Effect of calcium carbonate particle size on the available phosphorus requirement of broiler chicks.

Sixteen hundred broiler strain cockerels housed in battery brooders 1 to 21 days of age were used to determine the effect of feeding different commercially available particle-sized calcium carbonate (CaCO3) on the phosphorus requirement. Five replicates of 8 chicks each were fed corn-soy type diets consisting of either 12 to 20, 20 to 60, or 100 to 200 (passed-retained basis) United States Bureau of Standards (USBS) sieve-sized CaCO3. Each particle-sized CaCO3 was fed in diets containing either .20 to .30% (Experiment 2), or .20 to .45% (Experiment 3) available phosphorus (AP) with .05% increments. Supplementary phosphorus was added as sodium phosphate monobasic. Tibia ash and body weight were greater when the USBS 20 to 60 particle-sized CaCO3 was fed then when either the USBS 12 to 20 or 100 to 200 particle-sized CaCO3 was fed. 90% dietary calcium was fed to broiler chicks, the phosphorus requirement was either .35% AP with the USBS 20 to 60 particle-sized CaCO3 or at least .45% AP with either the USBS 12 to 20 or 100 to 200 particle-sized CaCO3. Blood alkaline phosphatase, which indicates bone calcification, was inversely correlated (r = -.65) with bone ash. Blood calcium and blood phosphorus increased, and blood alkaline phosphatase decreased with increasing dietary phosphorus. These data show that the 21-day-old broiler chick's available phosphorus requirement is less in corn-soybean meal diets containing a USBS 20 to 60 particle-sized CaCO3 than in diets containing either the USBS 12 to 20 or 100 to 200 particle-sized CaCO3.