The effect of calcium source and particle size on the production performance and bone quality of laying hens.

The efficacy of 3 local limestone sources as potential Ca sources for laying hens was studied. Limestone sources were assessed for in vitro solubility. Four Ca sources (control, A, B, or C) and 2 particle size combinations (ground, 100% ground; or mixed, 67% ground+33% large particle) was used. The control consisted of a commercial ground limestone for the ground Ca source and oyster shell of the large particle Ca source. DeKalb laying hens were randomly placed in 32 battery cage units (n=12/cage). At 19 wk of age, hens received 1 of 8 Ca source and particle size treatments (4 replicates/treatment) until 74 wk. Egg production, feed consumption, BW, and egg quality were measured throughout. Bone mineral density (by quantitative computed tomography), breaking strength, ash, and Ca were assessed at the end of lay. In vitro solubility was dependent upon Ca source and particle size (P<0.0001) with oyster shell generally having a greater in vitro solubility than test limestone sources A, B, and C of similar particle sizes. Feed consumption (100 to 117 g/bird per day), BW (1,500 to 1,800 g), egg production (92% peak egg production), egg weight (55 to 67 g), and egg specific gravity (1.090 to 1.078) did not differ among hens fed the different Ca sources (P>0.05). Tibia bone mineral density indicated the oyster shell treatment had a lower trabecular density than Ca source A; however, all other Ca sources had similar bone mineral density for all measures (P>0.05). Hens fed the mixed Ca particle treatments consistently had greater feed consumption from 27 to 70 wk than those fed the 100% ground Ca source (P<0.05). Bone mineralization was enhanced in hens that received the mixed Ca particle treatments (P<0.05). Overall, the results of this study indicate that the local limestone sources A, B, and C would be suitable alternatives to current commercial sources of Ca for laying hens. In addition, large particle Ca did improve bone quality.