Review: Utilizing industrial hemp (Cannabis sativa L.) by-products in livestock rations

Since its reintroduction as a legal crop in the United States in 2018, industrial hemp (Cannabis sativa L.) production for cannabidiol (harvested from inflorescence), seed, and fiber has steadily increased. This has led to an increase in the number of hemp-related products, many of which have retail value. However, many of the by-products resulting from further processing of hemp are discarded as waste. A potential use for these hemp by-products may be as a feedstuff for inclusion in livestock diets, thereby providing an additional source of feed in a world demanding increased sustainability. Of the three main components of the hemp plant (e.g., fiber, inflorescence, and seed), hemp seed and inflorescence are the most promising as feeds. Hemp inflorescence in livestock rations is the latest of the three hemp product categories to be investigated, with most published studies relying on in vitro methods. Due to inflorescence being the source of cannabinoids, potential contamination of foods entering the human supply chain represents a significant concern for the use of industrial hemp. Future research needs to demonstrate that feeding low levels of cannabinoids over prolonged periods does not result in appreciable amounts deposited in animal milk and tissues. Comparatively speaking, hemp seed research has received greater interest than inflorescence or fiber. Hemp seed and its associated by-products have been examined in diets for poultry, sheep, cattle, and swine. Hemp seed cannot produce cannabinoids, which mainly originate from cannabinoid-producing trichomes in the inflorescence. Due to its high protein and fat contents, particularly ruminal undegraded protein and unsaturated fatty acid composition, this low cannabinoid-containing concentrate may represent the most viable and least controversial livestock feedstuff derived from industrial hemp. However, further research is needed to confirm such a possibility. Comparatively, high fiber products harvested from hemp (i.e., stalk material) have very little nutritional value. Hemp fiber has been largely ignored as a potential feedstuff, as its strength, absorbency, and overall utilitarian properties make it a popular construction and bedding material. Overall, current scientific literature indicates hemp-related products may be suitable for livestock rations, but future investigations are warranted. Primary concerns are still concentrated around defining safe cannabinoid inclusion levels, as these may relate directly to transference rates into animal by-products destined for human consumption. However, secondary concerns such as animal growth performance, health, and behavior must also be considered as future research is formulated.