Cation exchange capacity, cell wall composition and fermentation kinetics in forages

Abstract

Physical and chemical properties of feedstuffs, mainly due to differences in cell wall composition, contribute to rumen buffering and may be important factors in the rumen environment. In particular, the evaluation of cell wall capacity in binding and holding metal ions on its surface may also contribute to understand the relationships between diet ingredients and microbial fermentation. Therefore, relationships between cation exchange capacity (CEC), cell wall composition and in vitro fermentation kinetics were investigated in some forages widely used in 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 (Pr III) at pH 7.0 for 24 h at 39°C. The digestibility of dry matter evaluated after 48 hours of incubation was negatively related to CEC of forages ( r=−0.516; P=0.059). Relationships between CEC of NDF 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 correlation between CEC and the lignin content probably due to a different ruminal behaviour of lignin and other polyphenolic compounds.