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The effects of dietary sucrose and the concentrations of plasma urea and rumen ammonia on the degradation of urea in the gastrointestinal tract of cattle

Published online by Cambridge University Press:  25 February 2008

P. M. Kennedy
P. M. Kennedy
Affiliation:
CSIRO. Tropical Cattle Research Centre, PO Box 542, Rockhampton, Queensland 4700., Australia
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Abstract

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1. The rates of entry of urea into plasma, of urea degradation in the gastrointestinal tract, and the partition of that degradation between the rumen and post-ruminal tract were determined by use of [14C]urea and NaH14CO3 in Hereford steers receiving hay diets with or without sucrose. The concentrations of plasma urea and rumen ammonia were varied by infusions of urea into the rumen or abomasum.

2. For all diets, plasma urea concentration was related to urea entry rate, to degradation of urea in the whole gastrointestinal tract, and to its degradation in the post-ruminal tract, but the relationship with its degradation in the rumen was poor.

3. Degradation of urea in the rumen was related in a multiple regression in a curvilinear manner in three groups of diets (pasture-hay alone, pasture-hay–lucerne (Medicago sativa) mixtures, diets with sucrose), and negatively to rumen ammonia concentration for pasture-hay diets, and diets with sucrose.

4. Ruminal clearance of urea (rate of urea degradation per plasma urea concentration) was negatively related to the rumen ammonia concentration for steers given diets with sucrose, of pasture-hay with or without urea infusions. Provision of sucrose in the diet significantly increased clearance.

5. Enhanced urea degradation in the rumen associated with dietary sucrose supplements accounted for 0.4 of additional microbial N synthesis in the rumen.

6. The partition of transfer of urea to the rumen via saliva and through the rumen wall is discussed.

Type
Papers on General Nutrition
Information
British Journal of Nutrition , Volume 43 , Issue 1 , January 1980 , pp. 125 - 140
Copyright
Copyright © The Nutrition Society 1980

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