The objective of this experiment was to explore the nutritional components of industrial hemp byproducts (industrial hemp ethanol extraction byproduct, IHEEB; industrial hemp stalk, IHS; industrial hemp seed meal, IHSM; industrial hemp oil filter residue, IHOFR) and provide theoretical support for the application of industrial hemp byproducts in dairy cattle production. This experiment used a combination of a wet chemical method with Cornell Net Carbohydrate and Protein System, in situ nylon bag technique, and three-step in vitro method to compare the chemical composition, carbohydrate and protein composition, in situ ruminal degradability and intestinal digestibility of industrial hemp byproducts and conventional feeds (alfalfa hay, AH; soybean meal, SBM). Available energy values were estimated based on the National Academies of Sciences, Engineering, and Medicine. The results showed that the nutritional composition of different feeds varied greatly. The two types of IHEEB were enriched with ash, crude protein (CP), neutral detergent fiber (NDF), and calcium, while the contents of neutral detergent insoluble crude protein, acid detergent insoluble crude protein, and acid detergent lignin were higher. As a result, the non-degradable carbohydrate and protein components were higher, and the effective degradation rate of rumen dry matter and protein was lower. IHS contains higher non-protein nitrogen and NDF, which enables it to provide more CP rumen effective degradation rate and carbohydrates, but the high acid detergent fiber also limits its application. IHSM possesses 296 g/kg CP and high rumen undegradable protein and intestinal digested protein, which can provide rumen bypass protein in dairy cows, making it a potentially good protein source. IHOFR had higher ether extract, rumen available protein degradation rate, and total tract digested protein, which can provide more energy and easily degradable protein for lactating cows. The available energy value of IHEEB and IHS was lower than AH, while SBM is between IHFOR and IHSM. In addition, the tetrahydrocannabinol of three industrial hemp byproducts that have not been assessed by the European Food Safety Authority (EFSA) was tested to evaluate their safety, and all of them were less than the limit set by ESFA. In conclusion, industrial hemp byproducts can be considered for inclusion in dietary formulations as unconventional feed sources for dairy cattle, but the purpose of use needs to be properly considered.

Making full use of feed nutrients, reducing energy losses and methane emissions, and maximizing production benefits have been ongoing goals of livestock production. Thirty-six healthy Dorper × Thin-tailed Han mutton ewes were divided into six groups using a completely randomized experimental design. A basal diet was provided to the control group, while the experimental group consumed a diet in which 15% was replaced by equal amounts of cottonseed meal (CM), rapeseed meal (RM), distillers dried grains with solubles (DDGS), soybean meal (SM), and fermented soybean meal (FSM). The study demonstrated that SM had the highest protein digestibility, followed by FSM, DDGS, and CM in that order. In terms of net energy, DDGS showed a significantly higher value compared to FSM (p < 0.05). Significantly higher abundances of Lactobacillaceae and Bifidobacteriaceae were observed in the CM group relative to the RM and FSM groups (p < 0.05). The methane emissions that we were most concerned about, whether it was daily emissions or metabolic weight basis, showed the same disparity between the groups, with the RM group having the most, followed in order by FSM, DDGS, and SM groups, and the least by the CM group. We found that the RM group had the highest relative abundance of Methanobrevibacter, followed by the FSM, SM, DDGS, and CM groups in that order, which is similar to the trend of methane emissions from each group. In summary, the highest apparent protein digestibility is SM, and the highest net energy value among these protein feeds is DDGS. RM will produce the most methane. In addition, the source of protein feed in the diet will affect the structural composition of rumen microorganisms.