The effects of feeding diets containing either NaHCO3 or NH4Cl on indices of bone formation and resorption and on mineral balance in the lamb.

The effects of diet-induced changes in blood acid-base status on mineral retention has been studied in lambs fed diets containing either 1% NH4Cl or 2% NaHCO3. Balance measurements using 45Ca and 32P showed no difference between them in the amounts of dietary Ca and P absorbed from the gut. Retention of both minerals, however, was lower and their excretion in urine higher in those fed the acid diet. Plasma Ca and P levels were unaffected but parathyroid hormone and 1,25-dihydroxyvitamin D3 levels were higher in lambs on this diet while measurements of tartrate-resistant acid phosphatase and alkaline phosphatase levels in rib samples indicated an increase in osteoclast and a reduction in osteoblast activity in these lambs. Cell-mediated changes in bone turnover together with changes in urinary mineral loss would thus appear to be the major factors contributing to the lower rates of mineral retention seen in lambs fed acid diets.