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Current Research on Donkeys and Mules: Second Edition
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Current Research on Donkeys and Mules: Second Edition

A Special Issue of Animals (ISSN 2076-2615) belonging to the section "Equids".

Deadline for manuscript submissions: 31 October 2026 | Viewed by 6613

Editors

Prof. Dr. Alejandro Pérez-Écija

E-Mail Website
Guest Editor
Faculty of Veterinary Medicine, University of Córdoba, 14071 Córdoba, Spain
Interests: donkeys; mules; clinical pathology; hematology; pathology; internal medicine
Special Issues, Collections and Topics in MDPI journals
Prof. Dr. Francisco J. Mendoza

E-Mail Website
Guest Editor
Department of Animal Medicine and Surgery, University of Cordoba, Campus Rabanales, 14014 Cordoba, Spain
Interests: donkeys; mules; clinical pathology; hematology; pathology; internal medicine
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are pleased to open a new edition of this exciting and fruitful Special Issue, dedicated to the latest and most promising research on donkeys and mules. Although there is a growing interest in these species due to their more recent uses (milk and meat production, assisted therapy, and pet/companion animals), their traditional importance (packing and agricultural work), and the efforts to maintain endangered breeds all over the world, they are still neglected and forgotten in many scientific fields, with little to no specific information available on some topics. This brings new opportunities to researchers interested in characterizing their idiosyncrasies or specific attitudes. This Special Issue is aimed at highlighting species-specific findings in physiology, genetics, welfare, behavior, internal medicine, epidemiology, pathology, and pharmacology, along with any research showcasing new applications for these species. Comparative studies with other equids will also be of interest. Both reviews and original articles are welcome. By collecting manuscripts on a wide variety of cutting-edge topics, we hope to support these species and help to preserve and maintain their populations. We look forward to receiving your contributions.

Prof. Dr. Alejandro Pérez-Écija
Prof. Dr. Francisco Mendoza García
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Animals is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • donkey
  • mule
  • internal medicine
  • behavior
  • pathology
  • clinical pathology
  • welfare
  • physiology
  • pathogens
  • milk
  • pharmacology

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Related Special Issue

Published Papers (6 papers)

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Research

17 pages, 1606 KB  
Article
DNase Promotes the Release of Sperm Trapped by NETs and Induces Important Changes in Donkey Sperm Motility Patterns
by Sandra Llorens, Sebastià Company, Luisina Chapero, Iván Yánez-Ortiz, Augusto Carluccio, Ippolito De Amicis, Jaime Catalán and Jordi Miró
Animals 2026, 16(14), 2185; https://doi.org/10.3390/ani16142185 - 14 Jul 2026
Viewed by 494
Abstract
A deeper understanding of the donkey’s reproductive strategy is essential to improve reproductive efficiency in this species. In the jenny’s uterus, sperm selection relies on the post-insemination endometrial reaction, characterized by the influx of polymorphonuclear neutrophils (PMNs), which form extracellular traps (NETs) that [...] Read more.
A deeper understanding of the donkey’s reproductive strategy is essential to improve reproductive efficiency in this species. In the jenny’s uterus, sperm selection relies on the post-insemination endometrial reaction, characterized by the influx of polymorphonuclear neutrophils (PMNs), which form extracellular traps (NETs) that capture spermatozoa. Of these, some are liberated through the action of a deoxyribonuclease (DNase) present in the seminal plasma. This study aimed to develop an in vitro model to evaluate the effects of NETs and DNase action on donkey sperm viability and motility. For this purpose, donkey ejaculates were collected, PMNs were isolated from the jenny’s blood and free spermatozoa were selected using a Silica gel filtration (EquiPure®, EP, Nidacon International AB, Mölndal, Sweden) to form five experimental groups: control (semen), SPZ-PMN, SPZ-PMN-DNase, SPZ-PMN-EP, SPZ-PMN-DNase-EP. Sperm viability and motility were assessed in all experimental groups using eosin-nigrosin staining and CASA sperm analysis system, respectively, at 1, 2 and 3 h of incubation. Sperm viability remained stable in the groups containing PMN, while it significantly (p < 0.05) decreased in the control group, suggesting a protective effect of PMN on sperm viability. Regarding kinetic parameters, spermatozoa initially captured by NETs and later liberated by DNase exhibited higher velocity (VCL, VSL, VAP), linearity (LIN), straightness (STR) and oscillation (WOB). These changes in sperm motility may be related to the physiological changes occurring before sperm capacitation. This study can improve the understanding of the unique reproductive strategy of donkeys and could be useful to improve in vitro sperm capacitation and embryo production. Full article
(This article belongs to the Special Issue Current Research on Donkeys and Mules: Second Edition)
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14 pages, 7744 KB  
Article
Preliminary Evaluation of Muscle Fiber Composition in the Middle Gluteal Muscle in Race Mules and Mammoth Donkeys
by Raja Zabeeh Ullah Khan, Neil Gray, Francisco Javier Navas González and Amy K. McLean
Animals 2026, 16(11), 1640; https://doi.org/10.3390/ani16111640 - 27 May 2026
Viewed by 521
Abstract
Research on mule and donkey muscle composition remains limited despite their global importance as working equids. The objective of this study is to identify Mammoth donkey jacks with higher percentage of fast twitch fibers for racing mule production. A total of 33 animals [...] Read more.
Research on mule and donkey muscle composition remains limited despite their global importance as working equids. The objective of this study is to identify Mammoth donkey jacks with higher percentage of fast twitch fibers for racing mule production. A total of 33 animals were biopsied; however, only 12 samples were suitable for analysis, including racing mules (n = 7) and male Mammoth donkeys (n = 5). Animals were sedated with detomidine (10 µg/kg body weight) and butorphanol (20 µg/kg body weight). Middle gluteal muscle biopsies were collected using a 6 mm Bergström biopsy needle at a site located 20 cm dorsocaudal to the tuber coxae at a 45° angle to the base of the tail. Collection depth was 7.5 cm in adult mules and 5 cm in donkeys. Samples were prepared aseptically, anesthetized subcutaneously with lidocaine hydrochloride, and frozen in liquid nitrogen. Histochemical analysis included myosin adenosine triphosphatase (ATPase) staining at pH 9.5, 4.6, and 4.3. Fibers were classified as Type I, Type IIA, or Type IIB, and CSA measurements were obtained using NIH ImageJ software. Statistical analysis included group contrasts, summarized as mean ± SD with 95% confidence intervals, while Bayesian ANOVA outputs were presented as exploratory evidence summaries. Type IIA fibers were greater in mules (47.84 ± 7.30%) than donkeys (38.47 ± 4.48%). Results suggest that differences in equid muscle architecture may be associated with variation in Type IIA fiber composition related to work or use. Full article
(This article belongs to the Special Issue Current Research on Donkeys and Mules: Second Edition)
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16 pages, 1784 KB  
Article
Movement Ecology and Disease Exposure in Free-Roaming Donkeys in California, USA
by Sarah R. B. King, Amy McLean, Jacob D. Hennig and Kathryn A. Schoenecker
Animals 2026, 16(8), 1269; https://doi.org/10.3390/ani16081269 - 21 Apr 2026
Viewed by 1090
Abstract
Feral donkeys (Equus asinus) are well adapted to arid ecosystems and are found in large populations in the deserts of Australia and the Americas. We assessed resource selection and seasonal home range size of female donkeys in southern California between 2020 [...] Read more.
Feral donkeys (Equus asinus) are well adapted to arid ecosystems and are found in large populations in the deserts of Australia and the Americas. We assessed resource selection and seasonal home range size of female donkeys in southern California between 2020 and 2022 based on telemetry data. We also examined whether dyads with greater encounter rates were more likely to test positive for asinine herpesvirus 5 (AHV-5) and/or Streptococcus equi zooepidemicus (SEZ). Donkey home ranges were non-significantly larger in the cool/wet season (November through March; mean 318.37 ± sd 417.65 km2) than in the hot/dry season (April through October; mean 159.35 ± 212.43 km2). Donkeys selected flatter areas closer to water year-round but selected greater herbaceous cover during the cool/wet season and lower heat loads during the hot/dry season. Individuals testing positive for SEZ selected lower elevations during the wet season and closer distances to water during the dry season; donkeys testing positive for AHV-5 selected areas farther from water during the wet season and steeper slopes during the dry season. The dyad encounter rate was unrelated to presence of either disease. Our results contribute to the understanding of donkey ecology, allowing feral populations to be better controlled by specific and focused management. Full article
(This article belongs to the Special Issue Current Research on Donkeys and Mules: Second Edition)
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15 pages, 604 KB  
Article
Both Season and Equid Type Affect Endogenous Adrenocorticotropic Hormone Concentrations in Healthy Donkeys, Mules and Hinnies in the United States
by Erin L. Goodrich, Sebastián Gonzalo Llanos-Soto, Renata Ivanek, Toby Pinn-Woodcock, Elisha Frye, Amy Wells, Stephen R. Purdy, Emily Berryhill and Ned J. Place
Animals 2026, 16(2), 290; https://doi.org/10.3390/ani16020290 - 16 Jan 2026
Cited by 1 | Viewed by 860
Abstract
Baseline plasma ACTH concentrations are frequently utilized as part of the diagnostic evaluation of equids when PPID is suspected. Baseline ACTH can be impacted by many factors including time of year, i.e., ACTH has generally been found to be elevated during late summer [...] Read more.
Baseline plasma ACTH concentrations are frequently utilized as part of the diagnostic evaluation of equids when PPID is suspected. Baseline ACTH can be impacted by many factors including time of year, i.e., ACTH has generally been found to be elevated during late summer through early autumn in the northern hemisphere. An understanding of ACTH concentrations in healthy equids over the course of a year is useful for the proper interpretation of concentrations in PPID-suspect animals. Previous studies assessing ACTH concentrations in healthy donkeys (Equus asinus) and hybrids (E. asinus × E. caballus) are limited, often utilizing very small numbers, equids from specific and limited geographical regions, limited timeframes or unspecified donkey types (miniature, standard, or mammoth). We aimed to characterize the seasonal variation in baseline ACTH concentrations in healthy miniature donkeys, standard donkeys and hybrids in the United States (US) and to compare those concentrations across these groups. Following outlier removal, 19 standard donkeys (from California (CA), Massachusetts (MA), New York (NY)), 14 miniature donkeys (CA and NY), and 28 hybrids (Texas (TX) and NY) were utilized for analysis. Samples were collected from each equid twice per month from June to November 2019 and once per month from December 2019 through May 2020. The mean ACTH concentration of all equids was higher from mid-August through the end of October compared to the rest of the year (being the highest in the second half of September with the mean (standard deviation) values of 109.6 (52.6), 134.6 (67.4), and 100.8 (189.6) in standard donkeys, miniature donkeys, and hybrids, respectively). Additionally, ACTH concentrations in hybrids were 23% (95% Confidence Interval (CI): 4–38%) and 51% (95% CI: 36–63%) lower than in standard and miniature donkeys, respectively, from mid-August through October. During the rest of the year, hybrids similarly showed 31% (95% CI: 16–43%) and 30% (95% CI: 15–42%) lower ACTH concentrations compared with standard and miniature donkeys, respectively. Full article
(This article belongs to the Special Issue Current Research on Donkeys and Mules: Second Edition)
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22 pages, 1543 KB  
Article
Morphological, Morphometric and Phaneroptic Variations of the Mediterranean Donkey and Tunisian Perspective on Conservation and Breeding
by Mohamed Aroua, Nour Elhouda Fehri, Antonella Fatica, Sana Khaldi, Samia Ben Said, Bayrem Jemmali, Mokhtar Mahouachi and Elisabetta Salimei
Animals 2026, 16(2), 207; https://doi.org/10.3390/ani16020207 - 9 Jan 2026
Viewed by 1512
Abstract
The domestic donkey (Equus asinus) remains an essential component of agricultural systems worldwide, particularly in rural Tunisia. This study aims to conduct a comprehensive morphological characterization of the Tunisian donkey population, focusing on phaneroptic variation, sexual dimorphism and live weight prediction. [...] Read more.
The domestic donkey (Equus asinus) remains an essential component of agricultural systems worldwide, particularly in rural Tunisia. This study aims to conduct a comprehensive morphological characterization of the Tunisian donkey population, focusing on phaneroptic variation, sexual dimorphism and live weight prediction. A total of 556 clinically healthy donkeys, consisting of 207 males and 349 females, were sampled from various governorates in Tunisia. Descriptive statistics revealed significant variability in withers height (98–147 cm), thoracic circumference (100–165 cm) and body length (86–144 cm). Principal Component Analysis identified coat color and belly pigmentation as major contributors to phaneroptic variation, explaining 69.556% of the total variance. Hierarchical Ascendant Classification further classified the population into three distinct groups, with Group I exhibiting smaller body dimensions, Group II having medium sizes, and Group III consisting of larger donkeys. Sexual dimorphism was detected in neck circumference (females: 64.30 cm vs. males: 61.97 cm; FDR-adjusted p = 0.0468). Regression models for predicting live weight indicated that thoracic circumference was the most reliable single predictor (R2 = 95.4%). Overall, the study documents a wide range of morpho-biometric variation within the Tunisian donkey population and provides practical tools for field-based weight estimation, offering valuable insights for future conservation strategies and management programs. Full article
(This article belongs to the Special Issue Current Research on Donkeys and Mules: Second Edition)
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10 pages, 3078 KB  
Article
Pilot Study: Heart Rate and Heart Rate Variability Indices in Mules Evaluated by 24-Hour Electrocardiogram
by Lauren T. Maas, Jessica M. Morgan, Jordan Case, David D. Chell and Amy K. McLean
Animals 2025, 15(16), 2438; https://doi.org/10.3390/ani15162438 - 20 Aug 2025
Cited by 1 | Viewed by 1332
Abstract
Mules and donkeys are the 5th largest equine population in the U.S., yet basic information such as heart rate and arrhythmia prevalence in mules has not been described. Analysis of heart rate variability (HRV) provides valuable insight into physiologic and autonomic differences between [...] Read more.
Mules and donkeys are the 5th largest equine population in the U.S., yet basic information such as heart rate and arrhythmia prevalence in mules has not been described. Analysis of heart rate variability (HRV) provides valuable insight into physiologic and autonomic differences between mules, horses, and donkeys. We aimed to pilot the evaluation of heart rate and variability in a healthy population of mules using a 24 h electrocardiogram. Twenty-four-hour ambulatory electrocardiogram (aECG) recordings were collected from an athletic population of seven privately owned healthy mules in Northern California. Vision 5 Holter Analysis Software was utilized for ECG review and analysis. An average heart rate of 32–42 bpm, with a mean of 36 ± 3 bpm for 23.8 ± 0.2 h, was recorded. Minimum heart rate was 16–24 bpm, and maximum was 70–156 bpm. Individual mules had supraventricular complexes, sinoatrial heart block, and second-degree atrioventricular block during the observation period. Electrocardiographic evaluation of mules over 24 h found heart rate (HR) to be similar to horses and lower than in donkeys. Arrhythmias were consistent with the range of cardiac rhythms observed in horses and more frequent than reported in donkeys. Further investigation with a larger sample size of mules is warranted to determine if reference values for horses should continue to be used to assess mules and to investigate the prevalence of arrhythmias and their clinical relevance in the mule. Full article
(This article belongs to the Special Issue Current Research on Donkeys and Mules: Second Edition)
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