Effects of feeding sheep rations containing hemp stubble on nutrient digestibility, rumen parameters and animal performance

The residue (stubble) following the harvest of a hemp crop for seed could be a useful feed for sheep (and cattle). However, the feeding value of this residue is unknown. Fifteen Merino wethers were maintained in individual pens and fed one of three pelletised experimental inclusion diets, as a 0% (Control), 28% (Hemp 1), and 56% (Hemp 2) pellet, which delivered a diet meeting the nutrient requirements of the animals.

Over the 42-day feeding period (following a 14-day adaptation period), inclusion of hemp stubble had no adverse effects on either intake or live weight gain of the sheep. Including the hemp stubble in the diets resulted in improved nutrient digestibility and it changed the profile of volatile fatty acids in the rumen, increasing the molar proportions of iso-butyric, iso-valeric, hexanoic and heptanoic acids. Volatile fatty acids are the key source of energy for sheep and cattle. Tetrahydrocannabinolic acid (THCA) was the only cannabinoid found in the plasma of the sheep fed the hemp-containing diets, and it was found at low concentrations (<16 µg/L). Tetrahydrocannabinolic acid was also detected in the liver of two sheep fed the Hemp 1 pellets (208 and 381 µg/kg DM) and two sheep fed the Hemp 2 pellets (163 and 201 µg/kg DM). Cannabidiol (CBD) was detected in the liver of one sheep fed the Hemp 2 pellets (188 µg/kg DM), but no liver THCA was detected in this sheep. Delta-9-tetrahydrocannabinol (Δ⁹-THC) was detected in the kidney fat and subcutaneous fat of all sheep fed hemp stubble while THCA was also detected in the subcutaneous fat of one of the sheep fed the Hemp 1 pellets. Four of the five sheep fed the Hemp 1 pellet and one of the five sheep fed Hemp 2 pellet had low levels (52-72 µg/kg DM) of Δ⁹-THC in their meat (loin). No other cannabinoids were detected in the meat.

Current food standards regulations in Australia prohibit presence of any cannabinoid residues in commercial meat products; thus, either review of these food standards or determination of a withholding period (WHP) is required to enable the safe feeding of hemp-stubble to sheep.