Chicken eggshell (ES) waste is a rich source of calcium carbonate (CaCO₃); however, the potential of ES as dietary calcium (Ca) in old laying hens has not been explored. This study compared the effects of feeding limestone, cockle shell, oyster shell, fine ES, and coarse ES as the sole Ca source on production performance, egg quality, blood biochemical constituents, and tibia characteristics in old laying hens. A total of 450 ISA-Brown laying hens at 73 wk of age with similar egg production rate (EPR) were randomly assigned to 5 treatment groups (90 hens/group, 9 hens/replicate) for 7 wk. Dietary treatment groups comprised a corn-soybean meal based diet containing different Ca sources: (i) limestone (LS; < 2 mm and 2–4 mm mixed in the ratio of 3:7) as control, (ii) cockle shell (CS; 1–4 mm), (iii) oyster shell (OS; 3–16 mm), (iv) ES fine particles (ESF; < 1 mm), and (v) ES coarse particles (ESC; 3–5 mm). Results indicated that dietary inclusion of coarse ES particles significantly increased average egg weight (P < 0.001) and daily egg mass (P < 0.05), and decreased feed conversion ratio (P < 0.001) as compared with the other treatments. However, no significant differences in EPR, feed intake, cracked egg proportion, and mortality were observed among the dietary treatments (P > 0.05). Notably, the use of ESF led to a lower proportion of cracked eggs than ESC (P < 0.05). ESC fed hens produced the heaviest eggs whereas CS fed hens produced the lightest (P < 0.001); the particle size of ES also affected the egg weight (P < 0.05). The eggs from OS and ESC fed hens showed a greater albumen height in comparison to eggs from CS group (P < 0.05); but no significant difference was observed among the LS, OS, ESF, and ESC groups (P > 0.05). The yolk color was darker in the eggs of group ESF as compared with other dietary groups (P < 0.01). However, no significant effects on Haugh units and shell properties were observed among the treatments (P > 0.05). The blood biochemistry results were not affected by the dietary Ca (P > 0.05) except for lower levels of high-density lipoprotein percentage (HDL %) in OS and ESC fed hens (P < 0.05). The tibia characteristics including weight, length, width, and breaking strength did not differ among the dietary groups (P > 0.05). However, the ESC and OS fed hens showed higher tibia bone mineral density (BMD) than the other groups (P < 0.001). In conclusion, coarse ES as a sole Ca source had beneficial effects on the production performance, egg quality, and tibia BMD in old laying hens.

鸡蛋壳（ES）废物是碳酸钙（CaCO ₃ ）的丰富来源；然而，ES 作为老年蛋鸡日粮钙 (Ca) 的潜力尚未被探索。本研究比较了饲喂石灰石、鸟蛤壳、牡蛎壳、细ES和粗ES作为唯一钙源对老蛋鸡生产性能、蛋品质、血液生化成分和胫骨特征的影响。总共 450 只 73 周龄、产蛋率 (EPR) 相似的 ISA-Brown 蛋鸡被随机分配到 5 个处理组（90 只母鸡/组，9 只母鸡/重复），为期 7 周。膳食治疗组包括以玉米-豆粕为基础的膳食，含有不同的钙源：(i) 石灰石（LS；< 2 毫米和 2-4 毫米以 3:7 的比例混合）作为对照，(ii) 鸟蛤壳（ CS；1–4 毫米），（iii）牡蛎壳（OS；3–16 毫米），（iv）ES 细颗粒（ESF；< 1 毫米），以及（v）ES 粗颗粒（ESC；3–5）毫米）。结果表明，与其他处理相比，日粮中添加粗 ES 颗粒显着增加了平均蛋重 ( P < 0.001) 和日蛋量 ( P < 0.05)，并降低了饲料转化率 ( P < 0.001)。然而，不同日粮处理之间的 EPR、采食量、破蛋比例和死亡率没有显着差异（ P > 0.05）。值得注意的是，使用 ESF 导致破裂鸡蛋的比例低于 ESC ( P < 0.05)。 ESC 喂养的母鸡产下的鸡蛋最重，而 CS 喂养的母鸡产下的鸡蛋最轻 ( P < 0.001)； ES粒径对蛋重也有影响( P <<0.05)。与 CS 组的鸡蛋相比，OS 和 ESC 喂养的母鸡的鸡蛋显示出更高的蛋白高度 ( P < 0.05);但 LS、OS、ESF 和 ESC 组之间没有观察到显着差异（P > 0.05）。与其他饮食组相比，ESF 组鸡蛋的蛋黄颜色更深（ P < 0.01）。然而，在处理之间没有观察到对哈夫单位和壳特性的显着影响（ P > 0.05）。除了 OS 和 ESC 喂养母鸡的高密度脂蛋白百分比 (HDL %) 水平较低 ( P < 0.05) 外，血液生化结果不受日粮 Ca 的影响 ( P > 0.05)。饮食组之间的胫骨特征（包括重量、长度、宽度和断裂强度）没有差异（ P > 0.05）。然而，ESC 和 OS 喂养的母鸡表现出比其他组更高的胫骨骨矿物质密度 (BMD) ( P < 0.001)。总之，粗ES作为唯一的钙源对老蛋鸡的生产性能、鸡蛋质量和胫骨骨密度有有益的影响。