ISSUE FOCUS FEED & ADDITIVE MAGAZINE September 2022 29 understood that the higher the brush border height, the larger the surface area, and the better the absorption of nutrients. Pacific white shrimp (L. vannamei) were fed 0, 1, and 5 g/ kg of MCFA for 5 weeks. At the end of the trial, the histological structure of hepatopancreas in the MCFA groups was improved compared with the control. It was found the arrangement of the hepatopancreas was more compact, the hepatic corpuscles were fuller and denser, the lumen was star-shaped, the basement membrane was intact, and the structure of star-shaped lumen were more obvious in MCFA groups (Figure 5). Minimizing injury to hepatopancreas Similar to the liver of vertebrates, the shrimp’s hepatopancreas is the main metabolic organ and detox center of the animal. Aspartate transaminase (AST) and alanine aminotransferase (ALT) are known indicators that reflect injuries in the hepatopancreas. Shrimp fed MCFAs were found to have decreased ALT and AST activity in their muscles, which may reflect the improved hepatopancreatic health. MCFAs have a higher pKa (4.90–5.00) than all the short-chain fatty acids (SCFA). The high pKa increases MCFAs efficacy in acidic environments like the stomach of a shrimp (pH 5.7) and allows for synergistic effects with pH-reducing acids (fumaric acid, lactic acid, butyric acid, etc.). The mode of action of MCFAs against pathogenic bacteria can be summarized in 3 steps: 1. Creating pores in the bacteria membrane through the lipophilic and hydrophilic ends of MCFA 2. Once through the membrane and inside the bacterial cell, MCFAs dissociate and acidify the cell’s contents to disturb cell metabolism and protein synthesis 3. Blocking bacterial DNA replication through DNA intercalation and stopping cell divisions. All these lead to bacterial cell death. Similarly, for viruses, especially enveloped viruses like WSV— where the envelope is made of a lipid bilayer—MCFAs do the same as they do to the bacteria membrane; create pores in the membrane, rupture the membrane, and kill the virus. MCFAs are useful in preventing and mitigating bacterial and viral disease challenges faced by shrimp farmers. Growing evidence shows that it can be a new tool for farmers, reducing reliance on antibiotics and securing a good production yield. For disease prevention, the dose range is typically 0.1 to 0.3% of the feed. For therapeutic use, the dose range is 0.5 to 1.0%. This also depends on the concentration of the MCFA as well as if it is incorporated into the feed by the feed mills or top-coated at the farm sites. When top-coated, higher doses are normally required to counter possible leaching to pond water. Figure 5. Effects of dietary MCFA on the HE-stained sections of the hepatopancreas of white shrimp. (A) Control, (B) 1 g/kg group, (C) 5 g/kg group About Fuci Guo Fuci Guo joined Royal Agrifirm Group as Global Category Manager - Aquaculture in October 2021. His objective is to replicate the successes of Agrimprove’s feed additives in terrestrial animals to aquatic species, especially shrimp. He has an Aquaculture degree from China Ocean University, a Masters from the National University of Singapore, and a Ph.D. from the University of Guelph, Canada. With strong network connections to both feed mills and farmers, Guo brings to Agrifirm over 25 years of experience in aquaculture nutrition and health from various multinational corporations.
RkJQdWJsaXNoZXIy MTUxNjkxNQ==