Gastrointestinal disorders and dysbiosis are frequent in veterinary practice. The maintenance of a stable intestinal microbiota is fundamental, requiring effective interventions to restore homeostasis. The product evaluated is a complementary feed formulated with a synergistic combination of a Multi-strain Probiotic System (Saccharomyces cerevisiae var. boulardii (DSM 34246), Lactobacillus acidophilus (D2/CSL), and Enterococcus faecium (DSM10663)), Vexantra® (Malus domestica and zinc), and a Prebiotic Matrix (fructooligosaccharides (FOS) and mannanoligosaccharides (MOS)). While S. boulardii is naturally antibiotic-resistant and reinforces the intestinal barrier, L. acidophilus contributes to microbial balance through organic acid production. Additionally, Vexantra® and prebiotics support mucosal integrity and beneficial bacterial growth. The clinical efficacy of oral probiotics depends on the "viability-activity" axis, requiring survival through the harsh gastric environment. This study aimed to evaluate the gastrointestinal resistance of this formulation using a standardized in vitro model simulating fed-state conditions (gastric phase at pH 4.8; intestinal phase at pH 7.5). The results demonstrated that the product matrix not only protected the microorganisms during simulated digestion but also promoted a significant numerical increase in their microbial load. All analyzed probiotic strains remained viable and showed higher counts in the digested product compared to the undigested one. These findings suggest that the formulation provides a protective environment that ensures the delivery of a functional microbial load to the intestine.
