The current calcium (Ca) recommendation for broilers is primarily based on studies conducted more than 30 years ago with birds of markedly different productive potentials from those which exist today. And the response indicators in these studies are mainly growth performance and bone ash percentage. Therefore, the present study was carried out to investigate the effect of dietary Ca level on growth performance, serum parameters, bone characteristics and Ca metabolism-related gene expressions, so as to estimate dietary Ca requirements of broilers fed a conventional corn-soybean meal diet from 1 to 21 days of age. A total of 420 1-day-old Arbor Acres male broilers were randomly assigned to 1 of 7 treatments with 6 replicates (10 birds per cage) and fed the corn-soybean meal diets containing 0.60%, 0.70%, 0.80%, 0.90%, 1.00%, 1.10% or 1.20% Ca for 21 days. Each diet contained the constant non-phytate phosphorus content of about 0.39%. The average daily gain decreased linearly (P < 0.001) as dietary Ca level increased. The serum and tibia alkaline phosphatase (ALP) activities, tibia bone mineral density (BMD), middle toe BMD, tibia ash percentage, tibia breaking strength, and tibia ALP protein expression level were affected (P < 0.05) by dietary Ca level, and showed significant quadratic responses (P < 0.02) to dietary Ca levels. The estimates of dietary Ca requirements were 0.80 to 1.00% based on the best fitted broken-line or quadratic models (P < 0.03) of the above serum and bone parameters, respectively. The results from the present study indicate that the Ca requirements would be about 0.60% to obtain the best growth rate, and 1.00% to meet all of the Ca metabolisms and bone development of broilers fed a conventional corn-soybean meal diet from 1 to 21 days of age.

中文翻译：

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1 至 21 日龄肉鸡饲喂常规玉米-豆粕日粮的日粮钙需求

目前对肉鸡的钙 (Ca) 建议主要基于 30 多年前对具有与今天存在的生产潜力显着不同的鸟类进行的研究。而这些研究中的反应指标主要是生长性能和骨灰分。因此，本研究旨在研究日粮钙水平对生长性能、血清参数、骨骼特征和钙代谢相关基因表达的影响，以估计饲喂常规玉米-豆粕日粮的肉鸡日粮钙需求量。从 1 到 21 日龄。总共 420 只 1 日龄 Arbor Acres 雄性肉鸡被随机分配到 7 个处理中的 1 个处理，6 个重复（每笼 10 只鸡），饲喂含有 0.60%、0.70%、0.80%、0.90% 的玉米豆粕日粮, 1.00%, 1.10% 或 1。20% 钙 21 天。每种饮食都含有约 0.39% 的恒定非植酸盐磷含量。随着膳食钙水平的增加，平均日增重呈线性下降（P < 0.001）。膳食钙水平对血清和胫骨碱性磷酸酶（ALP）活性、胫骨骨密度（BMD）、中趾骨密度、胫骨灰分率、胫骨断裂强度和胫骨ALP蛋白表达水平的影响（P < 0.05），对膳食钙水平显示出显着的二次响应（P <0.02）。根据上述血清和骨骼参数的最佳拟合折线或二次模型 (P < 0.03)，膳食钙需求的估计值分别为 0.80 至 1.00%。本研究的结果表明，钙的需求量约为 0.60% 以获得最佳生长速率，而 1.