Feeding spent hemp biomass to lactating dairy cows: effects on performance, milk components and quality, blood parameters, and nitrogen metabolism.

The legalization of industrial hemp by the 2018 Farm Bill in the US has driven a sharp increase in its cultivation, including for cannabinoid extraction. Spent hemp biomass (SHB), produced from the extraction of cannabinoids, can potentially be used as feed for dairy cows; however, it is still illegal to do so in the US, according to FDA-CVM, due to the presence of cannabinoids and the lack of data on the effect on animals. To assess the safety of this by-product as feed for dairy cows, late-lactation Jersey cows (245 ± 37 DIM; 483 ± 38 kg BW; 10 multiparous and 8 primiparous) received a basal TMR diet plus 13% alfalfa pellet (CON) or 13% pelleted SHB (SHB) for 4 wk (intervention period or IP) followed by 4 wk of withdrawal period (WP) where all cows received the basal TMR only during WP. The DMI, BW, BCS, milk yield, milk components and fatty acid profile, blood parameters, N metabolism, methane emission, and activity were measured. Results indicated that feeding SHB decreased DMI mainly due to the low palatability of the SHB pellet, as the cows only consumed 7.4% out of 13.0% of the SHB pellet offered in the ration. However, milk yield was not affected during the IP and was higher than CON during the WP, leading to higher milk yield/DMI. Milk components were not affected, except for a tendency in decreased fat %. Milk fat produced by cows fed SHB had a higher proportion of oleate and bacteria-derived FA than CON. The activity of the cows was not affected, except for a shorter overall lying time in SHB vs. CON cows during the IP. Blood parameters related to immune function were not affected. Compared with CON, SHB cows had a lower cholesterol concentration during the whole experiment and higher BHBA during the WP, while a likely low-grade inflammation during the IP was indicated by higher ceruloplasmin and reactive oxidative metabolites. Other parameters related to liver health and inflammatory response were unaffected, except for a tendency for higher activity of ALP during IP and a lower activity of gamma-glutamyl transferase during WP in SHB vs. CON. The bilirubin concentration was increased in cows fed SHB, suggesting a possible decrease in the clearance ability of the liver. Digestibility of the dry matter and protein and methane emission were not affected by feeding SHB. The urea, purine derivatives, and creatinine concentration in urine was unaffected, but cows fed SHB had higher N use efficiency and lower urine volume. Altogether, our data revealed a relatively low palatability of SHB affecting DMI with minimal biological effects, except for a likely low-grade inflammation, a higher N use efficiency, and a possible decrease in liver clearance. Overall, the data support the use of SHB as a safe feed ingredient for lactating dairy cows.