Taurine drives body protein renewal and accretion in beef steers

The aims of the present study were to investigate the effects of dietary supplementation with rumen-protected taurine (RPT) on the whole-body protein turnover, the plasma metabolomics, and the whole blood cell transcriptomics in steers. Eight steers, averaging 220 ± 3.26 kg of liveweight, were allocated in a replicate 4 × 4 Latin square design. The experimental treatments consisted of four levels of RPT supplementation: 0, 25, 50, and 75 g RPT per day, added to a basal diet. The results showed that supplementation with RPT linearly decreased the fecal nitrogen (N) excretion (<i>P</i> = 0.001) and the ¹⁵N fractional recovery rate (<i>P</i> = 0.047), while it linearly increased the urinary excretion of taurine (<i>P</i> = 0.045) as well as the average daily weight gain (<i>P</i> = 0.003), the protein synthesis (<i>P</i> < 0.001), the protein degradation (<i>P</i> < 0.001) and the whole-body protein turnover (<i>P</i> < 0.001). Supplementation with RPT linearly increased the plasma concentrations of growth hormone (<i>P</i> = 0.005) and quadratically affected the plasma concentration of insulin-like growth factor-1 (<i>P</i> = 0.013), and it linearly decreased the plasma concentration of albumin (<i>P</i> = 0.022). Supplementation with RPT altered the whole blood cell mRNA expression and upregulated the expressions of the marker genes, including <i>RPS6KB1</i>, <i>PRSS42</i>, <i>COL1A2</i>, <i>ENSBTAG00000013055</i> and <i>ENSBTAG00000038159</i> which are related to protein metabolism. The plasma metabolomics profiling indicated that supplementation with RPT upregulated the plasma concentrations of taurine, lysine and methionine. The experiment revealed the impact and the mechanisms of taurine on driving whole-body protein turnover and protein accretion in steers. Two novel marker genes which could be related to body protein degradation in steers were identified.