Abstract The objective of the present study was to investigate the effects of age on the apparent ileal calcium (Ca) digestibility of limestone for broiler chickens. Six treatment groups of different ages, namely days 1–7, 8–14, 15–21, 22–28, 29–35 and 36–42, were utilised. A maize-based diet (crude protein, 79 g/kg) containing limestone as the sole Ca source and, supplying 9.0 g/kg Ca, was fed to six replicate cages of broilers during each of the six periods. The birds were fed a commercial broiler starter diet until the introduction of the assay diet, except the day 1–7 age group. Ileal digesta were collected on day 7 (twelve birds per cage), 14 (ten birds per cage), 21 (eight birds per cage), 28 (six birds per cage), 35 (six birds per cage) or 42 (six birds per cage). A secondary objective was to examine the influence of dietary protein content on Ca digestibility. An additional diet containing a crude protein content of 153 g/kg was developed and fed to six replicate cages (eight birds per cage) from day 15 to 21 post-hatch. The birds in the age group of 15–21 days and fed the 79 g/kg crude protein diet served as the control treatment. Titanium dioxide (5 g/kg) was included in all diets as an indigestible marker for apparent ileal digestibility measurements. Total tract Ca retention, pH of gizzard digesta and relative weights of gizzard and gizzard digesta were also measured. Apparent ileal Ca digestibility coefficients declined linearly (P 0.05) on the apparent ileal digestibility and retention of Ca. Increasing dietary protein had no effect (P > 0.05) on the relative weights of gizzard and gizzard digesta. In conclusion, the present results showed that the Ca digestibility of limestone in broilers, fed a maize-based diet with limestone supplying 9 g/kg Ca, declined with advancing age.

中文翻译：

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日龄和日粮粗蛋白含量对肉鸡石灰石表观回肠钙消化率的影响

摘要 本研究的目的是研究年龄对肉鸡石灰石表观回肠钙（Ca）消化率的影响。使用了不同年龄的六个处理组，即第 1-7、8-14、15-21、22-28、29-35 和 36-42 天。在六个时期的每个时期，将含有石灰石作为唯一钙源并提供 9.0 克/公斤钙的玉米基日粮（粗蛋白，79 克/公斤）喂给六个重复的肉鸡笼子。除了第 1-7 天龄组外，在引入测定日粮之前，这些鸡只饲喂商业肉鸡起始日粮。在第 7 天（每笼 12 只）、14（每笼 10 只）、21（每笼 8 只）、28（每笼 6 只）、35（每笼 6 只）或 42（6 只）收集回肠食糜每个笼子）。第二个目的是检查日粮蛋白质含量对钙消化率的影响。开发了含有 153 g/kg 粗蛋白的额外日粮，并在孵化后第 15 天至第 21 天喂给六个重复的笼子（每笼 8 只鸡）。15-21 天龄组的鸡只饲喂 79 g/kg 粗蛋白日粮作为对照处理。二氧化钛 (5 g/kg) 被包含在所有饮食中，作为表观回肠消化率测量的难消化标志物。还测量了总肠道 Ca 保留、胼胝食糜的 pH 值以及胼胝和胼胝食糜的相对重量。表观回肠Ca 消化率系数随表观回肠消化率和Ca 保留率线性下降（P<0.05）。增加膳食蛋白质没有影响（P > 0。05）关于胼胝和胼胝食糜的相对重量。总之，目前的结果表明，肉鸡中石灰石的钙消化率随着年龄的增长而下降，饲喂以石灰石提供 9 g/kg 钙的玉米基日粮。