Composition of branched-chain amino acids modulates response to nucleotide supplementation of low protein diets in nursery pigs

Abstract A total of 160 pigs (initial body weight, 5.79 ± 0.01 kg) were used to investigate the effects of dietary nucleotides and branched-chain amino acids (BCAA) supplementation of low protein diets on growth performance, blood metabolites, short-chain fatty acids (SCFA), apparent ileal and total tract digestibility of nutrients (AID and ATTD). Following a 3-d adaptation period on a common diet after weaning, pigs were randomly assigned to one of five dietary treatments using a randomized complete block design. Each treatment consisted of 8 replicate pens with 4 pigs per pen. The experimental diets included a normal-crude protein (CP) Positive Control (PC) diet with CP at 22%, 20.6%, 19.4% for phases 1, 2 and 3, respectively; a BCAA-deficient low-CP Negative Control (NC) diet with CP at 16%, 14.6%, 13.4% for phases 1, 2 and 3, respectively; NC diet supplemented with crystalline isoleucine and valine (NC+BCAA); NC diet supplemented with 9 g/kg of dietary nucleotides (NC+NL9); and NC diet supplemented with both BCAA and nucleotides (NC+BCAA+NL9). Average daily feed intake (ADFI), average daily gain (ADG), and gain-feed ratio (G:F) were recorded. Fecal samples were collected on d 39, 40 and 41 to determine the ATTD of nutrients. Blood samples were collected on d 42 to measure blood metabolites and pigs were euthanized to determine the AID of nutrients and colonic SCFA. Pigs fed the PC diet had the highest (P ˂ 0.0001) overall ADG, G:F and final body weight (BW), with intermediate values in NC+BCAA+NL9 and NC+BCAA, and the lowest values in the NC+NL9 and NC. Blood urea nitrogen (BUN) concentrations decreased (P ˂ 0.0001) with reduced CP, while serum glucose, insulin and glutathione concentrations remain unaffected. The NC diet had the lowest (P < 0.0001) serum insulin-like growth factor-1 concentration (IGF-1), with partial recovery in the NC+BCAA diet and complete recovery in the NC+BCAA+NL9 diet, compared to PC. The NC+BCAA+NL9 diet tended to increase (P = 0.09) serum uric acid concentration and had the highest ATTD of nitrogen (N), gross energy, and dry matter (DM) (P < 0.05) as well as the highest AID of N and phosphorus (P < 0.0001 and P < 0.001 respectively). Additionally, the NC diet showed a tendency to decrease (P = 0.08) the total colonic SCFA concentration. Results suggest that nucleotide supplementation, following BCAA addition to low-CP diets, conferred additional beneficial effects on growth performance and nutrient digestibility in pigs.