Rumen-protected guanidinoacetic acid is associated with improved growth performance and altered portal nutrient and hepatic IGF-1 indices in Hu sheep

Introduction Guanidinoacetic acid (GAA), the direct precursor of creatine, has been shown to improve growth performance in monogastric animals, but its metabolic effects in ruminants remain unclear. This study examined whether dietary GAA and rumen-protected GAA (RPGAA) are associated with changes in intestinal creatine-related metabolism, portal nutrient concentrations, and hepatic IGF-1 expression in Hu sheep. Methods Twenty-seven Hu rams were randomly assigned to three treatments for 45 days: a basal diet (control), the basal diet supplemented with 1.0 g/kg GAA, or the basal diet supplemented with 1.0 g/kg RPGAA. Growth performance, intestinal mucosal GAA and creatine concentrations, expression of genes related to creatine metabolism and nutrient transport, portal blood nutrient concentrations, serum biochemical variables, and hepatic IGF-1 indices were determined. Results RPGAA significantly increased final body weight and average daily gain and decreased feed-to-gain ratio ( p < 0.05). RPGAA increased GAA and creatine concentrations in the jejunal mucosa, downregulated AGAT mRNA expression, and upregulated transporter-related genes ( p < 0.01). These changes were accompanied by higher concentrations of glucose, arginine, methionine, and lysine in portal blood ( p < 0.05), as well as increased hepatic IGF-1 mRNA expression and IGF-1 concentration ( p < 0.01). In addition, serum glucose and albumin increased, whereas total cholesterol and bilirubin decreased in the RPGAA group ( p < 0.05). Discussion These findings suggest that the improved growth performance induced by RPGAA is associated with enhanced jejunal GAA availability, portal nutrient concentrations, and hepatic IGF-1 expression in Hu sheep.