Studies on forage cell walls

Abstract

Food intake prediction relationships were developed from in vitro dry-matter digestibility determinations on food and resultant faecal material for a number of diets ranging from low quality roughage to high quality irrigated pastures.The relationship between true digestibility in vivo and in vitro food dry-matter digestibility was curvilinear, although true digestibility of food dry matter in vivo was highly correlated with apparent digestibility of food dry matter in vivo. The latter relationship was linear.For 122 sheep observations on voluntary dry-matter intake incorporating 11 diet types, introduction of either of the terms, cell-wall concentration in food: cell-wall concentration in the resultant faeces (CWFo/CWFe), or its converse, into conventional faecal index relationships did not increase precision of intake prediction using faecal nitrogen as an indicator substance. However, significant intake prediction relationships using food:faeces cell-wall ratios were generated.Values for in vitro digestibility of food and resultant faeces dry matter expressed as either a ratio (R) or as a difference (delta) yielded useful prediction relationships. For 'green' and for 'dry' classifications of the feedstuff's investigated some of these new relationships were either equal to or superior to the predictive efficiency of conventional faecal index relationships.Reasons are discussed for use of maximum potential in vitro digestibility values for food and faecal dry matter in such relationships in future work rather than a conventional 48 h fermentation.