Impact of dietary supplementation with β-alanine on the rumen microbial crude protein supply, nutrient digestibility and nitrogen retention in beef steers elucidated through sequencing the rumen bacterial community

This study investigated the effects of β-alanine (β-Ala) on ruminal 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 the 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. 002), 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 PrevotellaceaeUCG-003 (P = 0. 014) and decreased the relative abundance of NK4A214group (P = 0. 009) at the genus level. Feeding steers with β-Ala linearly increased the urinary N excretion (P = 0. 006) and urea excretion (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 concentrations of albumin (P = 0. 048) and linearly increased the plasma concentration of insulin-like growth factor-1 (P < 0. 001) and the total antioxidant capacity (P = 0. 011). 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 mechanism of the impact of absorbed β-Ala on the anti-oxidative ability of the steers.