Piglet weaning is accompanied by gastrointestinal tract (GIT) dysfunction, resulting in post-weaning diarrhea (PWD). The treatment involves antibiotics due to the susceptibility of the weaned GIT to pathogens. However, antibiotic resistance has shifted attitudes toward a nutraceutical approach by enriching feed with functional compounds. Polyphenols are touted for their antimicrobial activity and ability to improve GIT function. Thus, we investigated the protective effects of crude blueberry phenolic extracts (BPE) in vitro using porcine cells challenged with lipopolysaccharide (LPS) as a weaning model. Cells were pretreated with 1 µg/mL and 2.5 µg/mL BPE for 24 h, followed by 10 µg/mL LPS stimulation for 6 h. Antioxidant status, paracellular permeability, the gene expression of proinflammatory cytokines, and tight junction proteins were measured. The antimicrobial activity of the extract was evaluated against porcine pathogens. The pretreatment of cells with 1 µg/mL BPE preserved catalase (CAT) activity. Reduced paracellular permeability was observed in a dose-dependent manner. The BPE preserved the relative mRNA abundance of tight junctions and reduced inflammatory cytokine expression. Pretreatment with the BPE was able to preserve occludin (OCLN) protein levels. The minimum inhibitory concentration of the BPE against Enterotoxigenic E. coli (ETEC) and Salmonella typhimurium (ST) was 62.50 µg/mL. These findings indicate that blueberry polyphenols hold potential as feed additives in swine weaning.