TY - JOUR
T1 - Nitrogen metabolism in the rumen
AU - Bach, A.
AU - Calsamiglia, S.
AU - Stern, M. D.
N1 - Publisher Copyright:
© 2005 American Dairy Science Association.
PY - 2005/4/1
Y1 - 2005/4/1
N2 - Protein metabolism in the rumen is the result of metabolic activity of ruminal microorganisms. The structure of the protein is a key factor in determining its susceptibility to microbial proteases and, thus, its degradability. Ruminal protein degradation is affected by pH and the predominant species of microbial population. Ruminal proteolytic activity decreases as pH decreases with high-forage dairy cattle-type rations, but not in high-concentrate beef-type rations. Accumulation of amino acid (AA) N after feeding suggests that AA uptake by rumen microorganisms could be the limiting factor of protein degradation in the rumen. In addition, there are several AA, such as Phe, Leu, and Ile, that are synthesized by rumen microorganisms with greater difficulty than other AA. The most common assessment of efficiency of microbial protein synthesis (EMPS) is determination of grams of microbial N per unit of rumen available energy, typically expressed as true organic matter or carbohydrates fermented. However, EMPS is unable to estimate the efficiency at which bacteria capture available N in the rumen. An alternative and complementary measure of microbial protein synthesis is the efficiency of N use (ENU). In contrast to EMPS, ENU is a good measurement for describing efficiency of N capture by ruminal microbes. Using EMPS and ENU, it was concluded that optimum bacterial growth in the rumen occurs when EMPS is 29. g of bacterial N/kg of fermented organic matter, and ENU is 69%, implying that bacteria would require about 1.31. ×. rumen-available N per unit of bacterial N. Because the distribution of N within bacterial cells changes with rate of fermentation, AA N, rather than total bacterial N should be used to express microbial protein synthesis.
AB - Protein metabolism in the rumen is the result of metabolic activity of ruminal microorganisms. The structure of the protein is a key factor in determining its susceptibility to microbial proteases and, thus, its degradability. Ruminal protein degradation is affected by pH and the predominant species of microbial population. Ruminal proteolytic activity decreases as pH decreases with high-forage dairy cattle-type rations, but not in high-concentrate beef-type rations. Accumulation of amino acid (AA) N after feeding suggests that AA uptake by rumen microorganisms could be the limiting factor of protein degradation in the rumen. In addition, there are several AA, such as Phe, Leu, and Ile, that are synthesized by rumen microorganisms with greater difficulty than other AA. The most common assessment of efficiency of microbial protein synthesis (EMPS) is determination of grams of microbial N per unit of rumen available energy, typically expressed as true organic matter or carbohydrates fermented. However, EMPS is unable to estimate the efficiency at which bacteria capture available N in the rumen. An alternative and complementary measure of microbial protein synthesis is the efficiency of N use (ENU). In contrast to EMPS, ENU is a good measurement for describing efficiency of N capture by ruminal microbes. Using EMPS and ENU, it was concluded that optimum bacterial growth in the rumen occurs when EMPS is 29. g of bacterial N/kg of fermented organic matter, and ENU is 69%, implying that bacteria would require about 1.31. ×. rumen-available N per unit of bacterial N. Because the distribution of N within bacterial cells changes with rate of fermentation, AA N, rather than total bacterial N should be used to express microbial protein synthesis.
KW - Metabolism
KW - Microbial
KW - Nitrogen
KW - Rumen
UR - http://www.scopus.com/inward/record.url?scp=33644876943&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=33644876943&partnerID=8YFLogxK
U2 - 10.3168/jds.S0022-0302(05)73133-7
DO - 10.3168/jds.S0022-0302(05)73133-7
M3 - Article
C2 - 15876575
AN - SCOPUS:33644876943
SN - 0022-0302
VL - 88
SP - E9-E21
JO - Journal of Dairy Science
JF - Journal of Dairy Science
IS - S
ER -