Talk:Horse Development

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Cite this page: Hill, M.A. (2021, May 15) Embryology Horse Development. Retrieved from

Historic: Book_-_A Critical Period in the Development of the Horse (1897)


Agnew ME, Slack J, Stefanovski D, Linton JK & Sertich PL. (2019). Sonographic appearance of the late gestation equine fetal intestine. Theriogenology , 138, 121-126. PMID: 31326658 DOI.

Sonographic appearance of the late gestation equine fetal intestine

Abstract Variable gestation length in the mare poses a challenge for determination of fetal readiness for birth. The objectives of this study were to describe sonographic characteristics of the fetal GI tract in the late gestation mare and identify changes that occur with progressing fetal maturity. Based on these characteristics, a grading scale modeled after the existing human and canine scoring system was developed. Weekly sonographic examination of the fetus by one observer beginning 2-3 weeks prior to a calculated due date of 330 days was performed. Fetal assessment included; presence of stomach rugae, bowel segment definition (uniform echogenic, some defined, clearly defined), bowel segment dilation (none, segmental dilation), intestinal contents (none, mixed echogenicity) and peristalsis (none, occasional, every 3 s, continuous). Based on these characteristics a phase was assigned to the GI tract (1-5). Phase 1 was defined as a uniform echogenic grey area caudal to the diaphragm. The differentiation of Phase 2-5 was based primarily on the frequency of peristalsis, with Phase 2 exhibiting no peristalsis, Phase 3 exhibiting occasional peristalsis, Phase 4 exhibiting peristalsis every 3 s and Phase 5 exhibiting continuous peristalsis. Only data from mares with a normal parturition and healthy foals were included in the statistics (N = 10). Associations amongst sonographic fetal GI characteristics and days prepartum were validated using a simulation-based bootstrap approach with 1000 replicates using Stata 14. Stomach rugae, peristalsis, intestinal contents, tail head relaxation and udder development were all highly correlated with days prepartum. Using a multiple linear regression model, tail head relaxation and peristalsis predicted days prepartum with a 95% CI ± 6 days. The same model predicted days prepartum with a 95% CI ± 4 days when day of gestation, tail head relaxation and peristalsis were included as variables. Based on these findings, characterization of the fetal GI tract could provide valuable information concerning the maturity of the equine fetus. Further studies are needed comparing high risk mares to normal mares before this information could be used with confidence in the clinical setting. Copyright © 2019 Elsevier Inc. All rights reserved. KEYWORDS: Fetus; Gastrointestinal; Horse; Pregnancy; Ultrasound PMID: 31326658 DOI: 10.1016/j.theriogenology.2019.07.006

Fages A, Hanghøj K, Khan N, Gaunitz C, Seguin-Orlando A, Leonardi M, McCrory Constantz C, Gamba C, Al-Rasheid KAS, Albizuri S, Alfarhan AH, Allentoft M, Alquraishi S, Anthony D, Baimukhanov N, Barrett JH, Bayarsaikhan J, Benecke N, Bernáldez-Sánchez E, Berrocal-Rangel L, Biglari F, Boessenkool S, Boldgiv B, Brem G, Brown D, Burger J, Crubézy E, Daugnora L, Davoudi H, de Barros Damgaard P, de Los Ángeles de Chorro Y de Villa-Ceballos M, Deschler-Erb S, Detry C, Dill N, do Mar Oom M, Dohr A, Ellingvåg S, Erdenebaatar D, Fathi H, Felkel S, Fernández-Rodríguez C, García-Viñas E, Germonpré M, Granado JD, Hallsson JH, Hemmer H, Hofreiter M, Kasparov A, Khasanov M, Khazaeli R, Kosintsev P, Kristiansen K, Kubatbek T, Kuderna L, Kuznetsov P, Laleh H, Leonard JA, Lhuillier J, Liesau von Lettow-Vorbeck C, Logvin A, Lõugas L, Ludwig A, Luis C, Arruda AM, Marques-Bonet T, Matoso Silva R, Merz V, Mijiddorj E, Miller BK, Monchalov O, Mohaseb FA, Morales A, Nieto-Espinet A, Nistelberger H, Onar V, Pálsdóttir AH, Pitulko V, Pitskhelauri K, Pruvost M, Rajic Sikanjic P, Rapan Papeša A, Roslyakova N, Sardari A, Sauer E, Schafberg R, Scheu A, Schibler J, Schlumbaum A, Serrand N, Serres-Armero A, Shapiro B, Sheikhi Seno S, Shevnina I, Shidrang S, Southon J, Star B, Sykes N, Taheri K, Taylor W, Teegen WR, Trbojević Vukičević T, Trixl S, Tumen D, Undrakhbold S, Usmanova E, Vahdati A, Valenzuela-Lamas S, Viegas C, Wallner B, Weinstock J, Zaibert V, Clavel B, Lepetz S, Mashkour M, Helgason A, Stefánsson K, Barrey E, Willerslev E, Outram AK, Librado P & Orlando L. (2019). Tracking Five Millennia of Horse Management with Extensive Ancient Genome Time Series. Cell , 177, 1419-1435.e31. PMID: 31056281 DOI.

Tracking Five Millennia of Horse Management with Extensive Ancient Genome Time Series

Abstract Horse domestication revolutionized warfare and accelerated travel, trade, and the geographic expansion of languages. Here, we present the largest DNA time series for a non-human organism to date, including genome-scale data from 149 ancient animals and 129 ancient genomes (≥1-fold coverage), 87 of which are new. This extensive dataset allows us to assess the modern legacy of past equestrian civilizations. We find that two extinct horse lineages existed during early domestication, one at the far western (Iberia) and the other at the far eastern range (Siberia) of Eurasia. None of these contributed significantly to modern diversity. We show that the influence of Persian-related horse lineages increased following the Islamic conquests in Europe and Asia. Multiple alleles associated with elite-racing, including at the MSTN "speed gene," only rose in popularity within the last millennium. Finally, the development of modern breeding impacted genetic diversity more dramatically than the previous millennia of human management. Copyright © 2019 The Author(s). Published by Elsevier Inc. All rights reserved. KEYWORDS: ancient DNA; animal breeding; diversity; domestication; equestrian civilizations; extinct lineages; horses; management; mules; selection Comment in Ancient genomes shed light on dark horses. [Nat Rev Genet. 2019] PMID: 31056281 PMCID: PMC6547883 DOI: 10.1016/j.cell.2019.03.049


Proteins involved in embryo-maternal interaction around the signalling of maternal recognition of pregnancy in the horse

Sci Rep. 2018 Mar 27;8(1):5249. doi: 10.1038/s41598-018-23537-6.

Smits K1, Willems S2, Van Steendam K2, Van De Velde M3, De Lange V3, Ververs C3, Roels K3, Govaere J3, Van Nieuwerburgh F2, Peelman L4, Deforce D2, Van Soom A3.


During maternal recognition of pregnancy (MRP), a conceptus-derived signal leads to the persistence of the corpus luteum and the maintenance of gestation. In the horse, the nature of this signal remains to be elucidated. Several studies have focused on the changes in gene expression during MRP, but little information exists at the protein level. The aim of this study was to identify the proteins at the embryo-maternal interface around signalling of MRP in the horse (day 13) by means of mass spectrometry. A distinct influence of pregnancy was established, with 119 proteins differentially expressed in the uterine fluid of pregnant mares compared to cyclic mares and with upregulation of several inhibitors of the prostaglandin synthesis during pregnancy. By creating an overview of the proteins at the embryo-maternal interface in the horse, this study provides a solid foundation for further targeted studies of proteins potentially involved in embryo-maternal interactions, MRP and pregnancy loss in the horse.

PMID: 29588480 PMCID: PMC5869742 DOI: 10.1038/s41598-018-23537-6


Histological study of the external, middle and inner ear of horses

Anat Histol Embryol. 2015 Dec;44(6):401-9. doi: 10.1111/ahe.12151. Epub 2014 Oct 6.

Blanke A1, Aupperle H2, Seeger J3, Kubick C4, Schusser GF1.


Clinical, anatomical and histological aspects of the equine acoustic organ have been poorly investigated and illustrated in literature so far. It is understood that an intact acoustic organ and hearing function are of vital importance for the well-being of flight animals like horses. The knowledge of the acoustic organ is usually transferred analogously from other mammals to horses. The purpose of this study was to provide a detailed and complete histological description of the healthy equine auditory organ, and to determine its congruity to other mammalians. Anatomical dissections and histological preparations were carried out on ten cadaver heads. Specimens of various parts of the equine acoustic organ were taken and evaluated histologically. The histological composition of external, middle and inner ear structures are predominantly congruent to those of other mammals, especially to human beings. Unique inwardly directed rete pegs within the osseous ear canal and the prominent tensor tympani muscle are described for the first time. Results obtained in this study can be employed as references for further research on the equine acoustic organ and improve the understanding of the clinical development of hearing loss, otitis externa/media/interna or tympanosclerosis.

© 2014 Blackwell Verlag GmbH.

PMID 25283481


Sex determination in horses - current status and future perspectives

Anim Reprod Sci. 2014 Apr;146(1-2):34-41. doi: 10.1016/j.anireprosci.2014.01.014. Epub 2014 Feb 6.

Aurich C1, Schneider J2.


In the equine species, sex determination of the conceptus is of growing interest for the breeding industry. In horses, the sex ratio of the offspring depends on changes in body condition of the mother at conception and under natural conditions may thus markedly deviate from an expected 1:1 ratio. Insemination with sex-sorted spermatozoa allows a pronounced shift of the sex ratio but at present pregnancy rates are low and vary considerably under field conditions. In equine embryo transfer programmes, sex determination in embryos before transfer via genetic methods is a promising approach with high reliability. In ongoing pregnancies, fetal sex can be determined in utero by transrectal or transabdominal ultrasound between days 57 and 220 after ovulation, but experience is required to achieve satisfying accuracy. Recently, genetic sexing via identification of circulating cell-free fetal DNA in the maternal circulation has been successfully performed in the last three months of pregnancy. Development of this technique may also allow fetal sex determination at earlier stages of pregnancy. Further research is required to allow for techniques that enable sex determination in equine embryos as well as in ongoing pregnancies under field conditions. Copyright © 2014 Elsevier B.V. All rights reserved. KEYWORDS: Embryo; Environment; Fetus; Horse; Sex determination PMID 24598214

Prenatal Development of the Digestive System in the Horse

Anat Rec (Hoboken). 2014 Apr 29. doi: 10.1002/ar.22929. [Epub ahead of print]

Rodrigues MN1, Carvalho RC, Franciolli AL, Rodrigues RF, Rigoglio NN, Jacob JC, Gastal EL, Miglino MA. Author information


Since the horse has a highly precocial reproductive strategy, most organs are functionally well developed at birth and thus, embryonic and fetal life is interesting. Data on the development of important organs are very limited. Here, we detailed macroscopically and histologically the equine digestive system, focusing on the first third of gestation. At 21 days, the oral cavity was an empty space, and the liver contained proliferating endodermal cells. At 25 days, a fusiform stomach and the pancreatic bud were present. At 28 days, a small tongue and the esophagus occurred. At 30 days, primary and secondary palates were developed, the liver contained cords of hepatocytes, and the pancreas was triangular. At 40 days, crypts had formed in the intestinal loops, cell differentiation was observed in the hepatic parenchyma, and the pancreas was elongated. Pancreatic acini and islets were observed in fetuses of 50 days and intestines were highly convoluted. Three segments of the pharynx were distinguishable at 75 days. At 105 days, the intestinal villi were wide with round tips; especially, the liver, stomach, and oral cavity showed key steps of anatomical and cellular differentiation in early fetuses, whereas other areas, such as pancreas or pharynx were still immature in the investigated phase. Pluripotency analysis using Oct4 showed initial intense staining in all of the digestive system tissues and a later decreased becoming restricted to specific cell layers. In conclusion, our data may contribute to perform a chronological reference of developmental events for approaches predicting pregnancy disorders in horses. Anat Rec, 2014. © 2014 Wiley Periodicals, Inc. © 2014 Wiley Periodicals, Inc. KEYWORDS: development, embryology, equine, mare, pregnancy alteration

PMID 24778084


Random X inactivation in the mule and horse placenta

Genome Res. 2012 Oct;22(10):1855-63. doi: 10.1101/gr.138487.112. Epub 2012 May 29.

Wang X, Miller DC, Clark AG, Antczak DF. Source Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York 14853, USA. Abstract In eutherian mammals, dosage compensation of X-linked genes is achieved by X chromosome inactivation. X inactivation is random in embryonic and adult tissues, but imprinted X inactivation (paternal X silencing) has been identified in the extra-embryonic membranes of the mouse, rat, and cow. Few other species have been studied for this trait, and the data from studies of the human placenta have been discordant or inconclusive. Here, we quantify X inactivation using RNA sequencing of placental tissue from reciprocal hybrids of horse and donkey (mule and hinny). In placental tissue from the equid hybrids and the horse parent, the allelic expression pattern was consistent with random X inactivation, and imprinted X inactivation can clearly be excluded. We characterized horse and donkey XIST gene and demonstrated that XIST allelic expression in female hybrid placental and fetal tissues is negatively correlated with the other X-linked genes chromosome-wide, which is consistent with the XIST-mediated mechanism of X inactivation discovered previously in mice. As the most structurally and morphologically diverse organ in mammals, the placenta also appears to show diverse mechanisms for dosage compensation that may result in differences in conceptus development across species.

PMID 22645258


Proteomic analysis of mare follicular fluid during late follicle development

Proteome Sci. 2011 Sep 17;9:54. doi: 10.1186/1477-5956-9-54.

Fahiminiya S1, Labas V, Roche S, Dacheux JL, Gérard N.

Abstract BACKGROUND: Follicular fluid accumulates into the antrum of follicle from the early stage of follicle development. Studies on its components may contribute to a better understanding of the mechanisms underlying follicular development and oocyte quality. With this objective, we performed a proteomic analysis of mare follicular fluid. First, we hypothesized that proteins in follicular fluid may differ from those in the serum, and also may change during follicle development. Second, we used four different approaches of Immunodepletion and one enrichment method, in order to overcome the masking effect of high-abundance proteins present in the follicular fluid, and to identify those present in lower abundance. Finally, we compared our results with previous studies performed in mono-ovulant (human) and poly-ovulant (porcine and canine) species in an attempt to identify common and/or species-specific proteins. METHODS: Follicular fluid samples were collected from ovaries at three different stages of follicle development (early dominant, late dominant and preovulatory). Blood samples were also collected at each time. The proteomic analysis was carried out on crude, depleted and enriched follicular fluid by 2D-PAGE, 1D-PAGE and mass spectrometry. RESULTS: Total of 459 protein spots were visualized by 2D-PAGE of crude mare follicular fluid, with no difference among the three physiological stages. Thirty proteins were observed as differentially expressed between serum and follicular fluid. Enrichment method was found to be the most powerful method for detection and identification of low-abundance proteins from follicular fluid. Actually, we were able to identify 18 proteins in the crude follicular fluid, and as many as 113 in the enriched follicular fluid. Inhibins and a few other proteins involved in reproduction could only be identified after enrichment of follicular fluid, demonstrating the power of the method used. The comparison of proteins found in mare follicular fluid with proteins previously identified in human, porcine and canine follicular fluids, led to the identification of 12 common proteins and of several species-specific proteins. CONCLUSIONS: This study provides the first description of mare follicular fluid proteome during the late follicle development stages. We identified several proteins from crude, depleted and enriched follicular fluid. Our results demonstrate that the enrichment method, combined with 2D-PAGE and mass spectrometry, can be successfully used to visualize and further identify the low-abundance proteins in the follicular fluid. PMID 21923925

Functions of ectopically transplanted invasive horse trophoblast

Reproduction. 2011 Jun;141(6):849-56. doi: 10.1530/REP-10-0462. Epub 2011 Mar 9.

de Mestre AM, Hanlon D, Adams AP, Runcan E, Leadbeater JC, Erb HN, Costa CC, Miller D, Allen WR, Antczak DF. Source College of Veterinary Medicine, Baker Institute for Animal Health, Cornell University, Ithaca, New York 14853, USA. Abstract The invasive and fully antigenic trophoblast of the chorionic girdle portion of the equine fetal membranes has the capacity to survive and differentiate after transplantation to ectopic sites. The objectives of this study were to determine i) the survival time of ectopically transplanted allogeneic trophoblast cells in non-pregnant recipient mares, ii) whether equine chorionic gonadotropin (eCG) can be delivered systemically by transplanted chorionic girdle cells, and iii) whether eCG delivered by the transplanted cells is biologically active and can suppress behavioral signs associated with estrus. Ectopically transplanted chorionic girdle survived for up to 105 days with a mean lifespan of 75 days (95% confidence interval 55-94) and secreted sufficient eCG for the hormone to be measurable in the recipients' circulation. Immunohistochemical labeling of serial biopsies of the transplant sites and measurement of eCG profiles demonstrated that graft survival was similar to the lifespan of equine endometrial cups in normal horse pregnancy. The eCG secreted by the transplanted cells induced corpora lutea formation and sustained systemic progesterone levels in the recipient mares, effects that are also observed during pregnancy. This in turn caused suppression of estrus behavior in the recipients for up to 3 months. Thus, ectopically transplanted equine trophoblast provides an unusual example of sustained viability and function of an immunogenic transplant in a recipient with an intact immune system. This model highlights the importance of innate immunoregulatory capabilities of invasive trophoblast cells and describes a new method to deliver sustained circulating concentrations of eCG in non-pregnant mares. PMID 21389079

Transcriptional profiling of equine conceptuses reveals new aspects of embryo-maternal communication in the horse

Biol Reprod. 2011 May;84(5):872-85. doi: 10.1095/biolreprod.110.088732. Epub 2011 Jan 5.

Klein C, Troedsson MH. Source Gluck Equine Research Center, Department of Veterinary Science, University of Kentucky, Lexington, KY 40546, USA.


Establishment and maintenance of pregnancy are critically dependent on embryo-maternal communication during the preimplantation period. The horse is one of the few domestic species in which the conceptus-derived pregnancy recognition signal has not been identified. To gain new insights into the factors released by the equine conceptus, transcriptional profiling analyses of conceptuses retrieved 8, 10, 12, and 14 days after ovulation were performed using a whole-genome microarray. Selected array data were confirmed using quantitative PCR, and the expression of proteins of interest was confirmed using immunohistochemistry and Western blotting. Gene ontology classification of differentially regulated transcripts underlines the ongoing embryo-maternal dialogue. Transcript showing higher expression levels as conceptus' development proceeds mainly localizes to the extracellular environment, thereby having the potential to act upon the uterine environment. Genes involved in the positive regulation of the immune system are enriched among transcripts displaying decreased expression, reflecting the need of the semiallograft conceptus to be protected from the immune system. A subset of differentially expressed genes, such as BRCA1 and FGF2, has previously been described to be expressed by early stages of embryonic development, whereas other transcripts are apparently unique to equine conceptuses, as their expression has not been reported in other species. These transcripts include fibrinogen subunits, the expressions of which were confirmed at the mRNA and protein level. Furthermore, results indicate the counteraction of trophoblast invasion, and that the conceptus appears to regulate changes in sialic acid content of its capsule, an event suggested to be essential for successful establishment of pregnancy. PMID 21209420

Viability of equine embryos after puncture of the capsule and biopsy for preimplantation genetic diagnosis

Reproduction. 2010 Dec;140(6):893-902. doi: 10.1530/REP-10-0141. Epub 2010 Sep 15.

Choi YH, Gustafson-Seabury A, Velez IC, Hartman DL, Bliss S, Riera FL, Roldán JE, Chowdhary B, Hinrichs K. Source Department of Veterinary Physiology and Pharmacology, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas 77843-4466, USA.


The equine embryo possesses a capsule that is considered essential for its survival. We assessed viability after breaching the capsule of early (Day 6) and expanded (Day 7 and 8) equine blastocysts by micromanipulation. The capsule was penetrated using a Piezo drill, and trophoblast biopsy samples were obtained for genetic analysis. Pregnancy rates for Day-6 embryos, which had intact zonae pellucidae at the time of recovery, were 3/3 for those biopsied immediately after recovery and 2/3 for those biopsied after being shipped overnight under warm (∼28 °C) conditions. The pregnancy rates for encapsulated Day-7 expanded blastocysts were 5/6 for those biopsied immediately and 5/6 for those biopsied after being shipped overnight warm. Two of four encapsulated Day-8 blastocysts, 790 and 1350 μm in diameter, established normal pregnancies after biopsy. Nine mares were allowed to maintain pregnancy, and they gave birth to nine normal foals. Biopsied cells from eight embryos that produced foals were subjected to whole-genome amplification. Sex was successfully determined from amplified DNA in 8/8 embryos. Identification of disease-causing mutations matched in the analyses of 6/6 samples for the sodium channel, voltage-gated, type IV, alpha subunit (SCN4A) gene and in 6/7 samples for the peptidylprolyl isomerase B (PPIB) gene, in embryo-foal pairs. Thus, the capsule of the equine embryo can be breached without impairing viability. Further work is needed to determine whether this breach is transient or permanent. These findings are relevant to the understanding of equine embryo development and to the establishment of methods for micromanipulation and embryo cryopreservation in this species. PMID 20843896