摘要This study investigated the effects of β-alanine(p-Ala)on rumen fermentation,nutrient digestibility,nitrogen(N)metabolism,plasma biochemical parameters,and rumen bacterial communities in beef steers.Six steers with initial liveweight of 252.8±5.2 kg and 3 treatments of supplementing with 0,30,or 60 g β-Ala per day to basal diet were allocated in a replicated 3×3 Latin square design.Each experimental period was 20 d,of which the first 15 d were for adaptation and the subsequent 5 d were for sampling.The results showed that β-Ala linearly increased the ruminal concentration of microbial crude protein(MCP)(P=0.005),but it did not affect the ruminal concentrations of ammonia N and total volatile fatty acids(P＞0.10).β-Ala also linearly increased the dry matter(DM)(P=0.009),organic matter(OM)(P=0.017)and crude protein(CP)(P=0.043)digestibility,tended to decrease the acid detergent fiber digestibility(P=0.077),but it did not affect the neutral detergent fiber digestibility(P=0.641).β-Ala quadratically increased the relative abundance of ruminal Bacteroidota(P=0.021)at the phylum level,and increased Prevotella(P=0.028)and Prevotellaceae_UCG-003(P=0.014),and decreased the relative abundance of NK4A214_group(P=0.009)at the genus level.Feeding steers with β-Ala linearly increased the urinary N(P=0.006),urea excretions(P=0.002)and the N retention(P=0.004),but it did not affect the N utilization efficiency(P=0.120).β-Ala quadratically increased the plasma concentration of the total antioxidant capacity(P=0.011)and linearly increased the plasma concentration of insulin-like growth factor-1(P＜0.001).In summary,dietary supplementation with β-Ala improved the rumen MCP supply and increased the digestibility of DM,OM,CP and the N retention.Further research is necessary to verify the ruminal degradability of β-Ala and to investigate the mech-anism of the impact of absorbed β-Ala on the anti-oxidative ability in steers.