Digestive effects of diet supplementation with an exogenous fi brolytic enzyme preparation (cellulase and xylanase activities) were evaluated under in vivo and in vitro conditions. Eight lactating Murciano-Granadina dairy goats (four per treatment) were used to measure the total tract digestibility of an ad libitum total mixed ration (forage, 65%; concentrate, 35%) to which the enzyme was, or was not, added to the concentrate. In vitro degradability and gas production were also studied using 2 goats (1 per dietary treatment) as ruminal liquor donors. Dry matter digestibility increased by effect of the enzyme supplemented goats, while digestibilities of organic matter, protein and fi bre fractions did not vary. Differently, in vitro trial showed no differences either in dry matter or fi bre degradabilities or in gas production. In conclusion, supplementing dairy goat concentrate with a fi brolytic enzyme preparation, under our conditions, enhanced in vivo dry and organic matter digestibilities although the effects were not observed in vitro.