Cell population dynamics revealed by transcriptome deconvolution from femoral medullary tissue of laying hens subjected to mineral phosphorus depletion.

In female birds, the development of medullary bone within the cavities of long bones ensures a calcium reservoir used for eggshell formation. The transition from haematopoietic bone marrow in immature pullets to medullary bone in sexually mature female chickens is accompanied by pronounced structural and functional modifications. Phosphorus is interlinked via endocrine themes, which affect mineral utilization particularly under conditions of rapid daily calcium turnover. In this study, 80 laying hens of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) strains were fed diets with either mineral phosphorus supplement (1 g/kg feed) or without mineral phosphorus supplement (0 g/kg feed) for periods of 4 weeks at two different time points, either immediately before the onset of egg laying (from 15 to 19 weeks of age) or shortly after onset of laying (from 20 to 24 weeks of age). Responses on plasma metabolites and gene expression of medullary bone material were evaluated (n = 10 per strain per week of age per diet). Deconvolution analysis of bulk mRNA sequencing data was performed to estimate cell compositions. Cells of the erythroid lineage made up 85% of all cells located within the medullary bone cavity, while mesenchymal cells including osteoblasts made up 0.33%. During the maturation process, it was estimated that hens developed their macrophage and lymphatic cell populations at the expense of erythroid cells. Results indicated a complete absence of osteoblasts in both hen strains at week 19, whereas at week 24, LSL were estimated to exhibit a higher osteoblast percentage than LB, indicating an advanced molecular adaptation in LSL compared to LB. There was no evidence of impaired development of immune cells or osteoblasts due to the transient lack of mineral phosphorus supply.