The effect of the introduction into mixed diets of grape marc (GM) or maize cobs (MC) in partial or total substitution for lucerne hay was evaluated in 2 experiments with heavy Bergamasca lambs. The diets were pelleted and contained 40% (DM basis) concentrate and 60% hay and/or by product: GM(0), GM(30) and GM(60) first experiment and MC(0), MC(30) and MC(60) in the second. For each diet, the voluntary intake and live weight gain were measured with 3 lambs, initially 2 months old, over a period of 50 d. Digestibility was measured by intake/excretion balance in 4 4-month-old lambs. The digestibility of the dry matter (DM), organic matter (OM), gross energy (GE), crude protein (CP) and NDF in diets GM(0), GM(30) and GM(60) decreased (P < 0.05) with the increasing percentage of grape marc. Generally smaller and non-significant differences were observed in the second experiment, but in diets MC(30) and MC(60) the digestibility of GE was lower (P < 0.05) than in MC(0). In both trials there was a modest non-significant negative digestive interaction between the hay and the by-product. The maximum DM intake was recorded in diets containing both luceme and the by-products: 147 g/LW(0.75) for the GM(30) diet and 139 g/LW(0.75) for the MC(30) diet. The GM(60) diet produced a lower daily gain than the GM(0), diet (-98 g/d), while GM(30) had an intermediate gain. In the MC diets the best result was obtained with the MC(30) diet (70 g/d higher than MC(0)).
