title: Plasma amino acid response to graded levels of escape protein.
abstract: A trial was conducted to examine the potential of using plasma amino acid responses to graded levels of escape protein to determine limiting amino acids in cattle. Growing calves (n = 120; mean BW = 220 +/- 21 kg) were fed a basal diet of corncob:sorghum silage (61:39) and were individually supplemented with distillers' dried grains (DDG), heat-damaged DDG (H-DDG), feather meal (FTH), or urea. The urea supplement was mixed with DDG and H-DDG to allow 0, 20, 35, 50, 65, or 80% of the supplemental CP to come from distillers' protein and maintain an 11.5% CP diet. Urea supplement was mixed with FTH to allow 0, 22, 39, 56, 73, or 90% of the supplemental CP to come from FTH. Dietary CP ranged from 11.5% at the 0% level to 17.3% at the 90% level. Plasma concentration of most essential plasma amino acids responded (P less than .10) linearly and(or) quadratically to increased escape protein. The broken-line response of plasma methionine at low DDG intake suggested that methionine was limiting at low levels of escape protein. An initial decrease followed by a plateau fit by a broken line indicated that histidine became limiting in FTH diets, and lysine eventually became limiting for DDG, H-DDG, and FTH diets before maximum BW gain was reached. Results indicate that plasma amino acid responses may identify amino acids that become limiting with increasing escape protein.
authors.affiliation: Department of Animal Science, University of Nebraska, Lincoln 68583-0908.
authors.forename: D J
authors.initials: DJ
authors.lastname: Gibb
authors.forename: T J
authors.initials: TJ
authors.lastname: Klopfenstein
authors.forename: R A
authors.initials: RA
authors.lastname: Britton
authors.forename: A J
authors.initials: AJ
authors.lastname: Lewis
mesh_terms: D000596:Amino Acids / Q000097:blood*; D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000097:blood*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D002523:Edible Grain; D005241:Feathers; D006639:Histidine / Q000097:blood; D007532:Isoleucine / Q000097:blood; D008239:Lysine / Q000097:blood; D008715:Methionine / Q000097:blood; D012044:Regression Analysis; D014508:Urea / Q000008:administration & dosage
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D007532:Isoleucine; D006639:Histidine; D014508:Urea; D008715:Methionine; D008239:Lysine