Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/9/2007
Publication Date: 7/9/2007
Citation: Ipharraguerre, I.R., Reynal, S.M., Huhtanen, P., Clark, J.H., Broderick, G.A., Ahvenjarvi, S. 2007. A comparative review of the flow of nitrogen fractions at the omasal canal and duodenum of dairy cows [abstract]. Journal of Dairy Science. 90 (supplement 1):684. Interpretive Summary:
Technical Abstract: The objective of this paper was to review and compare published data for the passage of N fractions to the omasal canal and duodenum of lactating dairy cows. Two data sets were created; one with data from 14 studies in which digesta was sampled from the omasal canal (57 means) and the other with data from 67 studies in which digesta was taken from the duodenum (264 means). Mean, minimum, and maximum intakes of DM (DMI 19.7, 10.8, and 27.4 kg/d) and N (NI 537, 264, and 855 g/d) were similar between data sets. Flows of NAN, microbial N (MN), and NAN-nonmicrobial N (NANMN) averaged at the omasal canal 516 (SD 128), 342 (SD 100), and 173 (SD 48) g/d respectively; and at the duodenum 508 (SD113), 271 (SD 84), and 236 (SD 87) g/d, respectively. Although sampling from the omasum and duodenum resulted in similar mean NAN flows, 65% of the reported MN flows to omasum exceeded 300 g/d whereas only 32% of the reported MN flows to duodenum were greater than such amount. Consequently, MN represented more than 55% of the postruminal flow of NAN in 90% of the cases in which samples were taken from the omasum compared with 39% of the cases in which samples were obtained from the duodenum. Both data sets were combined and subjected to regression analysis using a mixed model approach that included study as random variable. Dependent variables were NAN, MN, and NANMN flow. Independent variables were sampling site (SS), NI or DMI plus dietary CP, and all possible two-way interactions. The effect of SS and its interaction with other variables was not significant (P >0.25) for all NAN-flow models. Conversely, the interaction between SS and DMI or NI was significant for the MN-flow (P <0.06) and NANMN-flow (P <0.01) models, respectively. These findings suggest that omasal canal and duodenal sampling may result in different estimates of the flow of MN and NANMN. More research is needed to determine the accuracy and origin of this difference.