Slowly digestible starch impairs growth performance of broiler chickens offered low-protein diet supplemental higher amino acid densities by inhibiting the utilization of intestinal amino acid

Abstract

The synchronized absorption of amino acids (AAs) and glucose in the gut is crucial for effective AA utilization and protein synthesis in the body. The study investigated how the starch digestion rate and AA levels impact intestinal AA digestion, transport and metabolism, breast muscle protein metabolism, and growth in grower broilers. A total of 720 21-day-old healthy male Arbor Acres Plus broilers were randomly assigned to 12 treatments, each with 6 replicates of 10 birds. The treatments comprised 3 different starch [corn: control, cassava: rapidly digestible starch (RDS), and pea: slowly digestible starch (SDS)] with 4 different AA levels [based on standardized ileal digestible lysine (SID Lys), 0.92%, 1.02% (as the standard), 1.12% and 1.22%]. An interaction between dietary starch sources and SID Lys levels significantly affected breast muscle yield (P = 0.033). RDS and SDS diets, or SID Lys levels of 0.92%, 1.02%, or 1.22%, significantly decreased the breast muscle yield of broilers in contrast to the corn starch diet with 1.12% SID Lys (P = 0.033). The SID Lys levels of 1.12% and 1.22% markedly improved body weight (BW), body weight gain (BWG) from 22 to 42 days of age, and mRNA expression of y+LAT1 and mTOR while reducing feed intake (FI) and feed/gain ratio (F/G) compared to the 0.92% SID Lys level (P < 0.05). The SDS diet significantly decreased BW and BWG of broilers from 22 to 42 days of age, distal ileal starch digestibility, jejunal amylase and chymotrypsin activities, and mRNA expression of GLUT2 and y+LAT1 compared to the corn starch diet (P < 0.05). The RDS diet suppressed the breast muscle mass by down-regulating expression of mTOR, S6K1, and eIF4E and up-regulating expression of MuRF, CathepsinB, Atrogin-1, and M-calpain compared to the corn starch diet (P < 0.05). Targeted metabolomics analysis revealed that the SDS diet significantly increased acetyl-CoA and α-ketoglutaric acid levels in the tricarboxylic acid (TCA) cycle (P < 0.05) but decreased the ileal digestibility of Lys, Tyr, Leu, Asp, Ser, Gly, Pro, Arg, Ile, and Val compared to the corn starch group (P < 0.05). The SDS diet impaired broiler growth by reducing intestinal starch digestibility, which inhibited intestinal AA and glucose absorption and utilization, increased AA oxidation for energy supply, and lowered the efficiency of protein synthesis. Although the RDS diet resulted in growth performance similar to the corn starch diet, it reduced breast muscle mass by inhibiting protein synthesis and promoting degradation.