The effect of dietary non-starch polysaccharide level and bile acid supplementation on fat digestibility and the bile acid balance in rainbow trout (Oncorhynchus mykiss)

T.W.O Staessen,M.C.J Verdegem,P Weththasinghe,J.W Schrama

doi:10.1016/j.aquaculture.2020.735174

T.W.O Staessen, M.C.J Verdegem + Show 2 more

Open Access

https://doi.org/10.1016/j.aquaculture.2020.735174

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Abstract

This study investigated in rainbow trout (Oncorhynchus mykiss) if dietary bile acid supplementation is effective in restoring hampered fat digestibility related to conditions that enhance fecal bile acid loss (i.e., high dietary non-starch polysaccharide (NSP) level and high feeding level). Four diets were formulated according to a two-by-two factorial design. A Low- and High-NSP level (0 vs. 160 g kg-1 inclusion of a NSP-rich ingredient mixture) and two bile acid supplementation levels (0 vs. 2 g kg-1 inclusion of sodium taurocholate) were tested. A contrast in feeding level (i.e., feed intake) was created by subsequently feeding fish restrictively (1.1% BW d-1) for four weeks and to satiation for three weeks. The apparent digestibility coefficient (ADC) of all nutrients was affected by feeding period (i.e., restricted vs. satiation feeding), but the effect was dependent on diet composition with the ADC decline between feeding periods being larger for the High-NSP diets. The ADC of all macronutrients decreased alongside dietary NSP level, but this decrease was much more pronounced for fat compared to starch and protein, especially during satiation feeding (6.7%). This large drop in fat ADC during satiation feeding of NSP-rich diets occurred alongside enhanced fecal bile acid loss and correlated with a negative bile acid balance. The correlation between the bile acid balance and fat ADC found during satiation feeding of diets without bile acid supplementation was not present in fish fed diets with bile acid supplementation. In contrast to fat ADC, the ADC of protein and starch were independent from bile acid supplementation. In conclusion, dietary bile acid supplementation is an effective way to remediate decreased fat ADC related to enhanced fecal bile acid loss in rainbow trout, but is not effective in improving protein and starch ADC.

Highlights

Current aquafeed formulations encompass a variety of plant ingredients to replace fishmeal (FAO, 2018; Gatlin III et al, 2007; Naylor et al, 2009)
Increasing the non-starch polysaccharide (NSP) level led to an increase of the feed intake, while bile acid supplementation (BAS) led to a decrease of the feed intake during satiation feeding
The decrease in feces production when supplementing diets with bile acids was largest during satiation feeding (0.48 and 0.41% body weight (BW) d-1 for the 0% BAS and 0.2% BAS diets, respectively) because in that period feed intake was lower for those diets (P < .01)

Summary

Introduction

Current aquafeed formulations encompass a variety of plant ingredients to replace fishmeal (FAO, 2018; Gatlin III et al, 2007; Naylor et al, 2009). The use of plant ingredients can interfere with growth, apparent nutrient digestibility (ADC) and health, especially in carnivorous fish as their digestive systems are not well-adapted (Kaushik et al, 1995; Krogdahl et al, 2010; Øverland et al, 2009) These negative effects on growth, ADC and health are ascribed to a range of characteristics inherent to plant ingredients (e.g., unbalanced amino acid profiles, absence of growth factors, low bioavailability of minerals and vitamins, presence of anti-nutritional factors, etc.) (Gatlin III et al, 2007; Hardy, 2010; Naylor et al, 2009; Sinha et al, 2011). Bile acids activate certain lipases in the intestine (Romarheim et al, 2006; Thirstrup et al, 1994)

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