Ovine Observer

Introduction

Industrial hemp is the low tetrahydrocannabinol (THC) variety of Cannabis sativa L. As a fast-growing summer annual, it presents opportunities to the livestock industry during times when green feed may be scarce, or as a by-product from the hemp industry.

Very little data exists on hemp biomass as a forage for ruminants (EFSA, 2015). The DPIRD-led project Opening the gates to hemp fed livestock in Australia is providing world-first data on nutritional value and animal performance of sheep on hemp forage, and the safety of their meat for human consumption in terms of THC residues.

The project has been divided into two phases. Phase 1, a pilot study (2020 – 2021), tested a wide range of parameters including nutrient digestibility, THC residues, animal performance and carcase traits in sheep, with the aim to guide research for the more intensive Phase 2. Phase 2 of the project is currently underway, with results expected early 2023. This article summarises results from Phase 1.

Led by DPIRD, this project is operating in partnership with ChemCentre and Charles Sturt University. AgriFutures Australia is the major project sponsor, delivered through their Emerging Industries program.

Aims

The high level aims of this research are to:

1. Provide initial data required for development of government regulation and recommendations for feeding hemp foliage to livestock.
2. Increased adoption of industrial hemp as a new forage option for irrigated and dryland farming regions (annual rainfall above 600mm) due to stronger understanding of grazing application and effect of feeding hemp on sheep productivity, nutritional value, meat quality and food safety.

The primary aims of Phase 1 were to:

1. Analyse nutritional value of post-seed harvest hemp biomass (stubbles) as a potential feed for ruminants.
2. Understand the effects of consuming hemp biomass on growth performance and carcase traits of sheep.
3. Measure cannabinoid excretion from sheep and accumulation in tissues.

Methods

The project objectives were met through a single experiment (Table 1) conducted at Charles Sturt University using 15 Merino wether sheep aged 12 months. The use and care of animals was approved by CSU Animal Care and Ethics Committee (Protocol number: A20016) and was compliant with the Animal Research Act 1985 (as amended) in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes.

Industrial hemp biomass (variety Morpeth Late) was grown and collected by a licensed, commercial grower in the Manjimup region of South West Western Australia. Three diets were used in this trial and included industrial hemp biomass (leaf, flowering heads, stem) at 0, 28 and 56% with oaten chaff as the substitute forage. They were formulated to be a complete ration for weaners and to be balanced in energy and protein, with the only major difference between the diets being the proportion of hemp to oaten chaff.

Table 1 Experimental phases and their respective measurements

Experimental Phase	Days	Measurements
Adaptation to diets	0-14	Liveweight (LW), dry matter intake (DMI), leftover feed (orts)
Digestibility study	15-21	LW, DMI, orts, faecal & urinary output, 1 x rumen fluid sample on day 21
Animal performance	22-56	LW, DMI, orts, 1 x blood sample on day 56
Carcase traits	56	Hot carcase weight, cannabinoid analysis of subcutaneous fat, striploin, liver & kidney fat

Results and discussion

Animal performance

Substitution of oaten straw with hemp stubble at two levels was not detrimental to feed intake, liveweight gain or carcase traits. In fact, there was a tendency for improved liveweight gain and further investigation is warranted. Overall, the results indicate hemp stubble to be a suitable replacement for cereal straw in pelleted rations.

Cannabinoid residues

Cannabinoids in the form of Δ9-THC and THCA were detected in all measured tissues but at extremely low levels (<300 μg/kg DM). Currently, regulations state zero tolerance for THC in animal tissues and this is what researchers and producers should work towards. The sheep in the current trial were given every opportunity to express cannabinoid residues via fat growth, and they were exposed to hemp for a long time (56 days). Whilst there indeed were residues, they were extremely low. This suggests there is plenty of scope to develop management practices for feeding hemp biomass to ruminants allowing their products to enter the market with zero THC. There may also be scope for Food Standards Australia New Zealand (FSANZ) to set a maximum allowable limit for THC in animal products in the future as more data becomes available.

A copy of the full report (Blake, 2021) can be found on the AgriFutures website, and more detailed results in Krebs et al (2021).

Key messages

• Hemp stubbles appear to be a suitable roughage for sheep.
• THC residues were detected, and Phase 2 is focusing on advancing understanding of cannabinoid metabolism and clearance from tissues.

References

Blake, B (2021). Opening the gates to hemp-grazed livestock in Australia; Phase 1 Final Report. AgriFutures Australia.

EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain), (2015). Scientific Opinion on the risks for human health related to the presence of tetrahydrocannabinol (THC) in milk and other food of animal origin. EFSA Journal ,13(6):4141, 125 pp. publication no. 21-152. https://doi.org/10.2903/j.efsa.2015.4141

Krebs G, De Rosa D, White, D, Blake B, Dods K, May C, Tai Z, Clayton E, Lynch E (2021). Intake, nutrient digestibility, rumen parameters, growth rate, carcase characteristics and cannabinoid residues of sheep fed pelleted rations containing hemp (Cannabis sativa L.) stubble. Translational Animal Science.,5,1-13. https://doi.org/10.1093/tas/txab213