The metabolites of proteolytic fermentation can lead to metabolic disorders and subsequent damage to the gut microstructure. Broilers are particularly susceptible to these negative effects as modern broilers have great potential to convert feed into live weigh but their health in terms of metabolic disorders and altered immune functions is compromised in the process. The damage caused by these disorders cannot be repaired because of the short growth period. The focus of this project will be on indigestible protein and broiler performance, covering the different techniques to measure indigestible protein and the effect of dietary factors including the source and level of protein, feed processing, anti-nutritional factors, enzymes and other additives as well as the interactions between these factors.