Nitrogen metabolism and recycling in Holstein heifers12
- 1 February 2003
- journal article
- ruminant nutrition
- Published by Oxford University Press (OUP) in Journal of Animal Science
- Vol. 81 (2), 545-552
- https://doi.org/10.2527/2003.812545x
Abstract
To study the effect of dietary N level on urea kinetics and recycling, four Holstein heifers (267 ± 3.6 kg) were used in a Youden square design. Isocaloric diets with a N content of 1.44, 1.89, 2.50, 2.97, and 3.40% were fed at approximately 1.8 times maintenance intake. Increasing the N content of the diet increased urinary N excretion (P < 0.001) and N balance (P < 0.01), but did not affect the fecal N excretion (P = 0.21). Increasing the level of dietary N, increased urea production (P < 0.001) and excretion (P < 0.001), but no effect (P = 0.24) could be detected in the amount of N recycled to the gut. Urea recycled with the saliva, however, increased (P < 0.001) both in absolute and relative terms, with increasing dietary N. No difference could be detected on the amount of recycled N that was used for anabolism or returned to the ornithine cycle, but less (P = 0.001) N originating from urea was excreted in feces as dietary N increased. Ruminal ammonia concentration increased (P < 0.001) with increasing N intake, but total tract neutral detergent fiber digestibility was depressed only on the lowest N intake diet. No difference (P = 0.30) was detected in ruminal microbial yield among diets, but more (P < 0.003) N was derived from blood urea at low N intakes, and the efficiency of use of the recycled N decreased (P < 0.001) with increasing levels of dietary N. Adaptive changes to low-N diets were a decrease (P < 0.003) in the renal clearance of urea and an increase (P < 0.001) in the gastrointestinal clearance of urea. Urea transporters were present in the rumen wall of the heifers and differentially expressed depending on dietary N content, but their role in the transfer of urea into the rumen remains uncertain. Different mechanisms of N salvage and recycling were involved when animals were fed low-N diets that ensured a supply of endogenous N to the gastrointestinal tract and, due to the reduced contribution of dietary N, an increased efficiency of the N recycled was observed.Keywords
This publication has 23 references indexed in Scilit:
- Urea flux in beef steers: effects of forage species and nitrogen fertilization.Journal of Animal Science, 2001
- The Effects of Accelerated Growth Rates and Estrogen Implants in Prepubertal Holstein Heifers on Growth, Feed Efficiency, and Blood ParametersJournal of Dairy Science, 1999
- Methods for Dietary Fiber, Neutral Detergent Fiber, and Nonstarch Polysaccharides in Relation to Animal NutritionJournal of Dairy Science, 1991
- HEPATIC UREA SYNTHESIS AND SITE AND RATE OF UREA REMOVAL FROM BLOOD OF BEEF STEERS FED ALFALFA HAY OR A HIGH CONCENTRATE DIETCanadian Journal of Animal Science, 1989
- Concentration of Ammonia Across Cell Membranes of Mixed Rumen BacteriaJournal of Dairy Science, 1987
- Urea synthesis and degradation in sheep given pelleted-grass diets containing flaked barleyBritish Journal of Nutrition, 1982
- THE DEGRADATION AND UTILIZATION OF ENDOGENOUS UREA IN THE GASTROINTESTINAL TRACT OF RUMINANTS: A REVIEWCanadian Journal of Animal Science, 1980
- Effect of ammonia concentration on rumen microbial protein production in vitroBritish Journal of Nutrition, 1974
- Dynamic aspects of ammonia and urea metabolism in sheepBritish Journal of Nutrition, 1972
- TRACER STUDIES OF UREA RECYCLING EN SHEEPCanadian Journal of Animal Science, 1970