Abstract: Four Holstein cows fitted with rumen cannulas were used for measuring degradability of dry matter and starch in potato residues samples，sweat potato residues samples and their silage samples by nylon bag technique.The results showed that the effective degradability and 72 h disappearance rate of dry matter and starch in rumen about potato residues and sweat potato residues were reduced significantly after ensiling （P＜0.01）.The disappearance rate of dry matter and starch in rumen about potato residues were reduced from 95.72% and 99.60% to 53.43% and 86.51% after ensiling.The disappearance rate of dry matter and starch in rumen about sweet potato residues were reduced from 97.65% and 99.81% to 66.72% and 84.69% after ensiling.The effective degradability of dry matter and starch about potato residues silage were reduced 47.34% and 35.98%, respectively, and sweat potato residues silage were reduced 51.48% and 57.39%, respectively. The effective degradability of dry matter about potato residues silage and sweat potato residues silage had no significant difference （P＞0.05），but the effective degradability of starch about potato residue silage was significantly higher than that about sweat potato residue silage （P＜0.05）.The amount of rumen bypass starch in potato residues silage and sweet potato residues silage were increased 57.43%（42.94 g/kg） and 151.37% （122.52 g/kg），respectively.The amount of rumen bypass starch in potato residues silage was extremely significantly lower than that in sweet potato residues silage （P＜0.01）. Therefore，the effective degradability of dry matter and starch about the tow kinds of potato residues were reduced effectively and the amount of rumen bypass starch were increased by ensiling.The amount of rumen bypass starch in sweat potato residues were obviously higher than that in potato residues.

Key words: potato residues; sweet potato residues; nylon bag technique; dry matter; starch; rumen degradability; rumen bypass starch