Age-dependent development in protein digestibility and intestinal morphology in weaned pigs fed different protein sources

•Digestibility coefficients of CP and amino acids may be overestimated in weaners.•CP digestibility at days 7 and 14 after weaning was much lower than in feed tables.•Digestibility of CP in casein increased from 0.50 to 0.97 at days 7–21 postweaning.•Time after weaning was more important for digestibility than protein source.•Low digestion capacity after weaning argues for feeding low-protein diets.