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The effect of variation in dietary protein or mineral supply on calcium and phosphorus metabolism in lactating ewes

Published online by Cambridge University Press:  09 March 2007

A. A. J. Rajaratne ,
D. Scott ,
W. Buchan  and
A. Duncan
A. A. J. Rajaratne
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
D. Scott
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
W. Buchan
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
A. Duncan
Affiliation:
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
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Abstract

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Two experiments are described in which changes in both nitrogen and mineral balance were monitored in ewes during lactation. In Expt 1, two groups (n 6) of ewes were fed on diets that were either high (15 g crade protein (N × 6.25; CP)/MJ metabolizable energy (ME)) or low (10 g CP/MJ ME) in protein content, and concurrent N and mineral balance studies were made at intervals during lactation with 45Ca and 32P being used to monitor faecal endogenous calcium and phosphorus losses. Ewes fed on the high-protein diet maintained a positive N balance during early lactation, whereas those fed on the low-protein diet were in negative N balance. Both groups, however, showed the same degree of negative Ca and P balance, with the amounts lost being directly related to milk yield. This indicates that loss of mineral from the skeleton at this time is not secondary to a loss of bone matrix due to a shortfall in dietary protein supply. In Expt 2, two groups of ewes (n 4) were fed on diets in late pregnancy that were either just adequate or generous in Ca and P supply relative to requirement (TCORN, 1990). After parturition both groups were fed on a diet which was formulated to meet their estimated Ca and P requirements for lactation. As in the previous experiment both groups were in negative Ca and P balance in early lactation and variation in dietary Ca and P supply during pregnancy had no effect on the extent of this loss. Alternative explanations for the cause of this loss of mineral from the skeleton are discussed.

Keywords

Calcium metabolismPhosphorus metabolismLactationSheep
Type
Lactation in Ruminants
Information
British Journal of Nutrition , Volume 64 , Issue 1 , July 1990 , pp. 147 - 160
Copyright
Copyright © The Nutrition Society 1990

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