Cysteamine (CS) is an essential nutritional regulator that improves the productive performance of animals by regulating somatotropic hormone secretion. To investigate the fattening potential and effects of CS on rumen microbial fermentation, 48 feedlot lambs were randomly assigned to four groups and fed diets supplemented with different CS concentrations (0, 20, 40, and 60 mg/kg BW). An increase in dietary CS concentrations linearly increased the average daily gain (ADG) and dry matter intake (p < 0.05) but decreased the feed-to-gain ratio (p < 0.01). For the serum hormone, increasing the dietary CS concentration linearly decreased somatostatin and leptin concentration (p < 0.01) but linearly increased the concentration of growth hormone and insulin-like growth factor 1 (p < 0.01). Regarding rumen fermentation, ruminal pH, ammonia-N, and butyrate content did not differ among the four treatments, although dietary CS supplementation linearly increased microbial protein and propionate and decreased the amount of acetate (p < 0.05). Furthermore, an increase in dietary CS concentrations quadratically decreased the estimated methane production and methane production per kg ADG (p < 0.05). High-throughput sequencing revealed that increased dietary CS concentrations quadratically increased Prevotella (p < 0.05), and Prevotella and norank_f__norank_o__Clostridia_UCG-014 were positively correlated with growth performance and rumen fermentation in a Spearman correlation analysis (r > 0.55, p < 0.05). Overall, a CS concentration higher than 20 mg/kg BW produced growth-promoting effects by inhibiting somatostatin concentrations and shifting the rumen toward glucogenic propionate fermentation by enriching Prevotella. In addition, Prevotella and norank_f__norank_o__Clostridia_UCG-014 were positively correlated with growth performance in lambs.
Keywords: blood metabolites; cysteamine; feedlot lamb; fermentation; rumen microorganism.