Effect of dietary supplementation of the quenching enzyme AiiO-AIO6 on growth performance, digestion and absorption capacity, and intestinal barrier function of grass carp (Ctenopharyngodon idella)

Abstract

Quenching enzymes have attracted wide attention as one of the alternatives to antibiotics because their positive effects on inhibiting pathogenic microorganism. Therefore, the objective of this study was to investigate the impact of dietary quenching enzyme AiiO-AIO6 on the growth performance, digestion and absorption capacity, intestinal structural integrity, and gut microbiota composition in juvenile grass carp. Healthy grass carp (4.73 ± 0.01 g) were assigned to 36 fish tanks (1.2 × 0.6 × 0.9 m), randomly divided into 6 groups, and fed on six diets with different levels of AiiO-AIO6 (0, 2.5, 5.0, 7.5, 10.0 and 12.5 U/g feed) for a duration of 10 weeks. The present findings demonstrated that dietary AiiO-AIO6 supplementation positively influenced the final body weight (FBW), specific growth rate (SGR), percent weight gain (PWG), and feed intake (FI) of juvenile grass carp. Moreover, our results indicated that the appropriate dietary AiiO-AIO6 supplementation promoted the number of goblet cells and improved the activities of chymotrypsin, trypsin, lipase, amylase, Na+-K+-ATPase, γ-GT and CK, which ultimately contributed to the enhancement of digestion and absorption capacity of juvenile grass carp. Additionally, the present study further found that dietary AiiO-AIO6 supplementation up-regulated the relative mRNA levels of tight junctions (TJs) and adhesive junctions (AJs) proteins, including ZO-1, occludin, claudin-b, −c, −f, −7a, −7b, −11, −12, α-catenin, nectin, afadin, and E-cadherin, thereby enhancing the physical barrier function, potentially attributed to the reduction in abundance of intestinal pathogenic bacteria, such as Pseudomonas. Ultimately, the optimal level of AiiO-AIO6 for juvenile grass carp, as determined by the percent weight gain (PWG), was found to be 4.5 U/g.