Bile acids: Normalization in aquaculture

Kayla Wong, Manuka Biotech

Fats and oils possess the highest caloric value of all nutrients compared to carbohydrate and protein feedstuff sources. Hence, fats are widely added to animal diets to meet the high energy demands of highly productive animals. However, there are several factors that would limit digestion and absorption of dietary fat, and this is apparent in young animals with underdeveloped digestive systems and limited bile and digestive enzymes secretion or animals with very short digestive tracts. Furthermore, with the high energy inclusions in aquatic feeds, the majority of farmed aquatic animals, including fish and shrimp, are often met with liver or hepatopancreatic dysfunction.

The types of feed additives used in aquatic feeds are very diverse and usually have functional properties, such as antioxidants, mold inhibitors, emulsifiers, stabilizers, binders, feed stimulants, attractants, growth promoters, molting inducers, immunomodulators, antibiotics, probiotics, prebiotics, mycotoxins, pigmentation agents, antimicrobial compounds, organic acids, bile acids, herbal extracts, etc.

Functions of bile acids

Bile acids are produced in the liver and are the major constituents of bile. It is secreted into the intestines where they promote fat utilization as a natural emulsifier, activating lipase to improve fat digestibility, and protecting the animal liver. Besides that, it also has many other functions that are somewhat less emphasized but equally important.

Facilitate fat and fat-soluble vitamin digestion and absorption.

1. Emulsify fats. Bile acids are biosurfactants that allow fat to be emulsified into microdroplets. This greatly increases the total surface area of fat, increasing its availability for digestion by lipase.

Figure 1. Effects of supplementing Macrobracium rosenbergii with 250 g of bile acids with 30% purity per ton feed on survival (A), plasma ALT and AST content on day 60 (B). Conclusion: Bile acid supplementation increased the survival rate of giant freshwater prawn and enhanced liver health.

2. Activate lipase. Bile salt-dependent lipase cleaves triglycerides when combined with micelles to hydrolyze fat. 3. Promote fat absorption. Only the formation of bile acids and fatty acids could facilitate fatty acids to reach the surface of small intestinal villi and be absorbed into the bloodstream. 4. Emulsifiers only act in the first step in fat digestion, which only emulsifies the fat into microdroplets.

However, bile acids can further activate lipase and promote the digestion of fat.

Lipid, glucose and energy metabolism.

1. Through the activation of FXR (Farsenoid X Receptors): a. Bile acids reduce triglyceride levels. b. Induce fatty acid oxidation. c. Regulate cholesterol homeostasis. d. Lower blood glucose levels by increasing glycogen synthesis in the liver. e. Regulate insulin sensitivity. 2. Bile acid synthesis is the major pathway for cholesterol catabolism.

Enhance hepatopancreas health and immunity – improve survival rate.

1. Improve disease resistance of shrimp by inhibiting pathogenic organisms and lowering intestinal pathogen load via antibacterial effects. a. Bile acids have been shown to inhibit the growth of bacteria in the small intestine (Inagaki et al., 2006). b. Conjugated bile acids regulate the expression of host genes which promotes innate defense against luminal bacteria. c. Unconjugated bile acid also has a high antibacterial ability shown in vitro (Hofmaan & Eckmann, 2006). 2. Prevent accumulation of toxins – promote liver/ hepatopancreas health. a. Eliminate bilirubin and waste products (drugs and toxins) via secretion into bile and elimination in feces. b. Increase efflux both across the canalicular and basolateral membrane thus preventing the hepatic accumulation of bile acids and liver damage.

Prevent softshell/abnormality during molting.

1. Bile acid facilitates improved nutrient and energy absorption and accumulation for molting and growth. 2. Prevent bacterial infections which can occur during molting as shrimp are at their weakest.

Increase growth and frequency of molting.

1. Molting hormones are synthesized from cholesterol and cholesterol catabolism and absorption are affected by bile acids. 2. Long-term supplementation of bile acid accelerates the speed of growth and metamorphosis, as bile acid can increase the molting frequency and promote shrimp growth.

Table 1. Feeding groups in the trial.

Product Color Origin

Manuka Biotech Milky white Bovine & Ovine

Other companies

Brown Poultry & Swine

Production process

Homogenized, coated: Made entirely of emulsifiers, high potency Carrier dilution: easily neutralized by alkaline substances in feed or destroyed by stomach acid

Table 2. Differences between regular emulsifiers, Lipotech BA and Lipotech Omega 3 Plus.

Product

Emulsifying fat Activate lipase Facilitate Contain / lipid, forming improves fatty acid EPA emulsion droplets fat digestion transportation and DHA

Regular Emulsifiers

P

O O O Lipotech BA P P P O Lipotech Omega 3 Plus P P P P

Prevent diseases such as white feces syndrome/white gut disease and hepatopancreas necrosis.

1. Bile acids protect the hepatopancreas of shrimp and reduce the pathogen load which reduces the occurrence of white feces syndrome/ white gut disease and hepatopancreas necrosis.

Our bile acid is extracted from bovine and ovine sources from New Zealand, a country well known to be relatively disease-free. Therefore, there is a reduced risk of homologous infections.

Conclusions

In conclusion, exogenous bile acids bring many benefits to aquaculture as they can effectively improve utilization and digestibility of fat thus providing animals with more energy which leads to increased production performance, lowering feed costs, prevention of fatty liver, liver protection and promotes intestinal health. Seeing the lengthy benefits of exogenous bile acid supplementation, bile acid should be a staple, especially in aquaculture feeds as it not only supports feed efficiency and animal health but also supports a more green and sustainable way to produce aquatic produce.

Manuka Biotech provides high-quality bile acid extracted from bovine sources from New Zealand – Lipotech BA and a patented product combining premium bile acid with EPA and DHA – Lipotech Omega 3 Plus (Table 2). Lipotech BA is a unique product made entirely of emulsifiers to ensure its potency as products made with carrier dilution can be easily neutralized by alkaline substances in feed. Lipotech Omega 3 Plus on the other hand is a water-soluble product suitable for top dressing on complete feed in farm applications. While bile acids allow for liver recovery, the EPA and DHA in the product also stimulate liver function and immunity simultaneously.

Bile acid promotes the molting of crustaceans such as shrimps and crabs.

References available on request.

More information: Kayla Wong

Technical Specialist Manuka Biotech E: enquiry@manukabiotech.com