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In order to determine the nutritional value of the Inranian rock phosphates as ,a phosphorus supplement in layer ration, an experiment was carried out on laying hens for three months period to study the effect of replacement of the dicalcium phosphats (DCP) by the two different rock phosphates (Soltanie and Dalir) either heated or unheated which their phosphorus bioavaiLlabilities were measured previously.
The phosphorus of the layer rations were supplied by the rocks except the control (DCP). In this trial, feed co feed conversion efficiency, egg production, egg weight, and egg specific gravity were measured weekly and the hens were weighed every month.
The best Iranian rock phosphates was found tobe the unheated Soltanie,s which its bioavailability was determined by the Bone Ash Method. The averages of egg production egg weigh, feed conversion efficiency and egg specific gravity were 4.8%, 2.1 gr. 0.184% and 1% respectively higher than those of control treatment.
The heating process of Iranian Phosphates reduced the bioavailability of their phosphorus.