CATION-EXCHANGE CAPACITY, CELL-WALL COMPOSITION AND FERMENTATION KINETICS IN FORAGES

Physical and chemical properties of feedstuffs, mainly due to differen ces in cell wall composition, contribute to rumen buffering and may be important factors in the rumen environment. In particular, the evalua tion of cell wall capacity in binding and holding metal ions on its su rface may also contribute to understand the relationships between diet ingredients and microbial fermentation. Therefore, relationships betw een cation exchange capacity (CEC), cell wall composition and in vitro fermentation kinetics were investigated in some forages widely used i n Northern Italy. Five samples of conserved forages (hays and silages) and 9 samples of fresh Lucerne forage (whole plant, leaves and stems) harvested at three different stages of maturity were studied. CEC of neutral detergent fibre was measured using the element praseodymium (P r III) at pH 7.0 for 24 h at 39-degrees-C. The digestibility of dry ma tter evaluated after 48 hours of incubation was negatively related to CEC of forages (r= -0.516; P = 0.059). Relationships between CEC of ND F and hemicellulose content or rate of digestion were not significant. Positive relation between lag time and CEC of cell wall was observed (r = 0.488; P = 0.077), this could be related to the lack of correlati on between CEC and the lignin content probably due to a different rumi nal behaviour of lignin and other polyphenolic compounds.