THE DIGESTIBILITY OF 3 CALCIUM PHOSPHATES FOR PIGS AS MEASURED BY DIFFERENCE AND BY SLOPE-RATIO ASSAY

Taking into account a series of factors possibly responsible for the w ide range in P-digestibility of Ca-phosphates for pigs as found in the literature, an experiment was performed in order to measure, as accur ately as possible, the apparent digestibility of three Ca-phosphates: di-hydrated dicalcium-phosphate; anhydrous dicalciumphosphate and mono calciumphosphate. A digestibility experiment involving seven treatment s with twelve 35-40 kg castrates per treatment, was carried out. Total faeces collection was applied over 10 days. The control diet was a ve ry low-P, semi-synthetic diet (0.37 g P/kg) supplemented with 1 or 2 g of P from each of the three phosphates investigated. In order to guar antee the absolute intake of the supplemented feed phosphates, the pho sphates were weighed separately per meal and, after double checking, h and mixed with the basal diet in the feeding trough of the metabolic c ages. The results of the P-digestibility measurements were virtually i ndependent of the method of calculation: difference method versus regr ession analysis (slope-ratio-technique). It may be concluded that the three Ca-phosphates differ significantly in apparent digestibility: Ca HPO4 . 2H(2)O, 72.9%, (95% confidence limits: 68.6-77.2); CaHPO4, 63.0 %, (95% confidence limits: 58.9-67.2); Ca(H2PO4)(2), 91.6%, (95% confi dence limits: 87.5-95.8). The digestibilities of CaHPO4 . 2H(2)O and C aHPO, are close to the Dutch standards. The digestibility of Ca(H2PO4) (2) however, is much higher (91-92% versus 83%), but in close agreemen t with some recent German findings. In relative terms, these results s how that CaHPO4 is 31% less digestible and CaHPO4 . 2H(2)O. is 20% les s digestible than Ca(H2PO4)(2).