eCommons

 

Urea-N Recycling And Its Utilization By Ruminal Microbial Populations In Lactating Dairy Cattle

Other Titles

Abstract

Two experiments were conducted to quantify urea-N kinetics and ruminal microbial populations and their nitrogen (N) transactions in lactating dairy cows under a variety of dietary nitrogen and carbohydrate conditions. In the first experiment, twelve ruminally fistulated Holstein cows were fed one of three diets to provide adequate MP supply and ruminal N balance (Control, 16.3% CP), adequate ruminal N but deficient MP supply (LoMP, 14.1% CP), or adequate MP supply but deficient ruminal N balance (LoRumN, 14.1% CP). A continuous jugular infusion of 15N15N-urea was conducted for a minimum of 72 hours to label the respective pools. Plasma, milk, urine, feces, and ruminal contents, including the liquid associated bacteria, particle associated bacteria, and protozoa, were collected before and after urea infusion for N enrichment analysis. Urea-N synthesis was greatest for cows fed the Control diets and lowest for the LoMP diets, with the LoRumN diets demonstrating intermediate urea-N synthesis regardless of the low N intake of cows on this diet. A greater proportion of urea-N entered the GIT instead being excreted in the urine of cows fed the LoRumN diet (75% vs. 63% for both the Control and LoMP diets). Approximately 8-14% of the microbial N pool was present as protozoal N, and the protozoa predated 4-17% of the total bacterial N yield, with the highest values observed for cows fed the Control diet.   A second study was conducted that fed differing amounts of dietary CP (14.3 vs. 15.8%), starch (23 vs. 29%), with or without the ionophore Rumensin. Urea-N kinetics were determined by dietary CP concentration, with little impact of dietary starch or Rumensin. Microbial pool sizes and N transactions were dependent on dietary interactions, suggesting the effect of Rumensin on these populations to be mediated by rumen conditions. Overall, these studies demonstrate control over urea-N kinetics by N intake, and particularly by urea-N synthesis, over a variety of dietary conditions. Low ruminal N balance, in conjunction with starch fermentation and ionophore effects, was able to stimulate urea-N entry to the GIT, improving efficiencies of N use. The amount of recycled N contributing to microbial N supply, in addition to protozoal predation of bacteria, varied by dietary conditions.

Journal / Series

Volume & Issue

Description

Sponsorship

Date Issued

2010-10-20

Publisher

Keywords

Location

Effective Date

Expiration Date

Sector

Employer

Union

Union Local

NAICS

Number of Workers

Committee Chair

Committee Co-Chair

Committee Member

Degree Discipline

Degree Name

Degree Level

Related Version

Related DOI

Related To

Related Part

Based on Related Item

Has Other Format(s)

Part of Related Item

Related To

Related Publication(s)

Link(s) to Related Publication(s)

References

Link(s) to Reference(s)

Previously Published As

Government Document

ISBN

ISMN

ISSN

Other Identifiers

Rights

Rights URI

Types

dissertation or thesis

Accessibility Feature

Accessibility Hazard

Accessibility Summary

Link(s) to Catalog Record