The estrous cycle in horses is a recurring reproductive cycle that mares undergo, typically during the breeding season. This cycle is characterized by a series of hormonal changes that prepare the mare for potential conception. The cycle is divided into two main phases: estrus and diestrus. During estrus, the mare is receptive to mating, and ovulation occurs. In contrast, the diestrus phase is a period when the mare is not receptive to a stallion. The regulation of the estrous cycle involves a complex interplay of hormones such as estrogen, progesterone, luteinizing hormone, and follicle-stimulating hormone. Understanding the estrous cycle is important for effective breeding management and reproductive health in horses. This page compiles peer-reviewed research studies and scholarly articles that explore the physiology, hormonal regulation, and implications of the estrous cycle in equine reproduction.
Reilas T, Katila T, Mäkelä O, Huhtinen M, Koskinen E.Intrauterine fluid (IUF) was collected using a tampon from mid-oestrous mares (n = 57) with and without ultrasonically detectable accumulations of free intraluminal fluid. Bacteria were cultured and neutrophils counted from all samples (n = 57). Total protein concentration, trypsin-inhibitor capacity (TIC), and plasmin, beta-glucuronidase (B-Gase) and N-acetyl-beta-D-glucosaminidase (NAGase) activities were determined in 27 IUF samples. The motility of spermatozoa in the presence of IUF, IUF extended with Kenney's medium (1:1) and Kenney's medium alone was analysed in 9 samples using a Hamilto...
Sharp DC, Thatcher MJ, Salute ME, Fuchs AR.The effect of transcervical endometrial biopsy on the concentrations of plasma immunoreactive oxytocin and 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM) was studied in 18 pony mares on days 8, 12 and 14 after ovulation, days 12 and 14 of early pregnancy and at oestrus. Five biopsy specimens were taken within 15 min and consecutive specimens from each mare were pooled two (A) and three (B) together for measurement of the number of oxytocin receptors. Blood samples were collected at intervals of 5 min for 15 min beginning just before the initial biopsy. Biopsy procedure elicited prompt oxy...
Gentry PA, Zareie M, Liptrap RM.The amounts of total protein, albumin, fibronectin, alpha 2-macroglobulin (alpha 2-M), immunoglobulin G, ceruloplasmin and antithrombin were determined in fluids collected from 53 preovulatory equine follicles and compared with the contents of estradiol-17 beta, progesterone and androstenedione, with follicle size and the amounts of the equivalent proteins in normal equine plasma. The concentration of fibronectin and the fibronectin/albumin ratios increased significantly with follicle size and with follicular estradiol levels. The alpha 2-M levels and alpha 2-M/albumin ratios correlated with f...
Rasch K, Schoon HA, Sieme H, Klug E.The aim of this field study was to examine the influence of the uterotonic substance oxytocin in 2 different therapeutic dosages of 15 and 25 i.u., respectively on the uterine drainage of oestrous mares and on their fertility. In addition endometrial biopsies of mares with and without intrauterine fluid accumulations around the time of ovulation were evaluated histomorphologically regarding the aetiology of susceptibility to uterine infection. A population of 59 Hanoverian Warmblood mares was used in this study. The mares were divided into Group A (mares with intrauterine fluid accumulations [...
Besognet B, Hansen BS, Daels PF.We have previously demonstrated that daily administration of the dopamine D2 antagonist, sulpiride, during seasonal anoestrus, effectively advances the mean time of onset of the breeding season in mares. The purpose of this study was to examine the effect of sulpiride administration on pulsatile FSH and LH secretion in seasonally anoestrous mares, follicular development, time of first ovulation and the fertility at the first ovulation. Fourteen anoestrous mares were selected based on progesterone concentrations < 1 ng ml-1 for 3 weeks and largest follicle diameter < 20 mm. Starting 30 Ja...
Fitzgerald BP.The purpose of this experiment was to investigate whether N-methyl-D,L-aspartate stimulated gonadotropin secretion in mares and to determine the response in two experimental paradigms where gonadotropin secretion is low or elevated. In Experiment 1, conducted during the breeding season (summer), eight long-term ovariectomized mares were treated daily for 21 d with progesterone plus estradiol (n = 4) or oil vehicle. Beginning on Day 14, each mare received, in a randomized design on alternate days, an intravenous injection of either 0, 0.5, 1.0, or 5.0 mg/kg NMA. Treatment with NMA was not accom...
Tunón AM, Rodriguez-Martinez H, Haglund A, Albihn A, Magnusson U, Einarsson S.Cyclical accumulation of uterine fluid occurs during oestrus and is often seen in excessive volumes in mares considered susceptible to endometritis. Since the mechanisms behind the formation of free uterine fluid remain to be clarified, the fine structure of the secretory equine endometrium was studied in biopsies collect during videoendoscopy from 14 endometritis-free, 4-9-year-old mares during oestrus. A distinct oedema of the tunica mucosa was evident. The surface epithelium had both ciliated and nonciliated cells and, particularly at the uterine body, often presented intra-epithelial macro...
Silvia PJ, Meyer SL, Fitzgerald BP.Twelve horse mares were used in a repeated-measures design consisting of 3 replicates of 4 mares each. On Day 6 following ovulation, luteolysis was initiated with an i.m. injection of prostaglandin F2 alpha (PGF2 alpha; Lutalyse, 10 mg). Either 12 (-12) or 36 (-36) h before PGF2 alpha (PRE), blood samples were collected simultaneously from the intercavernous sinus (ICS) and jugular (JUG) vein at 10-min intervals for an 8-h period. Pituitary capacity to exogenous GnRH (2 micrograms/kg BW, i.v.) was evaluated at the alternate time point within this period. Frequent sampling and GnRH challenge we...
Gomez-Cuetara C, Flores JM, Sanchez J, Rodriguez A, Sanchez MA.An histological study of the postpartum period in 29 mares was carried out. Uterine biopsies were taken daily during the first 10 days postpartum in a total of 87 samples. At day 0, equine endometrium was characterized in the surface by the presence of regularly ordered microcaruncles; the stratum spongiosum was oedematous and contained distended and scarce glands. Degenerative changes in microcaruncles and endometrial glands were present on day 1 postpartum. The epithelium of the microcaruncles from 2 to 5 days postpartum showed cytoplasmic vacuolization, karyorrhexis and an inflammatory reac...
McDowell KJ, Adams MH, Franklin KM, Baker CB.A cDNA library was constructed from poly(A) RNA obtained from Day 14 nonbred equine endometrium. A cDNA probe for porcine retinol-binding protein (RBP) was used to screen the library, and a complete cDNA sequence (1133 bp, excluding the poly(A) tail) was obtained. Endometrial biopsies were obtained from cycling, nonbred mares at Days 0, 1, 4, 8, 10, 11, 13, and 15 and from pregnant mares at Days 11, 13, 15, and 17 after ovulation (n = 2 mares each day). Endometrial biopsies were also taken from 18 noncycling anestrous mares after the following treatments: C (vehicle control for 1 day, n = 3), ...
Gånheim A, Gånheim A, Jöchle W.In a blinded trial, the effectiveness and safety of 2.2 mg of the GnRH analog deslorelin acetate, administered in a short-term implant (STI) to normally cycling mares in estrus with a dominant ovarian follicle of 30 mm in diameter or larger, were evaluated, using a placebo implant as a negative control. A total of 39 mares received treatments at admittance with pre-randomized implants containing either 2.2 mg or 0 mg deslorelin. Mares were teased daily and examined rectally with ultrasound at 24 h intervals to determine time to ovulation and duration of estrus. The number of breedings and the ...
Redina OE, Amstislavsky SYa , Maksimovsky LF.This study examined the developmental capacity of oocytes in DD mice after they had been injected with pregnant mares' serum gonadotrophin at different stages of the oestrous cycle. The superovulation of mature DD mice at pro-oestrus, oestrus and metoestrus resulted in a large yield of viable embryos. The proportion of abnormal embryos was highest after injection of pregnant mares' serum gonadotrophin at dioestrus. The pool of viable oocytes was most synchronized with normal development after the hormone was injected at oestrus. The results demonstrate that oocytes of different morphology coul...
Ferreira-Dias G, Nequin LG, King SS.Pathologic changes in the endometrium of mares may be rated according to Kenney's method of classification. Category I endometrium contains healthy tissue with no or few widely scattered pathologic changes. At the opposite end, severe widespread pathologic changes are associated with category III. Uterine biopsy specimens were collected aseptically from 16 mares during the estrous and diestrous stages of the cycle. Pathologic changes were evaluated, using light microscopy, and endometrium was classified as Kenney's category I, II, or III. Endometrial tissue of category I (n = 5 mares in estrus...
Thomas PG, Ball BA, Brinsko SP.Regulation of attachment of equine spermatozoa to homologous oviduct epithelium was investigated by co-culture of spermatozoa with oviductal epithelial cell explants. Stallion spermatozoa were incubated with explants derived from the isthmus and ampulla of follicular, postovulatory, and diestrous mares. Steroid treatments (estradiol, progesterone, or control) were applied across all explant groups. Estimates of motility and total numbers of attached spermatozoa were made 0.5, 24, and 48 h after initiation of co-culture. Equine spermatozoa attached by their rostral acrosomal region to both cili...
Watson ED, McDonnell AM, Cí·¯ord D.The characteristics of the cyclicity of 12 maiden thoroughbred mares kept in two groups were studied over a total of 58 cycles. On average, oestrus lasted 5.3 days and in 60 per cent of the cycles ovulation occurred in the last two days of oestrus. Oestrus and ovulation tended to be synchronised in each group of mares. The mean diameter of single-ovulating preovulatory follicles on the day before ovulation was 41.5 mm and during the seven days before ovulation they grew 2.5 mm/day. More than one follicle ovulated in 19 (33 per cent) of the cycles (seven double ovulations and 12 dioestrous ovul...
Ferreira-Dias G, Nequin LG, King SS.Equine endometria representative of Kenney's categories I, II, and III were incubated in vitro with phosphate buffer, Streptococcus pneumoniae, or S zooepidemicus. Endometrial tissues from mares in estrus and diestrus were first categorized according to Kenney's classification, then were tested for adherence of S pneumoniae and S zooepidemicus to the epithelia. Bacteria were not observed when the endometrial tissue was incubated with phosphate buffer or S pneumoniae. There was no statistical difference in attachment of S zooepidemicus to endometrial tissue from mares in estrus or diestrus if e...
LeBlanc M, Neuwirth L, Mauragis D, Klapstein E, Tran T.The effects of oxytocin on the percentage of technetium 99m albumin colloid (99mTc-microAA), cleared from the uterine lumen was measured in 13 mares. Scintigraphy was performed during 4 consecutive oestrous cycles, on Day 3 of oestrus during Cycles one and 3 and 48 h after ovulation during Cycles 2 and 4. Oxytocin (20 iu) was given i.v. after the initial scintigraphy image during Cycles 3 and 4. Seven multiparous mares (Group 1) were classified as 'susceptible' and 6 mares (2 nulliparous and 4 multiparous; Group 2) were classified as 'resistant' to endometritis. All mares cleared > 90% of 99mT...
Scudamore CL, Pemberton AD, Miller HR, McDonnell AM, Thomson SR, Dawson A, Watson ED.An enzyme linked immunosorbent assay (ELISA) was developed and used to estimate the concentrations of the serine proteinase inhibitor, alpha-1 proteinase inhibitor (API), in uterine flushings recovered from mares at different stages of the oestrous cycle and before and after the induction of experimental endometritis. There was a significant increase in the concentrations of API and albumin relative to total protein in flushings recovered during oestrus compared with dioestrus but no difference was observed in the concentrations of these proteins relative to total protein before and after the ...
Willis P, Sekhar KN, Brooks P, Fayrer-Hosken RA.To characterize further the events involved in fertilization and early embryonic development in the mare, effect of the estrous cycle on oviductal fluid proteins was investigated. Five mares had indwelling cannulas placed in their oviducts so that fluid could be collected throughout the estrous cycle. Daily fluid volumes were recorded and mares were monitored for signs of standing estrus. Oviductal fluid samples were pooled across mares according to stage of cycle (either estrus or nonestrus) for further analysis. Two-dimensional polyacrylamide gel electrophoresis (PAGE) was used to determine ...
Bostedt H, Lehmann B.By means of clinical and analytical procedures (enzyme immuno assay for progesterone with microtiterplate method) the ovarian activity from 27 mares was tested over a period of several weeks. The measurement of the progesterone level to determine the time of ovulation was proved as suitable in the period of 1-2 days after ovulation. In normocyclic mares (n = 17) a different development of the progesterone profile was detected, so that an insufficient development of the corpus luteum (35%) could be considered. By means of continuous measurement of progesterone (> or = 30 days) six of ten mares ...
Roser JF, McCue PM, Hoye E.An overnight double antibody RIA, employing a rabbit antiserum raised to bovine 31 kDa inhibin (rAs-#1989, NICHD) and purified bovine 31 kDa inhibin (bINH-I-90/1, NICHD) as trace and standard, was validated to measure immunoreactive inhibin (iINH) concentrations in equine peripheral plasma, follicular fluid (FF), ovarian vein (OV) plasma, testicular tissue extracts (TTE) and testicular vein (TV) plasma. The dynamic relationship of iINH and follicle stimulating hormone (FSH) was investigated during the estrous cycle of the mare and the annual reproductive cycle of the stallion. In the RIA, para...
Mumford EL, Squires EL, Jasko DJ, Nett TM.A lack of pituitary LH stores has been implicated as the cause of seasonal anestrus and failure to ovulate during the spring transition period in mares. In this experiment, 40 mares were used to study the effects of GnRH, estrogen, and an estrogen-GnRH combination on increasing releasable pituitary LH. Mares were stratified based on their ability to secrete LH in response to a 950-micrograms challenge of GnRH (n = 10 per group) and then assigned to one of four treatment groups: 1) controls, given no treatment; 2) 1 mg of estradiol-17 beta in oil i.m. daily for 8 d; 3) 200 micrograms of GnRH an...
Amri H, Silberzahn P, al-Timimi I, Gaillard JL.This present study was undertaken to clarify estrogen synthesis in the mare ovary. First of all, an evaluation of endogenous steroid contents was carried out in the follicular fluid and in the luteal tissue at different stages of the luteal phase. Radioimmunoassays were performed after separation and purification of each hormone by chromatography. High amounts of conjugated (0.9 mg/l) and unconjugated (4 mg/l) estradiol-17 beta were found in the follicular fluid of the large follicules (50 mm). These concentrations of estrogens decreased drastically in the luteal tissue, and only low levels of...
Perkins NR, Threlfall WR, Ottobre JS.Existence of ultradian variation in serum progesterone concentration and the relation between progesterone and luteinizing hormone (LH) secretory patterns were investigated in nonpregnant and pregnant mares. Blood samples were taken every 15 minutes for a 24-hour period on day 8 of the estrous cycle and day 18 of pregnancy, respectively. Progesterone and LH concentrations were determined by radioimmunoassay. Progesterone was secreted in pulsatile manner in nonpregnant and pregnant mares. Luteinizing hormone also was secreted in a pulsatile manner in both groups of mares. There was little tempo...
Yurdaydin N, Tekin N, Gülyüz F, Aksu A, Klug E.An Arab broodmare herd of 30 mares age ranging from 4 to 12 years was grouped into 3 groups (group A, B, C) with 10 mares each and exposed to three different methods of cycle synchronisation. Group A mares received two PGF2 alpha injections 14 days apart. Group B mares got additionally 2,500 IU of hCG 5 days after second prostaglandin application. Group C consisted of mares which had foaled in a synchrony of one week and got a PGF2 alpha injection 3 weeks after parturition. All the mares responding to synchronisation were inseminated closely to ovulation detected by serial rectal palpations wi...
Troedsson MH, Wiström AO, Liu IK, Ing M, Pascoe J, Thurmond M.A method for interpreting and analysing electromyographic (EMG) data of myometrial electrical activity was established. This method was used to study EMG activity in the uterus during the various stages of the oestrus cycle in mares. Recordings were analysed from four pairs of electrodes that were surgically implanted in the myometrium of four reproductively sound mares. The electrodes were placed at the tip, middle and base of the left horn and in the uterine body. Electrical activity was monitored by a polygraph. Data were transformed to a digitized form and statistically analysed. Myometria...
Fitzgerald BP, Peterson KD, Silvia PJ.During the breeding season, the effect of constant administration of an agonist analog of gonadotropin-releasing hormone (GnRH; goserelin acetate) on reproductive activity of mares was determined. Twenty-four mares undergoing estrous cycles were allocated at random to 6 groups (n = 4/group) and, on May 29 (day 0), received no treatment (group 1, controls), 120 micrograms (group 2), 360 micrograms (group 3), 600 micrograms (group 4), or 1,200 micrograms (group 5) of GnRH agonist/d for 28 days via a depot implanted subcutaneously. The final group of mares (group 6) was treated with 120 microgram...
McDowell KJ, Adams MH, Williams NM.Proteins synthesized and released in vitro by oviducts collected from horse mares during estrus and at day 4 after ovulation for bred and nonbred mares were examined by two-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (2-D SDS PAGE) and fluorography. Ampullary and isthmic regions both produced a wide array of nondialyzable proteins in culture. Major proteins or groups of proteins identified according to relative molecular weight (kDa) and apparent isoelectric point (pI) were at 100 kDa, pI 8; 100-200 kDa, pI 6; 150 kDa, pI 4.5; 60-100 kDa, pI 4; and an array of polypep...
Johnson AL.Cycling standardbred mares were infused with saline or 20 micrograms gonadotropin-releasing hormone (GnRH) in a pulsatile pattern (one 5-sec pulse/h, 2 h or 4 h) beginning on Day 16 of the estrous cycle. Although serum concentrations of luteinizing hormone (LH) increased significantly earlier in all three GnRH-treated groups (within one day of the initiation of infusion) compared to saline-infused controls, there were no differences in peak periovulatory LH concentrations among treatments (overall mean +/- SEM, 8.98 +/- 0.55 ng/ml). The number of days from the start of treatment to ovulation w...
Derar DR, Taya K, Watanabe G, Miyake YI.The aim of this study was to characterize ir-IGF-I pattern and its relation to other hormones during the oestrous cycle in mares. Nine non-pregnant non-lactating pluriparous thoroughbred mares were used. The studied mares were examined ultrasonically and bled daily to follow the ovarian changes and the hormonal milieu for a complete Interovulatory interval (IOI). Two (minor and major) follicular waves were characterized per IOI in thoroughbred mares. The largest follicle of the first follicular wave (DF1) was firstly detected at D - 1.75 ± 0.47 with a growth rate of 2.78 ± 0.14mm/day and max...
Palmer E, Jousset B.Eight mares were observed clinically for 14 months to detect oestrus and ovarian activity, and assays of urinary oestrogens and plasma progesterone were performed. Cyclical ovarian activity occurred during 60% of the experimental period. Persistent luteal activity was found over 20% of the period and for the rest of the time activity was absent. Cyclical activity was characterized by the alternation of periods of low and high progesterone levels corresponding to the follicular and luteal phases of the ovarian cycle. During the follicular phase, urinary oestrogen levels increased to a maximum o...
Henson KL, Alleman AR, Cutler TJ, Ginn PE, Kelley LC.A 9-year-old Arabian mare was admitted for evaluation of multiple subcutaneous nodules and infertility. Fine-needle aspiration of one of the subcutaneous nodules resulted in a cytologic diagnosis of histiolymphocytic lymphoma. Palpation per rectum and transrectal ultrasonography revealed a mass associated with the left ovary. Excision of the ovarian tumor was performed, and a histopathologic diagnosis of granulosa-theca cell tumor was made. After removal of the granulosa-theca cell tumor, subcutaneous nodules regressed. The referring veterinarian reported that the nodules had also disappeared ...
Boyd EH, Allen WE.Plasma concentrations of neomycin were measured following intrauterine infusion of 3.3 mg/kg bodyweight neomycin sulphate. Mares in oestrus absorbed approximately 6 per cent of neomycin infused whereas mares in a luteal phase absorbed 56 per cent. The volume of infusate also affected absorption as increased volume resulted in decreased absorption. The decreased absorption both during oestrus and when large volumes were used was probably due to reflux of antibiotic through the cervix.
Kimball FA, Wyngarden LJ.Preliminary studies indicate the presence of PGF2alpha specific binding sites in membrane fractions prepared from equine corpora lutea. The equilibrium binding data indicate an apparent dissociation constant of 3.2 X 10(-9)M and the concentration of binding sites of -0.1 pmoles/mg membrane protein. Competition of several natural prostaglandins for equine luteal PGF2alpha specific binding sites indicates specificity for the 9alpha-hydroxyl moiety and the 5,6-cis doublebond. Significant increases in relative binding affinities were demonstrated for PGF2alpha analogs with a phenyl ring introduced...
Ishak GM, Dutra GA, Gastal GDA, Elcombe ME, Gastal MO, Park SB, Feugang JM, Gastal EL.This study aimed to gain insight on the effect of different seasons of the year on the expression pattern of growth factor and hormone receptors involved in follicle development. A novel follicle wall biopsy technique was used to collect in vivo follicle wall layers (ie, granulosa, theca interna, and theca externa) and follicular fluid samples from growing dominant follicles, simultaneously and repeatedly, using the same mares during the spring anovulatory (SAN), spring ovulatory (SOV), summer (SU), and fall ovulatory (FOV) seasons. The immunofluorescent expression patterns of epidermal growt...
King SS, Douglas BL, Roser JF, Silvia WJ, Jones KL.There is a well-documented increase in luteolytic failure, resulting in spontaneously prolonged corpus luteum (SPCL) function, during estrous cycles of horses in autumn. The cause of this phenomenon may be due to seasonal alterations in PGF(2alpha) and/or in prolactin (PRL) secretion around luteolysis. To investigate this, progesterone (P4), 13, 14-dihydro, 15-keto PGF(2alpha) (PGFM) and PRL concentrations were compared between summer and autumn estrous cycles during natural luteolysis and luteolysis induced by benign uterine stimulation. A single estrous cycle from mares in June-July (n=12) w...
Käser R, Bruckmaier RM, Thomas S, Sieme H, Wedekind C, Burger D.Oxytocin is a hormone that may not only influence reproductive mechanisms in mammals but also their social behavior, including pair bonding. We therefore tested if the concentrations of oxytocin and other hormones reveal mate preferences of 13 mares in estrus. Each mare was first exposed to two stallions (haphazardly selected out of seven) and her behavior recorded. The mare was then returned to her box (i.e., no contact to stallions during that time). Approximately 4.5 hours later, venous blood samples were collected every minute during 30 minutes preceding exposure to one of the two previo...
Irvine CH, Alexander SL, McKinnon AO.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...
Aurich C, König N, Budik S.In mares, repeated embryo collection in successive oestrous cycles is necessary if a greater number of foals should be produced. We investigated effects of repeated embryo collection in fertile donor mares on embryo recovery rates. In addition, an influence of the individual mare and season on embryo recovery rates was studied. In nine mares, a total of 153 embryo collections were performed during 30 months (17 ± 2.2 embryo collections per mare). The overall embryo recovery rate was 64% and did not differ among mares. Between successive embryo collection procedures, recovery rate varied signi...
Wehrenberg WB, Kurt KJ, Hutz RJ.The incidence of anestrous mink during the normal breeding season has been reported to be as high as 5%. We sought to induce estrus in these mink by using various doses of equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG). Seventy-five female mink maintained under standard ranch conditions failed to demonstrate estrus during the annual breeding season in March. These anestrous mink were randomly assigned to treatment groups. Treatments were given on March 16 and again on March 18. On these 2 d, mink were treated with equal doses of saline, 25, 50, or 100 IU of eCG, or ...
Ginther OJ, Woods BG, Meira C, Beg MA, Bergfelt DR.Follicle growth and circulating hormone concentrations were compared between an interovulatory interval and the first 60 days of the anovulatory season in pony mares. Daily observations were made from November of three groups: (i) ablation of follicles of >/=6 mm in diameter at day 10 after an ovulation that initiated an interovulatory interval, as determined retrospectively (ovulatory group, n=8), (ii) ablation at day 10 after the last ovulation of the year (anovulatory-10 group, n=6); and (iii) ablation at day 60 after the last ovulation of the year (anovulatory-60 group, n=6). Follicular...
Cochran RA, Leonardi-Cattolica AA, Sullivan MR, Kincaid LA, Leise BS, Thompson DL, Godke RA.The effects of exogenous equine somatotropin (eST) administration on ovarian activity and plasma hormone levels were evaluated on horse and pony mares. The objectives of this study were to determine the effects of eST on follicular development and circulating concentrations of leutinizing hormone (LH), estradiol, progesterone, and insulin-like growth factor I (IGF-I) in cyclic horse and pony mares. Sixteen mares received daily injections (i.m.) of eST at a concentration of 25 micrograms/kg body weight on either Days 6 through 12 (Treatment A) or 13 through 19 (Treatment B) postovulation. In ad...
Blue MG, Brady AA, Davidson JN, Kenney RM.Forty uterine fluid samples were obtained during oestrus and dioestrus of successive cycles from 4 mares classified as resistant to bacterial infection of the uterus. The flushings were assayed for peroxidase activity and ability to influence phagocytosis by polymorphonuclear neutrophils. Uterine fluid volumes and protein concentrations and serum oestrogen values were similar during oestrus and dioestrus. Serum progesterone concentrations were depressed during oestrus. Equine neutrophils adherent to glass slides were exposed to a genital strain of Streptococcus zooepidemicus suspended in salin...
Shirazi A, Gharagozloo F, Ghasemzadeh-Nava H.The Caspian breed of horses is believed to be the direct descendant of the earliest equine animals. Some special characteristics of Caspian horse differentiate this breed of horses from other breeds. In the current study the ultrasonically observed characteristics of a preovulatory dominant follicle and the lengths of estrus, diestrus as well as some related parameters were studied during 42 interovulatory intervals in 11 healthy Caspian mares. The preovulatory dominant follicle deviated from subordinate follicles and became the largest follicle in the ovaries at Day -8.7 +/- 0.53 (Day 0=ovula...
Ginther OJ, Utt MD, Beg MA, Gastal EL, Gastal MO.The negative effect of estradiol-17beta (E2) on LH, based on exogenous E2 treatments, and the reciprocal effect of LH on endogenous E2, based on hCG treatments, were studied throughout the ovulatory follicular wave during a total of 103 equine estrous cycles in seven experiments. An initial study developed E2 treatment protocols that approximated physiologic E2 concentrations during the estrous cycle. On Day 13 (ovulation = Day 0), when basal concentrations of E2 and LH precede the ovulatory surges, exogenous E2 significantly depressed LH concentrations to below basal levels. Ablation of all f...
Varner DD, Forrest DW, Fuentes F, Taylor TS, Hooper RN, Brinsko SP, Blanchard TL.Eighteen fertile mares were used to determine the effects of the oestrous cycle and location in the reproductive tract on the amount and concentration of glycosaminoglycans in luminal fluids. Ovariohysterectomies were performed in 3 groups of 6 mares on Day 3 of behavioural oestrus, within 6 h after ovulation or on Day 8 of dioestrus. The lumina of the uterine horns and oviducts ipsilateral and contralateral to the active ovary were flushed and fluid was aspirated from the dominant follicle in the oestrous preovulation group. Glycosaminoglycans and protein concentrations were measured in these...
Santos VG, Bettencourt EM, Ginther OJ.Persistent CL (PCL; n = 10) in mares was studied daily from Day 20 (Day 0 = ovulation) to the ending ovulation. In addition, the 10 days before ovulation at the end of a PCL were compared with the end of an interovulatory interval (IOI; n = 28) during the same months. Concentration of P4, cross-sectional area of CL, and percentage of CL with Doppler signals of blood flow during PCLs remained constant from 64 to about 33 days before the end of luteolysis and then decreased linearly. Concentration of LH between Day 20 and beginning of the ovulatory LH surge increased linearly. A dominant follicl...
Sirois J, Kimmich TL, Fortune JE.Estrous cycles in mares have several unique characteristics, including the presence of a long period of estrus and the absence of a typical LH surge. Like follicles of other species, equine preovulatory follicles are characterized by their ability to secrete large amounts of 17 beta-estradiol, but it is not clear which follicular cell type is responsible for estradiol synthesis in mares. To better understand the relative roles of theca interna and granulosa cells in follicular steroidogenesis, presumptive ovulatory follicles were obtained from mares during early estrus (first or second day of ...
Brook D.A guarded, sterile swab is used to obtain samples for uterine culture. With the mare in stocks, the tail bandage and the perineum washed, the culture rod is introduced into the vagina with a gloved hand. After the rod is guided through the cervix, the guard cap is dislodged and the swab is rubbed along the endometrium, after which the rod is extracted. Samples for uterine culture should only be obtained during full estrus. Swabs should be directly plated onto agar within 2 hours of collection. Blood agar is appropriate for initial screening, but use of specialized types of agar expedites ident...
Tsukada T, Kojima AY, Sato K, Moriyoshi M, Koyago M, Sawamukai Y.The concentrations of androstenedione, estradiol-17β, progesterone and PGF2α contained in the follicular fluid produced by the follicles in collected ovaries of mares that have had estrous phase during the breeding season were measured and analyzed the relation between the growth stage of follicles and the hormone levels in the follicular fluid. An ultrasonographic diagnostic instrument was used to measure the diameter of the follicles in order to categorize the follicles into three groups the following: 8 small follicles (from 1.0 to less than1.5 cm), 8 medium follicles (from 1.5 to less th...
Newcombe JR, Cuervo-Arango J.It is believed that during the spring transition, the developing follicle tends to grow more slowly, persist longer and grow to a larger diameter prior to ovulation than at subsequent oestrus periods. A general suspicion, that the first ovulation of the year is less fertile than subsequent ovulations could be explained by a slower growth rate of the ovulatory follicle during transition with the consequent production of a subfertile oocyte. By detailed serial examination of the same group of Irish Draught mares over three winter/spring periods, no significant difference was found in either grow...
Neely DP, Hughes JP, Stabenfeldt GH, Evans JW.Intrauterine saline infusion in the dioestrous mare shortened the ovulatory interval by inducing premature luteolysis. Plasma progestagen levels began to decrease approximately 1 day after the infusion and had declined to less than 1-0 ng/ml in 4 days. The CL, including others formed from ovulations during dioestrus, must be 4 to 5 days old before intrauterine saline will induce luteolysis. Of 10 mares infused on Day 4 or 5 after ovulation, only six had a shortened ovulatory interval. Of 10 mares infused on Day 6 or 7 after ovulation, seven had a shortened ovulatory interval and three failed t...
von Reitzenstein M, Callahan MA, Hansen PJ, LeBlanc MM.An experiment was conducted to determine whether the uterotonic effects of oxytocin, a drug used to treat mares that have a delay in uterine clearance were affected by the sedative detomidine (an alpha2-agonist), a drug used to treat fractious mares. An additional objective was to identify propagation patterns of uterine contractions and determine whether these patterns differed between normal mares and mares with delayed uterine clearance (DUC). Intrauterine pressure was measured in five reproductively normal mares and four mares with DUC during estrus using an 8-F Milar catheter with two dis...
Cuervo-Arango J.Flunixin meglumine (FM), a prostaglandin synthetase inhibitor, causes ovulatory failure in the mare. However, the effect of the FM treatment relative to the time of hCG administration on the ovulation failure has not been determined nor has its effect on the luteal function of treated mares. Estrous mares with a follicle ≥32 mm (range of 32-38 mm) were treated with 1.7 mg/kg b.w. of FM iv at zero, 12, 24 and 36 h (n=6), at 24 and 36 h (n=6), at 28 and 36 h (n=6), at 24h (n=6) or at 30 h (n=6) after treatment with 1500 IU hCG. One group received no FM (control, n=6). Progesterone concentratio...
Ainsworth CG, Hyland JH.Continuous infusion of gonadotrophin releasing hormone (GnRH) has been shown to induce oestrus and ovulation in experimental mares in seasonal anoestrus. The present study sought to apply this form of treatment to anoestrous mares subjected to normal management procedures on 15 commercial Thoroughbred studfarms in Australia. The GnRH was delivered via subcutaneously implanted osmotic minipumps (OMP) at dose rates of 100 ng/kg/h and 200 ng/kg/h. The ovaries of treated mares were palpated on the day of OMP insertion (Day 0) and blood samples were collected twice weekly from a proportion of mares...
Lauderdale JW.Puberty: For the gilt and filly, the first corpus luteum (CL) appears to have a normal lifespan. For both species, first CL usually is associated with estrus but can form in the absence of estrus. For the ewe and cow, a transient (1 to 4 d, ewe; 3 to 10 d, cow) rise and fall of ovarian derived progesterone (P4) is detected in peripheral blood (80% of ewes; 50% of heifers) prior to first "normal" CL. The first CL of apparent normal lifespan is not accompanied by estrus in the ewe. The first CL in the cow may or may not be accompanied by estrus; first estrus in the cow can be anovulatory. Data a...
Ginther OJ, Bergfelt DR.The temporal associations between increases in FSH and growth of small follicles (2-20 mm) were studied during one oestrous cycle (ovulation to ovulation) in 15 horse mares. Follicular diameters were obtained ultrasonically. For each day, follicles were combined for both ovaries, grouped from largest to smallest (excluding dominant follicles), and divided into three to five tiers of six follicles for each mare (for example: tier 1, six largest follicles; tier 2, next six largest follicles). A significant increase in mean diameters followed by a significant decrease was used to define a follicu...
Evans JW, Hughes JP, Neely DP, Stabenfeldt GH, Winger CM.Jugular blood samples were obtained from 8 mares at 5- and/or 20-min intervals for 2 to 5 days during various phases of the oestrous cycle for plasma LH determination. An episodic release pattern was observed in 1 of 3 mares sampled during the ovulatory period. One mare had one secretory burst and the other mare had several periods of fluctuating plasma LH concentration. During dioestrus, episodic secretions were observed in 2 mares sampled 11 to 13 days before and, in 1 mare, 9 days after ovulation. During the 2 to 5-day period before ovulation, episodic secretion was not observed (3 mares) b...
