The objectives of the present study were to characterize and determine the parameters estimative of kinetics of carbohydrate degradation of alfalfa hay, elephant grass, tifton 85 hay, and corn silage, in different ratios of roughage:concetrate, using both in situ and in vitro technique. Five non pregnant non lactating goats, rumen cannulated, and averaging 58 kg were used during the experimental periods. A modified McDougall buffer was used for the in vitro assay to adjust pH to the values observed in the animals, by adding 1M of citric acid solution according to the roughage:concentrate studied. A 5×5 Latin square was used to evaluate five treatments consisted of roughage to concentrate ratio of 100:0, 80:20, 60:40, 40:60 e 20:80. It is suggested a significant influence of level of concentrate on ruminal digestibility of forages for all fractions studied. Associative effects of roughage and concentrate resulted on increment of degradation in the pH range of 6.2 to 6.8. Conversely a decrease on degradability was observed as pH reached values bellow 6.0. Lag time decreased as pH changed from 7.05 to 6.8 and maintained stable until 6.5, and a significant increase on lag values was observed thereafter, being noticed higher values at pH bellow 6.0 for all forages. Both in situ and in vitro incubation resulted in degradation curves of dry matter that were similar in shape for all feed studied as well as for rates of degradation. Thus it was suggested that both methods can be considered reliable to predict the observed parameters.