Functional feed additives not a magic bullet but study shows their efficacy in EMS control

By Jane Byrne

- Last updated on GMT

Related tags: Feed additives, Aquaculture, Bacteria

Functional feed additives not a magic bullet but study shows their efficacy in EMS control
Belgian headquartered, Nutriad, says new trial work carried out by it in conjunction with leading Vietnamese aquaculture researchers indicates functional feed additives - probiotics, organic acids, yeast extracts and phytobiotics – play a key role in any strategy to prevent EMS in shrimp.

Early Mortality Syndrome (EMS), or acute hepatopancreatic necrosis disease (AHPND), is now causing annual losses of more than US$1 billion across the major shrimp producing countries. 

The disease was first reported in China in 2009 and it then spread to Vietnam, Malaysia and Thailand.  EMS outbreaks typically occur within the first 30 days after stocking a newly prepared shrimp pond, and mortality can exceed 70%.

As it is caused by specific strains of Vibrio parahaemolyticus that are difficult to eradicate from the production environment, AHPND will require a very different approach to the current strategies against white spot virus (WSSV), say the scientists, led by Dr Loc of the Minh Phu Aqua Mekong shrimp vet laboratory in Ho Chi Minh City.

The researchers said their findings, using a controlled AHPND infection, are consistent with recent results from field trials in Mexico and Vietnam in EMS affected farms.

The data “indicated that specific health promoting feed additives [given at every meal] bring up survivals from medium levels – 60 to 70% - to pre-EMS levels – greater than 85%,”​ added Loc et al (2015).

They cited the ability of phytobiotics, for example, to enhance the establishment of probiotic bacteria and therefore boost the effects of probiotic inoculations in the production system.

No magic bullet

But the field results also show such feed additives are not a magic bullet, said the team, but rather “an essential component of a total farm management strategy aimed at controlling the microbial balance throughout the production cycle.”

In addition, techniques such as avoiding early contamination through the broodstock and larvae, combined with continued control of the microbial populations particularly during the initial month of the cycle, will be crucial to control EMS, added the scientists.

Dr Peter Coutteau, who heads up Nutriad’s aquaculture business unit, collaborated with Dr Loc on the study, and he told us there is not a single ingredient that will work to control EMS - a lot depends on the efficacy of the selected gut health promotor being used.

“It is about formulating a mix of natural feed additives combining different modes of action against Vibrio species such as direct bactericide and bacteriostatic properties as well as quorum sensing (QS) inhibition functionality,” ​he said.

QS, he said, is a way of blocking bacterial communication to prevent them from triggering pathogenicity, and it has been proving promising in reducing the impact of EMS in shrimp.

Vietnamese EMS trial results

In the trial, the researchers reported that two challenge methods were used: bathing (immersion) and direct feeding of bacteria (per os).

They evaluated three different types of additives against an un-supplemented control diet. These included Sanacore, a blend of antimicrobial compounds with multiple actions including bacteriostatic and quorum sensing inhibition (Coutteau & Goossens, 2013), Phyto, a botanical blend with antimicrobial activity and OAC, a blend of organic acids.

They found the shrimp fed on diets supplemented with Sanacore tended to show higher survival compared to the control in both types of challenges  - over 107% in the immersion challenge and over 62% in the per os​ challenge.

The group fed the botanical mix, Phyto, showed higher survival only in the immersion challenge (+135%). The shrimp fed the organic acid mix (OAC) did not show any effect in any of the two challenges, they added.

Collaborative research programs

Coutteau said working in partnership with research institutes in different parts of the globe is a more robust way for Nutriad to ensure efficacy of its additive portfolio for aqua feeds supplementation.

“In aquaculture, the challenges are vast and the species diverse, so relying only on in house R&D facilities can be very limiting in terms of species range and the level of expertise you can draw on.

It can take as long as five years to develop challenge tests around certain parasites that target marine species, for example, so being able to leverage an existing research base through collaboration is cost effective and accelerates NPD work.

We find shrimp and other aquaculture species producers are not so much interested in statistically proven results when faced with disease challenges in their ponds – they are willing to try a combination of different approaches to inhibit pathogen growth.

So with EMS, a lot of the research is carried out directly in the field, and then validated in the lab rather than the other way round,’’​ he said.

Developing the functional feed market

And he said aquaculture as a market for standard feed additives, compared to poultry, swine or cattle, is not particularly attractive as it is rather fragmented with low volume demand – 25 times less than in livestock sectors.

“Coupled with those challenges is the bureaucratic headache associated with product registration in multiple countries.

Thus, we are trying to develop the functional feed market side of aquaculture, which is practically non-existent.

At the moment, we are building the case for these blends, convincing the producers of the efficacy of natural antimicrobial compounds to help control disease and boost digestive performance in fish and shrimp. There is a huge amount of work involved but there is a lot to gain,’’​ said Coutteau.

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