Effects of Fermented Palm Kernel Meal on Lactation Performance, Rumen Fermentation, Rumen Microbiota, and Rumen Metabolomic Profiles in Holstein Dairy Cows

This study evaluated the impact of fermented palm kernel meal (FPKM) on the lactation performance, blood biochemical indices, rumen microbiota, and metabolic functions of Holstein dairy cows, aiming to enhance the nutritional value of palm kernel meal (PKM) through solid-state fermentation. A 3 × 3 Latin square design was used, involving 12 multiparous Holstein cows (parity = 3; body weight = 625 ± 25.8 kg; days in milk = 103 ± 19.6 day(s); milk yield = 32.6 ± 1.58 kg/d) over three 28-day periods. Cows were randomly assigned to three isocaloric and isonitrogenous diets: a basal diet with wheat bran (WB group), a diet with wheat bran replaced by PKM (PKM group), and a diet with wheat bran replaced by FPKM (FPKM group). Solid-state fermentation improved PKM’s nutritional profile by reducing fiber and β-mannan content while increasing protein availability and ruminal degradability. Compared to the WB group, the PKM group showed lower dry matter intake, milk yield, and nutrient digestibility. In contrast, the FPKM group had higher DMI and milk yield than the PKM group, improved nutrient digestibility, and the highest energy-corrected milk yield due to increased milk protein and lactose production. The FPKM group also had higher concentrations of total volatile fatty acids, propionate, acetate, and microbial protein synthesis than the PKM group. Pro-inflammatory cytokines (tumor necrosis factor-α, interleukin-8) were elevated in the PKM group but were reduced to levels similar to the WB group in the FPKM group. Plasma immunoglobulin G levels were higher in both the FPKM and WB groups compared to the PKM group. The FPKM group also showed increased relative abundances of Prevotella, Fibrobacterota, and Verrucomicrobiota, while Bacillota and Ruminococcus were reduced compared to the WB group. Metabolomic profiling revealed that FPKM upregulated energy metabolism and inflammation-related pathways, increasing metabolites such as riboflavin and adenine and decreasing succinic acid and guanine compared to the PKM group. In conclusion, FPKM improved the feeding value of PKM-based material and showed more favorable responses than PKM, with generally comparable responses to WB, supporting its potential as an alternative feed ingredient for lactating dairy cows.