New insights into the improvement of milk performance in lactating cows: A novel fermented liquid feed strategy that modulates fermentation profile and microbiome of the rumen and feces

This study evaluated the effects of replacing a concentrate supplement with fermented liquid feed (FLF) on gross feed efficiency (GFE), production performance, and blood parameters in lactating dairy cows. Twenty-four lactating Chinese Holstein cows with comparable body weight (657 ± 32.6 kg), milk yield (38.7 ± 4.7 kg/day), parity (2.8 ± 1.2), and days in milk (104 ± 10.8 d) were randomly assigned to either a control group (CON, total mixed ration without fermented products) or a treatment group (FLF, total mixed ration supplemented with FLF) in a randomized complete block design. Compared with the CON group, feeding FLF increased GFE, energy-corrected milk yield, milk fat and protein percentages, milk nitrogen efficiency, apparent total-tract digestibility of dry matter, crude protein, neutral detergent fiber, and acid detergent fiber, as well as fecal score. Additionally, compared with the CON group, ruminal total volatile fatty acid (VFA) concentration, microbial crude protein yield, and the molar proportion of propionate increased significantly in the FLF group, whereas ruminal pH, acetate proportion, and acetate-to-propionate ratio were decreased. Total VFA concentrations and the molar proportion of butyrate in the feces increased significantly, whereas pH was decreased. In addition, in the FLF group, the relative abundance of unclassified_Clostridia_UCG_014, Prevotella_7, and Lachnospiraceae_NK3A20_group in the rumen and the relative abundance of Bifidobacterium, Candidatus_Saccharimonas, unclassified_Clostridia_UCG_014, and unclassified_[Eubacterium]_coprostanoligenes_group in the feces increased significantly, whereas the relative abundance of NK4A214 group, Rikenellaceae_RC9_gut_group, Treponema, Succiniclasticum, and Isotricha in the rumen and UCG_005, Rikenellaceae_RC9_gut_group, and Bacteroides in the feces decreased. Compared with the CON group, supplement of FLF activated the secondary bile acid pathways, upregulating ursodeoxycholic acid, taurocholic acid, glycocholate, while downregulating deoxycholic acid, lithocholic acid, and chenodeoxycholate in the feces. Additionally, plasma glucose levels, total antioxidant capacity, and total superoxide dismutase activity significantly increased in the FLF group, while β-hydroxybutyric acid, nonesterified fatty acids, and malondialdehyde were significantly decreased. In conclusion, FLF effectively regulated the microbiota in the rumen and feces, improved lactation performance, GFE, and health condition of dairy cows, and provided a novel and promising nutritional regulation strategy for high-yielding dairy cows.