Activated zinc oxide: An innovative nutritional approach to reduce WSSV-induced mortality in shrimp

Benedikt Hein, Torben Liermann, Provita Supplements, Martin Rimbach, ISF GmbH

One of the most important fatal diseases in shrimp production is the White Spot Syndrome Virus (WSSV). WSSV is a virus causing high mortality rates, up to 100.0 % within 5 to 7 days and was first reported during the early 90s. Infected shrimp can be recognized by a loose cuticle with white spots (Lightner, 1996; Lin et al., 2011). Even though WSSV has been known for numerous years, shrimp producers still face enormous economic risks from high mortality rates due to the virus, especially during the cooler seasons. Treatment options against WSSV are still poorly developed and ineffective, mainly based on biomolecules like DNA or RNA vaccines, protein-based antigens and antibodies as well as herbal products (Feng et al., 2017). Furthermore, lower stocking densities have proven to reduce WSSV caused mortalities (Raja et al., 2015). While the abovementioned methods may be effective, they are neither very practical nor viable economically for shrimp producers.

For this reason, we investigated the effect of feeding diets including different levels of our activated zinc oxide (MAXACTIVAT/Zn) on the susceptibility of WSSV-induced mortality in shrimp (Penaeus vannamei). Previous R&D work has already shown the positive influence of MAXACTIVAT/Zn against bacterial pathogens such as E. coli in calves and piglets. MAXACTIVAT/Zn (aZnO) has also shown a comparable greater impact on reducing bacterial growth in vitro compared with conventional Zn oxide (Hoffmann et al., 2019). The above-mentioned effects are often concluded to be related to an improvement of the barrier function of the gut mucosa (Li et al., 2001; Sales, 2013). This in turn allows the assumption that this also

Figure 1. Total mortality over the experimental period of the different dietary groups, IMAQUA (2020). *significant at p < 0.05

Figure 2. Cumulative mortality over the experimental period of the different dietary groups, IMAQUA (2020).

has a positive influence on the resilience against viral infections as those often occur in the gastrointestinal system (Katsuma et al., 2012). Moreover, a general positive influence of zinc oxides (ZnO) on health parameters has been observed when supplemented with dietary feeds (Janczyk et al., 2013; Liu et al., 2014).

Material and methods

A challenge trial was conducted with three different groups. The differences between the groups arose from the different levels of MAXACTIVAT/Zn (0 ppm, 135 ppm and 405 ppm) added to the different diets. The zinc oxide has been activated through patented eccentric vibrating mill technology that creates higher reactivity when ingested by animals. The described process modifies the functional parameter, particle size and surface area of the aZnO (Hüttenrauch et al., 1985). The concentration of zinc in MAXACTIVAT/Zn is 74.5 %.

Shrimp were infected via oral route with the WSSV Thai-1 strain (Escobedo-Bonilla et al., 2005) and monitored for clinical signs of disease, with observations for mortality performed twice a day. In order to control unknown influencing factors during the experiment, a negative control group (MOCK: mock inoculation) was added. Clinical outcome was evaluated by: Onset of mortality, cessation of mortality and cumulative mortality by day 7.

Results

Data received from the WSSV challenge trial can be seen as valid due to the fact that mortality within the control (CTRL) group resulted to be within the expected range at 73.3 % while mortality within MOCK group was 0.0 %.

Challenged shrimp fed with MAXACTIVAT/Zn at 405 ppm showed significantly lower mortality of 33.3 %, which was 40 % points less compared to CTRL (Fig. 1). Moreover, the mortality of the group that received aZnO at a concentration of 135 ppm was reduced by 20 % points (Fig. 1).

With respect to cumulative mortality, a positive influence of the aZnO was observed. As illustrated in Figure 2, the onset of mortality within groups MA135 and MA405 was delayed by 18 and 30 hours, respectively, compared to CTRL. Moreover, next to a delayed onset of mortality, mortality levels remained constant once reached their peaks at 53.3 % after 108 hours and 33.3 % after 78 hours, respectively.

Discussion

The high mortality rates related to WSSV, also recognizable within the control group of this study, highlight the great risks shrimp producers face. The above-described results indicate the high potential to decrease those risks. Both, the lower dosage (MA135), as well as the higher dosage (MA405) of MAXACTIVAT/ Zn, showed a positive influence on reducing mortality rates. Considering the onset of mortality it becomes clear that diets containing aZnO did not only delay fatality but also lead to constant low rates.

Explanations of the mode of action of the tested aZnO can be described as follows. Previous studies

investigating the effect of zinc oxide have shown a positive effect in the gastrointestinal tract of pigs. However, those effects have been observed by feeding high pharmacological dietary doses (Davin et al., 2012; Sales, 2013) which may not allow a direct relation to this study. Another possible explanation for the positive effect of ZnO may be the improvement of the intestinal barrier function (Li et al., 2001), the non-allowance of bacterial adhesion to the epithelium (Roselli et al., 2003), as well as the modification of different stress responding proteins (Sargeant et al., 2011). Similar results were also reported by Janczyk et al. (2013), who described a positive influence of ZnO on the immune response of piglets. Moreover, Liu et al. (2014) observed significant effects on various characteristics of the colonic tissue by feeding also a low concentration of ZnO to piglets. Those findings with respect to improved immune response and an improved gastrointestinal tract may also be valid for the results of the present study.

Wang et al. (2018) already investigated the influence of WSSV on the microbiota of shrimp. They compared WSSV-infected with healthy shrimp and found significant differences between both groups. They concluded that WSSV could impact intestinal microbiota composition and, thus, function in L. vannamei. In addition, Huang et al. (2012) described possible adhesion mechanisms of WSSV. They identified the glucose transporter 1 (Glut1) surface protein in shrimp that may interact with VP53A, which is the envelope protein of WSSV. With regard to a possibly modified receptor system in the gut (through aZnO), the adhesion capacity of WSSV may be blocked. This mechanism in turn would be similar to observed positive effects of aZnO against bacterial pathogens in calves and piglets. Thus, improving gut integrity through aZnO may be a comprehensible explanation for lowered mortality rates observed in the challenge trial. Feng et al. (2017) mentioned the negative aspects of vaccines creating non-practical applications. In contrast, supplementing aZnO to shrimp diets provides a nutritional as well as a practical approach. As WSSV pressure underlies seasonal changes (Peña et al., 2007), aZnO concentrations contained in diets may be adapted accordingly.

Conclusion

The demand to clearly improve disease resistance in shrimp production is a considerable economic factor. This experiment consequently points out the significant efficacy of the novel activated trace mineral ingredient MAXACTIVAT/Zn on lowering WSSV induced mortality. This unique approach of a feed additive promotes interest for further research activities to investigate possible further antiviral effects of MAXACTIVAT/Zn.

Moreover, the use of aZnO provides a nutritional path to reduce mortality in shrimp and has proven its high potential.

References available on request.

More information: Benedikt Hein

Area Sales Manager Provita Supplements GmbH, Germany E: Benedikt.Hein@provita-supplements.de www.en.provita-supplements.com

AQUA FEED

PREMIUM PETFOOD

PETFOOD SNACKS

SINGLE SCREW MULTIPLE MARKETS

SINGLE SCREW EXTRUSION SYSTEM OPTIMIZES

Optimize the return on your capital investment FLEXIBILITY AND MARKET OPPORTUNITIES with a single screw extrusion system. Buy one system and cost-effectively deliver product to multiple market opportunities. Contact Extru-Tech today

at 785-284-2153 or visit us

• • One system capable of economy up to super premium fresh meat petfood Aquatic feeds that range from floating to sinking shrimp feed online at extru-techinc.com • Capitalize on high margin petfood treat opportunities • Significantly lower operating cost per ton versus competitive systems An Extru-Tech Single Screw Extrusion System provides all the flexibility and production efficiencies at around half the cost of competitive extrusion systems with high operating costs.

P.O. Box 8 100 Airport Road Sabetha, KS 66534, USA Phone: 785-284-2153 Fax: 785-284-3143 extru-techinc@extru-techinc.com www.extru-techinc.com

ET-337C.indd 1 1/28/21 8:32 AM