This work had as objective to evaluate the chemical composition alteration in the nitrogen and carbohydrate fractions, to estimate the digestion rate of fiber carbohydrates (FC) and non-fiber carbohydrates (NFC), to determine the in vitro dry matter digestibility (IVDMD) and to estimate the TDN of sorghum silage with different panicle proportions (0, 20 , 40, 60, 80 and 100%). The contents of dry matter (DM), crude protein (CP), ether extract (EE), ash, neutral detergent fiber (NDF), nitrogen fractions: NPN, B1+B2, B3 and C, non-fiber carbohydrate (NFC) and B2 and C fractions of total carbohydrates were determined. The digestion rates of the NFC and B2 fractions of total carbohydrates were estimated by in vitro gas production technique, the IVDMD was determined by two-stage technique and TDN, by chemical composition. The increase in the panicle in sorghum silage increased linearly the amounst of DM, CP, NFC, EE and lignin in NDF and reduced the ash and NDF amount. The NPN and the B1+B2, B3 and C fractions ranged from 9.19 to 21.24, from 67.63 to 75.98, from 3.85 to 6.09 and from 5.09 to 10.98% of total N. The NFC amount increased linearly and of the B2 fraction of total carbohydrates reduced by addition of panicle, ranging from 208.18 to 564.07 and from 381.29 to 0 g/kg of DM, respectively. The digestion rate of NFC and B2 fraction ranged from 0.1358 to 0.1563h-1 and from 0.0247 to 0.0294 h-1. The total gas production was not influenced by panicle addition and the maximum IVDMD of 69.52% was obtained with 60.10% of panicle. Althought the estimated TDN had increased linearly, considering the no alteration of gas production and the quadratical effect of IVDMD, it can be suggested that the utilization of these estimates are not correct.
digestion; kinetic; carbohydrate and protein fractions
