Studies on cattle with oesophageal fistulae. The relation of the chemical composition of feed to that of the extruded bolus

Abstract

Twelve feeds were given to oesophageally-fistulated cattle, and the chemical composition of each was compared with that of bolus material extruded while eating them. The nitrogen contents of the feeds ranged from 0.55 to 3.19 per cent on a dry matter basis. Feeds and complete boluses were dried and analysed for nitrogen, phosphorus, ash and neutral-detergent-soluble material (NDSM). Both nitrogen and NDSM in ingested feed could be reliably estimated by analysis of extruded bolus material ; the relation between feed and bolus nitrogen was slightly more precise when expressed on an organic matter basis, whereas that for material soluble in neutral detergent was closer on a dry matter basis. The phosphorus and ash contents of feeds were substantially and variably elevated by saliva and could not be estimated from analysis of the bolus. The nitrogen content of saliva secreted during rest was found to be significantly affected by dietary nitrogen concentration, but that of saliva secreted during chewing was not ; it is suggested that this explains the relative absence of an effect of salivary contamination on bolus nitrogen.