Effects of proanthocyanidins on digestion of fiber in forages

The ability of proanthocyanidins (PA) to form insoluble complexes with prot eins and polysaccharides affects fiber digestion and analysis. This review discusses these effects in relationship to the application of the detergent system of forage analysis. A fraction of the PA in plants remains after ex traction for analysis. Insoluble FA may be a natural Dart of the plant cell wall or may be insoluble because of high molecular weight and post harvest reactions. These reactions increase the amount of insoluble PA and decreas e the amount of soluble PA. The butanol-HCl assay is the most suitable meth od for analysis of insoluble PA. Insoluble PA are associated with negative apparent digestion coefficients for acid-detergent lignin (ADL), neutral-de tergent insoluble N and acid-detergent insoluble N, The addition of sodium sulfite to neutral detergent eliminates insoluble PA from NDF. However, the addition of sodium sulfite to neutral detergent will give misleading resul ts in relationship to true digestibility of protein, The difference between fiber fractions that are prepared with and without the addition of sodium sulfite to neutral-detergent may estimate the amount of PA/protein complex associated with NDF. A better understanding of the relationship between PA structure and function is necessary to manipulate PA in forages through bre eding or genetic engineering. The interaction between PA and fiber analysis and digestion is an important component of this research.