Introduction
Moderate levels of intestinal damage and inflammation are often seen in intensive fish aquaculture. This can be caused by stress, sub-optimal farming conditions or antinutritional factors present in plant meals. There is currently a lack of good models to explore these effects and how to mitigate the consequences. Thus, the aim of the present study was to develop a low-intestinal inflammation model using HP48, derived from solvent-extracted peeled soybeans and to test whether of the probiotic Pediococcus acidilactici CNCM I-4622 – MA 18/5 M (Bactocell) could diminish this effect.
Materials and methods
Atlantic salmon (Salmo salar) post-smolts (averaging 106.8 ± 5.8 g) were assigned three feeding groups. The Control diet contained 18.08% soy protein concentrate (SPC) and for the HP48 diets, most of the SPC were exchanged with HP48 to induce low intestinal inflammation. The Bactocell diet was identical to the HP48 diet but was supplemented with 0.03% Bactocell (Lallemand Animal Nutrition, Blagnac, France). The fish were fed to excess over ~ two months and weight were recorded at the start, mid and end of the experiment. At the end sampling, mid- and hind-intestine were collected for analysis of histology, Ussing chamber and RNA sequencing.
Results
Results revealed that fish fed the HP48 diet showed a reduced SGR (1.55 ± 0.04) compared to the Control diet (1.66 ± 0.03) (p < 0.05). The difference in SGR was greater in the first half of the experiment. The Bactocell diet showed intermediate growth (1.58 ± 0.03) which did not differ from the other groups. Histological assessment of the mid-intestine revealed few differences, except for wider lamina propria in the HP48 group, but transcriptomic and integrity data suggest that HP48 led to a disturbed mid-intestinal homeostasis with impaired cellular integrity and increased inflammation and cell turnover. Most of the transcriptomics effect were reversed with Bactocell. In the hind-intestine, HP48 led to several morphological changes, i.e., reduced vacuolisation and disrupted mucosal folds (Fig. 1) and upregulated immune related genes like CD99 and IL-17F. Bactocell alleviated several of the morphological changes, but did not reverse the gene expression.
Discussion
Plant-based ingredients like soybean meal (SBM) are commonly used to study intestinal inflammation in Atlantic salmon (S. salar), but the resulting damage may be too severe for functional ingredients to mitigate (Krogdahl et al., 2003, Booman et al., 2018). In this study, a milder inflammatory model was developed using HP48 to better assess probiotic supplementation. Feeding HP48 led to lower SGR, especially early on, but recovery towards the end indicated mild and reversible damage (Ali et al., 2003). Bactocell supplementation improved SGR, suggesting a protective effect. HP48 caused impaired epithelial barrier function and low-level inflammation in the mid-intestine (Bakke-McKellep et al., 2007, Booman et al., 2018, Wu et al., 2018). Bactocell restored collagen and immune-related gene expression in this intestinal segment. In the hind-intestine, HP48 induced inflammation, including morphological changes and increased expression of in CD99 and IL-17F (Knudsen et al., 2007, Marjara et al., 2012). Bactocell supplementation mitigated the morphological effects but was not able to reverse the transcriptional effects. This could indicate that Bactocell increased colonisation of probiotic bacteria in the mid-intestinal segment compared to the hind-intestine. A dose-response trial would be interesting to investigate whether a higher inclusion of Bactocell would lead to more effects lower down in the intestine.
Conclusion
Overall, HP48 successfully induced mild intestinal inflammation, providing a better evaluation platform for functional feed ingredients. Probiotic supplementation with Pediococcus acidilactici (Bactocell) mitigated several of the negative effects, particularly in the mid-intestine.
References
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