Short-chain fatty acids (SCFA) are described as promoters of good welfare state in animals. Butyrate is a SCFA that can be delivered to the intestinal tract through dietary tributyrin (TRB) supplementation. Through lipolysis in the intestine, TRB releases 3 butyrate fatty-acids (FA) and glycerol. TRB has been studied in fish, showing potential regarding its use as a supplement in high plant-based feeds, to ameliorate its adverse effects. The objective of our work focused on testing if the inclusion of TRB in high plant-based diets given to rainbow trout (Oncorhynchus mykiss ) improved animal welfare and performance. Specifically, we used 1H-NMR (Nuclear Magnetic Resonance) metabolomics to understand if different TRB inclusion percentages caused differences in the metabolite profile of plasma, intestine, liver, and muscle.
Juvenile rainbow trout were fed four experimental diets made up of only 10% fishmeal, 3% fish-oil, and 83% plant-based ingredients with increasing levels of supplementation of TRB, with concentrations of 0%, 0.1%, 0.2% and 0.4%. After 44 days, fish were euthanized at 6 h and 24 h after feeding and intestine, liver, and muscle samples were collected and stored. After separating the polar/nonpolar fractions, the aqueous fraction was analysed through 1H-NMR metabolomics. Multivariate analysis was used to infer if there were differences in metabolite profile between diets.
At 6 h after feeding, we found differences in the metabolite profile of all tissues, regarding all diets. At 24 h after feeding, differences in metabolite profile between all diets were found only in the muscle. These results are in accordance with fish metabolism, that at 6 h post-feeding is at its absorption peak, and at 24 h is at a basal state. Although metabolite profiles presented differences between diets, the inclusion percentages of TRB tested, regarding this species particularly, did not reflect differences in performance parameters (growth performance and feed efficiency), as evaluated in a zootechnical trial (same experimental design). These results can be tied to factors like fish genetics (reared to be predisposed to high plant-based ingredients content), and general superior quality of the plant meals used. As a potential tool in fish nutrition studies, NMR metabolomics seems to complement other trials pinpointing underlying metabolic differences, otherwise unintelligible when focusing only on the classical zootechnical parameters (fish growth, survival rate, feed intake).
Supported by Fundação para a Ciência e Tecnologia (FCT; Portugal), co-funded by the European Regional Development Fund (ERDF/FEDER) through the Operational Programme for Competitiveness and Internationalization (POCI/POFC) : ConTribuT PTDC/BAA-AGR/3550/2020; and structural funds Centre for Functional Ecology UIDB/04004/2020; Associate Laboratory TERRA LA/P/0092/2020.