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PloS one2026; 21(5); e0348772; doi: 10.1371/journal.pone.0348772

Ovarian follicle dynamics in the plains zebra (Equus quagga).

Abstract: Understanding follicular dynamics during the estrous cycle is essential for developing breeding programs and assisted reproductive technologies (ARTs) in any species. In this context, knowledge of follicular dynamics and related uterine changes in the plains zebra (Equus quagga) is essential to increase the declining population of this vital African species and to provide comparative insights into more endangered zebra species. Likely due to the difficulty of handling these wild species, no detailed reproductive study using ultrasonography has been performed in any zebra. Therefore, the present study aimed to describe follicular dynamics and endometrial echotexture changes in plains zebras using data collected daily via transrectal ultrasonographic monitoring of the ovaries and uterus during spontaneous estrous cycles (no exogenous hormones administered; Experiment 1) and induced ovulatory periods (exogenous hormones administered; Experiment 2). Data from four plains zebra mares revealed that their spontaneous estrous cycles (n = 9) are characterized by a long interovulatory interval (IOI; approximately 38 days), low daily antral follicle count during the IOI (approximately 3 follicles), an absence of follicular waves, a slow follicular growth rate (approximately 1 mm per day), and a relatively similar mean ovulatory follicle diameter (approximately 36 mm) compared to domestic equids. Furthermore, the zebra shows endometrial echotexture patterns similar to those of the horse mare during the preovulatory period. Additionally, by evaluating induced ovulatory periods in two zebras (n = 10 periods), it was shown that these animals respond reliably to luteolytic and ovulation synchronization drugs. Overall, the information provided in this study is vital for the development of breeding programs and ARTs in the plains zebra. In this way, conservation efforts can not only begin to improve the numbers of the plains zebra but also use the information learned from this species to inform efforts for other, more endangered zebras.
Copyright: © 2026 Barros et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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Publication Date: 2026-05-22 PubMed ID: 42172566PubMed Central: PMC13197168DOI: 10.1371/journal.pone.0348772Google 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.

Research Overview

  • This study investigates the ovarian follicle dynamics and uterine changes during the estrous cycle of the plains zebra (Equus quagga) using transrectal ultrasonography.
  • The research aims to provide essential reproductive data to support breeding programs and assisted reproductive technologies (ARTs) to aid conservation efforts for plains zebras and other zebra species.

Background and Importance

  • Understanding follicular dynamics during the estrous cycle is critical for developing effective breeding and ART programs in any species.
  • Plains zebras are a vital African species with declining populations, necessitating improved conservation strategies.
  • Prior to this study, detailed reproductive analysis of zebras using ultrasonography was lacking, mainly due to the challenges in handling wild animals.
  • The study also intends to provide comparative data that could benefit conservation of more endangered zebra species.

Methodology

  • Subjects: Four plains zebra mares were monitored in two experiments.
  • Experiment 1: Daily transrectal ultrasonographic monitoring of ovaries and uterus during spontaneous estrous cycles without hormone administration.
  • Experiment 2: Monitoring during induced ovulatory periods where exogenous hormones were administered for luteolysis and ovulation synchronization.
  • Data collected included follicle number, size, growth rates, interovulatory interval, and endometrial echotexture.

Key Findings on Follicular Dynamics

  • Spontaneous estrous cycles (9 cycles studied) had a long interovulatory interval (IOI) of approximately 38 days, which is longer than many domestic equids.
  • During the IOI, there was a low daily antral follicle count with about 3 follicles present on average.
  • Unlike many domestic horses, plains zebras did not exhibit distinct follicular waves, meaning less cyclical follicle recruitment during the estrous cycle.
  • The follicle growth rate was slow, about 1 mm per day.
  • The mean diameter of the ovulatory follicle before ovulation was roughly 36 mm, which is consistent with domestic horse data.

Endometrial Echotexture Changes

  • The endometrial (uterine lining) echotexture patterns observed were similar to those seen in horse mares during the preovulatory phase.
  • This similarity suggests comparable uterine changes in preparation for ovulation and possible conception.

Findings on Induced Ovulation

  • The study also evaluated 10 induced ovulatory periods in two zebras treated with luteolytic and ovulation synchronization drugs.
  • The zebras responded reliably to these hormone treatments, indicating potential for controlled breeding using ARTs.

Implications and Conservation Relevance

  • The detailed description of the plains zebra’s reproductive physiology provides critical baseline data for establishing breeding programs.
  • The ability to induce ovulation reliably using hormones is promising for assisted reproduction techniques such as artificial insemination.
  • Improving reproductive technologies for plains zebras can help boost declining populations.
  • The knowledge gained can also inform conservation efforts for other zebra species that are more endangered and less studied.

Summary

  • The plains zebra exhibits a long estrous cycle with slower follicle development and fewer antral follicles.
  • The reproductive physiology shares some traits with domestic horses, particularly regarding follicle size and uterine changes before ovulation.
  • Hormonal treatments can effectively synchronize ovulation, enabling potential use of ARTs in conservation breeding programs.
  • This study fills a gap in reproductive data for zebras and provides a foundation to support species survival through modern reproductive management.

Cite This Article

APA
Barros LO, Hyde KA, Gazzaniga N, Gastal MO, Aguiar FLN, Carneiro GF, Gastal EL. (2026). Ovarian follicle dynamics in the plains zebra (Equus quagga). PLoS One, 21(5), e0348772. https://doi.org/10.1371/journal.pone.0348772

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 21
Issue: 5
Pages: e0348772
PII: e0348772

Researcher Affiliations

Barros, Lawrence O
  • Equine Reproduction Veterinarian, João Pessoa, Paraíba, Brazil.
Hyde, Kendall A
  • Animal Science, School of Agricultural Sciences, Southern Illinois University, Carbondale, Illinois, United States of America.
Gazzaniga, Nathalie
  • Animal Science, School of Agricultural Sciences, Southern Illinois University, Carbondale, Illinois, United States of America.
  • Department of Veterinary Medicine, Sousa Campus, Federal Institute of Education, Science and Technology of Paraíba, Sousa, Paraíba, Brazil.
Gastal, Melba O
  • Animal Science, School of Agricultural Sciences, Southern Illinois University, Carbondale, Illinois, United States of America.
Aguiar, Francisco L N
  • Department of Veterinary Medicine, Sousa Campus, Federal Institute of Education, Science and Technology of Paraíba, Sousa, Paraíba, Brazil.
Carneiro, Gustavo F
  • Department of Veterinary Medicine, Federal Rural University of Pernambuco, Recife, Pernambuco, Brazil.
Gastal, Eduardo L
  • Animal Science, School of Agricultural Sciences, Southern Illinois University, Carbondale, Illinois, United States of America.

MeSH Terms

  • Animals
  • Female
  • Ovarian Follicle / physiology
  • Ovarian Follicle / diagnostic imaging
  • Ovarian Follicle / drug effects
  • Equidae / physiology
  • Estrous Cycle / physiology
  • Ultrasonography
  • Ovulation / physiology
  • Ovulation / drug effects
  • Uterus / diagnostic imaging
  • Uterus / physiology

Conflict of Interest Statement

The authors have declared that no competing interests exist.

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