Degradation profiles for NDF were estimated for grass/grass-clover, cereal whole crop and maize whole crop. To examine variation in rate of degradation, degradation profiles were analysed for rate of degradation in individual incubation intervals. For grass/grass clover and maize whole crop, rate of degradation first increased and then decreased with increasing incubation time, especially for grass/grass-clover, indicating both a lag time before maximum degradation is reached, and multiple NDF pools with different degradation rates. In contrast, whole crop cereals had a very high degradation rate in the first incubation interval, and thereafter degradation rate decreased, indicating that a small fraction of the NDF is very easily degradable. The non constant rate of NDF degradation means that estimated degradation parameters will be very dependent on the degradation times used for parameterization and therefore standardization of the method is essential.