Nitrogen endogenous urinary

The endogenous urinary nitrogen results from irreversible reactions involved in the breakdown and replacement of various protein secretions and structures within the body. Thus, both the faecal and urinary endogenous fractions represent nitrogen that has been absorbed and utilised by the animal rather than nitrogen that cannot be so utilised. Their exclusion from the faecal and urinary values in the above formula gives a measure of the true biological value. 

Protein requirements for maintenance are estimated from endogenous urinary nitrogen and metabolic faecal nitrogen excretion. There are also small losses of nitrogen in hair and scurf. In ruminants the protein requirement for maintenance can generally be met by microbial protein synthesis. 

Biological value is stated as the proportion of the nitrogen intake that is actually retained and takes account of endogenous urinary and faecal nitrogen, whereas chemical score and the essential amino acid index are based on the proportion of the main limiting amino acid of the protein in relation to that in a standard protein. 

The net requirement for nitrogen for maintenance is that required to replace the endogenous urinary loss (EUN) plus part of the metabolic faecal nitrogen loss (MFN) plus loss of nitrogen in hair and scurf (D).The total is termed the basal endogenous nitrogen (BEN) and is of the order of 0.35 g/kg W° /day, which translates to a metabolisable protein demand of 2.19 g/kg Metabolisable protein is assmned... 

This is a direct measure of the proportion of the food protein that can be utilised by the animal for synthesising body tissues and compounds, and may be defined as the proportion of the absorbed nitrogen that is retained by the body. A balance trial is conducted in which nitrogen intake and urinary and faecal excretions of nitrogen are measured, along with the endogenous fractions in these two materials. The biological value is then calculated as follows ... 

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