Worldwide, the amount of wasted food is around 1.3 billion tons per year. At the same time, the sustenance demand is expected to increase significantly. The recovery of food loss as animal feed addresses both waste reduction and zero-hungry challenges. Food industry leftovers, also called former foodstuff products (FFPs) can be differentiated into sugary confectionary FFPs (FFP-C) and salty FFPs from bakery production (FFP-B). The present study intends to test the impact of FFP-C and FFP-B in growing pig’s diet on the large intestinal microbial community composition and biodiversity, together with their metabolic status. Thirty-six post-weaning female piglets (Large White × Landrace, body weight 8.52 ± 1.73 kg) were randomly assigned to a standard diet (CTR), or diets in which traditional ingredients were partially replaced by the 30% inclusion (w/w) FFP-C or FFP-B for 42 days. Growth performance were measured. The faecal samples were collected after 42 days for 16S rRNA gene sequencing (NGS). Blood serum samples were collected at day 0 and 42 and analysed by UHPLC/MS-MS in ionization mode to quantify serum metabolites. All data were analysed in R (v 4.1.2). Data about serum metabolites were analysed through the software MetaboAnalyst (version 5.0). The three diets did not evidence any effect (P>0.05) on growth performance, gut microbial composition, alpha or beta diversity. Few bacteria differed in their abundance. Despite several metabolites were influenced by the age, only two were significantly affected by the interaction diet × age. The FFP-C strongly increased (P<0.001) the serum concentration of theobromine and caffeine compared to the CTR and FFP-B. No significant correlations between blood metabolites and bacterial taxa were found. Performances, faecal microbiota, and the metabolic status of the pigs were slightly affected by the partial replacement of standard ingredients with FFPs-C or FFP-B. Those sustainable products can be safely used in post-weaning and growing pig diets. The effect of the FFPs-diets for a longer feeding trial on pig physiology and product quality needs to be further investigated.
