Protein efficiency (PE) improvement is essential to develop sustainable pig production. The inefficient use of dietary protein by the animal results in excess excretion of unused protein that contributes to ammonia pollution. This study hypothesized that PE depends on a range of physiological processes such as intestinal amino acid uptake or the intestinal epithelial integrity in the pig. Thirty one Swiss Large White pigs (13 females and 18 castrated males) were reared until an average body weight (BW) of 22.5 kg (±1.6 kg) and subsequently allocated to a pen where they remained until slaughter (BW 106±5 kg). Pigs had ad libitum access to a protein-reduced grower and finisher diet and water. For the ex vivo evaluation, jejunum segments from the third meter distal to the pylorus were removed within 15 min after exsanguination. Tissues were stripped of outer muscle layers and mounted in Ussing chambers. Transepithelial difference (TEER) and short-circuit current (Isc) were continuously monitored. To evaluate L-Glutamate (L-Glut), L-Arginine (L-Arg) and D-Glucose (D-Gluc) uptake, tissues were equilibrated for 20 min before the mucosal addition of 5 mM L-Glut, followed by the addition of L-Arg, L-Meth and D-Gluc at the same concentration every 15 min. Simple linear models were run in R V 4.1.2 using lm() to investigate the influence of Isc, TEER, D-Glut, L-Arg and D-Gluc with PE, respectively. Sex did not influence any of the measured parameters. The TEER showed a negative relationship (P=0.009, R2=0.21) with PE, while no relationships were found between PE and amino acids uptake. A significant positive relationship between PE and D-Gluc uptake was also found (P=0.048, R2=0.14). The TEER strongly depends on the tight junction protein (TJs) expression. Further analysis are planned to investigate the intestinal TJs protein expression. Similarly, the protein expression of D-Gluc transporters will be the subject of future studies to clarify the correlation between PE and D-Gluc active transport.