Thirty-two non castrated Ile de France lambs fed corn silage or sugar-cane based diets with two roughage:concentrate ratios (60:40 or 40:60) were used. The animals were kept individually confined with control of the supplied food and leftovers, weekly weighted for determination of the daily weight gain and food conversion. Simultaneously, it was carried out digestibility and metabolism trials to determine the nutrient intake and digestibility and nitrogen balance of the experiment diets. The weight gain (294.6 g/day) was higher for the lambs fed corn silage, and regarding to roughage:concentrate 40:60 it was 314.3 g/day. The ratio roughage:concentrate only influenced the consume of digestible fiber in neutral detergent (NDF) and fiber in acid detergent (FAD) in which the highest values, 125.26 and 48.97 g/day obtained with the ratio roughage:concentrate 60:40. The lambs fed corn silage showed a higher intake of all digestible nutrients, except for crude protein (162.00 g/day) and non fibrous carbohydrates (471.42 g/day). The highest digestibility of organic matter (80.34%) and total carbohydrates (80.71%) were obtained with the 40:60 ratio and those of dry matter (78.91%), crude protein (81.30%) and gross energy (78.77%) were obtained for the lambs fed sugar cane. The highest values for ingested, absorbed and retained nitrogen, 32.6, 20.5 and 13.7 g/day, respectively, were observed in diets with 40% of roughage. The type of roughage influences more the nutrient digestibility than its proportion in the diet.
