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Topic:Reproduction
Reproduction in horses encompasses the biological processes and mechanisms involved in the breeding and development of equine offspring. This includes the study of reproductive anatomy, physiology, and endocrinology in both mares and stallions. Key areas of interest include the estrous cycle, ovulation, conception, gestation, and parturition. Researchers also examine factors influencing fertility, reproductive technologies such as artificial insemination and embryo transfer, and management practices that impact reproductive success. This page compiles peer-reviewed research studies and scholarly articles that explore the physiological, genetic, and environmental aspects of equine reproduction.
Maternal recognition of pregnancy in the horse: a mystery still to be solved. Maternal recognition of pregnancy in the horse is the sum of events leading to maintenance of pregnancy; in a narrow sense, maternal recognition of pregnancy refers to the physiological process by which the lifespan of the corpus luteum is prolonged. The horse is one of the few domestic species in which the conceptus-derived pregnancy recognition signal has not been identified. The presence of the conceptus reduces pulsatile prostaglandin F(2α) secretion by the endometrium during early gestation in the mare, partly attributed to the reduced expression of cyclooxygenase-2. Cyclooxygenase-2 has...
Persistent breeding-induced endometritis after hysteroscopic insemination in the mare. Low-dose insemination has been proposed to reduce persistent breeding-induced endometritis (PBIE) in mares with delayed uterine clearance (DUC). Others proposed that hysteroscopic insemination induces an exaggerated inflammatory response and should be avoided in DUC mares. The objectives here were to evaluate presence and severity of PBIE in normal and DUC mares after hysteroscopic insemination with fresh semen, and to determine if hysteroscopy could be used in DUC mares without inducing excessive inflammation. Reproductively normal (n = 4) and DUC (n = 5) mares received four treatments in ran...
Mating behavior increases workload of the heart in Thoroughbred stallions. To evaluate the influence of mating behavior on cardiac function, changes in heart rate (HR), electrocardiogram (ECG), hematocrit (Hct) and serum concentration of alpha-atrial natriuretic peptide (alpha-ANP) were evaluated in 10 clinically sound Thoroughbred stallions before and after mating behavior. The stallions were submitted twice to experimental pseudomating in the same month in 2009 and 2010. Measurements and blood samples were collected at a stable before mating (baseline) and at a covering yard before and after mating. ECG was recorded by a Holter-ECG system. Arrhythmias were detected...
The mare: a 1000-pound guinea pig for study of the ovulatory follicular wave in women. The mare is a good comparative model for study of ovarian follicles in women, owing to striking similarities in follicular waves and the mechanism for selection of a dominant follicle. Commonality in follicle dynamics between mares and women include: (1) a ratio of 2.2:1 (mare:woman) in diameter of the largest follicle at wave emergence when the wave-stimulating FSH surge reaches maximum, in diameter increase of the two largest follicles between emergence and the beginning of deviation between the future dominant and subordinate follicles, in diameter of each of the two largest follicles at th...
Expression of anti-Müllerian hormone, cyclin-dependent kinase inhibitor (CDKN1B), androgen receptor, and connexin 43 in equine testes during puberty. Sertoli cells are essential in development of a functional testis. During puberty, Sertoli cell maturation can be characterized by a number of markers, including anti-Müllerian hormone (AMH) and its receptor (AMHR2), androgen receptor (AR), cyclin-dependent kinase inhibitor (CDKN1B), and connexin 43 (Cx43). In the present study, immunohistochemistry (IHC) and real-time quantitative polymerase chain reaction (RT-qPCR) were used to characterize changes in expression of AMH, AMHR2, AR, CDKN1B, and Cx43 in prepubertal, postpubertal, and adult equine testes. During puberty, AMH expression decrease...
Effect of centrifugal fractionation protocols on quality and recovery rate of equine sperm. Centrifugal fractionation of semen is commonly done to improve quality of human semen in assisted-reproduction laboratories, allowing sperm separation based on their isopycnic points. Sperm with morphologic abnormalities are often more buoyant, promoting their retention above defined density media, with structurally normal sperm passing through the media following centrifugation. Three experiments were conducted to evaluate the effects of density-medium type, centrifuge-tube size, sperm number, and density-medium volume (column height) on stallion sperm quality and recovery rate in sperm pelle...
Purchase examinations and importation requirements for European performance horses and their semen entering the United States. A comprehensive purchase examination is expected by American clients intent on importing a horse from a foreign country. American veterinarians may be involved in performing purchase examinations in foreign countries or, more often, interpreting findings from foreign veterinarians for their American clients. Exportation and importation requirements for horses and semen vary from country to country. Detailed knowledge of the requirements by all involved veterinarians is essential for efficient and successful international equine travel.
Immunohistochemical localisation of progesterone and oestrogen receptors at the placental interface in mares during early pregnancy. Previous reports documenting progesterone receptors (PR) and oestrogen receptors (ER) in the endometrium of early pregnant mares included specimens only up to Day 20 post ovulation. This study aimed to localise PR and ERα on equine feto-maternal tissues between Days 20 and 68 to encompass the period around fixation of the conceptus, development of the endometrial cups and attachment and initial interdigitation of the allantochorion. During early pregnancy mares had the same pattern of PR in the endometrium as that reported for other mammals; namely, a loss of PR from the endometrial epithelia...
Standing laparoscopic peritoneal flap hernioplasty technique for preventing recurrence of acquired strangulating inguinal herniation in stallions. To describe a standing laparoscopic peritoneal flap hernioplasty (PFH) technique for closure of the vaginal ring, and to evaluate its effect on prevention of recurrent herniation in stallions, previously treated for acquired strangulating inguinal hernia (SIH). Methods: Case series. Methods: Stallions (n = 30) aged 3-15 that had previous acquired SIH. Methods: Bilateral standing laparoscopic PFH was performed on 30 stallions that had previous acquired SIH treated without castration. The vaginal rings were approached from 3 portals, 2 in the paralumbar fossa and a 3rd between the 17th and 18th ...
Disorders of sexual development in the domestic horse, Equus caballus. Abnormalities of sexual development causing infertility in horses have been investigated since the early 1970's. Conventional cytogenetic analysis by karyotyping has been the primary tool used to investigate these horses. Abnormalities have a broad range, from a phenotypically normal mare with gonadal dysgenesis to a horse with ambiguous external genitalia and internal male and female organs. Cytogenetic analysis can determine genetic sex but cannot identify mutations or deletions of genes involved in the sex determination pathway. Molecular technologies have been developed to confirm cytogene...
Influence of the uterine environment on the development of in vitro-produced equine embryos. The necessity for early interaction between the embryo and the oviductal and/or uterine environment in the horse is reflected by several striking differences between equine embryos that develop in vivo and those produced in vitro. Better understanding of the salient interactions may help to improve the efficiency of in vitro equine embryo production. In an initial experiment, cleavage-stage in vitro-produced (IVP) equine embryos were transferred into the uterus of recipient mares that had ovulated recently to determine whether premature placement in this in vivo environment would improve subse...
Consequences of butylated hydroxytoluene in the freezing extender on post-thaw characteristics of stallion spermatozoa in vitro. Ejaculates from six pure Spanish stallions were split, and one subsample frozen in a commercial extender supplemented with the lipid soluble antioxidant butylated hydroxytoluene (BHT), while the other subsample served as control. After at least 4 weeks of storage, samples were thawed and post-thaw sperm quality analysed: sperm motility and kinematics using a CASA system, membrane and acrosome integrity and mitochondrial membrane potential using flow cytometry. The outcome of cryopreservation varied significantly among stallions. However, the supplementation with 1 mm BHT had no significant eff...
GTG mutation in the start codon of the androgen receptor gene in a family of horses with 64,XY disorder of sex development. Genetic sex in mammals is determined by the sex chromosomal composition of the zygote. The X and Y chromosomes are responsible for numerous factors that must work in close concert for the proper development of a healthy sexual phenotype. The role of androgens in case of XY chromosomal constitution is crucial for normal male sex differentiation. The intracellular androgenic action is mediated by the androgen receptor (AR), and its impaired function leads to a myriad of syndromes with severe clinical consequences, most notably androgen insensitivity syndrome and prostate cancer. In this paper, w...
Cloning of equine herpesvirus type 1 438/77 strain genome as a bacterial artificial chromosome. Equine herpesvirus type 1 (EHV-1) is a major cause of respiratory and reproductive diseases in horses worldwide. The genome of EHV-1 strain 438/77 (isolated from an aborted equine fetus) was cloned as a bacterial artificial chromosome (BAC) in E. coli without any gene deletions. The mini-F plasmid sequence was inserted in the middle of ORF19 and 20 via homologous recombination following co-transfection of viral DNA and plasmid pE19_20/HA into RK13 cells. Circular viral DNA was extracted from RK13 cells infected with purified recombinant virus expressing green fluorescent protein (GFP) and elec...
Inbreeding in the Thoroughbred horse. Changes in the inbreeding coefficient, F, in the Thoroughbred horse over the past 45 years have been investigated by genotyping 467 Thoroughbred horses (born between 1961 and 2006) using the Illumina Equine SNP50 bead chip, which comprises 54,602 SNPs uniformly distributed across the equine genome. The Spearman rank correlation coefficient, r, between the year of birth and F was estimated. The results indicate that inbreeding in Thoroughbreds has increased over the past 40 years, with r = 0.24, P < 0.001 demonstrating that there is a highly significant, though relatively weak correlation be...
Harnessing the genetic toolbox for the benefit of the racing Thoroughbred. The understanding and application of genetics have grown extremely quickly since it has become possible to sequence the whole genome of an organism. The human genome sequence was completed in 2001 and that of the horse in 2007. The significance of this is that it makes it more feasible to explain how both genetically simple and complex traits are transmitted from one generation to the next and, therefore, to make informed breeding decisions, modify how horses are managed and trained to minimise the risk of disease and injury, and improve methods of prevention, diagnosis and treatment of many c...
Nucleolar organizer regions (NORs) distribution and behavior in spermatozoa and meiotic cells of the horse (Equus caballus). Nucleolar organizing regions (NORs) containing rDNA gene clusters have been assigned to the equine autosomes ECA1, ECA28, and ECA31. Active NORs (Ag-NORs) are associated with argyrophilic proteins, which allow them to be readily identified using silver staining techniques. Fluorescence in situ hybridization (FISH) for rDNA can also be used to visualize all NOR clusters in the nucleus, regardless of whether they are active or inactive. The present study analyzed the distribution and behavior of equine Ag-NOR and NOR clusters in horse spermatozoa and during male meiosis by FISH and silver staini...
In vitro acute exposure to DEHP affects oocyte meiotic maturation, energy and oxidative stress parameters in a large animal model. Phthalates are ubiquitous environmental contaminants because of their use in plastics and other common consumer products. Di-(2-ethylhexyl) phthalate (DEHP) is the most abundant phthalate and it impairs fertility by acting as an endocrine disruptor. The aim of the present study was to analyze the effects of in vitro acute exposure to DEHP on oocyte maturation, energy and oxidative status in the horse, a large animal model. Cumulus cell (CC) apoptosis and oxidative status were also investigated. Cumulus-oocyte complexes from the ovaries of slaughtered mares were cultured in vitro in presence of...
Relationship between dose of cloprostenol and age of corpus luteum on the luteolytic response of early dioestrous mares: a field study. The objective of this study was to establish and characterize the relationship between the dose of cloprostenol (37.5, 250, 500 and 750 μg) and the age of the early corpus luteum (CL) (80, 88, 96, 104 and 112 h) on the luteolytic response of mares. Behavioural oestrus and ultrasonographic signs of return to oestrus were considered as the occurrence of full luteolysis. A total of 298 mares were divided into groups according to dose of cloprostenol and CL age. There was an effect of dose of cloprostenol (p < 0.001) and age of the CL at the time of treatment (p 0.05); and that of 500 similar...
Unilateral and bilateral laparoscopic ovariectomy in 157 mares: a retrospective multicenter study. To evaluate surgical techniques, perioperative complications and outcome of laparoscopic surgery for unilateral and bilateral ovariectomy in mares. Methods: Retrospective multicenter case series. Methods: Mares (n = 157). Methods: Indications for surgery were neutering, fertility problems, elimination of hormone-related abnormal behavior, ovarian tumors as well as nonregressive ovarian hematomas or cysts. Ovariectomy (n = 206) were performed by a standard laparoscopic procedure in 157 standing sedated mares. Dissection and hemostasis were achieved by using either (1) a linear stapling device, ...
Equine pre-implantation conceptuses express neuraminidase 2–a potential mechanism for desialylation of the equine capsule. During the second and third week of pregnancy, the equine conceptus is covered by an acellular glycoprotein capsule. This capsule contains glycoproteins resembling those of the mucin family with sialic acid making up a high proportion of the carbohydrate. Coinciding with conceptus fixation, a marked decline in sialic acid content of the capsule occurs, which has been proposed to contribute to cessation of conceptus mobility. Herein, we describe the expression of neuraminidase 2 (NEU2) by pre-implantation stages of equine conceptus development. NEU2 transcript abundance was examined in conceptu...
Molecular and cytogenetic studies in a case of XX SRY-negative sex reversal in an Arabian horse. An 18-month-old Arabian foal characterized by a stallion-like appearance was submitted for cytogenetic and molecular genetics examinations due to abnormalities of external genitalia and the presence of ovotestis-like structures in the abdominal cavity. By RB-banding the animal showed the normal female equine karyotype (2n = 64,XX). Molecular analysis revealed the absence of the SRY and ZFY genes and the presence of ZFX, a typical female equine condition. The entire RSPO1 coding region was examined to exclude its involvement. Although a SNP was found in exon 3, it was not responsible for an ami...
Replacing egg yolk with soybean lecithin in the cryopreservation of stallion semen. The objective of this study was to determine whether replacing the egg yolk with soybean lecithin in the Botu-Crio® cryodiluent would maintain the fertility of cryopreserved stallion sperm. Two experiments were performed to evaluate cell freezability. In experiment 1, sperm from 15 stallions were frozen in Botu-Crio® (BC) or Botu-Crio® which contained 45g/L soybean lecithin (BCLS45) in place of the egg yolk. In experiment 2, we compared different concentrations of soybean lecithin: 0, 10.0, 12.5, 15.0, 17.5 and 20.0g/L (BC, BCLS10, BCLS12.5, BCLS17.5 and BCLS20, respectively). In experiment...
Cytogenetic and molecular characterization of Y isochromosome in a 63XO/64Xi(Yq) mosaic karyotype of an intersex horse. Sex chromosome aberrations commonly lead to abnormal sexual development. Here we cytogenetically and molecularly characterized Y isochromosome in an intersex horse. Blood lymphocyte analysis showed a mosaic karyotype with 96% 63,XO and 4% 64,Xi(Y) cells. Molecular analysis of the isochromosome was carried out by fluorescence in situ hybridization and polymerase chain reaction with male-specific and pseudoautosomal markers from the horse Y chromosome. We found that the isochromosome was monocentric, composed of 2 long arms, carrying 2 sets of genes of the pseudoautosomal region (PAR) and the ma...
Manual reduction of multiple embryos in the mare: the effect on subsequent pregnancy outcome. To determine whether manually reduced multiple pregnancies (MPs) are at a greater risk of pregnancy loss than single pregnancy (SP) in mares, and to examine if a difference exists in the timing of pregnancy loss between manually reduced MPs and SPs, 1916 Thoroughbred mares were ultrasonically monitored every 2 days during oestrus to confirm ovulation, and up to Day 40 post-ovulation to confirm pregnancy. Ultimate pregnancy outcome was ascertained from the General Thoroughbred Stud book and classified as live foal (LF), early abortion (EA; Days 40-150), slipped foal (SF; Days 150-term), and bar...
Equine fetal sex determination using circulating cell-free fetal DNA (ccffDNA). In this study, polymerase chain reaction (PCR) reamplification of the first PCR product (2nd-PCR) and a qPCR assay were used to detect the sex determining region Y (SRY) gene from circulating cell-free fetal DNA (ccffDNA) in blood plasma of pregnant mares to determine fetal sex. The ccffDNA was isolated from plasma of 20 Thoroughbred mares (5-13 y old) in the final 3 mo of pregnancy (fetal sex was verified after foaling). For controls, plasma from two non-pregnant mares and two virgin mares were used, in addition to the non-template control. The 182 bp nucleotide sequence corresponding to the ...
Hormone concentration changes temporally associated with the hour of transition from preluteolysis to luteolysis in mares. The temporal associations of cortisol, estradiol-17β, and oxytocin with pulses of PGFM at the common hour of transition between preluteolysis and luteolysis was studied in plasma from hourly blood samples in mares (n=8). The transitional hour was determined from progesterone concentrations and occurred between 2PM and 2AM in all mares. Pulses of PGFM were grouped into those occurring at the last pulse of preluteolysis (preluteolytic pulse), at the hour of transition (transitional), and during luteolysis (luteolytic). The preluteolytic PGFM pulse (45±16pg/ml at peak) and transitional pulse (4...
Dose-response effects of estrogenic mycotoxins (zearalenone, alpha- and beta-zearalenol) on motility, hyperactivation and the acrosome reaction of stallion sperm. The aim of this study was to investigate the in vitro effects of the Fusarium fungus-derived mycotoxin, zearalenone and its derivatives alpha-zearalenol and beta-zearalenol on motility parameters and the acrosome reaction of stallion sperm. Since the toxic effects of zearalenone and its derivatives are thought to result from their structural similarity to 17beta-estradiol, 17beta-estradiol was used as a positive control for 'estrogen-like' effects. Methods: Stallion spermatozoa were exposed in vitro to zearalenone, alpha-zearalenol, beta-zearalenol or 17beta-estradiol at concentrations ranging...
