Mounting the immune response and maintaining a competent immune system is thought to be a nutritionally demanding process. In terrestrial animals, the influence of an immune challenge on animal growth is well established (Huntley et al., 2018). In fish, and particularly in A. salmon, it remains to be investigated. An immune challenge and the associated lower feed intake can theoretically partition energy and nutrients away from productive processes such as muscle growth, and negatively impact efficiency. In this work, two experimental trials were carried out to first estimate the nutrient costs of immune stimulated A. salmon, and second to design diets to support the adequate immune response and performance during an immune stimulation, using vaccination as challenge model.
Material and Methods
To validate vaccination as a model to estimate nutrient utilisation during immune challenge a pilot trial (trial 1) was carried out in fresh water with A.salmon from 50 to 70g . Two groups of fish were vaccinated with either commercial vaccine 1 (V1) or commercial vaccine 2 (V2) , a third group of fish was injected with a saline solution (S) and a fourth gr oup was used as a control (C). All fish were fed with the same commercial diet . At the beginning of the trial and a fter 24 days post vaccination fish were sampled for body composition for nutrient balance estimation. To evaluate the dietary support to the immune response, a second trial (trial 2) was carried out with fish from 65 to 100g in fresh water. Three groups of fish were immunized with a commercial vaccine after 17 days of feeding with one of the following diets: energy rich (E), amino acid rich (A) and energy and amino acids ( EA). A fourth group consisted in non-injected fish (C) fed a commercial diet served as control . After 41 days post-immunisation, performance, n utrient retention, immune response, and gene expression were the response parameters measured.
In trial 1, the immune stimulation response affected nutrient retention. Vaccinated fish (V1 and V2) showed between 7 to 16% lower energy retention efficiency, between 15 to 20% lower fat retention and between 4 to 13% lower protein retention, in comparison with the non-vaccinated control group (C). Moreover, V2 fish showed lower amino acid retention efficiency for most of the amino acids in comparison with the rest of fish groups. In trial 2 , immunized fish ate 7% less compared to non-immunized. Increasing dietary energy improved protein retention with approximately 8%, suggesting higher energy requirement of immunized fish. Immune response was not different between dietary groups suggesting the primary importance of immune function. There were differences in gene expression regulation between dietary treatments and immune stimulated fish.
Overall, the results showed for the first time, the cost of mounting an immune response through vaccination in A. salmon . Nutrient retention and gene expression is modified under immune stimulation towards energy utilization , while the immune response was shown to be prioritized. It is possible to design feeds to precisely support performance under an immune challenge.
Huntley, N. F., Nyachoti, C. M., & Patience, J. F. (2018). Lipopolysaccharide immune stimulation but not β-mannanase supplementation affects maintenance energy requirements in young weaned pigs. Journal of Animal Science and Biotechnology, 9(1), 1–16. https://doi.org/10.1186/s40104-018-0264-y