Phase 1
As a pilot study, the aim of this experiment was to obtain data on a wide range of parameters to guide future research. Hemp stubbles, which is the remaining biomass after seed harvest, was selected for the investigation as it is currently an unutilised byproduct in hemp production systems.
Phase 1 objectives:
- Analyse and understand nutritional value of post-seed harvest hemp biomass (stubbles) as a potential feed for ruminants.
- Measure cannabinoid excretion from sheep and accumulation in animal tissues.
- Measure animal performance and carcase traits of sheep fed diets containing hemp at varying inclusion levels.
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.
| Experimental Phase | Days | Measurements |
|---|---|---|
| Adaptation to diets | 0-14 | Liveweight (LW), dry matter intake (DMI), 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
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 i.e. they grew fat and were exposed to hemp for a long time (56 d). 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 FSANZ to set a maximum allowable limit for THC in animal products in the future as more data becomes available.
Recommendations
As THC residues were detected, research should now focus on advancing understanding of cannabinoid digestion and metabolism in ruminants; including half-life, excretion pathways, and clearance from subcutaneous fat, muscle, liver and kidneys. This should be investigated in both sheep and cattle, as there is no evidence to suggest cannabinoid metabolism is the same across both species. Literature and our results suggest cannabinoids are endemically accumulated in fatty tissue and deposits. These tissues tend to have a slow turnover rate, indicating a clearance period will likely be a necessary management tool for livestock receiving hemp fodder.
A copy of the full report can be found on the AgriFutures website.