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Topic:Ovulation
Ovulation in horses is a physiological process involving the release of an ovum from the ovary, typically occurring during the mare's estrous cycle. This process is regulated by hormonal changes, primarily involving luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Ovulation is a key component of equine reproduction, influencing breeding management and fertility outcomes. The timing and detection of ovulation are critical for optimizing breeding strategies, often involving techniques such as ultrasound examination and hormone assays. This page compiles peer-reviewed research studies and scholarly articles that investigate the mechanisms, detection methods, and implications of ovulation in equine reproductive health.
Ovulation rate and distribution in the thoroughbred mare, as determined by ultrasonic scanning: the effect of age. Ovarian activity was monitored in 2181 oestrous cycles from 1136 thoroughbred brood mares to accurately determine overall ovulation rate, the relative distribution of ovulations between left and right ovary, whether mare age had an effect on these parameters and whether ovulation pattern in one cycle affected the pattern within the next. Ultrasonic scanning was used in preference to rectal palpation and slaughterhouse material due to its greater accuracy. Mare's ages ranged from 3 to 22 years. The results obtained indicated a similar incidence of ovulation occurring on the right (49.5% of all ...
Embryo production by ovum pick up from live donors. Embryo production by in vitro techniques has increased steadily over the years. For cattle where this technology is more advanced and is applied more, the number of in vitro produced embryos transferred to final recipients was over 30,000 in 1998. An increasing proportion of in vitro produced embryos are coming from oocytes collected from live donors by ultrasound-guided follicular aspiration (ovum pick up, OPU). This procedure allows the repeated production of embryos from live donors of particular value and is a serious alternative to superovulation. Ovum pick up is a very flexible technique...
Regulation of ovarian follicular dynamics in farm animals. Implications for manipulation of reproduction. In this review, the main features of folliculogenesis are summarized and compared among species. In the past few years, ultrasonography has clarified follicle growth patterns, and our understanding of follicle maturation has improved considerably. As the follicles develop towards the ovulatory stage, three features appear to be highly conserved across all species: 1) the sequence of events (recruitment, selection and dominance); 2) the sequential need for gonadotropins (FSH for recruitment, LH for dominance) and 3) the large variability of numerical parameters (number of waves per cycle, numbe...
Effects of ovarian input on GnRH and LH secretion immediately postovulation in pony mares. The potential involvement of ovarian factors in regulating GnRH and LH postovulation was studied in ovarian intact (Group 1; n=3) and ovariectomized (OVX; Group 2; n=3) mares (OVX within 12 hr of ovulation). Blood samples were collected every 10 min for 6 hr from jugular vein (JV) and intercavernous sinus (ICS) during estrus and on Day 8 postovulation for LH and GnRH analysis. Additionally, JV samples were collected twice daily (12-hr intervals) for 30 days for LH and progesterone (P4) analysis. A significant treatment x day effect (P<0.0001) describes declining plasma LH concentrations in ...
Effect of deslorelin acetate on gonadotropin secretion and ovarian follicle development in cycling mares. To evaluate gonadotropin secretion and ovarian function after administration of deslorelin acetate to induce ovulation in mares. Methods: Randomized controlled trial. Methods: 16 healthy mares with normal estrous cycles. Methods: 8 control mares were allowed to ovulate spontaneously, whereas 8 study mares received deslorelin to induce ovulation when an ovarian follicle > 35 mm in diameter was detected. Follicle development and serum concentrations of gonadotropins were monitored daily during 1 estrous cycle. Pituitary responsiveness to administration of gonadotropin-releasing hormone (GnRH)...
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 ...
Treatments resulting in pregnancy in nonovulating, hormone-treated oocyte recipient mares. Synchronization of follicle growth between oocyte donor and recipient mares is difficult. To avoid this, recipient mares in a clinical program were used during a period of low follicular activity, and were treated with estrogen before transfer and progesterone after transfer. Five pregnancies were established after oocyte transfer to nonovulating, hormone-treated recipient mares. One pregnancy was lost before 30 d gestation, and the other 4 foals were carried to term. One foal died at birth. Establishment and maintenance of pregnancy in these mares indicates that nonovulating, hormone-treated ...
Equine P450 cholesterol side-chain cleavage and 3 beta-hydroxysteroid dehydrogenase/delta(5)-delta(4) isomerase: molecular cloning and regulation of their messenger ribonucleic acids in equine follicles during the ovulatory process. The preovulatory LH rise is the physiological trigger of follicular luteinization, a process during which the synthesis of progesterone is markedly increased. To study the control of follicular progesterone biosynthesis in mares, the objectives of this study were to clone and characterize the equine cholesterol side-chain cleavage cytochrome P450 (P450(scc)) and 3 beta-hydroxysteroid dehydrogenase/Delta(5)-Delta(4)-isomerase (3 beta-HSD), and describe the regulation and cellular localization of their transcripts in equine follicles during hCG-induced ovulation. Complementary DNA cloning and pr...
Expression and regulation of transcripts encoding two members of the NR5A nuclear receptor subfamily of orphan nuclear receptors, steroidogenic factor-1 and NR5A2, in equine ovarian cells during the ovulatory process. Steroidogenic factor-1 (SF-1, NR5A1a) is a member of the NR5A nuclear receptor subfamily and has been implicated as a key transcriptional regulator of all ovarian steroidogenic genes in vitro. To establish links between the expression of SF-1 and that of the steroidogenic genes in vivo, the objectives of this study were to clone equine SF-1 and examine the regulation of its messenger RNA (mRNA) in follicular cells during human CG (hCG)-induced ovulation. The equine SF-1 primary transcript was cloned by a combination of RT-PCR techniques. Results showed that the transcript was composed of a 5'-...
Fertility of mares after unilateral laparoscopic tubal ligation. To develop a technique for laparoscopic tubal (oviductal) ligation and to evaluate pregnancy rates for mares that ovulated ipsilateral or contralateral to the ligated oviduct. Methods: Randomized prospective clinical trial comparing pregnancy rates after unilateral laparoscopic tubal ligation. Methods: Twelve mares of light horse breeds. Methods: One oviduct in each of 6 mares was surgically ligated with a laparoscopic technique; 6 other mares served as nonligated controls. Mares with unilateral tubal ligations (UTL) were inseminated with 500 million progressively motile sperm during 1 cycle w...
Factors affecting pregnancy rates and early embryonic death after equine embryo transfer. In the present study, 638 embryo transfers conducted over 3 yr were retrospectively examined to determine which factors (recipient, embryo and transfer) significantly influenced pregnancy and embryo loss rates and to determine how rates could be improved. On Day 7 or 8 after ovulation, embryos (fresh or cooled/transported) were transferred by surgical or nonsurgical techniques into recipients ovulating from 5 to 9 d before transfer. At 12 and 50 d of gestation (Day 0 = day of ovulation), pregnancy rates were 65.7% (419 of 638) and 55.5% (354 of 638). Pregnancy rates on Day 50 were significantl...
Control of follicular development and luteal function in the mare: effects of a GnRH antagonist. Control of the equine estrous cycle was studied by suppressing gonadotropin secretion by administration of a GnRH antagonist to cyclic pony mares. Four mares received vehicle (control cycle) or a GnRH antagonist, Antarelix (100 microg/kg) on Day 8 of diestrus, and blood samples were collected at 15-min intervals from 0 to 16 h, 24 to 36 h, and daily until the next ovulation. Ovarian activity was monitored by transrectal ultrasonography, and measurement of plasma concentrations of progesterone and estradiol. Antagonist treatment eliminated large diestrous pulses of LH. Progesterone concentratio...
Effect of dose and day of treatment on uterine response to oxytocin in mares. To determine the effect of dose and day of oxytocin treatment on intrauterine pressure, 6 normal mares were treated with 10 or 25 IU oxytocin 2 days before ovulation, on the day of ovulation and 2 days after ovulation. Intrauterine pressure (IUP) was measured using micro-tip-catheters (one placed intrauterine, a second and third serving as reference sensors in the vagina and external to the mare) and transmitted by telemetry for 30 min to establish a baseline before saline was administered, iv, and for an additional 30 min after saline administration. Oxytocin was then given, iv, and IUP was r...
Effect of intrauterine treatment with prostaglandin E2 prior to insemination of mares in the uterine horn or body. Two trials were conducted to investigate the effects of intrauterine infusion of PGE2 and uterine horn insemination on pregnancy rates in mares achieved by breeding with a suboptimal number of normal spermatozoa. Estrus was synchronized and mares were teased daily with a stallion to detect estrus. Mares in estrus were examined by transrectal palpation and ultrasonography to monitor follicular status. On the first day a 35-mm diameter follicle was present, hCG (1500 IU, iv) was administered and the mares were bred the next day. Mares (Trial 1, n = 34; Trial 2, n = 28) were inseminated with 25 m...
Reproductive hormone profiles in mares during the autumn transition as determined by collection of jugular blood at 6 h intervals throughout ovulatory and anovulatory cycles. The aim was to define precisely the FSH secretion pattern in mares during the two ovulatory cycles before, and for 24 days after, the last ovulation of the season and to compare this with the profiles of other reproductive hormones and follicular growth to identify changes which may lead to the termination of follicular cycles. Jugular blood was collected every 6 h from ten light horse mares for 6 weeks in autumn. Samples were assayed for FSH, LH, prolactin, inhibin, oestrone conjugates and progesterone. Luteolysis occurred earlier and periovulatory oestrone, but not inhibin, concentrations we...
The suitability of echotexture characteristics of the follicular wall for identifying the optimal breeding day in mares. Ultrasonically detected changes in the equine preovulatory follicle were characterized for the 3 d preceding ovulation early (n = 47) and late (n = 14) in the ovulatory season. Values for the following follicle end points increased progressively over the 3 d: diameter, incidence of nonspherical shape, echogenicity of the apparent granulosa layer, and prominence of an anechoic layer beneath the granulosa. The latter 2 echotexture end points were scored from 1 to 3 (minimal to maximal). Follicle diameter and the 2 echotexture characteristics were more prominent early than late in the ovulatory s...
Effect of PGE2 on uterine contractility and tone in mares. A technique for transvaginal, ultrasound-guided intrauterine injection was developed. After preliminary study using different approaches, the procedure was successful in 24 of 25 (96%) mares, based on detecting fluid in the uterine lumen during and after the injection. The technique was used to study the effect of PGE2, reportedly produced by the embryonic vesicle, on uterine contractility on Day 12 (Day 0 = ovulation). Uterine contractility was scored (1 = minimal, 4 = maximal) every 10 min for 1 h and every 30 min for the next hour by a continuous 1-min ultrasound examination of a longitudin...
Factors influencing ovarian activity and sexual behavior of postpartum mares under farm conditions. Management of the postpartum period is one of the most important factors of stud farm medicine. In horses, owing to the long gestation period, the time from parturition to repeat conception needs be short to maintain an optimal yearly foaling interval. For this reason the features of postpartum ovarian activity and sexual behavior were studied under farm conditions. During 2 consecutive breeding seasons, 107 mares on 5 commercial horse farms were monitored after parturition by regular teasing, transrectal ultrasonography and blood sampling for progesterone. Foalings took place from January 1 t...
Estrous cycle characteristics and response to estrus synchronization in mammoth asses (Equus asinus americanus). Breeding records from a herd of mammoth asses (Equus asinus americanus) maintained on pasture in southeast Texas from 1990 to 1998 were reviewed. Jennies were pasture or hand mated, and estrus was either observed while the jennies were on pasture or when exposed to a jack after being penned. Eighty-one estrus periods and 43 diestrus intervals were recorded in 33 jennies over 4 seasons of the year (January-March, April-June, July-September, and October-December). Estrous cycle length and the duration of estrus were similar among seasons. Over all seasons, estrous cycle length was 23.3 +/- 2.6 d...
Relationship between ultrasonic characteristics of the corpus luteum, plasma progesterone concentration and early pregnancy diagnosis in Friesian mares. The purpose of the present study was to evaluate the change in cross-sectional area of the early corpus luteum (CL) and progesterone production in relation to subsequent pregnancy diagnosis. The cross-sectional area of the CL of 75 Friesian brood mares was measured by ultrasonography on Day 1 or 2 and Day 8 or 9 after ovulation. The change in cross-sectional area was expressed in a volume ratio. Plasma progesterone concentrations were measured on Days 8 to 9, and ultrasonography to determine pregnancy status was carried out on Day 17. The data obtained were analyzed by using a multiple logisti...
Sperm transport and survival in the mare: a review. After the deposition of semen in the mare's uterus, spermatozoa must be transported to the site of fertilization, be maintained in the female tract until ovulation occurs, and be prepared to fertilize the released ovum. Sperm motility, myometrial contractions, and a spontaneous post-mating uterine inflammation are important factors for the transport and survival of spermatozoa in the mare's reproductive tract. Fertilizable sperm are present in the oviduct within 4 h after insemination. At this time, the uterus is the site of a hostile inflammatory environment. Our data suggest that spermatozoa...
The effects of perphenazine and bromocriptine on follicular dynamics and endocrine profiles in anestrous pony mares. Nineteen anestrous pony mares were used in a project designed to determine the effects of altered prolactin concentrations on follicular dynamics and endocrine profiles during spring transition. The dopamine antagonist, perphenazine, was administered daily to mares (0.375 mg/kg body weight) in Group A (n = 6), while Group B mares (n = 7) received 0.08 mg/kg metabolic weight (kg75) dopamine agonist, 2-bromo-ergocriptine, intramuscularly twice daily. Mares in Group C (n = 6) received 0.08 mg/kg75, i.m., saline twice daily. Treatment began January 20, 1994, and continued until ovulation occurred....
Effect of passive immunization against inhibin on FSH secretion, folliculogenesis and ovulation rate during the follicular phase of the estrous cycle in mares. Physiological roles of inhibin in mares were investigated by means of passive immunization using an antiserum to inhibin that had been raised in a castrated goat. Eight mares were given an intravenous injection of either 100 mL (n = 4) or 200 mL (n = 4) of inhibin antiserum 4 d after a single intramuscular injection of PGF2 alpha on Day 8 after ovulation, 4 control mares were treated with 100 mL castrated goat serum in the same manner. Jugular vein blood samples were collected after treatment with the serum until 192 h post treatment. Follicular growth and ovulations were monitored by ultrasou...
Evaluation of two treatments in superovulation of mares. The efficiency of superovulating mares with an enriched fraction of equine follicle-stimulating hormone (feFSH) and an equine pituitary extract (EPE) with similar FSH content but differing in the LH amount was compared. Mares were randomly assigned to an feFSH (n = 5) or EPE (n = 5) treatment. The experimental period was of 2 successive estrous cycles, with the first cycle as the control. At Days 6 and 7 of the estrous cycle, the mares received 250 micrograms i.m. cloprostenol. The treatments consisted of daily injections of 25 mg feFSH or EPE beginning on Day 6 post ovulation. Mares were inse...
Effects of melatonin implants in pony mares. 2. Long-term effects. The effects of melatonin implant treatment over a 4 wk period at the summer solstice on the transition into and out of the following anovulatory season were evaluated in ovary-intact and ovariectomized mares. Melatonin implants tended to delay the timing of the final ovulation of the breeding season (P = 0.0797) in the ovary-intact mares. Although the decline in LH secretion associated with the end of the breeding season was parallel between treatments and ovarian statuses, the rate of LH secretion, as expressed by its mathematical accumulation, was lower in ovariectomized, melatonin-treated m...
Temporal interrelationships among luteolysis, FSH and LH concentrations and follicle deviation in mares. The effect of altered LH concentrations on the deviation in growth rates between the 2 largest follicles was studied in pony mares. The progestational phase was shortened by administration of PGF2alpha on Day 10 (Day 0=ovulation; n=9) or lengthened by daily administration of 100 mg of progesterone on Days 10 to 30 (n=11; controls, n=10). All follicles > or = 5 mm were ablated on Day 10 in all groups to initiate a new follicular wave. The interovulatory interval was not altered by the PGF2alpha treatment despite a 4-day earlier decrease in progesterone concentrations. Time required for growt...
The current status of equine embryo transfer. The use of embryo transfer in the horse has increased steadily over the past two decades. However, several unique biological features as well as technical problems have limited its widespread use in the horse as compared with that in the cattle industry. Factors that affect embryo recovery include the day of recovery, number of ovulations, age of the donor and the quality of sire's semen. Generally, embryo recoveries are performed 7 or 8 d after ovulation unless the embryos are to be frozen, in which case recovery is performed 6 d after ovulation. Most embryos are recovered from single-ovulati...
Changes in equine endometrial oestrogen receptor alpha and progesterone receptor mRNAs during the oestrous cycle, early pregnancy and after treatment with exogenous steroids. Two experiments were performed to determine changes in the abundance of oestrogen and progesterone receptor (ER alpha and PR) mRNAs in equine endometrium during the oestrous cycle and early pregnancy, and under the influence of exogenous steroids. In Expt 1, endometrial biopsies were obtained from non-mated mares during oestrus and at days 5, 10 and 15 after ovulation, and from pregnant mares at days 10, 15 and 20 after ovulation. There were overall effects of day on the abundance of ER alpha (P = 0.0001) and PR (P = 0.0014) mRNAs. The amount of ER alpha mRNA decreased at day 10 of pregnancy, ...
Characterization of cellular and vascular changes in equine follicles during hCG-induced ovulation. In contrast to other species, the histology of the equine follicle during ovulation has not been described. Preovulatory follicles were isolated during oestrus at 0, 12, 24, 30, 33, 36 and 39 h (n = 5-6 follicles per time point) after an ovulatory dose of hCG to characterize the cellular and vascular changes associated with ovulation in mares. Pieces of follicle wall were formalin-fixed and processed for light microscopy to evaluate the general follicular morphology and quantify selected parameters. Marked changes were observed in the histology of equine follicles in the hours before ovulation...
Modulation of oviductal transport in mares by local application of prostaglandin E2. Equine embryos enter the uterus 144-156 h after ovulation, before which time the passage of embryos through the oviduct is halted in the region of the ampullary-isthmic junction. It is thought that further onward movement of embryos to the uterus is facilitated by secretion of prostaglandin E2 (PGE2) by the embryos, which relaxes the smooth muscle of the isthmus. In the present study, the effect of a single local application of PGE2 on oviductal transport was examined in 22 Thoroughbred and Pony mares that were inseminated on alternate days during oestrus. On day 4 after ovulation, the ipsilat...
