Calcium and phosphorus fractional excretion in Nellore before and during pregnancy

Abstract

The assessment of calcium and phosphorus nutrition is difficult when using serum concentrations of these elements, because they remain within normal ranges despite a wide variation in Ca and P contents in different diets due to the high efficiency of body homeostasis process. Significant alterations are observed in chronic deficiencies when economic losses have a relevant importance. The use of fractional excretion of Ca and P allow quantitative evaluation without need of timed urine volumetric determinations. Fractional excretion ratios for Ca and P were determined using eight consecutive 45-day urine and serum sample collections performed on 22 heifers before (two samplings) and during pregnancy (six samplings). The values presented by fractional excretion of Ca and P ranged from 1.06% to 3.72% and 1.09% to 2.70%, respectively. There was a tendency to diminishing fractional excretion median values of Ca when comparing before pregnancy with values observed during pregnancy. This experiment showed that there is wide variation in Ca and P fractional excretion in different animals at the same moment and this results in difficulties to access nutritional status of these elements in cattle raised on pasture using this method.