Effects of Particle Size on the Biological Availability of Calcium and Phosphorus in Defluorinated Phosphate for Chicks ,

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A total of 576 d-old, male, broiler chicks were used in two trials 1) to determine the range of Ca and P levels over which the response in bone characteristics is linear and 2) to determine the influence of particle size of defluorinated rock phosphate (DFP) on the bioavailability of Ca and P in DFP. Six treatments were used in Experiment 1 in which varying percentages of added Ca (.00, .06, .12, .24, .36, and .48%) and added P (.00, .05, .10, .20, .30, and .40%) were evaluated in a corn-soybean meal diet containing 23% CP, .47% Ca, and .39% P (.14% available P). Weight gain, feed intake, and tibia breaking strength increased (P<.001) with increasing levels of dietary Ca and P. Treatments in Experiment 2 consisted of: 1) Diet 1, a corn-soybean meal basal diet (23% CP, .50% Ca, .46% P, .21% available P), 2) Diet 1 with .12% added Ca from calcium carbonate (CC) and .07% added P from monosodium phosphate (MSP), 3) Diet 1 with .24% added Ca from CC and .14% added P from MSP, and 4 to 8), Diet 1 with .24% added Ca and .14% added P from five particle sizes of DFP. Feed intake, weight gain, and tibia breaking strength and ash percentage increased linearly (P<.01) and feed.gain ratio decreased quadratically (P<.10) with increasing percentages of added Ca and P in Diets 1 to 3. Feed intake, weight gain, bone breaking strength and bone ash did not differ (P>.10) among the five particle sizes of DFP or for the DFP versus the highest level of added CC and MSP. The availability of Ca and P in the DFP was determined by slope ratio; bone breaking strength and ash were regressed on added Ca and P intake. The bioavailability of Ca and P (combined), relative to that in CC and MSP (both given a value of 100%), in the five particle sizes of DFP was 101, 94, 87, 100, and 90%, respectively (P>.10). These data indicate that particle size, within the range tested, does not affect the bioavailability of Ca and P in DFP for the growing chick.