|Reynal, Santiago - UNIV OF WISCONSIN|
Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: July 9, 2007
Publication Date: July 9, 2007
Citation: Reynal, S.M., Broderick, G.A. 2007. Presence of purine metabolites in omasal digesta and bacteria: new analytical method and effects on microbial flows [abstract]. Journal of Dairy Science. 90 (supplement 1):565. Technical Abstract: A new HPLC method was developed to determine concentrations of purines [adenine (A) and guanine (G)], and their metabolites [xanthine (X) and hypoxanthine (HX)] in omasal digesta and bacterial samples and to assess the effect of using either purines (TP) or purines plus their metabolites (PM) as microbial markers for estimating flows of N fractions from the rumen of dairy cows. Four ruminally-cannulated lactating dairy cows (mean DMI 25.6 kg/d) were assigned to a 4x4 Latin square and fed 16.7%-CP diets supplemented with increasing amounts of sucrose (0, 2.5, 5, and 7.5% of DM). Digesta flow from the rumen was quantified using an omasal sampling technique and a triple-marker method. Individual purines and metabolites were separated using a C18 column with gradient flow rate and two mobile phases. Analytical precision within assay ranged from 0.6 to 3.1%. For all compounds, hydrolytic efficiencies and recoveries from their corresponding nucleosides when added to bacterial and omasal digesta samples averaged, respectively, 101, 103, and 104%. Concentrations (micromol/g) of A, G, X, and HX averaged across diets, respectively, 53, 58, 2.8, and 3.5 in omasal bacteria and 10, 12, 7.5, and 7.5 micromol/g in omasal digesta. Omasal flows of microbial and non-microbial N (g/d), and true ruminal digestibility of N (%) averaged, respectively, 449, 302, and 56 when estimated using PM; 284, 467, and 32 when estimated using TP; and 413, 209, and 69 when predicted by the NRC model. These results suggest that when total purines are used as a microbial marker, both TP and PM should be determined and used in the calculations. Because X and HX precipitate with silver nitrate, the method of Zinn and Owens (1986) would include both TP and PM. However, a portion of TP and PM may be of dietary origin, resulting in biased estimates of microbial flow.