To evaluate the effect of reduced calcium (Ca) and available P (aP) levels in starter diets on growth performance and tibia, sternum and serum characteristics, and to assay the association between Ca and P (aP) intakes and these variables, 600 one-day-old broiler chicks (Ross 308) were used in a 21-days trial. Broilers were randomly allotted to five treatments with five replicate pens. Chicks were fed on one of the five starter diets that were formulated with a 10% reduction in the Ca and aP contents, starting from the control diet and hence, named as C (0.96% Ca, 0.45% aP), L1 (0.85% Ca and 0.42% aP), L2 (0.77% Ca and 0.38% aP), L3 (0.68% Ca and 0.34% aP) and L4 (0.61% Ca and 0.31% aP). Declining dietary Ca and aP levels did not affect body weight and levels of Ca, P and alkaline phosphatase in serum, but reduced linearly feed intake, the feed conversion ratio and the bone weight and ash content. The Ca and aP intakes and Ca:aP ratio displayed a positive correlation with both tibia and sternum weights, and the mass of the bones were equally sensitive to dietary Ca and aP levels. In conclusion, the body weight of young broilers was irresponsive to changes in the skeleton when exposed to early dietary Ca and aP restrictions (up to 0.61% Ca and 0.31% aP) and the mechanostat had limits due to the association between Ca and aP intakes, and bone properties.

中文翻译：

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育雏期钙磷含量下降的肉鸡体重对骨骼变化无反应

为了评估起始日粮中钙 (Ca) 和有效磷 (aP) 水平降低对生长性能和胫骨、胸骨和血清特征的影响，并分析钙和磷 (aP) 摄入量与这些变量之间的关联，600 一在 21 天的试验中使用了 1 日龄的肉鸡 (Ross 308)。肉鸡随机分配到五个处理组，五个重复围栏。从对照日粮开始，用五种起始日粮中的一种喂养小鸡，这些起始日粮的 Ca 和 aP 含量降低了 10%，因此命名为 C（0.96% Ca，0.45% aP）、L1（0.85% Ca 和 0.42% aP）、L2（0.77% Ca 和 0.38% aP）、L3（0.68% Ca 和 0.34% aP）和 L4（0.61% Ca 和 0.31% aP）。日粮钙和磷水平下降不影响体重和血清中钙、磷和碱性磷酸酶的水平，但线性降低采食量，饲料转化率和骨重和灰分含量。Ca 和 aP 的摄入量以及 Ca:aP 的比率与胫骨和胸骨的重量呈正相关，骨骼的质量对饮食中的 Ca 和 aP 水平同样敏感。总之，当暴露于早期日粮 Ca 和 aP 限制（高达 0.61% Ca 和 0.31% aP）时，年轻肉鸡的体重对骨骼的变化没有反应，并且由于 Ca 和 aP 摄入量之间的关联，机械调节器有限制, 和骨骼属性。