By Prof. David Huyben, University of Guelph, Ontario, Canada
Restrictions on antibiotic use means the industry needs new mitigation strategies to improve the health and disease resistance of farmed fish. Functional feed supplements are one way we can support the growth of the aquaculture industry.
Our recent research on the gut health effects of feeding a mixture of organic acids and essential oils to rainbow trout shows promising results. Feeding a microencapsulated blend of organic acids and essential oils improves gut health and may serve as a part of an effective strategy to reduce antibiotic use in aquaculture.
The aim of our research, conducted in collaboration with Jefo Nutrition Inc., was to use a combination of traditional and advanced analytical methods to determine if these functional feed additives could improve the gut structure and microbiome of fish. More details on these new methods and our research below.
Background: Organic acids and essential oils (OA+EO)
Organic acids are short-chain compounds that are mainly used to alter the pH and preserve grains during storage. Essential oils are a complex mixture of volatile compounds extracted from plant raw materials, including thyme and cloves.
Both supplements are increasingly used in livestock feeds to improve gut health and disease resistance, although not much is known on their impacts on fish. Also, the combined use of both organic acids and essential oils (OA+EO) has not been studied and may produce synergistic effects.
Recently, a hydrogenated-fat based microencapsulation technique was developed in order to protect the blend of OA+EO, as well as release it into the targeted area of the intestine.
Increased research into these compounds paired with this microencapsulation technique has allowed further testing in animal feeds, including aquaculture.
Background: New tech advances “access” to the gut microbiome
Reduced costs and recent advancements in DNA sequencing technologies has allowed everyday scientists to identify billions of microbes in and around their bodies, as well as in animals. The community of bacteria along the gastro-intestinal tract of animals is referred to as the gut microbiome.
The gut microbiome has been recognised as an additional organ in the body due to its ability to ferment fibre into essential fats and vitamins, interactions with our immune system and even connections with the brain and our behaviour. Previous methods used media that was only able to grow a small number of living bacteria, whereas next-generation sequencing and bioinformatics can amplify and identify billions of bacteria – living or dead.
We can now test for both large and small changes in bacterial communities in the gut and downstream effects on the growth and health of individuals, including fish.
Results: OA+EO improve gut function
In our study, Dr. Kabir Chowdhury from Jefo Nutrition top-coated feeds with a microencapsulated blend of organic acids (thymol, vanillin, and eugenol) and essential oils (thymol, vanillin, and eugenol). These were fed to rainbow trout for four weeks at the Ontario Aquaculture Research Station (Alma, Ontario) managed by Dr. Marcia Chiasson.
Prof. John Lumsden and Dr. Phuc Pham from University of Guelph performed inflammation scoring and morphometrics on the proximal and distal intestine. They found that no inflammation existed, and villi length (wall of small intestine) was increased in fish fed the OA+EO treatment diet, compared to the control diet. Extended villi length and the absence of inflammation in the intestine suggest improved gut health and may lead to improved oxidative capacity and gut function.
Results: OA+EO reduce pathogens in the gut
Working with the Animal Health Laboratory at the University of Guelph, my research team found that cultured bacteria levels and diversity of sequenced bacteria did not change, but specific species of bacteria were associated with each diet.
Aeromonas hydrophila and Acinetobacter species were found to decrease when fish were fed the OA+EO treatment diet. These bacteria are known pathogens that cause severe mortalities on fish farms. It seems feeding OA+EO could target these species and improve fish health and production.
Using OA+EO feed supplements to target pathogens may become essential in the future due to increasing resistance of Aeromonas and Acinetobacter pathogens to antibiotics and their restricted use in aquaculture operations. More research is needed since there are many OA+EO compounds and combinations to be tested, as well as figuring out downstream improvements on disease resistance and growth performance.
More info on this study can be found in the 2021 publication in the journal Microorganisms: https://www.mdpi.com/2076-2607/9/10/2063
About the Author and University of Guelph
The University of Guelph is ranked No. 1 in Canada for Agricultural Science, and 18th in the world for Food Science and Technology. Prof. David Huyben joined the University’s Department of Animal Biosciences in 2020 after completing his PhD and postdoc research in Uppsala, Sweden and Stirling, United Kingdom. His research mainly focuses on better understanding the nutrition, microbiome and health of farmed fish. Prof. Huyben is a co-director of the University of Guelph’s Aquaculture Centre, which acts as a hub for aquaculture research, education and outreach in Ontario with links across Canada and internationally. More info: https://animalbiosciences.uoguelph.ca/aquacentre/
