Nutrient digestibility, rumen parameters, and (cannabinoid) residues in sheep fed a pelleted diet containing green hemp (Cannabis sativa L.) biomass

The feeding value for ruminants of green hemp biomass, from the low Δ⁹-tetrahydrocannabinol (Δ⁹-THC) variety of Cannabis sativa L. is unknown. Twelve Merino ewes were randomly allocated on a stratified liveweight basis to one of two pelleted dietary treatments, Control (0% hemp, n=6) or Hemp (42% green hemp biomass, n=6) that delivered a diet meeting the nutrient requirements of the animals. n=The experimental period consisted of a 17 d dietary and housing adaptation, followed by 7 d total urine and faeces collection for determination of apparent nutrient digestibility. A ruminal fluid sample was collected on day 27 and assessed for pH, and ammonia, volatile fatty acid (VFA) and cannabinoid concentrations. A blood sample and incisional subcutaneous fat biopsy were collected on day 28 with an additional incisional subcutaneous fat biopsy taken 35 d post feeding to measure cannabinoids. The dry matter (DM), organic matter (OM) and crude protein (CP) digestibility, along with total VFA concentration did not differ (p > 0.05) between the two diets; however, acid detergent fibre (ADF) and neutral detergent fibre (NDF) digestibility, water intake and faecal water output were significantly lower (P< 0.05) for the sheep fed Hemp. Rumen pH did not vary (P > 0.05) between diets, but ruminal ammonia concentration was significantly lower (P < 0.05) for sheep consuming Hemp, likely due to the high polyphenolics content creating rumen undegradable protein (RUP). Sheep fed Hemp had significantly higher (P< 0.05) molar proportions of butyric and hexanoic acids and lower molar proportions of propionic acid, potentially due to changes in the composition of the rumen microbiome. There were no differences (P > 0.05) between diets for N intake, faecal N output or N balance, with all sheep in positive N balance; however, there were significantly lower (P < 0.05) urinary N outputs for sheep fed Hemp, indicating a potentially higher efficiency of N utilisation. Cannabidiolic acid (CBDA) and tetrahydrocannabinolic acid (THCA) were detected in plasma of all sheep fed Hemp. ∆⁹-tetrahydrocannabinol was present in the subcutaneous fat of four of the six sheep on the final day of being fed Hemp, and in all (six) sheep 35 d post feeding Hemp. Thus, despite green hemp biomass being nutritionally a suitable feed for ruminants, under current Food Standards in Australia, the presence of these cannabinoid residues restricts its use in ruminant diets.