The UK metabolisable protein system

A measure of the effect of assuming one or other of the measures of amino acid composition can be gained if we consider the following daily ration  

A is calculated by assuming the amino acid composition of the whole protein. B is calculated by assuming the composition of the insoluble available fraction. 

Amino acids are usually considered to have the same true digestibUity as true protein, but there is evidence that the efficiency with which individual amino acids are metabohsed will vary with the biological value of the protein and the amino acid supply relative to requirement. 

A system for the quantitative nutrition of ruminant animals should embody the processes described, which requires that factors such as degradabUity, efficiency of nitrogen captme, microbial protein yield, digestibihty of microbial protein, digestibihty of dietary imdegraded protein and the trae biological value of the absorbed nitrogen or its essential amino acid content be quantified. 

The system is fully described in the 1992 report of the Agricultural and Food Research Council s Technical Committee on Responses to Nutrients (see Further reading). 

---

The UK metabolisable protein system divides the requirement of an animal into that which is required for supplying the needs of the rumen microbes and that which is required at tissue level. After estimating the contribution of microbial protein to satisfying this demand, the requirement for undegraded dietary protein is calculated. 

As indicated above, most of the protein systems for ruminants (see Chapter 13) used around the world base their estimates of protein requirements for maintenance on endogenous losses of nitrogen but use different factors to translate endogenous losses into dietary requirements. For example, using the UK metabolisable protein... 

On a dry matter basis, the crude protein (g/kg), neutral detergent fibre (g/kg) and estimated metabolisable energy (MJ ME/kg) contents of ryegrass were 216, 409 and 12.8, respectively, whereas the corresponding values for pellet were 156, 269 and 9.8, respectively. The 8-chamber animal respiration system was that described by Pinares-Patino et al (2008), with CH concentrations measured using a Servomex 4900 gas analyser (Servomex Group Ltd., East Sussex, UK), which was fitted with a electrochemical H2 detector. The detection ranges for CH and H2 were 0-200 and 0-50 ppm, with accuracies of 0.5 and 5 ppm, respectively. 

---