Seasonal variation in biochemical composition of cell walls, digestibility, morphology, growth and phenology in timothy

The dynamics of the evolution of the cell wall concentration and the changes in biochemical composition (lignin, carbohydrate and protein fractions) and digestibility of the cell walls of timothy (Phleum pratense L.) were studied during spring growth and summer growth in Sweden during 2 years. The influences of plant development, leaf proportion, dry matter (DM) production, time and environmental factors were investigated. It was found that both concentration and digestibility of the cell walls were strongly related to DM growth, much stronger than to plant development or leaf proportion. It was also found that indigestible fibre (IF) (the amount that was not digested during the IVDOM analysis) increased exponentially when neutral detergent fibre (NDF) concentration increased indicating that the cell wall concentration and thus the thickness of the cell wall was important for the IF concentration. Metabolisable energy (ME) is often calculated from the in vitro digestible organic matter (IVDOM), and the ash concentration. However, lVDOM and ash concentration are affected by different environmental factors and should be handled as separate parameters and not confounded with the ME concept. The lignin concentration was not a good criterion for optimal harvest quality, because the change in lignin over time did not follow a smooth curve, and the analytical errors were great compared with the total variation. At harvest time, the growth of stems and the change in stem properties was important, because leaf growth rates were very small of that time. (C) 2003 Elsevier B.V. All fights reserved.