Realizou-se um confinamento na ESALQ/USP, durante 56 dias, de 60 animais mestiços, machos, castrados, com idade media de 30 meses e peso vivo inicial de 345 kg. Os tratamentos constituiram-se, em % da MS total, de: T1) 0:50, T 2)10:40, T3) 20:30, T4) 30:20 e T5) 40:10, para bagaço auto-hidrolisado (BAH) e cana, respectivamente, sendo que o concentrado participou com 50% em todas as dietas. O delineamento estatístico foi o de blocos casualisados. A composição bromatológica estimada dos 5 tratamentos indicou que as dietas completas foram iguais. Pela regressão quadrática estimou-se que o maior consumo de MS foi ao nível de 34% de bah; o maior ganho de peso ao nível de 21% de bah; e a melhor conversão alimentar, próxima de 15% de bah na dieta. Concluiu-se que, em dietas com alto teor de concentrado, o bah pode participar em 10 a 20% e a cana, em 40 a 30% da MS total da dieta, para se obter os melhores desempenhos animais. Observou-se ainda que pode ter havido algum efeito mutuo de complementação ate o nível de 20% de bah e de inibição acima deste nível sobre a atividade ruminal que deveria ser pesquisado em experimentos futuros

In order-to verify the effect of increasing leveIs of steam-pressure treated sugar cane bagasse (SPTB) in diets, in substitution to chopped sugar cane, on the performance of cattle in confinement, an experimental feedlot at Escola Superior de Agricultulra "Luiz de Queiroz", USP-Piracicaba-SP, was conducted, during 56 days, with 60 crossbreed steers, aged about 30 months and initial weight of 345 kg. The treatments, in % of total dry matter (DM), were: Ti) 0:50, T2) 10:40, T3) 20:30, T4) 30:20 and T5) 40:10, with increasing levels of SPTB and decreasing levels of sugar cane, respectively, and the concentrate participating with 50% in all diets. The estimated bromatological composition of the 5 treatments indicated that the complete diets were equal. The levels of daily DM intake (kg) were ( P < (0,05): T1)9,55b; T2) 10,87ab; T3) 11,81a; T4) 12,14a and T5) 12,16a. The daily weight gains (kg) were (P < 0,05): T1) 0,84b; T2) 1,13a; T3) 1,12a; T4) 1,07a and T5) 0,96ab. The feed conversion (kg DM/kg DWG) was (P < 0,05): T1) 11,29ab; T2) 9,59c; T3) 10,47bc; T4) 11,31ab and T5) 12,57a. Quadratic equations with the respective curves in parable form for alI the parameters analysed were obtained by polinomial regression. The Xmáx estimated that the greatest DM intake was at the level of 34% of SPTB; the greatest weight gain, at the level of 21% of SPTB; and the best feed conversion, at about 15% of SPTB in the total DM of the diet. It was concluded that, in diets with 50% of concentrate, the SPTB can be used with 10 to 20% and the sugar cane with 40 to 30% of the diet's total DM, in order to obtain the best animal performance. It was also observed that, in the proportions of sugar cane and SPTB used, some mutual effect of complementation till the level of 20% of SPTB and of inhibition above this level may have occurred on the ruminal activity, which should be examined in future researches