Australia: Phase 2

The primary aim of this research was to understand the suitability of whole-plant hemp as a forage for ruminants. In this report, results from Phase 2 of the larger project Opening the gates to hemp-grazed livestock in Australia are presented.
In Phase 2, the nutritional value, pharmacokinetics, deposition and excretion of cannabinoids in sheep was investigated. Results from Phase 1, a pilot study investigating nutritional value, animal performance and cannabinoid residues of hemp stubble in sheep, can be found in a separate report.
Why this work is important
In Australia, current regulation states a contaminant such as Δ9-tetrahydrocannabinol (Δ9-THC), the psychoactive compound in cannabis, cannot be present in supplied animal products unless Food Standards Australia and New Zealand (FSANZ) has set a safe allowed level (a ‘maximum level’) for the contaminant, and the contaminant does not exceed that level. At the time this report was written, FSANZ had not set a maximum level for THC in animal products due to a lack of data. Globally, very little data exists on whole-plant hemp as a forage for livestock. Work in this area was therefore critical to progressing regulation and optimising utilisation.
Who the report is targeted at
The aim of this project was to provide information that may benefit the emerging hemp industry as well as the livestock and wider grain industries in Australia by potentially adding a new option for summer grazing and rotational cropping. Therefore, this report includes a level of detail suitable only for a multi-disciplinary audience. Higher-level detail is available in the appendices and will be published in peer-reviewed, scientific journals.
Where the relevant industries are located
This work is relevant to livestock producers in hemp-growing regions of Australia. As a summer crop, hemp can be grown in most agricultural regions, provided adequate soil moisture is present. Hemp is currently grown in all Australian states and territories, predominantly along the east coast of the mainland and in Tasmania.
Background
To date, most global research on hemp as a feed for livestock has focused on hemp seed and hemp seed meal, a byproduct of oil extraction. Since 2020, more than 20 reviews have been written on the use of hemp seed and associated byproducts as potential ingredients for inclusion in livestock rations (e.g., Semwogerere et al. 2020; Bailoni et al. 2021; Xu et al. 2021; Burton et al. 2022; Ely and Fike 2022; Franek et al. 2022; Altman et al. 2023; Lanzoni et al. 2023; Muedi et al. 2024). In many countries, including Australia, consumption of animals fed hemp seed meal is generally considered to be safe because the meal contains little to no THC. Currently, in Australia, there is no routine monitoring of cannabinoid residues in foods of animal origin. This is also true in international markets; the lack of cannabinoid residues is not a typical routinely checked market entry requirement.
Very little data exists on hemp biomass (stalk, leaf, flower) as a forage for ruminant livestock, yet the high biomass yield from this crop is one of its assets. Hemp plants can grow to heights of 3-5 m with a high growth density. This can deliver an estimated 5-15 t biomass/ha of potential forage material during critical forage-deficit periods for grazing ruminants in Australia. However, regulating bodies
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are currently unable to draw conclusions on the use of hemp biomass-derived feed materials due to lack of occurrence data (EFSA 2015). Work in this area is therefore critical to progressing regulation nationally and internationally, and in adoption of industry best practice.
Aims/objectives
Based on the detection of cannabinoids in animal tissues in Phase 1, the aims of Phase 2 were to investigate nutritional value and cannabinoid pathways (in ruminants) of hemp at the flowering stage. The flowering stage was selected because, in terms of plant maturity, this is when cannabinoid concentrations are peaking (Burgel 2020). The aim was to represent the worst-case scenario for ruminants consuming hemp forage. Ensuring key cannabinoids could be detected in the measured parameters was important to understand how they are metabolised, stored and excreted by ruminants.
Five key experiments investigated the following:
● Experiment 1A: The pharmacokinetics and bioavailability of THC (intravenous [iv] and per os [oral dosing, PO] administration) and the pharmacokinetics of cannabidiol (CBD) (PO administration) in sheep.
● Experiment 1B: The in vitro microbial metabolism of cannabinoids in bovine ruminal fluid.
● Experiment 2: Nutrient digestibility and rumen parameters in sheep fed diets containing conserved hemp forage.
● Experiment 3: The effects of feeding a hemp-containing diet on the microbiome of sheep.
● Experiment 4: The effect of exposure time on cannabinoid deposition, remobilisation and excretion from various tissues in sheep.
The data generated provided valuable insight into both the feeding value of hemp biomass and the elimination half-life of Δ9-THC and CBD in sheep. The results will contribute towards drafting an industry code of practice for feeding hemp forage to ruminants and assisting the regulatory authority and legislative process.
Methods used
Experiments 1A and 1B investigated cannabinoid pharmacokinetics, bioavailability and microbial metabolism using cannabis extracts. Experiments 2 and 3 incorporated whole-plant hemp into full-ration pellets at 42% inclusion. Experiments 1A, 1B, 2 and 3 were conducted at Charles Sturt University in Wagga Wagga, New South Wales (NSW), while Experiment 4 was conducted at the Department of Primary Industries and Regional Development’s Katanning Research Facility in Western Australia (WA). All cannabinoid analyses were completed at ChemCentre in Bentley, WA.
Key findings
Key findings from the study are:
● Hemp hay (harvested at the flowering stage) was found to be a nutritionally suitable feed for ruminants, and when incorporated (at 42%) 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 Δ9-THC in subcutaneous fat, which was still detectable up to 140 days post-exposure in sheep, which did not lose weight.
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● High cannabinoid concentration (87.5 mg Δ9-THC/kg BW, representing ruminant daily intake of a 0.25% 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 0.05% 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 0.01% and 0.25% 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 42% 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.
Implications for relevant stakeholders
Industry
As expected, due to the presence of cannabinoids in edible tissue, hemp at the flowering stage is currently unsuitable as a forage grazing system for finishing ruminant livestock destined for human consumption until acceptable human food safety limits for meat are established by FSANZ.
Hemp forage, as based on experimental data to date, appears to be a suitable feed option for sheep if grazed at a younger maturity stage when cannabinoid concentrations are lower. Hemp biomass containing 0.25% THC or higher is not suitable as a feed for ruminant animals due to the potential adverse effects on sheep health.
Policy makers
Maximum tolerance levels of cannabinoids, in particular total THC and CBD, in animal products for human consumption are necessary. Additionally, there needs to be a standardised method to analyse cannabinoids in animal-derived biological samples.
Recommendations
In this study, hemp at the flowering stage, when cannabinoid content is peaking, was investigated to improve understanding of cannabinoid metabolism in ruminants. For use as a grazing crop, future research is recommended to focus on early-growth hemp, which has a much lower cannabinoid content and a higher nutritional value. While the use of hemp forage (containing less than 0.25% THC) in finishing diets is unlikely to be practical, there may be scope for its use in other animal groups, such as breeding ewes, growing animals or animals whose products are not destined for the food market, such as wool-producing sheep. This can change if national regulators set an acceptance limit for THC (and CBD) in animal products (milk and meat).