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(Litopenaeus vannamei) to assess the effect of yeast deriva- tive supplementation on shrimp immunity. After four weeks of continuous supplementation, a numerically higher Total Hemocyte Count (THC; + 28%) was measured in the haemolymph of shrimp fed the yeast derivative compared to the non-supplemented control group. Furthermore, the THC profile revealed a significantly higher proportion of large- granular cells with the supplement (x 3.4 increase); this was in line with the higher respiratory burst, phenoloxidase (PO) and lysozyme activities (Figure 1) in the hemolymph. All of these parameters are described biomarkers of innate immune components in shrimp. These results suggest that shrimp pre- ventively fed the yeast derivative are better able to react to a pathogen challenge, with a larger quantity of immune cells and enhanced immune cell activity.


Another trial was conducted with the new yeast derivative on juvenile white shrimp challenged with EMS/AHPND (Vi- brio parahaemolyticus). The yeast derivative supplementa- tion for three weeks prior to the challenge was associated with a higly significant 4.6-fold improvement in shrimp sur- vival (56% survival vs. 12% for control). Similar findings were repeated in a subsequent trial under similar conditions, where the yeast derivative supplementation was associated with a significantly higher survival, reaching 49.6 % com- pared to 16.5 % in the control group. Such consistent results at the animal level confirm the in vitro agglutination results and (potentially) positively modulated immunity under non-challenging conditions. They clearly show thatspecific yeast fractions can be used as an efficient tool to support shrimp health in the context of one of the most damaging pathologies in aquaculture.


Reinforcing the first line of defense An eight-week trial was conducted in rainbow trout (Oncorhy- nchus mykiss) to evaluate the effect of the yeast derivative on skin mucus production. In this trial, skin mucus secretion in- creased over time in the control, indicating on-going recovery toward normal mucus levels following transfer into the rear- ing system. Compared to the control group, a positive effect of supplementation was observed within four weeks, with a 65% increase in skin mucus level. After twomonths (week 8), skin mucus level was 27% higher in the yeast supplemented group than in the control group. By supporting rapid recovery (in under four weeks) and high levels of skin mucus, the yeast derivative was shown to support a lower risk of secondary in- fection and physiological disruption following challenging conditions (Figure 2). Results related to skin mucus level were in agreement with the up-regulation of a molecular skin bio- marker which is indicative of the immune function and regen- erative capacity (wound healing) of the skin mucosal layer. These results have been demonstrated in several species, in- cluding seabass, seabream, trout and salmon. By supporting


the skin mucosal barrier, yeast fractions contribute to resil- ience and recovery from challenging conditions including parasitic challenges, chemical treatment and mechanical disruptions resulting from handling and transfers.


Performance benefits In the same trial, yeast derivative supplementation was also shown to enhance the microvilli density of intestinal epitheli- al cells, the second line of defense. A higher surface area of the intestinal brush-border is associated with enhanced gut health, protective barrier function and nutrient absorption. Similar outcomes were observed in juvenile seabass in condi- tions of digestive stress (incorporation of high level plant- based raw materials in the diet – 40% soybean meal). Follow- ing ten weeks of yeast derivative supplementation, the density of microvilli of the intestinal cells was increased, and significant differences in the length of microvilli and gut pe- rimeter ratio were also observed. These were associated with improved feed utilisation and growth performance. Weight gain (21.6 vs. 18.5 g/fish in control), daily growth rate (1.39% vs. 1.25% in control) and feed conversion ratio (1.45 vs. 1.66 in control) were improved (with a statistically significant dif- ference for all parameters) in fish fed with YANG. Finally, in the same trial, a strong correlation between dietary yeast de- rivative supplementation and the intestinal expression of genes involved in the immune response was demonstrated, indicating a positive modulation of the immune system.


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0 ▶ ALL ABOUT FEED | Volume 28, No. 8, 2020 21 *


The trial results suggest that shrimp preven- tively fed the yeast derivative are better able to react to a pathogen challenge.


PHOTO: SHUTTERSTOCK 


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