Influence of drying method and ageing on chemical and physical properties and in vitro degradation characteristics of grass and maize samples

The influence of different drying conditions on the chemical composition, physical properties, in vitro organic matter degradability and fermentation kinetics of forages was investigated using young and old grass (Lolium perenne) samples (harvested on 15 June and 9 July 1992 at Lelystad, The Netherlands) and young and old maize (Zea mays cv. Scana) stem samples (harvested on 19 August and 30 September 1991 at Lelystad). The samples were either freeze-dried with a maximum sample temperature of 10 degrees C, dried in a vacuum at 20 degrees C or air-dried at 30, 50, 70 and 105 degrees C. The different drying methods had little effect on ash, acid detergent fibre (ADF), acid detergent lignin (ADL), crude fibre and crude protein (CP) contents and in vitro degradation of the forage samples. However, some effects were found for sugars and phenolic acids. The neutral detergent fibre (NDF) content in protein-rich samples and the fermentation kinetics in rumen fluid differed significantly according to drying method. In samples dried other than by freeze-drying, proteins were bound to the NDF content and in some cases an effect on the amount of soluble sugars was also seen. Physical properties of the samples were determined by differential scanning calorimetry (DSC) and differences were found between freeze-dried materials and those dried at 70 degrees C. The influence of age on the maize samples was very pronounced, whereas it had little effect on the characteristics of the grass samples, with the exception of a decreased CP content and an increased sugar content after acid hydrolysis.