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Topic:Fertility
Fertility in horses encompasses the physiological processes and factors influencing reproductive success in equine species. It involves the study of reproductive anatomy, endocrinology, and behavior, as well as the management practices that affect breeding outcomes. Key aspects include the estrous cycle, conception rates, and factors impacting stallion and mare fertility. Reproductive technologies such as artificial insemination, embryo transfer, and hormonal therapies are also explored to enhance breeding efficiency. This page compiles peer-reviewed research studies and scholarly articles that examine the biological mechanisms, management strategies, and technological advancements related to equine fertility.
Morphology and chromatin integrity of stallion spermatozoa prepared by density gradient and single layer centrifugation through silica colloids. The objective was to investigate whether it is possible to improve the quality of stallion semen, with respect to sperm morphology and chromatin integrity, both of which have been linked to fertility, using either density gradient centrifugation (DGC) or a new method, hereby named single layer centrifugation (SLC). The two methods of colloidal centrifugation were evaluated using 38 ejaculates from 10 stallions. Sperm morphology, subjective motility and sperm chromatin integrity were compared in uncentrifuged samples and in centrifuged sperm preparations. The proportion of morphologically norma...
Temporal relationships and repeatability of follicle diameters and hormone concentrations within individuals in mares. Data were collected daily from 23 mares during two consecutive interovulatory intervals (IOIs). Several significant (p < 0.05) new observations on temporal relationships were made. The FSH increase that begins before ovulation temporarily plateaued on the day of discharge of follicular fluid into the peritoneal cavity in association with ovulation. During the declining portion of the pre-ovulatory oestradiol surge, an abrupt reduction in the rate of decrease occurred in synchrony with the peak of the LH surge and is consistent with a negative effect of LH on oestradiol. Repeatability within...
Effect of suppression of FSH with a GnRH antagonist (acyline) before and during follicle deviation in the mare. A GnRH antagonist (Acyline) was used to study the role of FSH in early development of a follicular wave in 61 mares. In Experiment 1, a single dose of 3 mg per mare, compared with 0 and 1 mg, suppressed both the FSH and follicle responses to exogenous GnRH. In Experiment 2, high concentrations of FSH were induced by two successive ablations of all follicles >/= 6 mm on days 10 and 13 (day 0 = ovulation). A single treatment with Acyline resulted in significantly greater suppression of plasma concentrations of FSH than a single treatment with charcoal-extracted follicular fluid (source of inh...
Aspiration of equine oocytes from immature follicles after treatment with equine pituitary extract (EPE) alone or in combination with hCG. This study examined the effect of treating mares with equine pituitary extract (EPE) alone or in combination with hCG on the recovery rate of immature follicles by transvaginal follicular aspiration (ovum pick-up; OPU). Ten normally cycling crossbred mares aged 3-15 years and weighing 350-400 kg were subjected to each of three treatments in a random sequence with each exposure to a new treatment separated by a rest cycle during which a spontaneous ovulation occurred. The treatments were (1) superovulated with 25mg EPE and treated with 2500 IU hCG, (2) superovulation with 25mg EPE, and (3) cont...
Treatment with human chorionic gonadotropin (hCG) for ovulation induction is associated with an immediate 17beta-estradiol decrease and a more rapid LH increase in mares. The effect of treatment with an ovulation-inducing dose of human chorionic gonadotropin (hCG) on 17beta-estradiol (estradiol) and LH concentrations was studied in mares. In Experiment 1, treatment with hCG resulted in ovulation in approximately 48 h. The LH surge centralized to ovulation and the preovulatory decline in estradiol were not different between hCG-treated (n=15) and control (n=13) groups. In Experiment 2, concentrations of hCG decreased 92% between 1 and 48 h after hCG treatment, estradiol decreased (P<0.003) within 6h, and LH increased at a greater (P<0.02) rate after 12h (n...
Centrifugation on a single layer of colloid selects improved quality spermatozoa from frozen-thawed stallion semen. The present study attempted to select the subpopulation of stallion spermatozoa that best survived a conventional freezing and thawing procedure, using centrifugation of post-thawed semen samples through a single layer of a glycidoxypropyltrimethoxysilane-coated silica colloid with a species-specific formulation (Androcoll-E). Sperm motility, sperm chromatin structure, membrane integrity and mitochondrial membrane potential were studied in filtered and non-filtered spermatozoa. Single-layer centrifugation (SLC) using Androcoll-E significantly improved all the sperm parameters studied, implying...
Factors influencing the “sortability” of stallion spermatozoa into X- and Y-chromosome bearing populations. Intrinsic differences between stallions exist for semen traits such as motility, morphology fertility and the ability of spermatozoa to survive cryopreservation processes. Ejaculates from 11 stallions were used to test the differences between stallions when selecting X- and Y-chromosome bearing spermatozoa using a modified flow cytometer. Data on orientation and viability of spermatozoa were collected during sex-sorting, and motility characteristics of sex-sorted and non-sorted (control) spermatozoa were assessed before and after cryopreservation. An index was created to rank each stallion in ...
Seasonal effects on the response of ovarian follicles to IGF1 in mares. The response of follicles to IGF1 was compared between the transition into the ovulatory season (transitional period) and the ovulatory season (ovulatory period) in eight mares using a cross-over experimental design within periods. Granulosa cells were collected from follicles 15-24 or 25-34 mm and expression of IGF1R, IGF2R, FSHR, LHCGR and PAPPA was determined by qPCR. In addition, 10 mg IGF1 or vehicle were injected into the largest follicle (transitional period) or the second largest follicle (ovulatory period) of a follicular wave before the beginning of diameter deviation between the two...
The use of electrochemically activated saline as a uterine instillation in pony mares. Twelve pony mares were randomly assigned to either a control or a treatment group and inseminated with fresh, raw semen from a single stallion of known fertility in a cross-over trial design. Pregnancy was diagnosed by transrectal ultrasound 12-14 days post-ovulation and then terminated by administration of a luteolytic dose of cloprostenol. Treatment mares received a uterine instillation of 100 ml of electrochemically activated (ECA) saline 4-12 hours post-insemination. Control mares received no treatment post-insemination. Per cycle pregnancy rate was 58.3 % in the control group and 50 % in ...
Use of a low dose of equine purified FSH to induce multiple ovulations in mares. The effects of a low dose of equine purified FSH (eFSH) on incidence of multiple ovulations and embryo recovery rate in mares were studied. During the physiological breeding season in Brazil (19 degrees 45'45'S), 14 Mangalarga Marchador donor mares were used in a crossover study and another 25 mares of the same breed, between 3 years and 12 years of age were used as recipients for the embryo transfers. Donors were monitored during two consecutive oestrus cycles, an untreated control cycle followed by a treated cycle, when eFSH was administered. In both cycles, after an embryo collection attemp...
Somatic cell nuclear transfer in horses. The cloning of equids was achieved in 2003, several years after the birth of Dolly the sheep and also after the cloning of numerous other laboratory and farm animal species. The delay was because of the limited development in the horse of more classical-assisted reproductive techniques required for successful cloning, such as oocyte maturation and in vitro embryo production. When these technologies were developed, the application of cloning also became possible and cloned horse offspring were obtained. This review summarizes the main technical procedures that are required for cloning equids an...
Mechanisms for dominant follicle selection in monovulatory species: a comparison of morphological, endocrine and intraovarian events in cows, mares and women. The selection of a single ovarian follicle for further differentiation and finally ovulation is a shared phenomenon in monovulatory species from different phylogenetic classes. The commonality of dominant follicle (DF) development leads us to hypothesize that mechanisms for DF selection are conserved. This review highlights similarities and differences in follicular wave growth between cows, mares and women, addresses the commonality of the transient rises in FSH concentrations, and discusses the follicular secretions oestradiol and inhibin with their regulatory roles for FSH. In all three spe...
Treatment with a High Dose Combination of PMSG/hCG Preparation of Mares Clinically Diagnosed with Ovarian Quiescence during the Breeding Season (Investigation from 1975 to 2000). A total of 88 thoroughbred mares were diagnosed with clinical ovarian quiescence and subjected to four treatment regimens. Using PMSG, hCG or combinations of both. A high dose combination of 5,000IU PMSG with 5,000IU hCG showed significantly higher rates of marked estrus and ovulation induction (P<0.01) as well as conception rates (P<0.05). In the present study, the administration of a high-dose combination of PMSG with hCG was shown to be an effective treatment of ovarian quiescence in light mares.
Factors impacting equine sperm recovery rate and quality following cushioned centrifugation. Two experiments were conducted to investigate modifications in cushioned centrifugation of stallion semen. Specifically, the effects of tube type, centrifugation medium, cushion type, and centrifugation force on post-centrifugation sperm recovery rate and quality were evaluated. In Experiment 1, sperm recovery rate was higher (P<0.05) in conventional plastic conical-bottom tubes (103%) than in newly developed glass nipple-bottom tubes (96%) following cushioned centrifugation; however, several measures of semen quality (i.e., % total motility [MOT], % progressive motility [PMOT], curvilinear...
Induction of estrus and ovulation: why some mares respond and others do not. The two most common procedures for breeding management of mares involve induction of luteolysis and induction of ovulation. Although both of these events are usually achieved, physiologic conditions affect the timing of the response. In a diestrus mare treated with prostaglandin F(2alpha) (PGF), or a PGF analogue, it is well documented that, on average, the interval from treatment to the onset of estrus is 3-4 days, whereas ovulation occurs 8-10 days after treatment. However, the diameter of the ovulatory follicle, as well as its status at the time of PGF treatment, determines the intervals fr...
Optimizing the use of frozen-thawed equine semen. This manuscript is a review of current protocols, advantages, and disadvantages of breeding mares with frozen-thawed equine semen. Issues affecting pregnancy rates are discussed, including proper mare selection, induction of ovulation, insemination dose, timing of insemination (single-dose versus multiple-dose insemination), methods of insemination (transrectal-guided deep-horn versus hysteroscopic insemination), and post-insemination mare management procedures. In a retrospective analysis of breeding records, a single-dose of frozen-thawed semen was inseminated within 6h post-ovulation; the p...
Seminal traits, suitability for semen preservation and fertility in the native Portuguese horse breeds Puro Sangue Lusitano and Sorraia: Implications for stallion classification and assisted reproduction. The Puro Sangue Lusitano (PSL) is the major national breed of horse in Portugal, but no studies exist on its seminal characteristics, or on the possibility of conserving semen for future use. The aim of this study was to evaluate semen parameters, fertility and the aptness to semen preservation in Lusitano Stallions. In order to compare characteristics defined by a single or by multiple semen collections per stallion 152 ejaculates obtained from 152 Lusitano stallions presented at an annual breeding soundness examination as well as data related to 371 ejaculates obtained from 9 PSL were analyz...
When should a mare go for assisted reproduction? The use of assisted reproductive techniques (ART) has helped owners to produce offspring from valuable mares that were considered infertile using standard breeding techniques. Before referring a mare for an ART, the practitioner should be able to identify the underlying cause of subfertility of the mare. The objective of this review is to provide information regarding embryo transfer, oocyte transfer and intracytoplasmic sperm injection, the three most common ART used in equine practice. Knowing the complexity as well as the risks of these techniques, enables practitioners to refer a subfertil...
When to refer an infertile mare to a theriogenologist. Most equine infertility cases can be solved with a methodical, thorough physical and reproductive examination and appropriate diagnostic laboratory aids. Repeated examinations may be needed in some cases to identify subtle anatomical abnormalities or irregularities between hormonal and physiological relationships of the reproductive tract. For pregnancy to occur, hormonal signaling must be exquisitely synchronized with physical changes of the reproductive tract and deposition of fertile semen in the uterus. Asynchrony of these events, infection, inflammation, previous trauma to the reproductiv...
Sperm production and sperm morphology of Swedish Warmblood stallions. The present study investigated daily sperm output and sperm morphology of fresh semen in eight Swedish Warmblood stallions aged 5-8 years. They were used for artificial insemination, and their fertility during the breeding season of semen collection exceeded 60% per cycle. One ejaculate of semen was collected daily for 10 consecutive days from each stallion. The gel-free volume was measured, and the sperm concentration was assessed with a Bürker chamber. The volume of gel-free fraction was multiplied by the sperm concentration to give the total number of spermatozoa (TSN). Sperm morphology wa...
Influence of long-term treatment with equine somatotropin (EquiGen) on gonadal function in stallions with poor semen quality. The aim of the present study was to investigate the spermatogenic and Leydig cell activity in stallions with impaired semen quality after treatment with equine somatotropin. Experiments were performed using 18 adult clinically healthy stallions with poor semen quality which did not pass breeding soundness evaluation. The animals were randomly divided into a treatment (n = 9) and a control (n = 9) group. Over a period of 90 days, nine stallions received a daily intramuscular injection of 10 mg recombinant equine somatotropin (EquiGen, BresaGen Limited, Adelaide, Australia) and 9 control animals...
Developments in stallion semen evaluation. The conventional approach to evaluation of stallion semen dates back several decades, and includes evaluation of spermatozoal concentration, semen volume, spermatozoon morphological characteristics, and spermatozoal motility patterns initially and following in-vitro storage. While an analysis performed in this manner does have predictive value, incorporation of some more newly developed techniques may improve the predictive value of the examination. This communication addresses some newer tests that can be applied today for evaluation of semen, as well some tests that may be available in the c...
The effects of cryptorchidism on the regulation of steroidogenesis and gap junctional communication in equine testes. Evidence collected over the years has demonstrated that cryptorchidism is associated with a defect in spermatogenesis and, as a consequence, with either reduced fertility or infertility. However, the effect of cryptorchidism on Leydig cell function is less clear. The aim of our study therefore was to investigate the regulation of steroid hormone biosynthesis and, additionally, intercellular communication in the cryptorchid equine testes. Methods: Testes of mature bilaterally cryptorchid horse and healthy stallions were used for this study. The expression of luteinising hormone receptor (LHR), ...
Regulation of testicular function in the stallion: an intricate network of endocrine, paracrine and autocrine systems. It is well established in many mammalian species, including the horse that normal testicular function is dependent upon a functional hypothalamic-pituitary-testicular (HPT) axis, which involves classic feedback mechanisms. The major HPT hormones involved in the stallion are gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone (T), estrogens (Es) and inhibin (INH). Although prolactin (PRL) fluctuates with season in the stallion and both PRL and thyroid hormone (TH) affect reproduction in other male species, their effects on stallion r...
Cryobiological determinants of frozen semen quality, with special reference to stallion. Success in cryopreserving stallion semen has been very variable. Several different freezing regimes have been published. However, because extenders and procedures used in each regime have differed, direct comparison of these techniques has been very difficult, and controlled studies comparing different techniques have not been reported. A number of different factors affect sperm cryosurvival. In this article we review briefly current cryopreservation procedures for stallion semen, and then in more detail cryobiological determinants of sperm function, and mechanisms of cryoinjury and cryoprotec...
Periparturient hemorrhage in mares: 73 cases (1998-2005). To determine signalment, physical examination and clinicopathologic abnormalities, outcome, and subsequent fertility of mares with periparturient hemorrhage (PPH) and identify factors associated with outcome (ie, survival vs death). Methods: Retrospective case series. Methods: 73 mares. Methods: Medical records were reviewed for information on age, breed, initial complaint, physical examination and clinicopathologic abnormalities, treatment, outcome, and subsequent fertility. Results: Median age was 14.0 years (range, 5 to 24 years), and median number of foals produced prior to the diagnosis o...
Three autosomal chromosome translocations associated with repeated early embryonic loss (REEL) in the domestic horse (Equus caballus). Repeated early embryonic loss (REEL) represents a considerable economic loss to the horse industry. Mares that experience REEL may be overlooked as potential carriers of a chromosome abnormality. Here we report three different autosomal translocations in Thoroughbred mares presented for chromosome analysis because of REEL. The karyotypes were 64,XX,t(1;21), 64,XX,t(16;22), and 64,XX,t(4;13), respectively. In order to confirm the chromosomes involved in the translocations, to map the breakpoints, and to determine if the translocations were reciprocal, genes surrounding the breakpoints were iden...
Practical review of self-mutilation in horses. Self-mutilation in horses includes biting, stomping and kicking, rubbing, and lunging into objects. Based on the author's clinical experience, three distinct types of self-mutilation are proposed and described. Type I represents normal behavioral response to continuous or intermittent physical discomfort. Type II, seen in stallions and geldings, can be recognized as self-directed intermale aggression. The behavior includes the elements and order of the natural interactive sequence typical of encounters between two stallions, except that the stallion himself is the target of his intermale behav...
Oxidative stress, osmotic stress and apoptosis: impacts on sperm function and preservation in the horse. Oxidative stress is an important component of the cytopathology of equine spermatozoa undergoing storage as liquid or frozen semen. Damage to chromatin, membranes and proteins of sperm are important components of oxidative damage to sperm. Similarly, sperm are exposed to a variety of osmotic stresses during storage that result from exposure to hypertonic media or result as a consequence of osmotic changes induced during freezing. A number of changes induced during processing and storage of equine sperm also appear to induce apoptotic-like changes which may adversely affect sperm survival and f...
