Effect of excessive inorganic phosphorus supplied by abomasal infusion on inorganic phosphorus metabolism in dairy cows

Abstract: The effects of inorganic phosphorus (Pi) supplied by abomasal infusion on phosphorus metabolism were tested in three cows of the Swedish red and white breed in a study with a 3×3 Latin square design. Monosodium dihydrogen orthophosphate dihydrate (NaH2PO4.2H2O) solution with three different levels of P (0, 14.4 and 28.8 g/d) was infused in the abomasum for four days in each experimental period. Blood, rumen liquid, feces and urine samples were collected. Co-EDTA was used as a marker for the estimation of rumen liquid phase volume and rumen fluid outflow rate. Pi absorption tended to increase as P supply increased. This was accompanied by a tendency for the reduction of Pi absorption efficiency suggesting mechanisms in the small intestine regulating Pi absorption. It appeared that the fractional absorption rate of Pi was negatively related to the increasing amount of P supply. In addition, P infusion resulted in increased salivary Pi concentration. It was suggested that salivary glands could have increased Pi secretion in response to increased Pi flux in plasma. This was evidenced from the unchanged plasma Pi concentration in relation to increased Pi absorption. Urinary Pi excretion played a negligible role in P balance. It was concluded that P homeostasis was controlled within gut through regulation of Pi uptake, salivary Pi secretion and fecal Pi excretion.