The in situ digestibility of dry matter (ISDDM) was assessed in three Holstein cows (560 ± 23 kg) with ruminal cannula. The proximal and Van Soest variables were analyzed with a complete randomized design, and for the variable ISDDM, a randomized block design was used. Significant differences for ISDDM (P≤0.05) between the Brachiaria varieties were found, with the highest percentages for the cv. B. decumbens Stapf and B. brizantha Marandú (63.9 and 63.2%, respectively). The diet with 10% C. cajan had average percentages of CP, NDF and ADF of 8.7, 70.7 and 47.6%, respectively, for all the Brachiaria varieties used in the study. It was found that diets with B. decumbens and B. Mulato II plus 10% of C. cajan were the best in terms of CP, NDF, ADF and ISDDM (9.3, 70.5, 46.4 and 64.1% and 8.6, 69.9, 50.3 and 63.5%, respectively). The results of this research showed that the value of CP meets the minimum requirements of nitrogen in the ration and that the ISDDM, DM, CF, NDF, ADF and ADL values are within the ranges reported for the genus Brachiaria.

The purpose of the present study was to compare two types of "in vitro" digestibility assays by using commercial enzymes and guinea pig cecalliquor with the in vivo assay, to identify the assay that most resembles the in vivo response. The alfalfa was used in two cutting times of 30 and 45 days. The "in vivo" digestibility of alfalfa was analyzed, obtaining that after 30 days of cutting the digestibility was 53.64% and at 45 days it was 47.72%, while for the digestibility "in vitro", the DaisyII®-Ankom Technology with cecal liquor and commercial pepsin; for the cecal liquor a value of 55.46% and 49.90% was obtained, for the alfalfa in the two cutting times, while the digestibility with enzymes was 71.01% and 66.34% respectively. It was determined that the method with more relation to the in vivo test corresponds to the trial with cecal liquor, because it presents a lower statistical difference (p <0.05) for both cut-off times. At the same time, it is identified that the protein is the nutrient that has a higher digestibility coefficient, becoming an indicator of the nutritional quality of the food.