Effect of the dietary inclusion of former food products on subcutaneous adipose tissue and on serum metabolites in post-weaning piglets

The 30% of food production is lost after harvest and wasted in retail and households. This amount accounts for 10% of global greenhouse gas (GHG) emissions. In parallel, animal feed production is the largest cost of livestock production, accounting for around 40% of GHG emissions of livestock production. The use of food by-products as feed ingredients could reduce food waste and increase environmental sustainability. Among food by-products, former food products (FFPs) generate high amounts of waste. FFPs are divided into sugary confectionary FFPs (FFPs-C) and salty bakery FFPs (FFPs-B). The aim of this study was to assess the impact of the inclusion of FFPs into post-weaning piglets’ diet on fatty acid profile of subcutaneous adipose tissue and on selected metabolites. Thirty-six post-weaning female piglets (Large White × Landrace) were assigned to a standard diet (CTR), or with a 30% replacement of conventional cereals with FFPs-C or FFPs-B for 42 days. Growth performance and feeding behaviour were measured. Subcutaneous abdominal fat samples were collected from 12 selected piglets after slaughtering. Gas chromatography was performed on feed samples and adipose tissue samples. Untargeted metabolomics was performed on blood samples with UHPLC/MS-MS. Data were analyzed with MetaboAnalyst (v5.0). The growth performance and feeding behaviour were not altered by FFPs. The PUFA level was significantly higher (P<0.05) in CTR (47%) than FFPs-C (34%) and FFPs-B (27%) diets. In FFPs diets, the fatty acid profile was equally distributed (P>0.05) among SFA, MUFA, and PUFA. The subcutaneous adipose tissue showed no differences (P>0.05) between groups for SFA level. The MUFA level was reduced (P<0.001) in CTR (34%) compared to FFPs-C (41%) and FFPs-B (40%), whereas PUFA level was reduced (P<0.01) in FFPs-C (12%) compared to FFPs-B (19%) and CTR (20%). The untargeted metabolomics identified a total of 104 metabolites, with only two being significantly different (P<0.001) between groups. Specifically, the serum concentration of theobromine and caffeine was higher in FFPs groups compared to CTR. To conclude, piglets rebalanced the fatty acids profile despite the differences in the diets. The metabolic status was not deeply altered by the dietary inclusion of FFPs. Thus, FFPs could be safely applied in post-weaning pig diets. Further studies are needed to assess the effect of FFPs on pig physiology and metabolic status in growing phase and for a longer feeding time.