Abstract
Fetal mortality significantly impacts reproductive efficiency in sheep, with approximately 30% of fetuses failing to survive until lambing. In multifetal gestation, partial litter loss (PLL) occurs in 28% to 37% of cases. The biochemical composition of allantoic fluid (ALF), which plays a key role in metabolic regulation and fetal waste clearance, has been shown in other species to reflect fetal development and maturity. However, ALF metabolomics in sheep, especially in relation to PLL, remains unexplored. This study investigated late-gestation fetal mortality in multifetal sheep pregnancies by analyzing maternal metabolic status, placental gene expression, and ALF composition to identify potential metabolic compounds associated with PLL. The study was conducted on 25 ewes, of which 14 experienced PLL, and 11 had vital litters (VL). Plasma analysis revealed that VL ewes have higher β-hydroxybutyrate concentrations than PLL ewes, whereas plasma insulin and cortisol levels are higher in PLL ewes. Analysis of gene expression in the placental cotyledon demonstrated increased androgen receptor expression in PLL pregnancies and trends toward elevated solute carrier family 2 member 1, and reduced nuclear receptor subfamily 3 group C member 1 expression. Insulin-like growth factor 2 expression tended to be higher in VL placentas. Allantocentesis was performed on 25 ewes with multifetal pregnancies (11 VL and 14 PLL). ALF samples were collected from 74 fetuses at 140.4 ± 2.0 days in pregnancy, and 41 samples were selected for metabolomic profiling. Using genomic analysis, 25 ALF samples were confidently matched to individual lambs. Untargeted lipidomics of ALF from 14 lambs in PLL (7 born alive vs. 7 stillborn) revealed 24 differentially abundant lipid compounds. Stillborn lambs exhibited lower phosphatidylglycerol (PG) 15:0_20:1, but higher levels of sphingomyelin (SM), lysophosphatidylcholine (LPC), ether-linked phosphatidylethanolamines (PEs), lysophosphatidylethanolamines (LPEs), and monogalactosyldiacylglycerols (MGDGs). Collectively, PLL in multifetal ewe pregnancies is linked to maternal metabolic imbalance, elevated cortisol levels, dysregulated placental gene expression, and altered ALF lipid profiles in stillborn fetuses. Elevated SM and LPC, and lower PG, suggest immature lungs. These molecular and metabolic signatures may provide new insights into the mechanisms underlying PLL in late-gestation multifetal pregnancies.
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The authors wish to thank the entire staff in charge of the experimental flock at the Volcani Center, Rishon LeZion, Israel, for their assistance with animal care.This sentence is added to the manuscript.
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This research was financially supported by the Chief Scientist of the Ministry of Agriculture, Rishon LeZion – grant number 362081023.
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**TA: ** Methodology, Conceptualization, Project administration, Ultrasound monitoring, Data curation, Visualization, Laboratory analysis, Formal analysis, Validation, and Writing. **MR** : Allantocentesis. **JS** : Data curation, Visualization **. PDSS** : Laboratory analysis, Formal analysis. **AR** : Data curation, Animal care, Formal analysis, Methodology. **LL** : Data curation, Laboratory analysis, Methodology, Validation. **GK** : Laboratory analysis, Formal analysis. **MG** : Genomic data processing. **SM** : Formal analysis, Metabolomics, Lipidomics. **MI** : Formal analysis, Metabolomics, Lipidomics **. RR** : Data processing, Statistical analysis. **UM: ** Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Resources, Software, Supervision, Visualization, Writing – review & editing. All authors have read and agreed to the published version of the manuscript.
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Alon, T., Ross, M., Spirer, J. et al. Lipidomics of allantoic fluid collected by allantocentesis indicates a possible mechanism underlying partial litter loss in multifetal pregnancies of ewes. Sci Rep (2026). https://doi.org/10.1038/s41598-026-44636-9
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DOI: https://doi.org/10.1038/s41598-026-44636-9


