Removal of three proteinaceous antinutrients from a soybean cultivar and effects of inclusion in diets processed at two heat levels on nutritional value and gut health for Atlantic salmon (Salmo salar L)

Abstract

The worldwide, rapid grow of the aquaculture industry is imposing an increasing demand for ingredient feed resources for aquafeeds. Plant-derived ingredients like full fat soybean meal have been widely investigated in recent years as alternative protein and energy sources. However, presence of a variety of anti-nutritional factors in soybeans can lead to reduced growth performance and affect gut health and function. Researchers from the University of Arizona and the University of Illinois have developed a new soybean cultivar in which three proteins with anti-nutritional characteristics (Kunitz trypsin inhibitor, soybean lectin and recognized allergen (P34)) have been removed though a non-GMO breading program. The cultivar is named “Triple Null”. The present study addressed the nutritional value of Triple Null (TN) for salmon production, and whether elimination of the antinutrients also eliminated the ability of soybean meals to induce enteritis in the distal intestine. In this study, also possible effect of variation in specific mechanical energy (SME) during extrusion might affect the quality of the experimental diets. Three basal diets processed at high and low SME, i.e. a total of six experimental diets, were fed to the fish in triplicate tanks (18 tanks in total with 55 fish per tank) for each diet for 56 days to evaluate the performance and efficiency of soy diets in aquafeeds for Atlantic salmon.

The results showed that removal of the proteinaceous components did not significantly alter dietary feed intake, growth, condition factor, relative carcass and organ weight, nor apparent digestibility of protein, most essential amino acids, body composition. Also, the chyme bile salt concentration in the distal sections of the intestine and plasma biomarkers of fish fed NT and CSBM were similar in the feeding period. The same was the case for several of the indicators of gut health conditions, i.e. faecal dry matter, distal intestinal morphology, activity of brush border LAP, there was no significant difference between TN and CSBM diet. For the gene expression profile, the TN fed fish showed higher expression of tgfβ, CD3γδ and mmp13 but the effects were minor. indicating For the other investigated genes, i.e. ifn γ, myd88, pcna, fabp2b, aqp8ab, sod1, cat, hsp70, no significant difference was seen between TN and CSBM. The likely reason for the lack of effect of antinutrient removal was fact that the heat treatment involved in typical extrusion processing used for salmon feed may be sufficient to inactivate heat labile soybean inhibitors. High SME compared to the low SME did not induced major differences in nutritional quality but increased fecal dry matter content and apparent digestibility of protein, lipid and energy by high SME, significantly, supposedly related to structure unfolding of the protein molecules by temperature. For both ALAT and ASAT, indicators of liver stress high SME caused significantly higher values than low SME, possibly caused by the heating process might have developed components which represented a challenge to the liver.