The inclusion of high levels of soybean meal and other plant ingredients have been shown to trigger inflammatory response and induce dysbiosis in the distal intestine of Atlantic salmon. Functional feed additives (FFAs) such as brewers’ yeast (Saccharomyces cerevisiae) may confer immunomodulatory effects in fish. In this experiment, we investigated the ability of two brewers’ yeast FFAs from Leiber GmBH to modulate the known pathological effects of high SBM in Atlantic salmon parr. Product A (β-glucan) contains cell wall extracts rich in β-1,3 and -1,6-glucans while product B (yeast extract) is made of soluble dried cell extracts rich in amino acids, glutamic acids, nucleotides and peptides.
A total of 450 salmon parr (ca. 24 g) were randomly assigned into 15 experimental units and fed one of 5 experimental diets: 1] Neg_ctrl (0% SBM), 2] Pos_ctrl (30% SBM), PβG (30% SBM + 0.02% β-glucan), SDYE_1 (30% SBM + 1% yeast extract) and SDYE_2.5 (30 % SBM + 2.5% yeast extract), with each treatment replicated three times. Fish were fed between 1% - 2% of body weight per day with feeding rate adjusted following periodic batch weighing. At the end of the experiment, samples of skin and distal intestine samples were collected for light microscopy, scanning and transmission electron microscope, gene expression, and microbiome analysis following relevant protocols.
The results from this experiment showed that the high SBM treatment (Pos_ctrl) induced extensive signs of enteritis with significantly wider lamina propria (Table 1) and higher density of goblet cells in the epithelium than the Neg_ctrl diet (Fig 1). These negative physiological changes were not observed in the yeast treated groups, evidencing a protective role against enteritis. However, there was no significant difference among the treatments in zootechnical performance (weight gain, SGR and FCR; data not shown).
On-going analyses include 1] electron microscopy to establish the physical modulations induced by the treatments at the ultrastructural levels, 2] the transcriptional responses of enteritis biomarkers, immunological and barrier-regulating genes and, 3] metabarcoding analysis using full-length 16S sequencing (SMRT, PacBIO®) to obtain high resolution data on microbial diversity and taxa relative abundance.