Effects of butyrate, propionate, and their combination in vitro, and the impacts of their supplementation in high-plant-protein diets to the production performance, innate immune responses, and intestinal microbiota of red drum (Sciaenops ocellatus)

Abstract The objective of this study was to investigate possible effects of sodium butyrate and sodium propionate individually, and in combination, against common pathogenic bacteria and intestinal microbiota in vitro, and when supplemented in high-plant-protein diets for the carnivorous red drum. These organic acids (OA) presented synergistic effects when inhibiting Aeromonas hydrophila and Streptococcus agalactiae. Additionally, red drum intestinal microbiota were incubated under anaerobic conditions in vitro with feed-broth media preparations containing the OA. The microbial communities proved to be mildly affected in vitro by the OA, with the butyrate and propionate treatments having 90% similarity with the basal diet when analyzed by denaturing gradient gel electrophoresis. Next-generation sequencing revealed a higher relative abundance of the order Clostridiales and class Clostridia compared to the control diet. For the in vivo comparative feeding trial, the OA were supplemented at either 0 or 5 g kg−1 of butyrate, propionate, or their combination (5 g kg−1 of each OA). Five tanks containing 18 juvenile red drum initially weighing ~4.5 g/fish were fed each diet for 8 weeks after which production performance, whole-body proximate composition, whole-blood and plasma immunological responses, as well as intestinal microbial community profiles were evaluated. Data were analyzed as a mixed model, having a 2 × 2 factorial design (absence or presence of butyrate and propionate as main factors) and the disposition of the aquaria was used as statistical block. Fish fed diets containing propionate had slightly impaired growth performance, and red drum fed diets with butyrate presented slightly impaired protein conversion efficiency, while dietary butyrate reduced the production of reactive oxygen species in whole-blood compared to fish fed the control diet. Fish fed diets supplemented with butyrate presented a higher relative abundance of Cetobacterium spp. suggesting a potential beneficial effect of this additive. The predicted metabolic functions of the intestinal microbiome using PICRUSt2 were most affected by dietary butyrate, which resulted in communities predicted to have enrichment of the cobalamin biosynthesis related pathway. However, supplementation of butyrate with propionate resulted in a higher relative abundance of bacterial taxa associated with intestinal dysbiosis.