The objective of this experiment was to evaluate the effects of levels 0, 100, 200, 300 and 400 kg of nitrogen/ha and cutting ages of 28, 42, 56 and 70 days on the kinetic parameters of ruminal degradation of carbohydrate of the following tropical forages: Setaria grass (Setaria anceps Stapf), Limpo grass (Hemarthria altissima [Poir] Stapf. & Hubbard), California grass (Brachiaria purpurascens [Raddi] Henr.) and Nilo grass (Acroceras macrum Stpaf). The results were submitted to a factor analysis. After reduction and evaluation of the combined variation from the total variables, three factors comprising 86.44% of the total variation were considered, where the first factor (Factor 1) was strongly associated with the gas volume of substrates of slow and rapid digestion, as well as the fractional rate of substrate of rapid degradation (Vf1, Vf2 and k2). The second factor (Factor 2) was associated to the fractional degradation rate of the slow degradable substrate and lag phase (k1 and L) and the third factor (Factor 3) was related to the in vitro dry matter digestibility (IVDMD). Cutting age had an effect on the grass kinetics, where the growth age resulted on reduced IVDMD. No significant responses of the supply of nitrogen fertilizer in relation to the parameters analyzed were found. Due to its high digestibility, the Limpo grass demonstrated to have an outstanding performance when compared to the other grasses.
California grass; degradation rate; gas production; Limpo grass; Nilo grass; Setaria grass
