Different starch sources and amino acid levels on growth performance, starch and amino acids digestion, absorption and metabolism of 0- to 3-week-old broilers fed low protein diet.

The synchronized absorption of amino acids and glucose in the gut is essential for amino acid utilization and protein synthesis in the body. The study aimed to investigate how the starch digestion rate and amino acid levels impact the growth and intestinal starch and amino acid digestion, transport, and metabolism in juvenile broilers. The experiment was conducted with 702 Arbor Acres Plus broilers at 1 d old, which were randomly divided into 9 treatments with 6 replicates of 13 chickens each. The treatments included 3 different starch sources (corn, waxy corn, and tapioca) with 3 different apparent ileal digestible lysine (AID Lys) levels (1.08%, 1.20%, and 1.32%). A notable interaction was noted for dietary starch sources and AID Lys levels in the feed-to-gain ratio (F/G) and distal ileal starch digestibility (P < 0.01). The tapioca starch and waxy corn starch diets with 1.32% of AID Lys significantly decreased F/G compared with corn starch (P < 0.01). There was no significant difference in F/G of broilers among waxy corn starch diet with 1.08% AID Lys level, tapioca starch diet with 1.20% AID Lys level, and corn starch diet with 1.32% AID Lys level (P > 0.05). The 1.32% AID Lys level and the waxy corn starch both improved the body weight (BW) of broilers from 0 to 3 weeks of age, intestinal starch digestibility, and intestinal villi height or the ratio of villi height to crypt depth (P < 0.05). Compared with the corn starch diet, waxy corn starch and tapioca starch diets significantly elevated the AID of Met, Glu, Lys, Arg, Asp, His, Ile, Tyr, Gly, and Val levels (P < 0.05). The carbon metabolomics results revealed that the waxy corn starch diet significantly reduced malic acid and cis-aconitic acid levels (P < 0.05) in the tricarboxylic acid cycle compared to the corn starch diet. It was concluded that a waxy corn starch diet improves the growth performance of broilers by improving intestinal morphology, increasing the absorption and transport of amino acids, reducing the amino acid oxidation for energy supply in the intestinal mucosa, and promoting protein synthesis in muscles, which not only reduces the need for dietary AID Lys but also saves on production costs.