EFFECT OF DIETS VARYING IN NITROGEN OR PHOSPHORUS-CONTENT ON INDICATORS OF BONE-GROWTH IN LAMBS

Growing lambs were fed diets low in nitrogen and phosphorus (LNLP), lo w in nitrogen and high in phosphorus (LNHP), high in nitrogen and low in phosphorus (HNLP) or high in nitrogen and phosphorus (HNHP) and the effects on bone growth and on blood and urinary bone marker levels or excretion rates were monitored. Plasma calcium concentrations were hi gher, and phosphorus concentrations lower, in lambs fed the low phosph orus diets but there were no differences in plasma 1,25-dihydroxyvitam in D-3 (1,25(OH)(2)D-3) concentrations. Lambs Fed both low phosphorus diets (LNLP and HNLP) had lower plasma osteocalcin and higher bone-spe cific alkaline phosphatase concentrations than those fed the high phos phorus diets. Urinary pyridinoline and deoxypyridinoline excretion wer e also affected by treatment, with their rates of excretion being high est in lambs fed the diet low in both nitrogen and phosphorus (LNLP). Lambs fed the low phosphorus, diets were lighter in weight at. slaught er and had lighter bones that were less well mineralized than those fe d the high phosphorus diets. Reducing the nitrogen content of the diet appeared to have little effect on bone composition. These results sug gest that bone markers that have proved useful in the diagnosis and tr eatment of bone disease are sensitive to variation in nutrient supply and may prove useful in the early detection of nutrient deficiencies t hat affect bone growth.