Hemp (Cannabis sativa L.) Seed and Co-Products Inclusion in Diets for Dairy Ruminants: A Review

Simple Summary Hemp (Cannabis sativa L.) is an annual herbaceous plant, globally distributed and cultivated in the past as an important source of fiber. Recently, the interest in hemp cultivation has significantly increased, considering its positive impact on the environment and the production of feed and food of high nutritional value. The authorized hemp varieties are registered in the EU's Common Catalogue of Agricultural Plant Species and have content in psychotropic 9-tetrahydrocannabinol (THC) less than 0.2-0.3%. In this review, the chemical and nutritional values of hemp are presented and the effects of inclusion of the hempseed, and products obtained by the processing of seed (co-products), in diets for dairy ruminants (i.e., cows, ewes, goats, and buffaloes) are discussed. Hemp supplementation could be a good feeding strategy to improve the bioactive compounds in milk and derivatives: the content of n-3 fatty acids and isomers of conjugated linoleic acid, substances beneficial to human health, increased in milk and cheese obtained with hemp addition. However, up to now, few publications do not allow to suggest the optimal dosage of the co-products for the different species. In addition, no experiments are published on the use of whole plants as forage for dairy ruminants. Recently, hemp (Cannabis Sativa L.) was rediscovery as a plant that offers a wide variety of applications (textile, pharmaceuticals, construction, etc.), including also the use in animal and human nutrition. The inclusion of whole seeds and co-products obtained by processing of seeds (cake, meal, and oil) in the diets of farm animals can allow the transfer of bioactive substances to human food. Few publications are available on the use of hemp in dairy ruminants but some authors reported a positive effect on the fatty acids profile of milk and cheese with an increase of n-3 fatty acids and c9,t11 conjugated linoleic acid. The protein content, amino acids profile, and rumen undegradable protein (RUP) of hempseed and co-products of hemp appear interesting and suitable for ruminant nutrition. Negative effects of anti-nutritional factors (i.e., phytate) are not observed. However, the researches on the effects of the use of hempseed and co-products in diets for dairy ruminants do not allow to suggest optimal levels of inclusion. In addition, no data are published on the use of whole or part of the hemp plant as forage, as another possibility to use the hemp in the perspective of the circular economy.