Failure of bone phosphorus levels to indicate dietary intake of phosphorus by sheep

Fifteen actively growing lambs were divided into 3 groups and fed diets similar in all respects except for their calcium (Ca) and phosphorus (P) levels. The diets (Group 1; 1,47% Ca, 0,36% P: Group 2; 0,85% Ca, 0,47% P: Group 3; 0,37% Ca, 0,64% P) were fed to the animals for 98 days, when rib biopsy specimens were removed and analysed for Ca and P (Group 1; 21,20% Ca, 10,49% P: Group 2; 19,54% Ca, 9,42% P: Group 3; 19,10% Ca, 9,24% P). Although there were no differences (P greater than 0,01) in the bone analyses between the groups, there was a tendency for bone calcium levels to follow dietary calcium levels. Bone phosphorus levels, again, followed bone calcium levels and were opposite to dietary phosphorus levels. This work re-emphasizes the dominance of calcium over phosphorus in bone formation. Implications of these findings are discussed in the light of the use of bone phosphorus analyses to estimate the phosphorus intake and status of grazing sheep.