Effect of particle size of the calcium source on performance of broiler chicks fed diets with different calcium and phosphorus levels.

Broiler chicks were fed diets differing in calcium (Ca) level, source, and particle size. The basal diet fed in most experiments contained .62% total phosphorus and .49% Ca from sources other than the Ca sources being compared. Performance was not affected by Ca source in diets with .9% Ca. In diets with 1.5% Ca, gain and bone ash were significantly lower with a powdered, USP grade calcium carbonate than with limestone particles passing through a 1,000-mu screen and retained by a 417-mu screen. Crushing these particles to allow them to pass through a 74-mu screen caused them to behave like the powdered calcium carbonate. Particles of this limestone had to at least pass through a 147-mu screen to cause a greater reduction in gain; the finest particles tested (passed a 74-mu screen) reduced performance most. When graded levels of fine and medium particles were fed, the higher levels reduced gain, and less of the fine particles was required to produce a given reduction. In a high Ca-low P diet, fine particles of the Ca source were more deleterious than medium. Apparently, chicks can shunt excess Ca in the form of medium particles (150 to 1,000 mu) through the digestive system better than they can the more reactive, fine particles.