Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/25/2005
Publication Date: 7/25/2005
Citation: Reynal, S.M., Broderick, G.A., Bearzi, C. 2005. Comparison of 15-N, total purines, AA profiles, and urinary allantoin excretion as markers for quantifying microbial protein flow from the rumen of lactating dairy cows [abstract]. Journal of Dairy Science. 88 (suppl. 1):90. Interpretive Summary:
Technical Abstract: Eight ruminally cannulated lactating cows were assigned to 4 x 4 Latin squares and fed diets with different levels of rumen-degraded protein (RDP) to compare 15N, total purines (TP), AA profiles, and urinary excretion of allantoin [a purine derivative (PD)] as microbial markers for quantifying the flow of microbial protein at the omasal canal. Dietary RDP was gradually decreased from 13.2 to 10.6% of DM by replacing solvent soybean meal (SSBM) and urea with lignosulfonate-treated soybean meal (LSBM). The guanine to adenine ratio of the fluid phase of omasal digesta was 4.6 times greater than that of fluid-associated bacteria, suggesting different degradation rates between purines. When estimated using TP, flows of microbial NAN did not change and flows of non-microbial NAN (NMNAN) decreased linearly (from 273 to 219 g/d; P < 0.01) when SSBM and urea were replaced in the diet with the less degradable LSBM. However, as RDP decreased, microbial NAN flow decreased linearly (P < 0.01) when measured using 15N (from 470 to 384 g/d), AA profiles (from 392 to 311 g/d), and PD (from 365 to 280 g/d), while NMNAN flow (expressed as percent of total NAN flow) increased linearly (P < 0.01) when estimated based on 15N (from 30.4 to 37.8%) and AA profiles (from 44.5 to 52.0%). The slope of the regression (P < 0.01) of TP on 15N for microbial NAN flow was 0.57. Averaged across diets, microbial NAN flows estimated using 15N, TP, AA profiles and PD were 429, 401, 360, and 284 g/d, respectively, and were lowest for PD and highest for 15N and TP (P < 0.01). The lack of agreement between the direct (TP) and indirect (PD) measurements of purine flow from the rumen may have resulted from incomplete ruminal and intestinal degradability of purines from LSBM. Microbial and dietary NAN flows from the rumen estimated using 15N appeared to be more accurate and precise than flows estimated with the other markers.