The objective of this study was to evaluate the morphogenetic traits and chemical composition of Tanzania grass using a fixed resting period (FR) or according to 95% light interception (LI, by accuparLP-80) for managing Tanzania-grass pastures. As the LI of the herbage mass reached 95%, the animals were allowed to graze each paddock for 3 d; and (2) 30 d defoliation interval with a 3 d grazing period (FR). Experimental unit consisted of 11 paddocks grazed by 5 Holstein-Gir cows allowing for 2 replicates per defoliation treament in the first year with the same areas assigned to the same treatment the following year grazed by 4 Holstein-Gir cows per experimental unit. Six samples per paddock were taken on 2 crossed transect lines. Sward height, forage mass, and morphological components and their chemical composition were evaluated. The fixed effects were treatments (LI or FR), year (one or 2), and the interaction, whereas the random effect was area within treatment and the model was fitted as a mixed model with yearly repeated measures (using SAS). The interaction was significant only for senescent material (P = 0.026). The treatments did not affect pasture mass, height, and the proportion of stems in the pre- (P = 0.455, 0.715, 0.457, respectively) and post-grazing (P = 0.199, 0.160, 0.457, respectively) conditions. However, the proportion of leaves and crude protein content of the herbage mass were greater in LI than FR paddocks (P = 0.031, and 0.018, respectively). The concentration of other nutrients were not affected by treatments (P > 0.05). Therefore, LI might affect at least some quality traits of the paddock.