Utilization of Inorganic Ortho-, Meta- and Pyrophosphates by Lambs and by Cellulolytic Rumen Microorganisms in vitro

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Abstract
Both in vivo and in vitro studies were used to measure the relative availability of calcium ortho- and sodium and calcium meta- and pyrophosphates. Sodium orthophosphate was also included in the in vitro studies. In the in vivo study 20 lambs receiving a natural diet were used to determine the absorption and tissue deposition of radioactive phosphorus from the different phosphates in a 7-day total fecal and urinary collection period. One-half of the lambs received 600 ppm of supplemental magnesium as magnesium carbonate. In the in vitro studies cellulose digestion with phosphorus-depleted rumen microorganisms and solubility tests of 0.4% hydrochloric acid, 2% citric acid, neutral ammonium citrate and water were the criteria used. The neutron irradiated phosphates, which had decayed to background radioactivity, and non-irradiated phosphates were compared on the basis of cellulose digestion, solubility and X-ray diffraction patterns. Based on both in vivo and in vitro studies, calcium orthophosphate, sodium ortho- and metaphosphate appeared to be equally valuable as sources of phosphorus. Sodium pyrophosphate was equal to the above phosphates when solubility, cellulose digestion and tissue deposition of P32 were considered, but its apparent absorption value was somewhat lower. Calcium pyrophosphate was essentially unavailable to rumen microorganisms, was least soluble in citric acid and neutral ammonium citrate, and was the least available of the phosphates based on absorption and tissue deposition. Calcium metaphosphate was intermediate in absorption, tissue deposition and cellulose digestion, and was the least soluble in 0.4% hydrochloric acid. The presence of 600 ppm supplemental magnesium in the diet did not affect the absorption and tissue deposition of P32 from the different phosphates. X-ray diffraction patterns indicated detectable but unidentifiable changes resulting from the neutron irradiation of calcium and sodium metaphosphates, while no changes were evident in the other phosphates. Cellulose digestion was similar for neutron irradiated and non-irradiated phosphates. Solubility was not influenced by neutron irradiation except for a suggested increase in the solubility of calcium pyrophosphate in neutral ammonium citrate.

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