[Determination of endogenous N-excretion and nitrogen balance in the range of low N-intake in rats].
The investigations were carried out in order to develop foundations for a complex growth model including the effect of N-efficiency mechanism first of all for the rat. Therefore N-balance trials with rats of different live weights were made using diets of equal protein quality. The curve of the regressively calculated N-efficiency function courses relatively linear in its lower part, i.e. for low N-intakes. The protein quality value "A.b" was proved to be constant for all investigated live weight ranges. In similar trials with different protein qualities was also found a linear course for low N-intakes. The regressively estimated N-maintenance requirement (for N-Intake = 0) related to metabolic live weight (NMR/LWkg0.67) amounts to 180 mg/d. In addition endogenous N-excretions were determined in 15N tracer experiments on animals of different live weight fed graduated amounts of a quality constant protein. The NMR-values (sum of endogenous excretions from faeces and urea) depend on the level of N-intake, i.e. they can not be considered as constant. The endogenous faecal N-loss related to metabolic live weight is relatively constant indeed, whereas the amount of endogenous urea N-loss is dependent on the level of N-intake. Therefore calculations based on the N-efficiency curve, e.g. amino acid requirement dependent on performance and prediction of N-deposition respectively, should not be carried out on the basis of "N-retention" (N-balance + NMR) but only on the basis of N-balance.
Wissenschaftsbereich Tierenährungsphysiologie und Futtermittelkunde, Universität Leipzig, Germany.
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T
Pahle
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Köhler
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M
Müller
D000818:Animals; D001835:Body Weight; D002364:Caseins / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism*; D005243:Feces / Q000737:chemistry; D005983:Glutens / Q000008:administration & dosage / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D009584:Nitrogen / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism* / Q000652:urine; D051381:Rats; D017208:Rats, Wistar / Q000254:growth & development / Q000378:metabolism*; D012044:Regression Analysis; D014908:Triticum; D014508:Urea / Q000652:urine
D002364:Caseins; D004044:Dietary Proteins; D005983:Glutens; D014508:Urea; D009584:Nitrogen
Bestimmung der endogenen N-Ausscheidungen sowie der N-Bilanz im Bereich geringer N-Aufnahmen an Ratten.