Estimates of genetic and environmental (co)variances for vertebral deformities and vaccine induced side effects in Atlantic salmon

Bjarne Ragnar Gjerde^1*Tale Marie Karlsson-Drangsholt¹Jørgen Ødegård²Frode Finne-Fridell³Ingunn Thorland⁴Kirsti Hjelde¹

• ¹Norwegian Institute of Food, Fisheries and Aquaculture Research (Nofima), Tromsø, Norway
• ²Norwegian University of Life Sciences, As, Akershus, Norway
• ³VMRD Aquatic Health, PHARMAQ part of Zoetis, Oslo, Norway
• ⁴Benchmark Genetics (Norway), Bergen, Hordaland, Norway

Vaccination is an effective tool to prevent disease outbreaks in Atlantic salmon. However, oiladjuvant vaccines which may lead to negative side effects in form of adhesions of abdiminal organs and melanin deposits on abdominal organ and the abdominal wall have been linked to vertebral deformities. The main objective of this study was to estimate both the genetic and environmental (residual) correlations between vaccine induced side effects and vertebral deformities, and the genetic correlation between vertebral deformities measured at different ages. The recorded fish were the offspring of 85 sires and 150 dams from SalmoBreed (yearclass 2007) and included two groups of vaccinated fish: pre-smolts exposed to 17°C freshwater for three-months (FW), and a group of post-smolts (SW) evaluated after six (SW6) and 12 (SW12) months in a net cage in the sea. Adhesions of abdominal organs and viscera (score 0-6), and melanin deposits on abdominal organs and the abdominal wall (score 0-3), were evaluated by trained personnel and vertebral deformities were recorded by radiography. The frequency of vertebral deformities was 6.4%, 5.2% and 6.4% for the FW, SW6 and the SW12 group, respectively. Fused vertebrae was the most common type of deformity in all groups, and with fused vertabrae (4.2%) in the FW group and low percentage of missing intervertebral space in the SW6 (0.5%) and SW12 (0.6%) group. Mean adhesion score was 2.06, 1.68 and 1.46, and mean melanin score was 0.95, 1.49 and 1.45, for group FW, SW6 and SW12, respectively. The heritability on the liability scale for fused vertebrae was of medium magnitude for the FW (0.28±0.11) group as well as for the SW6 (0.20±0.10) and the SW12 (0.20±0.10) groups.Across the experimental groups, the genetic and residual correlations of fused vertebrae with adhesions scores or melanin scores were all close to and not significantly different from zero. Therefore, no evidence was found of a genetic or environmental association between negative side effects of vaccination (adhesions and melanin deposits) and fused vertebral in Atlantic salmon.