[Problem of nitrogen metabolism in monogastric animals]

A new method has been developed for determining the proportion of endogenic and exogenic faecal N by measuring the degree of specific labelling in the feeding-stuff (administered orally) and in the excreta (faeces and urine). The method has also been developed to find out whether the endogenic excretion of intestinal N is actually independent of the N intake. The present technique had been worked out on the basis of the model that had been originally established by Czarnetzki et al. in 1969 with the aim of characterizing processes of nitrogen metabolism in monogastric animals. As a result, a multi-compartment model was developed and a number of conclusions were derived from it. These conclusions were tested in 3 series of experiments on rats fed 15N labelled spring barley and 15N labelled feed yeast. Additionally, 15N labelled experimental rats were used receiving unlabelled extracted soya bean meal. The proportion of endogenic intestinal nitrogen (DVN) varied between 15-22% relative to the proportion of N ingested. The relative proportion of endogenic faecal N in the tota faecal N was found to be 100% in the case of the nitrogen-free diet. With increasing levels of dietary N this proportion lended to decrease down to a final value that was quite characteristic for each partitular feeding-stuff. The absolute amount of endogenic faecal N, however, was found to increase with increasing N levels. This shows that contrary to current views, DVN is not constant and is not independent of protein intake. Rather, a close relationship was found to exist between the level of N intake and DVN excretion (r = 0.951...0.972). So, the proportion of exogenic N contained in the faeces is much smaller than was previously assumed on the basis of the classical and regressive methods. These were based on the assumption that DVN is constant. Consequently, higher digestibility values will be obtained in comparison with those calculated on the basis of the previous methods. Digestibility data for spring barley increased from 83.9 to 95.6, i.e. by 11 digestibility units; for feed yeast there was an increase by 6.2 units, from 83.3 to 90.0; and for extracted soya bean meal an increase of 6.2 units was observed (from 90.7 to 96.9).