biostudies-literatureUnknown15Wei XThis study was conducted to evaluate the effects of dietary crude protein (CP) and rumen-protected lysine (RPL) supplementation on lactation performance, amino acid (AA) balance, nitrogen (N) utilization and hindgut microbiota in dairy cows. Treatments were in a 2 × 2 factorial arrangement, and the main effects were CP concentration (16% vs. 18%) and RPL supplementation (with or without RPL at 40 g/cow per day). Forty cows were randomly allocated to 4 groups: low-CP diet (LP), low-CP diet plus RPL (LPL), high-CP diet (HP), high-CP diet plus RPL (HPL). The experiment was conducted for 8 weeks. Results showed that RPL increased the dry matter intake (<i>P</i> < 0.01), milk protein yield (<i>P</i> = 0.04) and energy corrected milk (<i>P</i> = 0.04), and tended to increase milk fat yield (<i>P</i> = 0.06) and fat corrected milk (<i>P</i> = 0.05). Cows in the HP group tended to have higher milk urea N (<i>P</i> = 0.07). Plasma concentrations of Arg, Ile, Lys, Met, Pro, total essential AA and total nonessential AA were increased by RPL (<i>P</i> < 0.05). The total essential AA, total nonessential AA and most AA (except Ile, Phe, Gly and Pro) were increased in the HP group (<i>P</i> < 0.05). N excretion was increased in the HP group through an increase in urea N excretion (<i>P</i> < 0.01) and an upward trend in plasma urea N (<i>P</i> = 0.07). In addition, RPL tended to increase milk protein N secretion (<i>P</i> = 0.08), milk N (<i>P</i> = 0.07) and microbial protein synthesis (<i>P</i> = 0.06), and decreased plasma urea N (<i>P</i> < 0.001). In the hindgut, the bacterial community were different between the LP and LPL groups (<i>P</i> < 0.01). The probiotic abundances of <i>Christensenellaceae_R-7_group</i> and <i>Acinetobacter</i> were increased by RPL (<i>P</i> = 0.03 and 0.03, respectively). The pathogenic abundances of <i>Clostridium_sensu_stricto_1</i> (<i>P</i> < 0.001) and <i>Turicibacter</i> (<i>P</i> < 0.01) were decreased by RPL. In conclusion, supplementing RPL with low dietary CP could balance AA supply and increase milk protein yield, resulting in an improvement in N utilization efficiency, and altered the composition of the hindgut microbiota to favor the lactation performance of dairy cows.Animal nutrition (Zhongguo xu mu shou yi xue hui)320-331https://www.ebi.ac.uk/biostudies/studies/S-EPMC10694044biostudies-literatureRumen-protected lysine supplementation improved amino acid balance, nitrogen utilization and altered hindgut microbiota of dairy cows.PMC10694044Zhu JWang CWei XWang WWang YWang ZWang JWu HfalseRumen-protected lysine supplementation improved amino acid balance, nitrogen utilization and altered hindgut microbiota of dairy cows.This study was conducted to evaluate the effects of dietary crude protein (CP) and rumen-protected lysine (RPL) supplementation on lactation performance, amino acid (AA) balance, nitrogen (N) utilization and hindgut microbiota in dairy cows. Treatments were in a 2 × 2 factorial arrangement, and the main effects were CP concentration (16% vs. 18%) and RPL supplementation (with or without RPL at 40 g/cow per day). Forty cows were randomly allocated to 4 groups: low-CP diet (LP), low-CP diet plus RPL (LPL), high-CP diet (HP), high-CP diet plus RPL (HPL). The experiment was conducted for 8 weeks. Results showed that RPL increased the dry matter intake (<i>P</i> < 0.01), milk protein yield (<i>P</i> = 0.04) and energy corrected milk (<i>P</i> = 0.04), and tended to increase milk fat yield (<i>P</i> = 0.06) and fat corrected milk (<i>P</i> = 0.05). Cows in the HP group tended to have higher milk urea N (<i>P</i> = 0.07). Plasma concentrations of Arg, Ile, Lys, Met, Pro, total essential AA and total nonessential AA were increased by RPL (<i>P</i> < 0.05). The total essential AA, total nonessential AA and most AA (except Ile, Phe, Gly and Pro) were increased in the HP group (<i>P</i> < 0.05). N excretion was increased in the HP group through an increase in urea N excretion (<i>P</i> < 0.01) and an upward trend in plasma urea N (<i>P</i> = 0.07). In addition, RPL tended to increase milk protein N secretion (<i>P</i> = 0.08), milk N (<i>P</i> = 0.07) and microbial protein synthesis (<i>P</i> = 0.06), and decreased plasma urea N (<i>P</i> < 0.001). In the hindgut, the bacterial community were different between the LP and LPL groups (<i>P</i> < 0.01). The probiotic abundances of <i>Christensenellaceae_R-7_group</i> and <i>Acinetobacter</i> were increased by RPL (<i>P</i> = 0.03 and 0.03, respectively). The pathogenic abundances of <i>Clostridium_sensu_stricto_1</i> (<i>P</i> < 0.001) and <i>Turicibacter</i> (<i>P</i> < 0.01) were decreased by RPL. In conclusion, supplementing RPL with low dietary CP could balance AA supply and increase milk protein yield, resulting in an improvement in N utilization efficiency, and altered the composition of the hindgut microbiota to favor the lactation performance of dairy cows.2023-01-01T00:00:00Z2023 Dec2025-06-01T02:26:36.04Z2025-06-01T02:26:36.04ZS-EPMC106940443805380310.1016/j.aninu.2023.08.001