Losses of N and C in Drying Feces of Cattle

Abstract

In respiration trials for the determination of the N and C balances errors may result from losses of N and C during the drying of feces for analysis.

The N losses can be avoided by determining the N in fresh instead of dry samples of the excreta. The N determination in fresh samples involves more work than the determination in a composite sample of the dried feces. This extra work is, however, justified since the N losses during drying are considerable.

In order to measure the N losses by drying, aliquot samples of the feces, that were removed daily from the respiration chamber, were immediately mixed with concentrated H₂SO₄ in Kjeldahl flasks. The digestion was either made at once or the flask was closed until the next day's sample was added to it. Aliquot parts from the same feces that had been analyzed fresh were dried at 100° C. The N determination was then carried out with a part of the composite dry sample. The official Kjeldahl-Gunning-Arnold method 1 was used for the N determinations.

The difference in the N content of the total feces of a 10-days'respiration trial calculated from the analyses of the fresh samples and the N content calculated from the analysis of the composite dried sample was considered the N loss by drying and expressed in per cent of the N content as determined in the fresh samples. For 12 respiration trials with beef heifers this N loss amounted to 7.19 ± 0.49%. In a sample taken immediately after defecation only 4.48% of the N was lost by drying.