The objective of this work was to determine the fractions and rates of degradation of the carbohydrates for sugar cane, with different cycles of production (early and intermediate), in three cut times (426, 487 and 549 days). The total carbohydrates (TC), non-fibrous carbohydrates (NFC), fractions potentially digestible (B2) and indigestible (C) of the neutral detergent fiber (NDF), corrected for ashes and protein (NDFcp), were obtained. The kinetic parameters of NFC and fraction B2 were obtained from the technique of in vitro gas production. The contents of TC and fraction B2 did not differ among varieties, even though the early ones showed higher contents of the fraction C and smaller of NFC. By establishing a relationship between concentration of obtained lignin and observed C fraction, with adjustment of equation of simple linear regression, without intercept, it was obtained the value of 4.38, that differed of 2.4, suggested by the Cornell system. Therefore, for sugar cane, the fraction C could be estimated from the lignin multiplied by 4.38. The progress of the cut time caused linear increase of the C fraction and reduction of B2, without interaction with the cycle of production; although it has been linear, the increment was relatively small, 6% of the fraction C, when compared to the other tropical gramineas, with the same cut time. The kinetic parameters did not show differences among varieties; however, the estimated average digestion rates for NFC were lower than the suggested by the Cornell system. The adjustment of the curve of cumulative gas production (bicompartimental system) was shown appropriate because the sugar cane has fractions of available carbohydrate very different with relationship to the degradation rate (CNF and B2). By presenting high content of NFC (sucrose) and low rate of degradation of the B2 fraction, researches with different sources of N to supplement sugar cane based diets are necessary.
in vitro gas production; degradation rate; carbohydrate fractions
