Former foodstuff products (FFPs) are promising alternative feed ingredients that help prevent food waste and reduce the environmental impact of food production. However, concerns exist regarding their potential effects on animal behavior and welfare, particularly due to the presence of caffeine, theobromine, and ultra-processed sugars in confectionery-based FFPs. This study evaluates the behavioral responses of thirty-six Swiss Large White male castrated pigs fed diets incorporating salty and sugary FFPs during the growing (G) and finishing (F) phases. Pigs were assigned to one of three dietary treatments: (1) a standard diet (ST-G, ST-F) with 0% FFPs, (2) a diet where 30% of conventional ingredients were replaced by sugary FFPs (SU-G, SU-F), and (3) a diet where 30% of conventional ingredients were replaced by salty FFPs (SA-G, SA-F). Behavioral traits—including social interactions, exploratory behavior and aggression—were assessed using continuous video recordings at eight time points throughout the trial. Additionally, skin and tail lesions were monitored to evaluate potential welfare implications. Key behavioral ratios were analyzed using linear mixed-effects models with treatment, time, and their interaction as fixed effects, and Pig ID as a random factor. Collinear and rare variables were excluded. Log transformation was applied where needed. Lesion scores were analyzed using one-way ANOVA, with repeated measures for timebased data. Significance was set at p < 0.05. Analyses were performed in R (v4.2.1). Pigs receiving the sugary and salty feed diets reduced (P=0.045) lying in contact over time in comparison to pigs that received the standard feed. Pigs receiving the SA feed had a higher (P=0.002) eating ratio (i.e., were observed eating more often) compared to the other two groups. No significant differences (P > 0.05) between the experimental groups and the standard diet group in terms of abnormal behaviors or skin lesions were found. These findings indicate that replacing up to 30% of conventional feed ingredients with either salty or sugary FFPs does not negatively affect pig behavior, health, or welfare. This supports the feasibility of integrating FFPs into pig diets as a sustainable feeding strategy, contributing to circular agriculture while maintaining animal well-being. Further research should explore long-term effects on growth performance, metabolic adaptations, and meat quality to optimize the use of FFPs in livestock nutrition
