Abstract
This study was conducted to evaluate the mucosal immune responses of rainbow trout when supplementing an experimental formulated feed with multi-strain yeast fraction product (Saccharomyces cerevisiae and Cyberlindnera jardinii). In total, 360 fish (initial BW 23.1 ± 0.2 g) were randomly allotted into three dietary treatments in an 8-week feeding trial. The dietary treatments included basal diet (control) and control + 1.5 g/kg multi-strain yeast fraction product (MsYF) fed continuously and pulsed every two weeks between control and MsYF diet. No negative effects on growth performance of feeding the MsYF supplemented diet were observed. SGR and FCR averaged 2.30 ± 0.03%/day and 1.03 ± 0.03, respectively, across experimental groups. Muscularis thickness in the anterior intestine after 8 weeks of feeding was significantly elevated by 44.3% in fish fed the MsYF continuously, and by 14.4% in fish fed the MsYF pulsed (P < 0.02). Significant elevations in goblet cell density in the anterior and posterior (>50% increase) intestine were observed after 8 weeks of feeding the MsYF supplemented diet (P< 0.03). In contrast, lamina propria width was significantly lower in fish fed the experimental diets (>10% reduction). The gene expression analysis of the intestine revealed significant elevations in expression of tlr2, il1r1, irak4, and tollip2 after 4 weeks of feeding the MsYF. Significant elevations in effector cytokines tnfα, il10 and tgfβ were observed after 4 weeks of feeding the MsYF regime. After 8 weeks significant elevations in the gene expression levels of il1β, ifnγ, and il12 were observed in fish fed the MsYF. Likewise, the expression of the transcription factor gata3 was significantly elevated (P<0.01). Supplementation of the multi-strain yeast fraction product positively modulates the intestinal mucosal response of rainbow trout through interaction with toll-like receptor two signalling pathway and potential for increased capacity of delivery of antigens to the underlying mucosal associated lymphoid tissue.
Highlights
With increased awareness of antibiotic resistant bacterial strains, the aquaculture industry is increasingly integrating functional health feeds as a preventative health and welfare management strategy
The authors measured two regions of the intestine to access the effects of the multi-strain yeast fraction product (MsYF) on both the anterior intestine (AI), where the function of the enterocytes can be considered as absorptive cells, and posterior intestine (PI) where enterocytes are characterised by antigen sensing and uptake [34,35]
In the anterior intestine a significant elevation in muscularis thickness and a significant reduction in laminar propria width were observed compared to the control in both continuously (+44.3% and -11.4%, respectively) and pulsed (+14.4% and -21.7%, respectively) fed MsYF groups
Summary
With increased awareness of antibiotic resistant bacterial strains, the aquaculture industry is increasingly integrating functional health feeds as a preventative health and welfare management strategy. To minimize the use of veterinary drug usage significant interest in finding alternative in feed solutions such as using feed supplements from yeast cell wall extracts have been widely studied as a strategy to improve animal welfare and health [1]. Among the range of yeast-based products, extracts from the cell wall of Saccharomyces cerevisiae have received much research focus across aquaculture species validating their subsequent inclusion and contribution to improving animal health and welfare [2,3]. Many studies have concluded positive benefits of inclusion of yeast cell wall extracts such as β-glucans and mannan-oligosaccharides at doses of inclusion 20 g/kg to fish mucosal associated lymphoid tissues (MALT) [3,4,5,6]. The notion of ‘trained immunity’ will become an important focus in future investigations into how MALT is affected by the different yeast cell wall extracts
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