Effects of diet quality on urea fates in sheep as assessed by refined, non-invasive [(NN)-N-15-N-15]urea kinetics

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Abstract

The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49.5 kg). The animals received, in a crossover design, each of two rations, hay-grass pellets (1:1 HG) and a mixed concentrate-forage (CF). Measurements were made of N balance and urea kinetics based on a 4 d continuous intravascular infusion of [(NN)-N-15-N-15]urea. Enrichments of [(NN)-N-15-N-15]- and [(NN)-N-14-N-15]urea in the urine, and faecal N-15 content were determined each day. After 24 h of infusion, urinary [(NN)-N-15-N-15]urea enrichments reached constant enrichment but a further 24 h was required before [(NN)-N-14-N-15]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to (NH3)-N-15 in the digestive tract with subsequent absorption and re-conversion to urea. The diets were not isonitrogenous (14.3 v. 17.1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16.3 v. 11.1 g/d; P=0.011) for CF compared with HG and more urea-N entered the GIT (9.9 v. 7.7; P=0.07). A larger proportion of GIT entry was returned to ureagenesis (51 v. 42 %; P=0.047) for the CF diet but a smaller fraction was lost in the faeces (3.3 % v. 7.1 %; P=0.013). In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH3) and the absolute amount available for anabolic purposes was similar between the rations (3.9 v. 4.5 g N/d).

Original languageEnglish
Pages (from-to)459-468
Number of pages10
JournalBritish Journal of Nutrition
Volume84
Issue number4
Publication statusPublished - Oct 2000

Keywords

  • urea
  • N-15 kinetics
  • gastrointestinal tract
  • sheep
  • BEEF STEERS
  • NITROGENOUS COMPOUNDS
  • OVINE LIVER
  • METABOLISM
  • TISSUES
  • FORAGE
  • BLOOD
  • AMMONIA
  • GLUCOSE
  • INVIVO

Cite this

@article{51a21f22b6254a10aa30beacecc28d12,
title = "Effects of diet quality on urea fates in sheep as assessed by refined, non-invasive [(NN)-N-15-N-15]urea kinetics",
abstract = "The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49.5 kg). The animals received, in a crossover design, each of two rations, hay-grass pellets (1:1 HG) and a mixed concentrate-forage (CF). Measurements were made of N balance and urea kinetics based on a 4 d continuous intravascular infusion of [(NN)-N-15-N-15]urea. Enrichments of [(NN)-N-15-N-15]- and [(NN)-N-14-N-15]urea in the urine, and faecal N-15 content were determined each day. After 24 h of infusion, urinary [(NN)-N-15-N-15]urea enrichments reached constant enrichment but a further 24 h was required before [(NN)-N-14-N-15]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to (NH3)-N-15 in the digestive tract with subsequent absorption and re-conversion to urea. The diets were not isonitrogenous (14.3 v. 17.1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16.3 v. 11.1 g/d; P=0.011) for CF compared with HG and more urea-N entered the GIT (9.9 v. 7.7; P=0.07). A larger proportion of GIT entry was returned to ureagenesis (51 v. 42 {\%}; P=0.047) for the CF diet but a smaller fraction was lost in the faeces (3.3 {\%} v. 7.1 {\%}; P=0.013). In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH3) and the absolute amount available for anabolic purposes was similar between the rations (3.9 v. 4.5 g N/d).",
keywords = "urea, N-15 kinetics, gastrointestinal tract, sheep, BEEF STEERS, NITROGENOUS COMPOUNDS, OVINE LIVER, METABOLISM, TISSUES, FORAGE, BLOOD, AMMONIA, GLUCOSE, INVIVO",
author = "Gerald Lobley and David Bremner and G Zuur",
year = "2000",
month = "10",
language = "English",
volume = "84",
pages = "459--468",
journal = "British Journal of Nutrition",
issn = "0007-1145",
publisher = "Cambridge Univ. Press.",
number = "4",

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TY - JOUR

T1 - Effects of diet quality on urea fates in sheep as assessed by refined, non-invasive [(NN)-N-15-N-15]urea kinetics

AU - Lobley, Gerald

AU - Bremner, David

AU - Zuur, G

PY - 2000/10

Y1 - 2000/10

N2 - The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49.5 kg). The animals received, in a crossover design, each of two rations, hay-grass pellets (1:1 HG) and a mixed concentrate-forage (CF). Measurements were made of N balance and urea kinetics based on a 4 d continuous intravascular infusion of [(NN)-N-15-N-15]urea. Enrichments of [(NN)-N-15-N-15]- and [(NN)-N-14-N-15]urea in the urine, and faecal N-15 content were determined each day. After 24 h of infusion, urinary [(NN)-N-15-N-15]urea enrichments reached constant enrichment but a further 24 h was required before [(NN)-N-14-N-15]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to (NH3)-N-15 in the digestive tract with subsequent absorption and re-conversion to urea. The diets were not isonitrogenous (14.3 v. 17.1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16.3 v. 11.1 g/d; P=0.011) for CF compared with HG and more urea-N entered the GIT (9.9 v. 7.7; P=0.07). A larger proportion of GIT entry was returned to ureagenesis (51 v. 42 %; P=0.047) for the CF diet but a smaller fraction was lost in the faeces (3.3 % v. 7.1 %; P=0.013). In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH3) and the absolute amount available for anabolic purposes was similar between the rations (3.9 v. 4.5 g N/d).

AB - The effect of diet quality on urea production, entry into the gastrointestinal tract (GIT) and subsequent diversion to anabolic or catabolic fates was examined in four sheep (mean live weight 49.5 kg). The animals received, in a crossover design, each of two rations, hay-grass pellets (1:1 HG) and a mixed concentrate-forage (CF). Measurements were made of N balance and urea kinetics based on a 4 d continuous intravascular infusion of [(NN)-N-15-N-15]urea. Enrichments of [(NN)-N-15-N-15]- and [(NN)-N-14-N-15]urea in the urine, and faecal N-15 content were determined each day. After 24 h of infusion, urinary [(NN)-N-15-N-15]urea enrichments reached constant enrichment but a further 24 h was required before [(NN)-N-14-N-15]urea enrichment was at plateau. The latter is derived from hydrolysis of urea to (NH3)-N-15 in the digestive tract with subsequent absorption and re-conversion to urea. The diets were not isonitrogenous (14.3 v. 17.1 g N supplied daily for HG and CF respectively) but showed no difference in N balance. Urea-N production was much greater (16.3 v. 11.1 g/d; P=0.011) for CF compared with HG and more urea-N entered the GIT (9.9 v. 7.7; P=0.07). A larger proportion of GIT entry was returned to ureagenesis (51 v. 42 %; P=0.047) for the CF diet but a smaller fraction was lost in the faeces (3.3 % v. 7.1 %; P=0.013). In consequence, most of the additional urea-N which entered the GIT on the CF diet was returned to the ornithine cycle (probably as NH3) and the absolute amount available for anabolic purposes was similar between the rations (3.9 v. 4.5 g N/d).

KW - urea

KW - N-15 kinetics

KW - gastrointestinal tract

KW - sheep

KW - BEEF STEERS

KW - NITROGENOUS COMPOUNDS

KW - OVINE LIVER

KW - METABOLISM

KW - TISSUES

KW - FORAGE

KW - BLOOD

KW - AMMONIA

KW - GLUCOSE

KW - INVIVO

M3 - Article

VL - 84

SP - 459

EP - 468

JO - British Journal of Nutrition

JF - British Journal of Nutrition

SN - 0007-1145

IS - 4

ER -