In China, the use of antibiotics growth promoters as feed additives has been banned. The goal of raising dairy heifers is to gain a relatively high body weight on a high-fiber diet at first mating or calving, thus increasing economic benefits. The objective of this experiment was to explore the effects of supplemental Clostridium butyricum (C. butyricum) on growth performance, rumen fermentation and microbiota, and blood parameters in Holstein heifers. Twenty Holstein heifers [mean ± standard deviation (SD); age = 182 ± 4.20 d, body weight = 197.53 ± 5.94 kg, dry matter intake (DMI) = 6.10 ± 0.38 kg] were randomly assigned to one of two diets group for a 42-day feeding period: (1) basal diet (an untreated control group, i.e., the CON group) or (2) basal diet plus daily 2 × 108 (colony-forming unit, CFU) of C. butyricum per kg of DMI per heifer (the CB group). The results demonstrated that C. butyricum supplementation increased the average daily gain from d 21 to 42 and DMI compared to the control group. Supplementation with C. butyricum significantly decreased the molar proportion of acetate and the acetate to propionate ratio but increased the molar proportion of butyrate and propionate. Compared with the control group, the relative abundance of Butyrivibrio fibrisolvens, Ruminococcus albus, Ruminobacter amylophilus, Ruminococcus flavefaciens, and Streptococcus bovis increased during the trial period in the CB group. However, C. butyricum had no significant effect on the blood parameters in Holstein heifers. In conclusion, these results show that feeding C. butyricum can improve growth performance and rumen fermentation without any negative impact on blood parameters in Holstein heifers.

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.