The protein degradation of alfalfa hay after tannin supple-mentation was monitored during wethers digestion. Three rumen-cannulated wethers were infused a tannin solution, and water for control, through the cannula. The digestion time-points samples were collected in vivo in the rumen and in vitro in the abomasum, and the small intestine com-partments. The digestomic dataset was acquired by identi-fying and quantifying the peptides resulting from the pro-tein degradation, using high-resolution LC-MS/MS mass spec-trometry and label-free quantitation. The digestomic dataset is the compilation of proteomic data acquired in the rumen and peptidomic data acquired in the abomasum and in the small intestine. The proteomic analysis identified 20 Med-icago proteins in the rumen fluid, based on 169 peptides of which 140 are unique. The peptidomic analysis identified 28 Medicago proteins in the abomasum, based on 575 peptides of which 363 are unique, and 11 Medicago proteins in the small intestine, based on 94 peptides of which 63 are unique. This digestomic dataset of proteolysis during sheep post ru-men digestion after tannin supplementation reveals the pro-tein regions protected by tannin supplementation, and could be reused in studies related to the protein use efficiency by ruminants.