Effects of dietary yeast cell wall β-glucans and MOS on performance, gut health, and salmon lice resistance in Atlantic salmon ( Salmo salar) fed sunflower and soybean meal

Abstract

This experiment examined and compared the effects of a highly purified immune modulating β-1,3/1,6-glucan product (BG) and of a putative receptor blocking, mannan oligosaccharide rich product (MOS) in Atlantic salmon fed extruded diets containing extracted soybean meal (SBM) or a combination of SBM and extracted sunflower meal (SFM). The BG and MOS products were derived from the cell walls of baker's yeast. A control diet was based on LT-fish meal (FM) and contained no plant protein. Two basic experimental diets were formulated with 32% SBM (FM + S) or with 14% SBM + 14% SFM (FM + SS). Following extrusion, four FM + S batches were supplemented with 500 or 1000 mg BG or 1000 or 2000 mg MOS kg − 1 , while two FM + SS batches were supplemented with 1000 mg BG or 2000 mg MOS kg − 1 . Each diet was fed to three groups of 150 salmon kept in sea pens, and effects on feed intake, growth, nutrient utilisation, gut health, sea lice infestation, and overall performance of the fish were recorded over a period of 70 days. The initial weight of the fish was 0.68 kg, and the different feed groups grew to final weights ranging from 1.33 to 1.72 kg. Compared to the control group, fish fed the diet with 32% SBM ate 18% less, grew 30% slower, had 24% poorer feed efficiency ratio (FER), and also suffered from serious SBM-induced enteritis, diarrhoea, and reduced capacity to digest lipid. Adding BG or MOS to this diet had no detectable effects. Fish fed the diet with 14% SBM + 14% SFM ate as much as the control group, but still grew 5% slower, had 7% poorer FER, and suffered from a diarrhoea-like condition and moderate enteritis. Noteworthy, 27% fewer of these fish were infested with salmon lice when compared to the other groups. Adding BG to this diet further reduced the number of lice-infested fish by 28%. Adding MOS to this diet did not affect appetite or lice infestation, but resulted 10% better FER, 8% faster growth (similar to the control group), 11% higher protein retention, less diarrhoea, and most noteworthy: elimination of the SBM-induced enteritis. This clearly demonstrates that gut health is an important production parameter for Atlantic salmon.