This research was carried out in the Agricultural Biotechnology Institute laboratories and in the Tesorito farm from Universidad de Caldas. Nine raise cattle about 200 Kg were used in this experiment, divided into three groups which were fed with Kikuyu grass (Pennisetum clandestinum) in addition to 0, 15 and 30% commercial concentrate food using an experimental design of randomized complete blocks. The independent variable was the level of supplementation, the blocking variable was the date of initiation of each replication, and the experimental unit was a group of three animals. Methane (CH4) and volatile fatty acids (VFA) were taken through direct ruminal puncture in 7 ml vacutainer® tubes in duplicate. These samples were analyzed through gas chromatography techniques with flame ionization detection GC/FID and gaseous chromatography coupled with mass spectrometry GC/MS. With the chromatographic conditions determined in the laboratory, different retention times of volatile compounds were observed: CH4 (1.865 min) propionic acid (3.141 min) acetic acid (2.281 min) and butyric acid (4.387). In this experiment differences (NS) between the three treatments were not observed. Differences (NS) for weight gain between treatments were not found.