Effects of starch structure on the absorption of encapsulated amino acids in laying hens fed low-protein diets

Low-protein (LP) diets supplemented with encapsulated crystalline amino acids (CAAs) have been proven to improve amino acid absorption kinetics and post-absorptive amino acid balance. This study investigated the effects of dietary starch structure, expressed as the amylose-to-amylopectin ratio (AAR), on encapsulated amino acid (EAA) utilization and laying performance in hens fed LP diets. A total of 672 healthy 34-wk-old Jingfen laying hens (1534.7 ± 5.4 g) were randomly assigned to seven treatments with eight replicates of 12 hens each for 10 weeks. The dietary treatments included a control (16% crude protein [CP]) diet, a LP diet (13% CP) supplemented with CAAs, the LP diet supplemented with EAAs, and the LP diet supplemented with EAAs containing four AARs (0.128, 0.228, 0.428, and 0.528, respectively). The results showed that, compared with the control, both CAA and EAA diets maintained comparable laying performance ( P > 0.05) but reduced body weight gain ( P = 0.041). Increasing dietary AAR linearly increased laying rate and egg mass ( P < 0.05) and reduced feed conversion ratio ( P = 0.005). Compared with CAA, EAA supplementation improved eggshell breaking strength ( P = 0.023) and reduced plasma uric acid concentration ( P = 0.004), which further declined linearly with increasing AAR ( P = 0.018). The AAR0.428 diet significantly increased plasma Lys, Met, and Thr concentrations compared with the control ( P < 0.05). Moreover, compared with the control, ileal apparent digestibility of Lys and Thr was higher in the CAA group ( P < 0.05), whereas EAA supplementation alone had no significant effect ( P > 0.05); however, most amino acid digestibility increased linearly with increasing AAR ( P < 0.05) except Cys, Tyr, Phe, His, and Pro. The mRNA expressions of CAT1 and EAAT3 in the jejunum and PepT1 and y + LAT1 in the ileum were elevated ( P < 0.05) by AAR0.428 and AAR0.528 treatments compared with the other two AAR groups. In conclusion, LP diets (13% CP) supplemented with CAAs alone could not fully achieve comparable production performance to that of the hens fed a normal-protein diet (16% CP). However, increasing dietary amylose proportion in LP diets enhanced laying performance, egg mass, and body weight gain, suggesting that synchronized glucose and amino acid release improves the efficiency of LP diets. These findings provide a theoretical basis for the precision formulation of LP diets in laying hens.