Nitrogen metabolic faecal

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. 

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... 

Figure 9.1 shows an overview of protein metabolism in addition to the dietary intake of about 80 g of protein, almost the same amount of endogenous protein is secreted into the intestinal lumen. There is a small faecal loss equivalent to about 10 g of protein per day the remainder is hydrolysed to free amino acids and small peptides, and absorbed (section 4.4.3). The faecal loss of nitrogen is partly composed of undigested dietary protein, but the main contributors are intestinal bacteria and shed mucosal cells, which are only partially broken down, and the protective mucus secreted by intestinal mucosal goblet cells (see Figure 4.2). Mucus is especially resistant to enzymic hydrolysis, and contributes a considerable proportion of inevitable losses of nitrogen, even on a protein-free diet.

---