Measurements of in-vitro protein digestion of plant-based feeds and by-products using the pig-adapted Infogest model  Saliu E.-M..1, Schulze Holthausen J.1, Zentek J.1, Martinez-Vallespin B.1, Vahjen W.1, Aschenbach J.R.2; Fulde M. 3, Ghazisaeedi F. 3; Rothkötter H-J.4;  Grześkowiak L.1  1Institute of Animal Nutrition, Department of Veterinary Medicine, Freie Universität Berlin, Berlin, Germany; 2Freie Universität Berlin, Institute of Veterinary Physiology, Oertzenweg 19b, 14163 Berlin, Germany; 3 Institute of Microbiology and Epizootics, School of Veterinary Medicine at the Freie Universität Berlin, Robert-von-Ostertag-Str. 7, 14163 Berlin; 4Institute of Anatomy, Otto-von-Guericke University Magdeburg, Magdeburg, Germany E-mail: Johannes.Holthausen@fu-berlin.de  Inefficient use of dietary protein must be avoided to use resources sustainable. Hence, raw materials which can be consumed by humans should not be used as feed. Low protein digestibility leads to increased costs and contributes to environmental pollution through excessive nitrogen excretion [1]. Our experiment aimed to identify alternative protein sources with the highest digestive potential for sustainable pig nutrition.  Methods: Ten different plant-based by-products and feedstuff were evaluated in an in vitro pig digestion model following the Infogest protocol [2]. The simulated digestive process. was divided into three phases: oral, gastric, and small intestinal. The protein concentration in the liquid phase were measured using the Bradford method [3] after the gastric phase and at multiple time points during the intestinal phase. Results: There were differences in the amount and kinetics of protein release from the feed samples in the intestinal phase. Thus, digestibility differed between the feedstuffs (p<0.001). Low digestibility was found for rapeseed meal, soybean meal and tofu (44-62%). High digestibility was observed for alfalfa, peas, quinoa and brewer's spent grains (97-139%). Products such as alfalfa silage and quinoa showed a sinusoid-like kinetic of the protein concentration in the liquid phase. While the kinetics of lentil and pea samples was constantly decreasing, soybean meal, quinoa and tofu showed a decrease in protein concentration after an initial increase. Conclusion: Variations in both total protein digestibility and protein concentration kinetic in the liquid phase were observed for different feedstuff in the in-vitro method.