Mature sheep fitted with rumen and duodenal cannulae, and fed a pelleted hay diet, were given supplementary phosphorus by continuous infusion into the rumen and the effects on salivary phosphorus secretion, net intestinal phosphorus absorption and faecal endogenous phosphorus excretion were studied. In control periods little phosphorus was excreted in the urine and little increase was seen in response to supplementation, the faeces being the major pathway for excretion. Increasing phosphorus intake led to an increase in net intestinal phosphorus absorption, a rise in plasma phosphate concentration, an increase in salivary phosphorus secretion and an increase in faecal endogenous phosphorus excretion. Overall net intestinal absorptive efficiency for phosphorus did, however, decrease as intake rose so that changes in faecal endogenous phosphorus excretion were in part due to increased salivary phosphorus secretion and in part to a reduction in overall absorptive efficiency. The significance of these changes in relation to the control of phosphorus balance in ruminants is discussed. INTRODUCTIONMATERIALS AND METHODS

SUMMARYGrowing lambs were fed diets low in nitrogen and phosphorus (LNLP), low 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 higher, and phosphorus concentrations lower, in lambs fed the low phosphorus diets but there were no differences in plasma 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) concentrations. Lambs fed both low phosphorus diets (LNLP and HNLP) had lower plasma osteocalcin and higher bone-specific alkaline phosphatase concentrations than those fed the high phosphorus diets. Urinary pyridinoline and deoxypyridinoline excretion were also affected by treatment, with their rates of excretion being highest in lambs fed the diet low in both nitrogen and phosphorus (LNLP). Lambs fed the low phosphorus diets were lighter in weight at slaughter and had lighter bones that were less well mineralized than those fed the high phosphorus diets. Reducing the nitrogen content of the diet appeared to have little effect on bone composition. These results suggest that bone markers that have proved useful in the diagnosis and treatment of bone disease are sensitive to variation in nutrient supply and may prove useful in the early detection of nutrient deficiencies that affect bone growth.

SUMMARYGrowing pigs were fed diets supplying 45 % (low), 70% (intermediate) and 100% (high) recommended dietary allowances of calcium (the Ca:P ratio was kept constant), but otherwise adequate in nutrients. The effects of varying calcium and phosphorus intakes on bone and plasma osteocalcin were monitored. Mineral content of the diet did not affect feed conversion and live weight gain. Plasma phosphorus concentrations decreased significantly in pigs fed a low mineral diet compared with those fed the high mineral diet, but there were no changes in plasma calcium and osteocalcin concentrations. Bones from the low mineral group had marked reductions in dry matter, calcium and phosphorus contents, as well as increased collagen, pyridinoline and deoxypyridinoline concentrations: osteocalcin concentrations in bone were unaffected by treatment. The results showed no direct link between osteocalcin and the degree of bone mineralization.

SUMMARYMature sheep fitted with rumen and duodenal cannulae were fed either a hay or a concentrate diet and the effects on salivary phosphorus secretion, net intestinal phosphorous absorption and pathway for phosphorous excretion were examined. Route of excretion was markedly affected by diet with urine phosphorus levels being much higher and faecal levels lower when the concentrate diet was fed. This difference was not due to differences in phosphorus intake nor could it be related to differences in either plasma phosphorus levels or net intestinal phosphorus absorption. Salivary phosphorus secretion and renal tubular reabsorptive efficiency for phosphorus were, however, both lower when the concentrate diet was fed. The significance of these effects ofdiet in relation to the control ofphosphorus balance in ruminants is discussed.

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