Osteoporosis is a common degenerative metabolic bone disease in caged laying hens. Intensive egg production mobilizing large amounts of Ca from bone for eggshell formation, consequently leading to Ca deficiency, has been recognized as a critical factor causing osteoporosis in commercial laying hens. The aim of this study was to examine the effect of Ca deficiency on the function of the gut microbiota–bone axis and related egg production traits and bone health in laying hens. Twenty-four 48-week-old laying hens were fed a control diet (Control, 3.72%) or a low Ca diet (LC, 2.04%) for 60 d (n = 12). Compared to the Control hens, the LC hens had higher levels of alkaline phosphatase and tartrate resistant acid phosphatase (P < 0.05) with lower bone strength, eggshell thickness, and eggshell strength (P < 0.05). In addition, the LC hens had higher plasma estradiol concentrations, while having lower concentrations of interleukin-1 (IL-1) and IL-6. The LC hens also had a lower pH value in the ileum with an increased Ca retention. The principal co-ordinates analysis showed significantly separate cecal microbiota populations between the Control and LC hens. The Prevotellaceae_UCG-001, Subdoligranulum, Peptococcus, and Eubacterium_hallii_group (P < 0.05) were higher, while the CHKC1001 and Sutterella (P < 0.05) were lower at the genus level in the LC hens. In addition, Prevotellaceae_UCG-001, Subdoligranulum and Eubacterium_hallii_group had a negative correlation, while Sutterella was positively correlated with ileal pH values. The transcriptome analysis revealed that the low Ca diet caused 20 and 31 genes to be significantly up- and down-regulated, respectively. The gene expressions of cystic fibrosis transmembrane conductance regulator, solute carrier family 26 member 3 of the anion exchangers, and mitogen-activated protein kinase 12 of pro-inflammatory factors were lower in the LC birds, which was correlated with the lower ileal pH values. These results suggest that the hens with low Ca diet-induced osteoporosis have an increased intestinal Ca retention with a decreased ileal pH value, correlated with the changes in Prevotellaceae_UCG-001, Subdoligranulum, and Eubacterium_hallii_group of beneficial genera. The results provide insights for further understanding and preventing osteoporosis in laying hens.

骨质疏松症是笼养蛋鸡常见的退行性代谢性骨病。集约化产蛋从骨骼中动员大量钙用于蛋壳形成，从而导致钙缺乏，已被认为是导致商品蛋鸡骨质疏松症的关键因素。本研究的目的是检查钙缺乏对蛋鸡肠道微生物群-骨轴功能和相关产蛋性状以及骨骼健康的影响。24 只 48 周龄的蛋鸡被喂食对照日粮 (Control, 3.72%) 或低钙日粮 (LC, 2.04%) 60 天 ( n  = 12)。与对照母鸡相比，LC 母鸡具有更高水平的碱性磷酸酶和抗酒石酸酸性磷酸酶（P < 0.05) 具有较低的骨强度、蛋壳厚度和蛋壳强度 ( P  < 0.05)。此外，LC 母鸡的血浆雌二醇浓度较高，而白细胞介素 1 (IL-1) 和 IL-6 的浓度较低。LC 母鸡在回肠中的 pH 值也较低，钙保留增加。主坐标分析显示对照组和 LC 母鸡之间的盲肠微生物群明显不同。Prevotellaceae_UCG -001、Subdoligranulum、Peptococcus和Eubacterium_hallii_group（P  < 0.05）较高，而CHKC1001和Sutterella（P  < 0.05）在 LC 母鸡的属水平上较低。此外，Prevotellaceae_UCG-001、Subdoligranulum和Eubacterium_hallii_group呈负相关，而Sutterella与回肠pH值呈正相关。转录组分析显示，低钙饮食分别导致 20 和 31 个基因显着上调和下调。囊性纤维化跨膜电导调节因子、阴离子交换剂溶质载体家族26成员3和促炎因子丝裂原活化蛋白激酶12的基因表达在LC鸡中较低，这与较低的回肠pH值相关。这些结果表明，低钙饮食诱发骨质疏松症的母鸡肠道钙滞留增加，回肠 pH 值降低，与Prevotellaceae_UCG-001、Subdoligranulum和Eubacterium_hallii_group有益属。该结果为进一步了解和预防蛋鸡骨质疏松症提供了见解。