Die Bedeutung der Stickstoffverbindungen des Bodens und der Pflanzen für die Tierernährung sowie experimentelle Untersuchungen zur Wertbeurteilung des Nahrungsstickstoffs

[The exactness of nitrogen balance in long-term metabolic studies]

The N-retention calculated by balance experiments should, theoretically, be identical with the results obtained by chemical analysis of the animals. Experimental comparisons of both methods being reported in the literature are contradictory. To scrutinize this problem measurements of N-retention were conducted with 22 pigs by continuous balance experiments from 20-40 kg LW up to 110 kg LW (n = 16) or up to 160 kg LW (n = 6), respectively. At the end of the experimental period the animals were slaughtered and the N-content was determined quantitatively by chemical analysis of the whole bodies of the pigs. To calculate the N-content of the pigs at the beginning of the balance experiments 19 pigs were slaughtered and analysed quantitatively at 25 kg LW (n = 11) and 40 kg LW (n = 8), respectively. In all animals N deposits as determined by slaughter investigations were less as compared to balance experiments, the differences amounting to 6.7% of the calculated N-retention being equivalent to 93.3% analytical recovering of the N-retention as measured in balance experiments. The differences between both methods increased slightly with longer duration of the experiments resulting in 6.2% and 8.1% with the pigs of 110 kg and 160 kg final live weight, respectively. The differences must be regarded as being caused by accumulation of small errors completely coinciding into the same direction. Thus a certain overestimation of N-deposits by balance experiments might be looked at as being unavoidable irrespective considering any meticulous care in conducting the experiments.(ABSTRACT TRUNCATED AT 250 WORDS)