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Topic:Developmental Biology
Developmental biology in horses involves the study of the processes by which horses grow and develop from a single fertilized egg into a fully formed organism. This field encompasses various stages, including embryonic development, fetal growth, and postnatal maturation. Researchers in this area examine cellular differentiation, gene expression, and morphogenetic movements that contribute to the formation of tissues and organs in equine species. Key topics include the molecular mechanisms that regulate developmental pathways, the influence of genetic and environmental factors on development, and the identification of developmental disorders. This page compiles peer-reviewed research studies and scholarly articles that explore the fundamental aspects of equine developmental biology, offering insights into the mechanisms driving normal and abnormal development in horses.
Development of biochemical heterogeneity of articular cartilage: influences of age and exercise. The objective of this study was to document the development of biochemical heterogeneity from birth to maturity in equine articular cartilage, and to test the hypothesis that the amount of exercise during early life may influence this process. Neonatal foals showed no biochemical heterogeneity whatsoever, in contrast to a clear biochemical heterogeneity in mature horses. The process of formation of site differences was almost completed in exercised foals age 5 months, but was delayed in those deprived of exercise. For some collagen-related parameters, this delay was not compensated for after a...
Equine placentation. A tough, elastic glycoprotein capsule envelops the equine blastocyst between Days 6 and 23 after ovulation. It maintains the spherical configuration of, and provides physical support for, the embryo as it traverses the entire uterine lumen during Days 6-17, propelled by myometrial contractions that are stimulated by pulsatile release of prostaglandin F2alpha and prostaglandin E2. The capsule also accumulates constituents of the exocrine secretions of the endometrial glands ('uterine milk') as nutrients for the mobile embryo as it releases its antiluteolytic maternal recognition-of-pregnancy si...
Biochemical development of subchondral bone from birth until age eleven months and the influence of physical activity. Subchondral bone provides structural support to the overlying articular cartilage, and plays an important role in osteochondral diseases. There is growing insight that the mechanical features of bone are related to the biochemistry of the collagen network and the mineral content. In the present study, part of the normal developmental process and the influence of physical activity on biochemical composition of subchondral bone was studied. Water content, calcium content and characteristics of the collagen network (collagen, hydroxylysine, lysylpyridinoline (LP) and hydroxylysylpyridinoline (HP)...
Developmental competence in vivo and in vitro of in vitro-matured equine oocytes fertilized by intracytoplasmic sperm injection with fresh or frozen-thawed spermatozoa. This study was undertaken to evaluate the development of equine oocytes in vitro and in vivo after intracytoplasmic sperm injection (ICSI) with either fresh or frozen-thawed spermatozoa, without the use of additional activation treatments. Oocytes were collected from ovaries obtained from an abattoir and oocytes classified as having expanded cumulus cells were matured in M199 with 10% fetal bovine serum and 5 microU FSH ml(-1). After 24-26 h of in vitro maturation, oocytes with a first polar body were selected for manipulation. Fresh ejaculated stallion spermatozoa were used for the experiment...
The testis as a major source of circulating inhibins in the male equine fetus during the second half of gestation. Immunolocalization of the inhibin (a) and inhibin/activin (beta3A and betaB) subunit proteins in equine fetal testes was investigated to determine the ability of the fetal testis to produce inhibins at 120, 150, 200, and 250 days of gestation. In addition, concentrations of immunoreactive (ir)-inhibin, inhibin pro-aC, and inhibin A in both the maternal and fetal circulation were measured. It was found that plasma concentrations of ir-inhibin, inhibin pro-alphaC, and inhibin A were much higher (P < .05) in the fetal than in the maternal circulation at any stage of gestation examined. Similar...
Development of the equine brain motor system. The purpose of the present study was to demonstrate the structural maturation of the horse brain in the critical period of development emergence of coordinated locomotion. Equine brains from 14 days before expected birth to adulthood were fixed in formaldehyde and embedded in paraffin. After taking the outer parameters of the brains, full series of large-area coronal sections were prepared on a special microtome and stained with Nissl's cresyl violet and Haidenhain's iron-haematoxylin. Microscopic images of sections were digitized and were subjected to computer-aided image analysis. The gross ...
Biochemical markers of bone metabolism in growing thoroughbreds: a longitudinal study. This study describes longitudinal changes in serum levels of biochemical markers of bone cell activity in a group of 24 thoroughbred foals from birth to 18 months of age. The markers of bone formation included the type I collagen carboxy-terminal propeptide (PICP), the bone-specific isoenzyme of alkaline phosphatase (BAP), and osteocalcin (OC). Levels of the cross-linked telopeptide of type I collagen (ICTP), a marker of bone resorption, and the N-terminal propeptide of type III collagen (PNIIIP), a marker of soft tissue turnover, were also measured. Levels of all markers fell significantly be...
Immortalization of equine trophoblast cell lines of chorionic girdle cell lineage by simian virus-40 large T antigen. Immortalized cell lines have many potential experimental applications including the analysis of molecular mechanisms underlying cell-specific gene expression. We have utilized a recombinant retrovirus encoding the simian virus-40 (SV-40) large T antigen to construct several immortalized cell lines of equine chorionic girdle cell lineage - the progenitor cells that differentiate into the equine chorionic gonadotropin (eCG) producing endometrial cups. Morphologically, the immortalized cell lines appear similar to normal chorionic girdle cells. Derivation of the immortalized cell lines from a cho...
Morphologic stages of the equine embryo proper on days 17 to 40 after ovulation. To describe the gross and histologic changes that develop in the equine embryo proper (ie, the portion of the embryo that becomes the fetus) from days 17 to 40 after ovulation and to compare the external features of equine embryos with those of porcine, ovine, and human embryos. Methods: 34 embryos collected from mixed-breed pony mares. Methods: External features for each embryo proper, including length, number of branchial arches, growth of appendages, face and head features, and body features, were examined, using a dissecting microscope, for embryos collected on days 17 to 40. Internal feat...
Organisation of the cytoskeleton during in vitro maturation of horse oocytes. Meiotic maturation of mammalian oocytes is a complex process during which microfilaments and microtubules provide the framework for chromosomal reorganisation and cell division. The aim of this study was to use fluorescence and confocal laser scanning microscopy to examine changes in the distribution of these important cytoskeletal elements and their relationship to chromatin configuration during the maturation of horse oocytes in vitro. Oocytes were cultured in M199 supplemented with pFSH and eLH and, at 0, 12, 24, and 36 hr after the onset of culture, they were fixed for immunocytochemistry ...
Influence of insulin-like growth factor-I and its interaction with gonadotropins, estradiol, and fetal calf serum on in vitro maturation and parthenogenic development in equine oocytes. The effects of insulin-like growth factor-I (IGF-I) and its interaction with gonadotropins, estradiol, and fetal calf serum (FCS) on in vitro maturation (IVM) of equine oocytes were investigated in this study. We also examined the role of IGF-I in the presence or absence of gonadotropins, estradiol, and FCS in parthenogenic cleavage after oocyte activation with calcium ionophore combined with 6-dimethylaminopurine (6-DMAP), using cleavage rate as a measure of cytoplasmic maturation. Only equine cumulus-oocyte complexes with compact cumulus and homogenous ooplasm (n = 817) were used. In experim...
Developmental capacity of equine oocytes matured and cultured in equine trophoblast-conditioned media. The objective was to compare culture media for in vitro maturation of equine oocytes and for in vitro culture of zygotes produced from IVF of partially zona-removed oocytes. Cumulus-oocyte complexes from slaughterhouse-derived ovaries were washed in m-Dulbecco's PBS and cultured in TCM-199, F10-DMEM or c-F10-DMEM (50% F10-DMEM + 50% F10-DMEM conditioned medium from culture of an equine trophoblast monolayer for 3 or 4 days). All media included FSH, LH, E2, and 10% FCS. After 28 to 30 h maturation, cumulus expansion was scored from 0 (no expansion) to 4 (fully expanded). Oocytes with a 1st pola...
Developmental anomalies and abnormalities of the equine iris. The iris is derived from interaction between neural crest tissue and the adjacent neuroectoderm of the optic cup. Developmental anomalies of the equine iris are common, and include congenital miosis, iris cysts, various manifestations of iris hypoplasia, heterochromia, and persistent pupillary membrane remnants. They may be found alone or in combination with other ocular defects.
Confocal microscopy of germinal vesicle-stage equine oocytes. The objectives were to compare cumulus type with nucleus form in equine cumulus oocyte complexes (COCs), to define the percentage of germinal vesicle (GV)-stage oocytes within a population of mares, and to further define GV nucleus shapes of equine oocytes. Cumulus types were as follows: 1) compact (56/208, 26.9%), 2) slightly expanded (37/208, 17.8%), 3) moderately expanded (27/208, 13.0%), 4) greatly expanded (15/208, 7.2%), or 5) denuded (73/208, 35.1%). One hundred thirty of 208 COCs (62.5%) were GV-stage, 21/208 (10.1%) were condensed chromatin-stage, 8/208 (3.8%) were polar body-stage, 4...
Fetomaternal interactions and influences during equine pregnancy. The equine embryo takes 6 days to traverse the oviduct and, when it finally enters the uterus, it remains spherical in shape and moves continually throughout the uterine lumen until day 17 after ovulation to deliver its maternal recognition of pregnancy signal to the entire endometrium. Between day 25 and day 35 after ovulation, the trophoblast cells of a discrete annulate portion of the chorion multiply rapidly and acquire an invasive phenotype and, between day 36 and day 38, migrate deeply into the maternal endometrium to form the equine-unique endometrial protuberances known as endometrial ...
Closure of the abdominal wall at the umbilicus and the development of umbilical hernias in a group of foals from birth to 11 months of age. The closure of the body wall defect at the umbilicus was studied in relation to the development of umbilical hernias in a group of 44 normal foals, 25 of which were followed from birth until five months of age, and 19 from birth until 11 months of age. At birth, 19 of the foals had a defect in the body wall at the umbilicus that was termed a 'palpable umbilical ring'. In 18 of them this defect disappeared within four days, but in the other the ring did not close and a hernial sac with abdominal contents was palpable. This foal was considered to be the only foal to have a truly congenital umbil...
Scanning electron microscopy of the microcotyledonary placenta of the horse (Equus caballus) in the latter half of gestation. Scanning electron microscopy was used to examine the microstructure of the maternal and fetal placenta from 25 pregnant ponies (Equus caballus) throughout the second half of gestation. Samples of placenta, 2-6 cm(2)in area, were collected from the antimesometrial region of the pregnant horn at 105 days (n=1), 165-219 days (n=5), 260 days (n=3), 270-277 days (n=3), 313-337 days (n=11) and immediately after spontaneous delivery at term (n=2). The maternal microcaruncle appears to be created from a clustering of about 16 uterine crypts encapsulated in a connective tissue sheath. There is a gestat...
A unique exocelom-like space during early pregnancy in the horse. The free allantois and allantochorion of conceptuses from 17 mares between 20 and 90 days of gestation were examined to determine the manner in which the associated mesodermal derivatives differentiated. It was found that a robust basement membrane developed under the allantoic endoderm, and that this basement membrane was partially isolated from the vascular layer of the allantois by a mesothelial layer and an exocelom-like space. The exocelom-like space persisted until approximately the stage of villous formation, and remnants of the space persisted over larger allantoic vessels even later. ...
Glycosylation in the near-term epitheliochorial placenta of the horse, donkey and camel: a comparative study of interbreeding and non-interbreeding species. Studies from this laboratory have shown great diversity in the glycosylation of tissues comprising the interhaemal barrier of species with different placental types. This diversity may be one of the factors preventing interbreeding between species. Glycan expression within the uterine epithelium and trophoblast of the interhaemal barrier was examined to test this proposition in three species with similar diffuse, microcotyledonary, epitheliochorial allantochorionic types of placenta: the horse (Equus caballus) and donkey (Equus asinus), which can interbreed with each other, and the camel (Came...
Comparative aspects of equine embryonic development. The developmental changes in the equine conceptus, its maternal environment and their interaction during the first 4 weeks following fertilization are reviewed. Attention is drawn to species-specific events to show why the horse is such a valuable model in which to study early pregnancy.
The early fetal life of the equine conceptus. This paper will discuss development of the equine conceptus, especially from the perspective of the maternal environment in which it develops and to which it has considerable influence.
The teeth of the horse: evolution and anatomo-morphological and radiographic study of their development in the foetus. The aim of this work was to study the ontogenetic process in teeth from their early appearance in the ossifying matrix of the mandible and maxilla, in different foetuses of scalar ages. Radiographic examinations of the skull and mandible hemisections were performed and the latero-medial (LM) and dorsoventral (DV) projections for the skull and mandible were analysed. A high-definition film-screen combination was used for this study. The exposure values ranged from 35 kV/6 mAs to 58 kV/10 mAs, according to the size of the skulls and their degree of ossification. The first dental germ observed wa...
Cell proliferation patterns during development of the equine placenta. Placentation involves considerable growth and reorganization of both maternal and fetal tissues. In this investigation, immunohistochemical localization of the proliferation marker Ki-67 antigen was used to monitor cell division during placentation in mares. Endometrial biopsies were obtained from eight mares between day 14 and day 26 of pregnancy and from eight anoestrous mares that had been treated with various combinations of progesterone and oestrogen. Samples of endometrium and fetal membranes were obtained from 19 mares carrying normal horse conceptuses between day 30 and day 250 of gest...
Differential gene expression in day 12 and day 15 equine conceptuses. Complex changes in gene expression must occur at the proper time and in the appropriate tissues for pregnancy to be successful. Therefore, research aimed at defining the regulation of gene expression in conceptuses is of critical importance. However, information on developmentally regulated changes in gene expression in horse conceptuses is sparse and inadequate. In the present study, suppression subtractive hybridization was used to identify genes that are expressed more highly at day 15 than on day 12 of gestation. This period encompasses maternal recognition of pregnancy and the beginning o...
Quantitative histological analysis of equine embryos at exactly 156 and 168 h after ovulation. Equine embryos were collected at exactly 156 +/- 0.5 (n=8) and 168 +/- 0.5 h (n=11) after ovulation. The embryos were fixed in glutaraldehyde, sectioned serially and observed using light microscopy. In the 156 h group, all embryos were early blastocysts except for one, which was a morula. The morula and one early blastocyst had no capsule. The capsules of the other embryos were thin. The mean +/- SD total number of cells was 275 +/- 105 (range 117-417). The mean +/- SD proportions of mitotic and pycnotic cells were 2.5 +/- 1.2 and 1.1 +/- 1.8%, respectively, and there were no differences betwe...
Development of equine endometrial glands from fetal life to ovarian cyclicity. Branched tubular endometrial glands are key features of the uterine lining in mares. The epithelium in the neck regions of the glands is similar to that lining the lumen of the uterus, whereas the epithelium in the deeper, coiled portions of the glands secretes protein rich histotrophe or 'uterine milk' during dioestrus and pregnancy. The present study was performed to characterize endometrial histology in perinatal and peripubertal fillies and to investigate the influences of specific steroid treatments on endometrial gland development in the prepubertal period. Uteri obtained from equine fet...
Maternal influence on pre- and postnatal growth of foals born after embryo transfer. In the present study the growth and development of three pairs of matching gender foals from birth to maturity were compared. One Polish Pony embryo of each pair was transferred from a donor mare (mass 387-400 kg) to a much larger heavy type recipient mare (mass 561-780 kg). The other embryo of each pair underwent normal gestation (control). The transferred and control horses were examined at 9 and 13 years of age, and X-ray pictures were taken of their front legs to measure the length of the bones. On the basis of the results of this study, it is concluded that the processes of growth and dev...
Developmental changes in blood pressure and the renin-angiotensin system in pony fetuses during the second half of gestation. Blood pressure, heart rate and the plasma concentrations of cortisol and components of the renin-angiotensin system were measured in chronically catheterized Pony mares (n=15) and their fetuses during the second half of gestation (day 153-336 of gestation; term is normally between day 320 and day 340 of gestation). Fetal blood pressure increased towards term with the prepartum surge in plasma cortisol concentration, and there was a correlation between fetal blood pressure and both gestational age (r = 0.88, P < 0.0005) and plasma cortisol concentration (r = 0.88, P < 0.0005). Plasma concentrat...
Morphological study on pigmented cells in the horse testis. One of the most attractive characteristics of a horse testis is the change of the weight during development. As the testicular weight changes and the number of Leydig cells decreases, pigments appear in interstitial tissues. In the present study, the characteristics of the pigments found in the interstitial tissues were examined histochemically and ultrastructurally. Specific stainings indicated that the pigmented granules showed almost all of the histological and histochemical characteristics of ceroid or ceroid-like pigment. The cells showed positive reaction for acid phosphatase while the p...
