Protein evaluation for ruminants - Basics, analytical developments and perspectives
- Publication Type
- Journal contribution (peer reviewed)
- Authors
- Steingaß H und Südekum K-H.
- Year of publication
- 2013
- Published in
- Übersichten zur Tierernährung
- Band/Volume
- 41/
- Page (from - to)
- 51-73
- Keywords
- Aminosäure, digestibility, Dünndarmverdaulichkeit, feedstuff, Futtermittel, Methode, Pansen, Protein, small intestine, Verdaulichkeit
<p style="margin: 0cm 0cm 0pt;"><span style="font-family: 'Arial','sans-serif'; font-size: 10pt; mso-ansi-language: EN-US;"><span style="color: #000000;">After a brief appraisal of strengths and limitations of the current German protein evaluation system for dairy cows and heifers (“utilisable crude protein at the duodenum“, uCP), this review focuses on the estimation of the protein value of feedstuffs as basis for the quantification of protein supply to dairy cows. The authors believe that it is both, essential and possible, to estimate the protein value of feedstuffs for ruminants and, eventually, milk protein synthesis using laboratory methods albeit lack or absence of <i>in vivo </i>reference data hinder calibration and validation of simplier methods. This, however, requires the use of consistent and standardized methods are used which have to be checked regularly in ring tests. When <i>in vivo </i>values are not available, calibration of laboratory methods can be conducted against <i>in situ </i>values, provided that this method is also strictly standardized; suggestions for standardized procedures are summarized in this review. Laboratory methods allow estimating protein value characteristics such as ruminally undegraded crude protein (UDP) and uCP using either rumen fluid-based methods (modified Hohenheim gas test, modHGT) or methods not requiring rumen fluid, e.g., enzymatic degradation using a <i>Streptomyces griseus </i>protease. Alternatively, protein value estimates can be based on solubility characteristics using a chemical CP fractionation procedure. The modHGT has the advantage that, in addition to a direct estimation of uCP values, the two constituting uCP fractions, namely UDP and microbially synthesized CP, can also be estimated from <i>in vitro </i>incubations using the same general procedure. Methods without rumen fluid do not offer this opportunity. Furthermore, the authors discuss how the variation in digesta passage from the rumen – largely determined by dry matter intake – affects the extent of ruminal CP degradation. This extend has to be considered as variable instead of a constant value when rations for dairy cows are planned. </span></span></p> <p><span style="color: #000000; font-family: Times New Roman; font-size: small;"> </span><span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; mso-fareast-font-family: Calibri; mso-fareast-theme-font: minor-latin; mso-ansi-language: EN-US; mso-fareast-language: EN-US; mso-bidi-language: AR-SA;">In the second part of the review consideration is given to aspects related to developments of the protein evaluation system. Where possible, also approaches to transfer progress into farming practice are scheduled. In the current uCP system it is unsatisfactory that the proportion of amino acid nitrogen (AA-N) of uCP and the absorbability of AA-N from the small intestine are part of the requirements, although both variables are influenced by individual feedstuffs and ration characteristics. The authors recommend switching from constant values to variable values which would imply that requirements are <b>no longer </b>expressed as uCP but as “digestible true protein” or “absorbable amino acids”. Modifications, improvements and further developments of the uCP system might be achieved without fundamentally changing the protein evaluation system. Similarly, accounting for requirement and supply of essential AA can also be accomplished without changing the uCP system.</span></p>