Bioactive additive for modulation of immune responses and gut microbiota in weanling pigs: In vitro and in vivo study

The post-weaning period in pigs is marked by intestinal disturbances and behavioral stress. This study evaluated a microencapsulated bioactive additive composed of essential oils (thymol and carvacrol) and organic acids (citric, fumaric, malic, and phosphoric acids) as an alternative to antimicrobial growth promoters. Two experiments were conducted using five treatments: a negative control (NC, basal diet), a positive control (PC, basal diet with 120 mg/kg chlorohydroxyquinoline), and the basal diet supplemented with the additive at 200 (NC200), 400 (NC400), or 800 (NC800) mg/kg. In vitro, treatments were evaluated using a simulated digestion model assessing microbial responses to Escherichia coli, Salmonella spp., and Lactobacillus spp.. In vivo, 120 piglets (21 ± 3 days old; 5.34 ± 0.74 kg) were randomly assigned to treatments and monitored for growth performance, intestinal health, and behavior. A quadratic response was observed for Lactobacillus spp. in the intestinal phase in vitro (p = 0.013). In vivo, the additive did not affect growth performance but reduced diarrhea incidence at NC200 and NC800 (p < 0.05). Fecal lactic acid bacteria increased linearly with additive inclusion (p = 0.031), while serum IL-6 tended to decrease at higher doses (p = 0.057). Overall, the additive effectively reduced diarrhea and inflammatory responses without affecting growth, promoting a favorable microbial balance at 200 and 800 mg/kg. These results highlight the bioactive additive as a promising, sustainable alternative to AGP in pig production.