Lactation and gestation are among the physiological events that trigger the most intense changes in body calcium (Ca) fluxes. Along with the composition of the animal 2021 diet, these events are suspected to impact the Ca isotopic composition of Ca body reservoirs but their dynamics are poorly understood. In this study, we monitored a group of domestic sows across a full reproduction cycle. We collected tissues and fluids (blood, urine, milk, colostrum, umbilical blood, adult and piglet bones) at different steps of gestation and lactation, and analyzed their Ca isotopic compositions (i.e. δ44/42Ca) by means of multi-collector inductively coupled plasma mass spectrometry. Among other results, we report the first observations of Ca isotopic fractionation between maternal and umbilical blood (Δ44/42Caumbilical blood-sow blood = -0.18 ± 0.11‰, n = 3). Our data also highlight that gestation and lactation periods are characterized by small diet-bone Ca isotopic offsets (Δ44/42Cabone-diet = -0.28 ± 0.11‰, n = 3), with 44Ca-enriched blood compositions during nursing (Δ44/42Canursing blood-gestation blood = + 0.42-0.12+0.11‰, n = 3). Under the light of an up-to-date mammalian box model, we explored different scenarios of gestation and lactation Ca fluxes experienced by a sow-like animal. These simulations suggest that gestation changes on body δ44/42Ca values may result from the intensification of Ca absorption by the animal, whereas the production of 44Ca-depleted milk is the main driver for the 44Ca enrichment in blood during lactation. In addition, our results also support that bone mineralization could be associated with a more restricted Ca isotopic fractionation than previously envisioned. Together, these results refine the framework of Ca isotope applications, notably regarding the monitoring of human bone balance and the study of species and ecosystems from the present and the past.
We thank Yoann Bailly, Stéphane Moreau, Tony Terrasson and the rest of the team of GenESI for their dedicated investment in the project regarding animal management and samplings. For technical assistance on spectrometers, we thank F. Arnaud Godet and P. Telouk. We thank Gildas Merceron for organizing the meeting that planted the seeds of this project as well as many others. The authors are grateful to all the institutions that supported the project.
This study was supported by the Interrvie program of INSU, CNRS (to J.E.M.), by the INRAE (previously INRA), and by the ENS de Lyon.
Data Availability StatementThe data underlying this article are available in the article and in its online supplementary material. The Isopybox program used for building box model simulations and its resources are accessible on Github at the following address: https://github.com/ttacail/isopybox.git.
- CA ISOTOPES