EXCRETION OF PHOSPHORUS AND ACID IN THE URINE OF SHEEP AND CALVES FED EITHER ROUGHAGE OR CONCENTRATE DIETS

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Abstract
Sheep and calves fed a roughage diet (53% straw + other components) excreted an alkaline urine poor in phosphate whereas when they were fed concentrate diets (80% barley + other components) the urine was acid and contained large amounts of phosphate of which a high proportion were present as titratable H2PO‐4. These differences in phosphorus excretion were not related to differences in phosphorus intake nor did they appear to be directly related to acid excretion. Over a wide range in the amount of phosphate filtered at the glomerulus the amount reabsorbed by the renal tubule was consistently less in animals fed the concentrate diets. These differences in tubular reabsorption appeared to be related to differences between diets in the amounts of phosphorus absorbed from the gut but there were no differences between diets in the level of parathyroid hormone in blood.Both sheep and calves fed a concentrate diet composed of barley and fish meal excreted considerably more acid in the urine than when fed a similar diet in which soya bean meal was substituted as the source of protein. The reasons for this difference in acid excretion are not yet clear.

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