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Lowering dietary phosphorus concentrations reduces kidney calcification, but does not adversely affect growth, mineral metabolism, and bone development in growing rabbits

Published online by Cambridge University Press:  09 March 2007

J. Ritskes-Hoitinga ,
H. N. A. Grooten ,
K. J. H. Wienk ,
M. Peters ,
A. G. Lemmens  and
A. C. Beynen
J. Ritskes-Hoitinga*
Affiliation:
Biomedical Laboratory, Faculty of Health Sciences, University of Southern Denmark, Winsloewparken 23, DK-5000, Odense C, Denmark
H. N. A. Grooten
Affiliation:
Department of Laboratory Animal Science, Utrecht University, Utrecht, The Netherlands
K. J. H. Wienk
Affiliation:
Department of Laboratory Animal Science, Utrecht University, Utrecht, The Netherlands
M. Peters
Affiliation:
Central Animal Facility, Wageningen University, Wageningen, The Netherlands
A. G. Lemmens
Affiliation:
Department of Laboratory Animal Science, Utrecht University, Utrecht, The Netherlands
A. C. Beynen
Affiliation:
Department of Large Animal Medicine, Utrecht University, Utrecht, The Netherlands
*
*Corresponding author: Dr Merel Ritskes-Hoitinga, fax +45 65 90 68 21, email mritskes@health.sdu.dk
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Abstract

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New Zealand White rabbits were used to investigate the influence of increasing dietary P concentrations on growth performance, mineral balance, kidney calcification and bone development. The minimum dietary P requirement of 0·22% (National Research Council) is usually exceeded in commercial natural-ingredient chows, leading to undesirable kidney calcifications. In order to study the optimal dietary P level, rabbits were fed semi-purified diets with four different P levels (0·1, 0·2, 0·4, and 0·8%; w/w) at a constant dietary Ca concentration (0·5%) during an 8-week period. Body weight and growth were not influenced by the dietary P level. During two periods (days 20–23 and 48–51), faeces and urine were collected quantitatively for the analysis of Ca, Mg and P and balances were calculated. Increased dietary P intake caused increased urinary and faecal P excretion and P apparent absorption and retention. Faecal Ca excretion increased with higher dietary P levels, whereas urinary Ca excretion reacted inversely. The apparent absorption of Ca became reduced at higher dietary P concentrations, but Ca retention was unchanged. The response of Mg was in a similar direction to that of the Ca balance. Kidney mineral content increased with higher dietary P levels, indicating the presence of calcified deposits. Nephrocalcinosis became more severe in kidney cortex and medulla at increasing dietary P levels, as was confirmed by histological analysis. Femur bone length was not differentially influenced by dietary P. Bone density (g/cm3) of the femur diaphysis became significantly lower at the 0·8% dietary P level as compared with the 0·2% P group only. The bone Mg content was significantly increased on the 0·8% P diet, both in the diaphysis and epiphysis. Plasma P concentration increased and plasma Ca decreased with higher dietary P levels, whereas plasma Mg levels were unaffected. The present study shows that the current recommended minimum dietary P level of 0·2% for rabbits, as advised by the National Research Council in 1977, leads to a normal growth and bone development, but also causes some degree of kidney calcifications at a dietary Ca level of 0·5%. As the dietary P level of 0·1% virtually prevented kidney calcification and at the same time did not give evidence for any deleterious effects on growth and bone development, this indicates that the current recommended dietary P level for rabbits should be regarded as a maximum advisable concentration, and that a lower P level may be more optimal.

Keywords

Dietary phosphorus requirementMineral balanceKidney calcificationBone mineralisationRabbits
Type
Research Article
Information
British Journal of Nutrition , Volume 91 , Issue 3 , March 2004 , pp. 367 - 376
Copyright
Copyright © The Nutrition Society 2004

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