Plasma phosphorus content and dietary phosphorus availability in adult sheep

Abstract

This study was aimed at discriminating different quality phosphorus sources using plasma phosphorus kinetics in sheep. Four adult castrated Vendean sheep received successively two preliminary usual then low phosphorus diets (three weeks on 2.5 g P·kg -1 DM and three weeks on 1.5 g P·kg -1 DM), and then one of four compared diets (2.5 g P·kg -1 DM) in a Youden square design. The four compared diets included either dicalcium phosphate, calcium aluminium phosphate, stan- dard rapeseed meal or formaldehyde-treated rapeseed meal as the main phosphorus source. Inorganic plasma phosphorus was determined in samples taken from the jugular vein from the last week of the first preliminary phase to the last week of the test phase. The first preliminary diet stabilised the plasma phosphorus content (51.2 mg·L -1 , no day effect; no animal effect). The low phosphorus diet induced an initial rapid decrease in plasma phosphorus. After four days, plasma phosphorus in- creased probably resulting from an adjustment in phosphorus homeostasis. During the test phase, dicalcium phosphate and both rapeseed meals were more efficient than calcium aluminium phos- phate in restoring the initial plasma phosphorus levels. Both, rapeseed meal diets induced the highest plasma phosphorus concentration. The physiological significance of these results is discussed. availability / phosphorus / plasma / sheep