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The objective of this study was to evaluate the effect of particle size of adietary Ca source on egg production and eggshell quality when added to hens'diets that have different levels of calcium. The experiment was carried out on216 ISA Brown hens (25 to 70 weeks of age), allocated to 9 groups of 12replicates (cages), with two birds in each cage. A 3 × 3 factorialarrangement was used, with three dietary levels of calcium (3.20, 3.70 and 4.20 %)and three levels of dietary substitutions (0, 25 and 50 %) of fineparticles of limestone (FPL, diameter 0.2–0.6 mm) with large particles oflimestone (LPL, diameter 1.0–1.4 mm) as a Ca source. The level of Ca in the diet had no effect on egg production, mean eggweight, feed intake, feed conversion ratio or eggshell quality parameters(P > 0.05). Substitution of FPL with LPL did not affect layingperformance indices or eggshell quality at 30, 43 and 53 weeks of age(P > 0.05); however, it increased (P < 0.05) eggshellpercentage, thickness, density and breaking strength in older hens (69 weeksof age). In conclusion, the results of this study demonstrated that a levelof 3.20 % Ca in a layer's diet is sufficient through the entire layingcycle to maintain good egg production and eggshell quality and that partial(25 or 50 %) substitution of fine- with large-particle limestone can,irrespective of the level of Ca in the diet, improve eggshell quality inaged laying hens

Effects on performance and eggshell quality of particle size of calcium sources in laying hens' diets with different Ca concentrations