Effects of varying phosphorus intake and requirement on measures of skeletal mineralization in the ewe

Abstract

Merino ewes were fed a specifically phosphorus-deficient ration, with or without supplementary phosphorus, for 20 weeks, spanning approximately the last 5 weeks of gestation and a 15-week lactation. Non-lactating ewes were employed as controls. No significant differences occurred between groups in liveweight change of ewes or lambs, nor did the groups differ in the mean interval from weaning to first oestrus. Biopsy samples of rib bone taken at the beginning and end of treatment showed significant loss of bone mineral by the end of lactation; ewes suckling twins lost 42 per cent of bone phosphorus, and those with single lambs, 17 per cent. Feeding supplementary phosphorus prevented the significant loss of bone mineral. Fortnightly measurement of the bone density of the hock by radiation absorption also showed differences dependent upon the number of lambs suckled, but failed to detect any effect of phosphorus supplementation. The detection of significant skeletal changes in the absence of effects on production demonstrates the sensitivity of these measures as indices of variations in phosphorus storage. The greater sensitivity of observations on rib bone is probably a reflection of differences between bones in the degree of lability of mineral.