Estrus in horses refers to the recurring reproductive cycle in mares during which they exhibit signs of sexual receptivity and fertility. This phase is part of the larger estrous cycle, which includes several stages: estrus, metestrus, diestrus, and proestrus. During estrus, mares experience physiological changes, such as follicular development and ovulation, which are regulated by hormonal fluctuations, primarily involving estrogen and luteinizing hormone. Behavioral changes, including increased vocalization, restlessness, and receptivity to stallions, are also observed. This page compiles peer-reviewed research studies and scholarly articles that explore the physiology, endocrinology, and behavioral aspects of estrus in horses, as well as its implications for breeding management and equine reproductive health.
Loy RG, Buell JR, Stevenson W, Hamm D.Sixty-two non-cycling mares were classified according to the size of largest follicles at the time of treatment with Prostalene, an analogue of prostaglandin (PG) F-2 alpha. Although oestrus occurred in only 77.4% of mares, 98.4% ovulated at an average of 6.8 days after treatment. Greatest variance of interval to ovulation was observed in mares having follicles greater than or equal to 40 mm at the time of treatment. This was due to regression of large follicles about one-third of the time and later ovulation of a succeeding follicle. This resulted also in greatest uncertainty of prediction of...
Freedman LJ, Garcia MC, Ginther OJ.A 16 h daily photoperiod hastened the onset of the ovulatory season (first ovulation); gonadotrophin and follicular changes prior to the onset were similar in intact light-treated and control mares. A preovulatory decline in FSH concentrations before the onset of the ovulatory season preceded the decrease in number of follicles (15--25 mm) and the rise in LH concentrations which was temporally associated with the growth of an ovulatory follicle. Seasonal changes of FSH and LH concentrations were found in ovariectomized mares and were influenced by photoperiod. During the anovulatory season, th...
Hurtgen JP, Whitmore HL.In 10 mares, lysis of the corpus luteum was induced by endometrial biopsy and culture on day 4 after estrus, as evidenced by a sharp decline in serum progesterone concentration and a shortened interestrous interval. Estrus following the manipulations was prolonged. Endometrial biopsy and culture on days 1 and 3 after estrus or manually dilating the cervix on day 4 after estrus also decreased the serum progesterone concentration (within 24--48 hr after manipulation), shortened diestrus, and prolonged the subsequent estrus. In a 2nd experiment, endometrial biopsy on day 4 after estrus shortened ...
Hunt B, Lein DH, Foote RH.Plasma and milk progesterone concentrations in 13 mares were determined 3 times a week for 5 months, beginning at parturition. The estrous cycle was divided into 2 phases. Estrus was considered to occur when the plasma progesterone concentration was less than 1 ng/ml, with diestrus occurring when plasma progesterone content was greater than or equal to 1 ng/ml. Based on this classification, the period of estrus averaged 8.9 days, diestrus averaged 13.9 days, and the estrous cycle averaged 22.8 days. During estrus, the progesterone concentration in plasma averaged 0.4 ng/ml and in milk averaged...
Oxender WD, Noden PA, Hafs HD.On December 11, 1974, 15 seasonally anestrous mares were assigned at random to 1 of 3 experimental groups: outdoor-control, indoor-control, or indoor light-treated (a 16-hour photo-period). This experiment was terminated on April 21, 1975. The five mares in the indoor light-treated group ovulated 59.0+/-6.9 days later, which was 74 days earlier (P less than 0.01) than 2 of the 5 outdoor-controls (the other 3 ovulated after April 21 during a subsequent experiment) and 50 days earlier (P less than 0.05) than the indoor-controls. Durations of the 1st estrus for the 3 groups of mares were 13.3+/-3...
Shepherd GE, Findlay JK, Cooper MJ, Allen WR.A clinical trial involving 359 mares was conducted to ascertain the clinical value of a synthetic prostaglandin analogue (fluprostenol, ICI-81,008) structurally related to PGF2oc for treating mares in prolonged dioestrus. Some 263 mares (73.3%) displayed oestrus within 5 days of a first intramuscular injection of 250 mug fluprostenol and, of those mares later examined for pregnancy, 108 (40%) were found to have conceived during the first induced oestrus. A further 21 mares (8%) cycled normally and conceived to services during the second oestrus. Most (80.3%) of the plasma samples obtained from...
El-Ghannam F, El-Sawaf S.A study of the estrus cycle of Arabian mares in Egypt gave the following results:
1. The estrus cycle was as short as 12 and as long as 240 days.
2. Cycles considered as normal ranged between 16 and 34 days and were more concentrated in the period 20–26 days.
3. Periods of anestrum caused elongation of the cycles to varying lengths, from double the normal cycle period to four times or more.
4. Seasonal variations in the length of the estrus cycle are discussed.
Kooistra LH, Ginther OJ.At day 24 of gestation, pregnant mares were allotted to 1 of 5 treatment groups (3 to 5 mares/group): group A--nontreated controls; group B--intraembryonic injection of 4 mg of colchicine on day 24; group C--removal of embryo on day 24; group D--subcutaneous injection of 1.25 mg of prostaglandin F2alpha (PGF2alpha) on day 32; and group E--removal of embryo on day 24 and subcutaneous injection of PGF2alpha on day 32. In all mares treated with colchicine (group B), the fetal bulge was absent within 2 days. The interval from injection of colchicine to onset of estrus was very short (mean, 4 days)...
Loy RG, Hughes JP, Richards WP, Swan SM.The injection of 100 mg of progesterone/day from Days 5 to 14 after foaling blocked or delayed oestrus and ovulation in 6/9 mares; the remainder ovulated during treatment without showing oestrus. Urinary oestrogen concentrations in these mares were highest between Days 9 and 15 after foaling but the peak levels were only about half those seen in untreated mares during the post-partum oestrus and ovulation. The injection of 200 mg progesterone/day blocked oestrus and ovulation in two mares but did not depress oestrogen excretion maxima any further. Follicles prevented from developing beyond a c...
Lovell JD, Stabenfeldt GH, Hughes JP, Evans JW.The levels of progesterone and total progestins increased during late pregnancy and then fell dramatically during the last few days before parturition, although birth occurred in the presence of significant amounts of plasma progesterone. Oestrogen levels decreased slowly but insignificantly until birth occurred, and then remained at a low level until the post-partum oestrus 10 to 12 days later. Total 11beta-hydroxycorticosteroids were unchanged from Day 45 before to Day 15 after birth. The endocrine pattern of one ovariectomized pregnant mare during the last month of gestation was similar to ...
Noden PA, Oxender WD, Hafs HD.The duration of the oestrous cycle and day of ovulation were recorded in six mares which were used for concurrent assay of plasma levels of sex steroids and pituitary LH concentration. Peak of progesterone were reached during dioestrus and those of oestradiol and androstenedione occurred 2 days before ovulation and were in decline on the day of ovulation. Plasma oestrone remained constant (between 9 and 12 pg/ml) throughout the cycle. Plasma LH rose to a maximum near to the time of ovulation, and thereafter decreased gradually until mid-dioestrus. The pattern of secretion is compared with that...
Douglas RH, Ginther OJ.Several experiments indicated that prostaglandin F2alpha (PGF2alpha) has luteolytic and abortifacient properties in mares. A single subcutaneous injection of 1-25 mg PGF2alpha on Day 6 of dioestrus was as effective as 10 mg PGF2alpha in inducing luteolysis. Oestrus and ovulation appeared to be synchronized when a single injection of 1-25 mg PGF2alpha was given on Days 7, 10 or 13 after ovulation but not on Days 1 or 4 after ovulation or on Day 2 of oestrus. Intramuscular administration was as effective as subcutaneous administration and 1-25 mg PGF2alpha was the minimal effective systemic dose...
Hughes JP, Stabenfeldt GH, Evans JW.In eleven non-pregnant mares examined for 2 years, oestrous cycle length was 20-6 days (range 13 to 34) excluding any anoestrous periods. The duration of oestrus was 5-7 days (range 1 to 24); from February to May it was 7-6 days (range 2 to 24) and from May to November 4-8 days (range 1 to 10). The majority of ovulations occurred between 16.00 and 08.00 hours and 78% of the mares ovulated within 48 hr of the end of oestrus. Mean follicular diameter was 45 mm on the day of ovulation and there was a 25-5% incidence of multiple ovulations. It was uncommon for oestrus to occur without ovulation, w...
Voss JL, Pickett BW.The effect of rectal palpation of fertility of non-lactating, normal cyclic mares was studied over 3 years. During the first year (1971), the conception rates in mares after daily paplaption during oestrus only, and during oestrus and the first 50 days of pregnancy, were not significantly lower (P greater than 0-05) than the conception rates recorded in mares not palpated. No abortions could be attributed to palpation. Oestrus lasted longer (P less than 0-05) in non-palpated than palpated mares. During the second year (1972), first-cycle pregnancy rates in two groups of mares palpated daily du...
Oxender WD, Noden PA, Hafs HD.The luteolytic effect of PGF2alpha, administered by intrauterine infusion or subcutaneous injection during early dioestrus, was observed in mares of mixed breeds. An infusion of 10 mg on Days 7 to 9 after ovulation caused a sharp fall in plasma progesterone levels and induced oestrus and ovulation. Oestrus was significantly longer than in the natural cycle but the time of ovulation in relation to the end of oestrus was normal. The time of return to oestrus following luteolysis was not dependent on the amount of PGF2alpha within the range of doses given. Luteolysis could be induced as early as ...
Stalheim OH, Gallagher JE, Deyoe BL.The luminal surface topography of bovine, equine, porcine, and caprine uterine tubes was studied by scanning electron microscopy. The main types of epithelial cells were secretory and ciliated. Both types were more active during estrus. Cilia were observed in both the infundibular and the ampular parts of the uterine tube, but ciliated cells were more numerous than secretory cells on the surface of the fimbriae. Sperm were observed in the ampulla of the uterine tube of the cow 2 hours after artificial insemination.
Brand A, de Bois CH, Vandenhende R.Parenteral administration of 2.5-5 mg. of prostaglandin F2alpha to horses, 15 mg. to heifers or 25-30 mg to lactating cows and 15 mg. to sheep will induce regression of the corpus luteum (luteolysis) and a fertile oestrus within 48-72 hours. Because of their luteolytic effect prostaglandins may be used in various indications in the field of reproduction. An exception is the pig in which administration of prostaglandins does not induce luteolysis before D12 and therefore fails to induce oestrus. In horses, cattle and sheep, administration of prostaglandins during the first four days of the cycl...
Hooper RN, Taylor TS, Behrens EA, Varner DD.Ovariohysterectomy was performed in 20 mares at three stages of estrus. An ecraseur was used to severe the ovarian branch of the ovarian artery and vein and the ovarian suspensory ligament en masse. All other vessels supplying the ovaries and uterus were doubly ligated and transected. All mares survived. Complications were intraoperative hemorrhage in three mares, postoperative vaginal bleeding in two mares, and a hematoma in the remnant of the broad ligament in one mare. No adhesions between the uterine stump or remnants of the broad ligament and abdominal structures were detected by palpatio...
Henneke DR, Kreider JL.Quarter Horse mares (n = 30) and their foals were used in a 2-year study. Objectives of the study were (i) to determine the effects of a treatment regimen, which permitted nursing for four 1-hour periods each day, on the postpartum reproductive performance of the dams, and (ii) to assess the effects of this procedure on the growth and development of foals. Mares in the restricted suckling treatment group showed estrus and ovulated sooner (P less than 0.01) after parturition than did control mares during the first year of the study, but not during the second year. Plasma progesterone concentrat...
Caron JP.Laparoscopic removal of the gonads from male and female horses is regularly performed for a variety of reasons. In female horses, common indications for ovariectomy include behavioral problems and signs of abdominal pain that are linked to estrus. Another indication is an abnormal, enlarged ovary, typically due to ovarian neoplasia, the most common being granulosa thecal cell tumor. Ovariectomy is also a treatment option for ovarian hematomas and other abnormalities. In addition, ovariectomy is used to sterilize mares intended for artificial insemination or embryo transfer programs.
Wittek T, Sobiraj A.In the present study the concentrations of L-carnitine (total carnitine, free carnitine, and acyl carnitine) and several parameters of the lipid metabolism were measured during the estrus in 10 broodmares. The carnitine concentrations varied in a wide range between the mares. The differences of the mean carnitine concentrations during the estrus did not reach the level of significance (P < 0.05). There was no relationship between the concentrations of total and free carnitine to the follicle size; however, the concentration of acyl carnitine was significantly correlated (r = -0.42). Because...
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...
Gunther JD, Foley CW, Gaverick HA, Plotka ED.Progesterone concentrations were measured in milk and blood plasma for 15 mares throughout a normal estrous cycle and early pregnancy to determine the feasibility of utilizing progesterone in milk as an indicator of pregnancy. Samples were obtained daily from foaling until diagnosis of pregnancy by rectal examination at 30 to 35 days of gestation. Progesterone in milk and blood plasma was quantified by radioimmunoassay. Mean progesterone concentrations (+/- SE) in plasma from foaling to foal heat and during estrus, luteal phase and pregnancy were .51 +/- .09 ng/ml, .53 +/- .08 ng/ml, 3.88 +/- ...
Sertich PL.Pregnancy was established by transcervical transfer of embryos from performance mares into recipient mares. Estrus was synchronized between donor (n = 17) and recipient (n = 43) mares. After a greater than or equal to 25-mm follicle was detected, donor mares were bred artificially daily until ovulation. Day of ovulation was recorded. Uterine flushes (n = 111) were performed on donor mares 7 days after ovulation, and recovered embryos were transferred transcervically to recipient mares within 2 hours. Embryos were recovered from 40.5% of uterine flushes. Of transferred single embryos, 65.7% res...
Rizzo A, Mutinati M, Spedicato M, Minoia G, Trisolini C, Punzi S, Roscino MT, Jirillo F, Sciorsci R.The beta-subunits of thyroid stimulating hormone (TSH) and human chorionic gonadotropin (hCG) share a high homology, just like the ectodomains of their receptors, do. As a consequence, hCG was shown to exert a thyrotropic action in humans and hamsters. This study aimed to investigate whether hCG, used to induce ovulation, displays a thyrotropic effect in the equine species too. Forty mares at estrus were divided in two groups; 20 were intravenously treated with sterile saline solution (NaCl 0.9%) (group A); 20 were intravenously treated with 4000 I.U. of hCG (group B). All the mares were artif...
Shand N, Alexander SL, Irvine CH.For aqueous extracts of pituitary glands of oestrous mares, luteinizing hormone (LH) profiles were found to be similar to each other and to earlier work after chromatofocussing (CF) and isoelectricfocussing (IEF). After CF, both LH and follicle-stimulating hormone (FSH) in pituitary extracts focussed in multiple peaks in the acidic range, with 86% of LH and 80% of FSH found between pH 4 and 6. By contrast, in pituitary venous plasma, only 18% of the LH focussed in this range, whereas a significantly greater proportion (P less than 0.01) eluted above pH 7 than occurred in pituitary extracts (37...
Vernunft A, Löhrke B, Tuchscherer A, Weitzel JM, Viergutz T.Anti-Muellerian hormone (AMH) is synthesized only by granulosa cells in female mammals as an inhibiting factor for early follicular recruitment. Especially in preantral and small antral follicles, expression of AMH is very intensive. However, we hypothesize that AMH affects also the development of large follicles by an estrogenesis modification. This current investigation provides for the first time information about concentrations of AMH in equine follicular fluid and demonstrates their relationship to functional characteristics of follicle development. Therefore, fluids of follicles in diffe...
Silva ESM, Newcombe JR, Cuervo-Arango J.Oestrogens treatment is often used to induce oestrus behaviour in anoestrous mares to aid in the collection of stallion semen and as recipient mares to receive embryos when combined with progesterone. However, there are no studies to describe the effect of dose and individual mare on the intensity and duration of the response, in both anoestrous and cyclic mares. In Experiment 1, 13 anoestrous mares were treated with one of five doses of oestradiol benzoate (OB) (1, 1.5, 2, 3 and 4 mg) per mare in five consecutive treatment periods (n = 65), to determine the response in terms of endometrial oe...
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...
Thompson DL, Reville SI, Derrick DJ, Walker MP.Eight seasonally anestrous mares were administered intravaginal polyurethane sponges on December 15 and then weekly thereafter until February 1. Control mares received no sponges or genital contact. Sponge insertion caused an immediate surge in follicle-stimulating hormone (FSH) concentrations in jugular plasma in 50% of treated mares whereas no control mares had surges in FSH (P less than .05). The effect of treatment on luteinizing hormone (LH) concentrations was much less dramatic and only three treated mares appeared to have positive responses. Sponge-treated mares exhibited positive respo...
Cebulj-Kadunc N, Cestnik V, Kosec M.The onset of puberty and duration of seasonal cyclicity in Lipizzan fillies and young mares have been determined mostly by empirical data, but very little is known about the hormonal changes at puberty and during the seasonal cyclicity in this breed. Objective: To determine the onset of puberty and the course of the cyclicity in young Lipizzan mares from age 1-4 years. Methods: Blood samples were collected twice a month for 2 years from 46 Lipizzan fillies age 1-4 years. Progesterone concentrations, indicating ovarian activity, were measured using an EIA kit. Values above 6.4 nmol/l were taken...
Plata-Madrid H, Loch WE, Youngquist RS, Thompson DL, Bennett-Wimbush KG, Wilkerson C, Bouchard G, Smith MF, Braun WF, Aveiro JJ.Twenty-two pony mares were used in a project designed to determine the effectiveness of different treatments in controlling FSH, follicular development and synchronization of estrus and ovulation. Mares in Group 1 (n=8) received daily oral altrenogest (0.044 mg/kg); those in Group 2 (n=7) received daily altrenogest (0.044 g/kg) and, during the last 4 days of treatment they received steroid-free follicular fluid, (15 cc) intravenously (I.V.) two times a day; Mares in Group 3 (n=7) received daily intramuscular (I.M.) injections of progesterone (80 mg) and estradiol valerate (7 mg). All treatment...
Bristol F.Oestrus was synchronized in 220, 300 and 272 mares in 1983, 1984 and 1985 respectively. Mares were given two injections of 250 micrograms fenprostalene 15 days apart except in 1983 and 1984 when 56 and 53 of the synchronized mares were given 1-10 daily injections of 150 mg progesterone and 10 mg oestradiol-17 beta to delay and synchronize post-partum oestrus. At 2 days after the second PG injection or 7 days after the last progesterone + oestradiol treatment, mares were divided into groups of 15-21, and each group was placed in a separate pasture with a stallion for 7 weeks. Pregnancy rates we...
Voss JL, Pickett BW.The effect of rectal palpation of fertility of non-lactating, normal cyclic mares was studied over 3 years. During the first year (1971), the conception rates in mares after daily paplaption during oestrus only, and during oestrus and the first 50 days of pregnancy, were not significantly lower (P greater than 0-05) than the conception rates recorded in mares not palpated. No abortions could be attributed to palpation. Oestrus lasted longer (P less than 0-05) in non-palpated than palpated mares. During the second year (1972), first-cycle pregnancy rates in two groups of mares palpated daily du...
de Vries PJ, Zandee AR.As part of the veterinary surveillance of horse breeding management, the veterinarian is increasingly often requested to predict ovulation and to give a breeding or insemination advice accordingly. The result of a teasing procedure is indispensable for this advice. A suggestion is made for the quantification of oestrus signs. Oestrus symptoms are classified into four categories. In addition, various factors are mentioned, which affect the result of a teasing procedure.
Plotka ED, Eagle TC, Vevea DN, Koller AL, Siniff DB, Tester JR, Seal US.Five groups of 30 captive feral mares each were implanted with silastic rods containing estradiol (E) and/or progesterone (P): E only with 8 g, P only with 24 g, P+HE with 8 g P + 8 g E, HP+E with 12 g P + 4 g E, HP+LE with 12 g P + 2 g E. Arbitrary group designations were differentiated by relative high (H) and low (L) amounts of steroid. Thirty mares received silastic rods containing no hormone (CI). Five mares from each group were bled every 2 wk for 4 mo and monthly for another 5 mo. All mares were tested for estrus by allowing them to stand in an alley between two pens of stallions and vi...
Ball BA, Dobrinski I, Fagnan MS, Thomas PG.To examine glycoconjugates in the isthmic and ampullar regions of the uterine tube (oviduct) of horses during estrus, diestrus, and pregnancy. Methods: Oviductal samples from 17 mares. Methods: Oviducts were collected during estrus (n = 3), diestrus (n = 3), or pregnancy (n = 3), embedded, and snap frozen in liquid nitrogen. Frozen sections (5 to 6 microns in thickness) were stained with 100 micrograms/ml of fluorescein-isothiocyanate-conjugated lectin (30 min at 38.5 C) and were evaluated by use of epifluorescence microscopy and video image analysis. Specificity of lectins was established by ...
Epper P, Glüge S, Vidondo B, Wróbel A, Ott T, Sieme H, Kaeser R, Burger D.To successfully inseminate mares, precise detection of ovulation time is crucial, especially when using frozen-thawed semen. Monitoring body temperature, as has been described in women, could be a noninvasive way to detect ovulation. The objective of this study was to investigate the relationship between the time of ovulation and the variation of body temperature in mares based on automatic continuous measurements during estrus. The experimental group included 21 mares for 70 analyzed estrous cycles. When the mares showed estrous behavior, they were administered intramuscular deslorelin acet...
Pascoe DR, Stabenfeldt GH, Hughes JP, Kindahl H.Thirty mares with normal estrous cycles were allotted equally to 5 groups and infused with 250 ml of saline (NaCl) solution in utero on the seventh day after ovulation to test the effects of temperature, osmolarity, or pH of the saline solution on prostaglandin F2 alpha (PGF2 alpha) release and luteolysis. Intrauterine infusion of phosphate-buffered saline solution failed to alter the duration of the luteal phase, compared with the control group. Similarly, increasing the temperature of phosphate-buffered saline solution to 42 C or increasing (600 mosm) or decreasing osmolarity (less than 10 m...
Sönmez C, Eroglu A.The present study was carried out to investigate the pregnancy rate after covering in the foal heat (Group I), in the subsequent spontaneous heat (Group II), and in the induced heat (Group III) after administration of 7.5 mg of the prostaglandin F2 alpha analogue Luprostiol (Reprodin, Bayer) between the 20th and 22nd day post partum. Breeding during foal heat resulted in a pregnancy rate of 43.9% compared to 48.6% in the subsequent spontaneous heat post partum. Of 18 mares in group III, 14 mares had a foal heat, whereas 4 others had not shown a foal heat. 1-8 days after treatment, 14 mares (77...
Brand A, de Bois CH, Vandenhende R.Parenteral administration of 2.5-5 mg. of prostaglandin F2alpha to horses, 15 mg. to heifers or 25-30 mg to lactating cows and 15 mg. to sheep will induce regression of the corpus luteum (luteolysis) and a fertile oestrus within 48-72 hours. Because of their luteolytic effect prostaglandins may be used in various indications in the field of reproduction. An exception is the pig in which administration of prostaglandins does not induce luteolysis before D12 and therefore fails to induce oestrus. In horses, cattle and sheep, administration of prostaglandins during the first four days of the cycl...
Booth LC, Oxender WD, Douglas RH, Woodley SL.A gonadotropin-releasing hormone (GnRH) was injected in mares given prostaglandin F2 alpha (PGF2 alpha) to induce luteolysis in an attempt to sunchronize ovulation. Pretreatment with estradiol-17 beta (E2-17 beta) was used to determine whether or not estradiol would enhance the release of luteinizing hormone (LH) after treatment with GnRH. Twelve mares were used in a balanced Latin square crossover design. Mares were injected with PGF2 alpha, treatment A; PGF2 alpha mgnRH, treatment B; or PGF2 alpha me2-17 beta mgnRH, treatment C. The interval +/- SEM from PGF2 alpha injection to estrus was 3....
Neely DP, Stabenfeldt GH, Kindahl H, Hughes JP, Kendrick JW.The intrauterine infusion of 500 ml of warm sterile saline solution into mares on days 12, 13, or 14 after ovulation failed to alter the ovulatory interval, although intervals were shorter for days 12 and 13 (20.6 days) when compared with those in control mares (21.6 days). The IU fusion shortened luteal-life-span on days 12 (12.0 vs 13.8 days) and 13 (13.0 vs 14.4 days) (P is less than 0.05), but not day 14 (14.0 vs 13.5 days), when comparing the effects of IU infusion with an average of before and after base-line data. There was no effect on the interval from corpus luteum regression to ovul...
Shand N, Irvine CH, Turner JE, Alexander SL.Jugular blood samples were collected at 4 h intervals from six mares during an oestrous cycle to study the hormonal events that occur around the time of luteolysis. Blood samples from day 10 (day 0 = ovulation) until day 3 of oestrus were assayed for prostaglandin metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM), oxytocin, prolactin, progesterone and oestrogen conjugates. PGF2alpha (0.5 or 1.5 mg) was administered to six mid-dioestrous mares and the oxytocin and prolactin responses were measured. One to five large (peak > or =2 x nadir) pulses of PGFM, oxytocin and prolactin were detected ...
Khan Y, El-Shalofy A, Kaps M, Gautier C, Aurich C.We aimed to determine associations between experimentally impaired uterine clearance or treatment with ecbolic drugs on luteal development in estrous mares after insemination. In a crossover design, eight mares were treated with saline (CON), clenbuterol (CLEN), oxytocin (OXY) and carbetocin (CARB) from the day of first insemination until 2 days after ovulation. Between treatments, the mares rested for one cycle. Estrous mares were examined for the presence of free intrauterine fluid by transrectal ultrasound. Endometrial swabs for cytology and bacteriology were collected on days 1 and 14. Blo...
Bukhari SSUH, Urooj S.In winter anestrous, prolonged melatonin secretion inhibits gonadotropin-releasing hormone (GnRH). However, synthetic GnRH analogues such as buserelin can stimulate follicular development. We aimed to investigate clinical relationship between retinol, cholecalciferol, and buserelin for inducing estrous in anestrous mares (Equus caballus). We used a total of twenty-one anestrous mares, randomly divided into three groups of seven animals. Group A received retinol, cholecalciferol, and buserelin; group B received buserelin; and group C was control. Groups A, B, and C had 71.42% (n = 5; 95% CI...
Vallejo-Soto P, Dorado J, Herrera-García R, Álvarez-Delgado C, Gómez-Laguna J, Santiago Á, Manrique M, González Ariza A, León Jurado JM....Assisted reproductive techniques are often extrapolated from horses to donkeys, despite poorer fertility outcomes in jennies. This issue has been attributed to unknown uterine species-specific differences. This study compared, through histomorphometry, the endometrium of jennies and mares. Endometrial biopsies (N = 12) were taken from reproductively sound jennies (n = 6) and mares (n = 6) in estrus. Histomorphometric analysis evaluated luminal (LE, µm) and glandular epithelium height (GE, µm), glandular lumen diameter (LD, µm), glandular area (GA, µm), the number of glands (#G), and glandu...
