Potential beneficial effects of Bactocell on HP48 induced intestinal inflammation in Atlantic salmon

The feed composition of Atlantic salmon (Salmo salar) has changed from being mainly based on marine ingredients, to include higher amount of terrestrial ingredients such as soybeans. However, it is well known that soybean meal (SBM) contains antinutritional factors that cause hind intestinal inflammation in salmon. Probiotics such as Bactocell (Pediococcus acidilactici) have the potential of alleviating this response improving intestinal health and increasingcan alleviate this response, improve intestinal health, and increase the potential of higher inclusion of plant ingredients in fish feed. However, as the effect of SBM is likely to be too severe to detect any potential beneficial effect of functional feed ingredients on the intestinal health, the present study created a low-inflammation model using HP48 and. It investigated whether Bactocell supplementation could dampen this effect. Atlantic salmon post-smolt were fed three diets in triplicates; a control diet containing 18.08% soy protein concentrate (SPC), HP48 diet where most of the SPC was replaced by HP48, and Bactocell diet that was identical to the HP48 diet but contained 0.03% Bactocell supplementation. After approximately 10 weeks of feeding, the mid- and hind intestinal health and integrity was were assessed by histology, Ussing chamber and gene expression (RNAseq). Transcriptomic and integrity data suggests that the HP48 diet led to disturbed mid intestinal homeostasis with impaired cellular integrity and increased inflammation and cell turnover, although not very evident in the morphological assessments. Most of the transcriptomic effects was were reversed in the Bactocell diet compared to the HP48 diet, including downregulation of immune genes and upregulation of transmembrane proteins such as type IV collagen, that which is important in restoring epithelial homeostasis. In the hind intestine, the HP48 diet led to morphological changes such as increased lamina propria and stratum granulosum width, disrupted mucosal folds and loss of absorptive vacuoles in addition to the loss of absorptive vacuoles, and upregulation of several immune regulated genes and downregulation of genes involved in solute- and water transport. The intestinal integrity assessed by Ussing chamber was not affected. Bactocell supplementation did alleviate several of the morphological effects bu. However, it was not able to change the expression of immune- or transport genes, possibly indicating a higher effect of probiotic supplement in the mid intestine compared to the hind intestine.