RESUMO
The study aimed at the effect of different regrowth ages on chemical, productive, and morphological characteristics, in addition to the kinetics of gas production and in vitro digestibility of grasses of the genus Brachiaria. The treatments consisted of two regrowth ages (21 and 35 days) and two grass species (Brachiaria brizantha and B. ruziziensis), in plat with a dimension of 10 × 10 with four replications, totaling 16 plats in a completely randomized design. The regrowth age did not change the leaf:stem ratio of the grasses. Ruziziensis-grass had higher crude protein (CP) content in leaves than Marandu-grass (14.0% versus 10.9% respectively). Marandu-grass leaf had higher NDF content than Ruziziensis-grass (65.0 and 58.3%, respectively) and ADF content (39.6 and 33.2%, respectively). The accumulation rate is high in Marandu-grass regardless of the age of regrowth; however, the in vitro digestibility of dry matter of Ruziziensis-grass is better both in the leaf and in the stem. The regrowth age did not influence the dry matter (DM) and neutral detergent fiber (NDF) in vitro digestibility (ivD) of the leaves. The ivDNDF of leaves of both types of grass were similar. There was an increase in the ivDDM of stem when the regrowth age was 21 days. The DM degradation rate was higher in Marandu-grass at both regrowth ages, and the total gas production was higher at 21 days. The parameters evaluated in the dual-pool logistic model showed interaction for age and cultivar, except for fractions λ (lag time) and total gas production. Marandu-grass presented a greater volume of gas for the rapidly degradable fraction and a lower degradation rate. There was a significant interaction for the parameters evaluated in the models between ages and grasses. The exponential model showed interaction in all fractions. Grasses had reduced CP content and increased fibrous fraction as a function of age, with no reduction in leaf DM and NDF digestibility. The Ruziziensis-grass has higher digestibility at the regrowth ages evaluated, while Marandu-grass has higher yields. We recommend adjusting the in vitro degradation kinetics by the dual-pool logistic model.