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Reproduction in domestic animals = Zuchthygiene2025; 60(10); e70131; doi: 10.1111/rda.70131

Prediction Values for the Influence of Fetal Sex on Plasma Progesterone Concentration in Crioulo Breed Mares: A Preliminary Investigation.

Abstract: In equine reproduction, determining foetal sex is of economic and strategic importance, but currently available methods are often invasive, costly, or require specialised expertise. This study aimed to assess whether plasma progesterone concentrations could serve as a predictive tool for foetal sex determination in Criollo mares between the 4th and 8th months of gestation and to determine whether these measurements could identify foetal sex. Blood samples were collected at 30-day intervals from 17 Crioula mares between 114 days and 240 days of gestation. Maternal plasma progesterone concentrations were determined by radioimmunoassay and the sex of the foals was confirmed at birth. Analysis of Variance (ANOVA) was made to verify the variation in maternal progesterone concentrations according to foetal sex and month of gestation. In mares carrying male foetuses (n = 7), there was a significant difference in progesterone concentrations between months 4 and 8, as well as between months 7 and 8. In mares carrying male foetuses (n = 7), progesterone concentrations were higher (p = 0.028) during the 4th month of gestation and lower at the 8th month (p = 0.020), compared to the values in mares with female foetuses (n = 10). In the 8th month of pregnancy, the sensitivity and specificity of progesterone concentrations for the predicted sex were 80% and 100%, respectively. A limit value of progesterone (12.45 ng/mL) was established through the ROC (receiver operating characteristic) Curve. Prediction values were 78.8% and 100% for males and females, respectively. Detection rates were 100% and 80% for males and females, respectively. The diagnostic accuracy for both sexes was 88.2%. It is concluded that foetal sex influences plasma concentrations of progesterone in pregnant mares.
© 2025 The Author(s). Reproduction in Domestic Animals published by Wiley‐VCH GmbH.
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Publication Date: 2025-10-07 PubMed ID: 41055121PubMed Central: PMC12502008DOI: 10.1111/rda.70131Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Overview

  • This study investigated whether measuring plasma progesterone levels in pregnant Criollo mares can help predict the sex of the foal between 4 and 8 months of gestation.
  • The research found significant differences in progesterone concentrations depending on fetal sex, suggesting progesterone as a potential non-invasive tool for fetal sex determination in horses.

Background and Purpose

  • In equine reproduction, knowing the sex of the fetus beforehand has both economic and strategic value for breeders and trainers.
  • Existing methods to determine fetal sex are often invasive, expensive, or require specialized practitioners.
  • The study focused on Criollo mares, a specific horse breed, aiming to explore if plasma progesterone levels—a hormone involved in pregnancy maintenance—can reflect fetal sex during mid-gestation (4 to 8 months).

Study Design and Methods

  • A total of 17 Criollo mares were included in the study, all between 114 and 240 days (roughly 4 to 8 months) pregnant.
  • Blood samples were collected every 30 days during this period to measure maternal plasma progesterone levels using radioimmunoassay, a sensitive hormone detection technique.
  • The foetal sex was confirmed at birth to compare with the progesterone data.
  • Statistical analysis using Analysis of Variance (ANOVA) was conducted to assess differences in progesterone levels by fetal sex and month of gestation.

Key Findings

  • In mares carrying male fetuses (n=7):
    • Progesterone levels were significantly higher during the 4th month of gestation compared to mares with female fetuses.
    • Progesterone levels dropped significantly by the 8th month, being lower than in females at this time.
    • Significant differences were noted between months 4 and 8, and months 7 and 8 for males.
  • In mares carrying female fetuses (n=10), progesterone levels exhibited different patterns, generally lower at month 4 and higher by month 8 compared to males.
  • At the 8th month of pregnancy, plasma progesterone concentration could predict fetal sex with:
    • 80% sensitivity for males (true positive rate)
    • 100% specificity for males (true negative rate)
  • A progesterone cutoff value of 12.45 ng/mL was identified using ROC curve analysis to differentiate male and female fetuses.
  • Prediction accuracy was high:
    • 78.8% predictive value for males
    • 100% predictive value for females
    • Detection rates of 100% (males) and 80% (females)
    • Overall diagnostic accuracy was 88.2%

Conclusions and Implications

  • The study concludes that fetal sex influences maternal plasma progesterone concentrations during gestation in Criollo mares.
  • Plasma progesterone has potential as a non-invasive, cost-effective biomarker to predict fetal sex in mares during mid to late pregnancy.
  • This method could offer advantages over traditional fetal sexing approaches that are invasive or require specialized skills.
  • Since this is a preliminary investigation with a modest sample size, further studies are recommended to confirm these findings and refine prediction protocols.

Cite This Article

APA
de Lara NSS, Weiss RR, Oba E, Kozicki LE, Souza FA, Bergstein-Galan TG, Muehlbauer E, Silvestri M, de Lima PHL, Vaz ES. (2025). Prediction Values for the Influence of Fetal Sex on Plasma Progesterone Concentration in Crioulo Breed Mares: A Preliminary Investigation. Reprod Domest Anim, 60(10), e70131. https://doi.org/10.1111/rda.70131

Publication

Reproduction in domestic animals = Zuchthygiene
ISSN: 1439-0531
NlmUniqueID: 9015668
Country: Germany
Language: English
Volume: 60
Issue: 10
Pages: e70131
PII: e70131

Researcher Affiliations

de Lara, Natália Santana Siqueira
  • Universidade Federal Do Paraná - Curitiba, Paraná, Brazil.
Weiss, Romildo Romualdo
  • Universidade Federal Do Paraná - Curitiba, Paraná, Brazil.
Oba, Eunice
  • Universidade Estadual Julio Mesquita - Botucatu, São Paulo, Brazil.
Kozicki, Luiz Ernandes
  • Pontifícia Universidade Católica - Curitiba, Paraná, Brazil.
Souza, Fernando Andrade
  • Universidade Federal Do Paraná - Curitiba, Paraná, Brazil.
Bergstein-Galan, Tacia Gomes
  • Universidade Estadual de Ponta Grossa - Ponta Grossa, Paraná, Brazil.
Muehlbauer, Eloisa
  • Universidade Federal Do Paraná - Curitiba, Paraná, Brazil.
Silvestri, Mayara
  • Universidade Federal Do Paraná - Curitiba, Paraná, Brazil.
de Lima, Pedro Henrique Lomba
  • Pontifícia Universidade Católica - Curitiba, Paraná, Brazil.
Vaz, Eduarda Stankiwich
  • Universidade Federal Do Paraná - Curitiba, Paraná, Brazil.

MeSH Terms

  • Animals
  • Progesterone / blood
  • Horses / blood
  • Horses / physiology
  • Female
  • Pregnancy
  • Male
  • Sex Determination Analysis / veterinary
  • Sex Determination Analysis / methods
  • Sensitivity and Specificity
  • Gestational Age

Conflict of Interest Statement

The authors declare no conflicts of interest.

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