Yufeng Liu,Cheng Liu,Shuo Zhang,Jinming Hu,Meng M. Li,Guangyong Zhao
The objectives of the experiment were to compare the effects of rumen-protected taurine (RPT) and rumen-protected methionine (RPM) on the nitrogen (N) metabolism, plasma biochemical parameters, and metabolomics in beef steers and to clarify whether taurine plays similar roles as methionine (Met) in improving the regulation of N metabolism in beef steers. Six Simmental steers aged 12 months (liveweight 325 ± 7 kg) were used as experimental animals. The experimental treatments included a basal diet, the basal diet + 70.0 g/d RPT and the basal diet + 74.2 g/d RPM. The treatments were assigned in a replicated 3 × 3 Latin square design. Each experimental period included 15 d of adaptation and 5 d of sampling. The results showed that supplementing the diet with RPT or RPM did not affect the apparent nutrient digestibility ( P > 0.05). Supplementing the diet with RPT or RPM increased the N retention ( P < 0.05) and the N utilization efficiency (NUE) ( P < 0.05) and decreased the urinary excretion of 3-Methylhistidine ( P < 0.05) and the estimated skeletal protein degradation rate ( P < 0.05). Supplementing the diet with RPT increased the plasma concentrations of taurine ( P < 0.001), cysteine ( P = 0.010), valine ( P = 0.013) and total non-essential amino acids (NEAA) ( P = 0.047) and tended to increase the plasma concentrations of essential amino acids (EAA) + NEAA ( P = 0.087), but it did not affect the plasma concentrations of total EAA ( P > 0.05). Supplementing the diet with RPM increased the plasma concentrations of methionine ( P = 0.033), lysine ( P = 0.047), cysteine ( P = 0.007), leucine ( P = 0.046), isoleucine ( P = 0.046), valine ( P = 0.034), total EAA ( P = 0.028), total NEAA ( P = 0.004) and EAA + NEAA ( P = 0.004). The plasma metabolomics profiling revealed that supplementing the diet with RPT upregulated the plasma concentrations of taurine ( P < 0.001), L-Cysteine ( P = 0.004) and some amino acid (AA) analogues ( P < 0.05) and RPM upregulated the plasma concentrations of Met ( P = 0.021), L-Isoleucine ( P = 0.036), L-Tryptophan ( P = 0.006) and some AA analogues ( P < 0.05). In conclusion, taurine has similar impacts to Met in improving the N retention and the NUE in beef steers. Taurine deficiency is one of the main reasons that the NUE of beef steers is low. Supplementation of the diet with taurine is beneficial to the N utilization in beef steers.
Taurine is a sulfur-containing nonproteinogenic amino acid. Recent studies have shown that taurine can improve rumen microbial crude protein (MCP) synthesis. This experiment aimed to investigate the action mechanism of taurine on rumen MCP synthesis and nitrogen (N) metabolism in beef steers using sodium sulfate (Na 2 SO 4 ) as a contrast. Six steers (bodyweight 506 ± 17 kg) were assigned to three experimental groups including a basal diet (control), a basal diet supplemented with 45 g taurine/d or 50 g Na 2 SO 4 /d, and were allocated in a replicated 3 × 3 Latin square design. The amounts of sulfur from taurine and Na 2 SO 4 were equal (11.38 g/d). The results showed that, compared with the control group, both taurine and Na 2 SO 4 increased ruminal production of MCP ( P < 0.05) by 37.50% and 29.17%, respectively, and increased the concentration of sulfide (S 2- ) ( P < 0.001). Both taurine and Na 2 SO 4 increased the digestibility of neutral detergent fiber ( P < 0.05). Taurine tended to increase ( P = 0.087) while Na 2 SO 4 decreased plasma urea concentration ( P = 0.049), with the taurine group exhibiting higher plasma urea concentrations than the Na 2 SO 4 group ( P = 0.003). Taurine did not affect urinary urea excretion ( P = 0.246) whereas Na 2 SO 4 decreased urinary urea excretion compared with the control group ( P = 0.002). Compared with the control group, both taurine and Na 2 SO 4 increased urinary allantoin excretion ( P < 0.05), total purine derivatives excretion ( P < 0.05), and the estimated rumen microbial N flow ( P < 0.05). The urinary urea excretion of the taurine group was higher than the Na 2 SO 4 group ( P = 0.019). Compared with the control group, taurine did not affect N excretion, N retention (NR) or N utilization efficiency (NUE) ( P > 0.10), but Na 2 SO 4 decreased urinary N excretion ( P = 0.018) and total N excretion ( P = 0.024), and increased NR ( P = 0.024) and NUE ( P = 0.022). No differences were found in NR and NUE between the taurine and Na 2 SO 4 groups ( P > 0.10). Taurine improved ruminal MCP synthesis by enriching the pathways associated with sulfur and amino acid metabolism while Na 2 SO 4 improved ruminal MCP synthesis by enriching pathways related to nucleotide and purine metabolism. In summary, both taurine and Na 2 SO 4 improved ruminal MCP synthesis by modulating different pathways. Taurine was less effective in decreasing total N excretion than Na 2 SO 4 but no differences in NR and NUE were found between the two groups of beef steers.
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