Effects of guanidino acetic acid and betaine supplementation on growth, dietary nutrient digestion and intestinal creatine metabolism in sheep

Background: The intestine of young ruminants is in the developmental stage and has weaker resistance to the changes of external environment. Improving intestinal health is vital to promoting growth of young ruminants. This study investigated effects of guanidino acetic acid (GAA) and rumen-protected betaine (RPB) supplementation on growth, dietary nutrient digestion and GAA metabolism in the small intestine of sheep. Methods: Eighteen healthy Kazakh rams (27.46 +/- 0.10 kg of body weight and 3-month old) were categorized into control, test group I and test group II, which were fed a basal diet, 1500 mg/kg GAA and 1500 mg/kg GAA + 600 mg/kg RPB, respectively. Results: Compared with control group, test group II had increased (p < 0.05) average daily gain, plasma creatine level, ether extract (EE) and phosphorus digestibility on day 30. On day 60, the EE apparent digestibility, jugular venous plasma GAA, GAA content in the duodenal mucosa and GAA content in the jejunal and ileal mucosa of test group II were higher (p < 0.05) than other groups. Transcriptome analysis revealed that the differentially expressed genes (DEGs) involved in the duodenal pathways of oxidative phosphorylation and non-alcoholic fatty liver disease were significantly altered in test group II versus test group I (p < 0.05). Moreover, in the jejunum, the MAPK signalling pathway, complement and coagulation cascade and B-cell receptor signalling pathway were significantly enriched, with ATPase, solute carrier transporter protein, DHFR, SI, GCK, ACACA and FASN being the significantly DEGs (p < 0.05). Conclusion: Dietary supplementation of RPB on top of GAA in sheep diets may promote sheep growth and development by improving the body's energy, amino acid, glucose and lipid metabolism capacity.