In Situ Ruminal Disappearance of Essential Amino Acids in Protein Feedstuffs 1 G. COZZI, I. ANDRIGHETIO, and P. BERZAGHI Department of Animal Science University of Padova Padova, Italy C. E. POLAN Department of Dairy Science Virginia Agricultural Experiment Station College of Agriculture and Life Sciences Virginia Polytechnic Institute and State University Blacksburg 24061-0315 ABSTRACT Four protein sources were incubated in situ to estimate AA disappearance. Bags containing either soybean meal, corn gluten meal, herring meal, or meat were washed in water or suspended In the rumen of two Holstein cows for 8, 12, 16, 24, 48, 72, and 120 h. Cytosine, a bacterial marker for microbial contami- nation, was used to correct the essential AA profile for microbial contribution to determine the residual essential AA com- position of the protein sources after incu- bation. Ruminal disappearance of in- dividual essential AA was different among feedstuffs. Relative to original feed protein, soybean meal and corn glu- ten meal decreased the concentration of specific essential AA in the RUP. Con- centration of all essential AA, except Arg and His, increased in undegraded meat meal protein. The difference be- tween original and residual AA concen- trations in herring meal approached statistical significance. Use of the origi- nal AA profile of the feed protein to predict essential AA available for ab- sorption is not accurate because accuracy differs with sources. (Key words: essential amino acids, rumi- nal disappearance in situ, protein supple- ments) Received April 7. 1994. Accepted September 2, 1994. lThis study was supported by a grant from Cortal Extrasoy s.r.l., 35013 Cittadella (PO), Italy. Abbreviation key: CGM = corn gluten meal, EAA = essential AA, EUEAA = estimated undegraded EAA, HM = herring meal, MM = meat meal, PUEAA = predicted undegraded EAA, SBM = soybean meal. INTRODUCTION Diet formulation to meet the AA require- ments for ruminants is a challenging goal in animal nutrition (14). Current limitations of this approach are the lack of information regarding the efficiency of absorption and utilization of individual AA and the inability to estimate accurately the individual AA supply at the duodenum (19). The amount of AA that is available for absorption in the small intestine is a combina- tion of microbial protein that is synthesized in the rumen and the dietary protein that survives ruminal degradation. Several studies have been conducted to define the ruminal fate of dietary AA. Differences in degradation rate for specific AA within feed protein have been observed with in vivo (21, 23) and in vitro methods (5, 8), indicating selective removal of certain AA by the ruminal microorganisms. Analyses of AA composition of feed residues after incubation in situ are not always consistent with this result. In some studies (27, 28), the AA profile of the residues in bags after ruminal exposure resembled closely that of the original feedstuff. Other research (6, 16), which evaluated the AA composition of RUP after correction for microbial contamination, found differences in the AA profile between ingested protein and RUP. Thus, prediction of feed AA supply at the duodenum by applying the origi- 1995 J Dairy Sci 78:161-171 161 In Situ Ruminal Disappearance of Essential Amino Acids in Protein Feedstuffs 1 G. COZZI, I. ANDRIGHETIO, and P. BERZAGHI Department of Animal Science University of Padova Padova, Italy C. E. POLAN Department of Dairy Science Virginia Agricultural Experiment Station College of Agriculture and Life Sciences Virginia Polytechnic Institute and State University Blacksburg 24061-0315 ABSTRACT Four protein sources were incubated in situ to estimate AA disappearance. Bags containing either soybean meal, corn gluten meal, herring meal, or meat were washed in water or suspended In the rumen of two Holstein cows for 8, 12, 16, 24, 48, 72, and 120 h. Cytosine, a bacterial marker for microbial contami- nation, was used to correct the essential AA profile for microbial contribution to determine the residual essential AA com- position of the protein sources after incu- bation. Ruminal disappearance of in- dividual essential AA was different among feedstuffs. Relative to original feed protein, soybean meal and corn glu- ten meal decreased the concentration of specific essential AA in the RUP. Con- centration of all essential AA, except Arg and His, increased in undegraded meat meal protein. The difference be- tween original and residual AA concen- trations in herring meal approached statistical significance. Use of the origi- nal AA profile of the feed protein to predict essential AA available for ab- sorption is not accurate because accuracy differs with sources. (Key words: essential amino acids, rumi- nal disappearance in situ, protein supple- ments) Received April 7. 1994. Accepted September 2, 1994. lThis study was supported by a grant from Cortal Extrasoy s.r.l., 35013 Cittadella (PO), Italy. Abbreviation key: CGM = corn gluten meal, EAA = essential AA, EUEAA = estimated undegraded EAA, HM = herring meal, MM = meat meal, PUEAA = predicted undegraded EAA, SBM = soybean meal. INTRODUCTION Diet formulation to meet the AA require- ments for ruminants is a challenging goal in animal nutrition (14). Current limitations of this approach are the lack of information regarding the efficiency of absorption and utilization of individual AA and the inability to estimate accurately the individual AA supply at the duodenum (19). The amount of AA that is available for absorption in the small intestine is a combina- tion of microbial protein that is synthesized in the rumen and the dietary protein that survives ruminal degradation. Several studies have been conducted to define the ruminal fate of dietary AA. Differences in degradation rate for specific AA within feed protein have been observed with in vivo (21, 23) and in vitro methods (5, 8), indicating selective removal of certain AA by the ruminal microorganisms. Analyses of AA composition of feed residues after incubation in situ are not always consistent with this result. In some studies (27, 28), the AA profile of the residues in bags after ruminal exposure resembled closely that of the original feedstuff. Other research (6, 16), which evaluated the AA composition of RUP after correction for microbial contamination, found differences in the AA profile between ingested protein and RUP. Thus, prediction of feed AA supply at the duodenum by applying the origi- 1995 J Dairy Sci 78:161-171 161