Post-weaning diarrhea causes economical loss and leads to an increased need and use of antibiotics. In a world where antibiotic resistance is becoming an increasing pressing problem, restriction of their use of is imperative. Therefore, a more clear understanding of what causes diarrhea in weanlings is essential. A possible contributing factor to the development of post-weaning diarrhea is the incomplete digestion of proteins during weaning. As a result of incomplete digestion, protein ends up in the colon, where it is fermented by resident bacteria. Protein fermentation end-products, such as branched chain fatty acids and phenols negatively impact gut barrier function. Disruption of the intestinal barrier function results in development of diarrhea. Intestinal barrier function is maintained by healthy enterocytes. Optimal mitochondrial function is necessary for cell survival. We hypothesize that protein fermentation derived end-products negatively affect mitochondrial function in enterocytes. To test our hypothesis, we will first test the effects of known and newly discovered protein fermentation derived end-products on intestinal epithelial cell lines. Using the Seahorse Extracellular Flux Analyzer, we can assess the impact of the compounds on mitochondrial function of enterocyte-like cell-lines. Additionally, we will perform animal experiments in both mice and piglets to test the effect of high and low digestible diets on protein fermentation, intestinal barrier and mitochondrial function. In the end, we aim to improve piglet health by gaining a deeper understanding of the challenges young piglets face during weaning. This will aid the improvement of feed composition, to better help piglets cope with their changing environment.