he rumen solubility of P in the four concentrates was characterised by residue P, after a
one-stage in vitro incubation. Five hundred milligram of feed were pretreated by removing
the fat and starch and then added to a strained rumen fluid:buffer solution (1:50). After anaerobic incubation in a water bath at 38 ◦C for 96 h, the residue was filtered with hot water and
acetone and oven dried overnight (Lindgren, 1979). Five samples of each concentrate were
incubated and the residues combined prior to analysis for P. Amounts were not corrected
for the P in the rumen fluid or buffer as these sources presumably only contained soluble P