Effect of purified equine follicle-stimulating hormone on follicular development and ovulation in transitional mares

Horse owners want to have their mares bred as early as possible in the breeding season after February 1. Numerous medical treatments, such as progesterone, dopamine antagonists, and gonadotropin-releasing hormone have been administered to anestrous or transitional mares in an attempt to induce follicular development. Some of these treatments are ineffective or impractical, so there is a need in the horse industry to develop alternative techniques to stimulate follicular development and ovulation early in the breeding season. Twenty transitional mares were assigned to one of two treatment groups. Mares in group 1 (n = 10) served as untreated controls, and mares in group 2 (n = 10) were administered 12.5 mg of purified equine follicle-stimulating hormone (eFSH) (Bioniche Animal Health USA, Inc., Athens, Ga) intramuscularly twice daily for a maximum of 15 consecutive days. Mares were considered to be in transition when the diameter of the largest follicle was ≥25 mm. Once one or more follicles >35 mm were detected, eFSH treatment was discontinued and human chorionic gonadotropin was administered intravenously. The percentage of mares ovulating during the 15-day observation period was compared by means of chi-square analysis. The interval to ovulation and the number of ovulations per mare were compared between the two groups by Student t test. In 8 of 10 mares treated with eFSH follicles developed and ovulation occurred during the 15-day observation period, compared with 0 of 10 control mares. Interval from onset of treatment to ovulation was 7.6 ± 2.4 days for these eight mares. The eight mares were treated for an average of 5.2 ± 1.3 days with eFSH. Thus, the eFSH treatment was effective in advancing the first ovulation of the year in transitional mares.     

Effect of eFSH on Ovarian Cyclicity and Embryo Production of Mares in Spring Transitional Phase

The use of equine FSH (eFSH) for inducing follicular development and ovulation in transitional mares was evaluated. Twenty-seven mares, from 3 to 15 years of age, were examined during the months of August and September 2004, in Brazil. Ultrasound evaluations were performed during 2 weeks before the start of the experiment to confirm transitional characteristics (no follicles larger than 25 mm and no corpus luteum [CL] present). After this period, as the mares obtained a follicle of at least 25 mm, they were assigned to one of two groups: (1) control group, untreated; (2) treated with 12.5 mg eFSH, 2 times per day, until at least half of all follicles larger than 30 mm had reached 35 mm. Follicular activity of all mares was monitored. When most of the follicles from treated mares and a single follicle from control mares acquired a preovulatory size (≥35 mm), 2,500 IU human chorionic gonadotropin (hCG) was administered IV to induce ovulation. After hCG administration, the mares were inseminated with fresh semen every other day until ovulation. Ultrasound examinations continued until detection of the last ovulation, and embryo recovery was performed 7 to 8 days after ovulation. The mares of the treated group reached the first preovulatory follicle (4.1 ± 1.0 vs 14.9 ± 10.8 days) and ovulated before untreated mares (6.6 ± 1.2 vs 18.0 ± 11.1 days; P < .05). All mares were treated with prostaglandin F_2α (PGF_2α), on the day of embryo flushing. Three superovulated mares did not cycle immediately after PGF_2α treatment, and consequently had a longer interovulatory interval (22.4 vs 10.9 days, P < 0.05). The mean period of treatment was 4.79 ± 1.07 days and 85.71% of mares had multiple ovulations. The number of ovulations (5.6 vs 1.0) and embryos (2.0 vs 0.7) per mare were higher (P < 0.05) for treated mares than control mares. In conclusion, treatment with eFSH was effective in hastening the onset of the breeding season, inducing multiple ovulations, and increasing embryo production in transitional mares. This is the first report showing the use of FSH treatment to recover embryos from the first cycle of the year.     

Selected Ovarian Ultrasonographic Characteristics During Vernal Transition are Useful to Estimate Time of First Ovulation of the Year

It is important to get mares pregnant as early as possible after vernal transition and thus, identification signs of impending 1st ovulation of the year are warranted. To identify clinical indicators of an approaching first ovulation of the year, mares were teased with a stallion for oestrous detection starting January 3 and subjected to ultrasonographic examination. Day of first appearance of uterus oedema, follicular wall invagination, intrafollicular echogenicity, double contour of the follicle wall, increase in granulosa thickness, follicular wall hyperechogenicity and appearance of pear‐shaped follicles was registered, as well as follicle diameter and number. Seventy per cent of the mares had anovulatory oestrous periods of 4.6 ± 3.6 days, with an interoestroual interval of 12.5 ± 12.2 days. Number of anovulatory oestruses per mare was 2.4 ± 2.3. Uterine oedema occurred in 77% of the mares, 32.4 ± 25.6 days before ovulation. Invagination of the follicular wall appeared in 44.4% of the animals, 24.5 ± 18.4 days before ovulation. Intrafollicular echogenicity was seen in all mares and double contour of the follicle was seen in 77% of the animals. Both last two characteristics appeared 1–72 days before ovulation. Increased thickness of the granulosa occurred in 66% of the mares, 1–19 days before ovulation. Pear‐shaped follicles and follicular wall hyperechogenicity were detected 3 or less days before the first ovulation, in 44.4% and 55.5% of mares, respectively. Mean number of follicles >15 mm decreased at least 16 days before ovulation. We concluded that no isolated characteristic was a reliable indicator. However, increase in granulosa thickness, formation of a pear‐shaped follicle and follicular wall hyperechogenicity, associated with the reduction of the number of follicles >15 mm in diameter to <3, resulted in the first ovulation of the year in 44–67% of the transitional mares, 1–19 days after the characteristics appeared.     

Clinical experience with native GnRH therapy to hasten follicular development and first ovulation of the breeding season

Breeding records of 48 Thoroughbred and Standardbred mares treated with native GnRH (500μg im, bid) during February—April, 1999 or 2000, on 7 farms in central Kentucky were retrospectively examined. Treated mares were classified as being in anestrus or early transition (n=42; if no signs of estrus occurred within 31/2 weeks and the largest follicle remained ≤25 mm in diameter or the first larger follicle(s) of the season regressed without ovulating), or were classified as being in late transition (n=6; if follicular growth achieved 30-40 mm diameter but ovulation had not yet occurred during the breeding season). Thirty-eight mares (38/48; 79%) ovulated in 13.7 ± 7.4 days. Interval to ovulation was negatively associated with size of follicles at onset of native GnRH therapy (P < 0.01). Per cycle pregnancy rate was 53% (19/36 mares bred). Ovulation inducing drugs were administered to 32 of the native GnRH treated mares (2500 units hCG intravenously, n = 20; deslorelin implant [Ovuplant™] subcutaneously, n=12), while 6 mares were not administered any additional drugs to induce ovulation. Per cycle pregnancy rate did not differ among mares treated only with native GnRH (2/5 mares bred; 40% PR), mares treated with native GnRH plus hCG (12/19 mares bred; 63% PR), or mares treated with native GnRH plus Ovuplant™ (5/12 mares bred; 42% PR) (P > 0.10). Additional treatment with either hCG or Ovuplant™ did not alter mean follicle size at ovulation or interovulatory interval (P > 0.10). The proportion of interovulatory intervals > 25 days was not different between mares receiving no additional treatment to induce ovulation (0/4; 0%) compared to mares receiving hCG to induce ovulation (3/8; 38%) (P > 0.10), but the proportion of interovulatory intervals > 25 days was greater for mares receiving Ovuplant™ to induce ovulation (5/7; 71%) compared to mares receiving no additional treatment to induce ovulation (P < 0.05). The proportion of mares with extended interovulatory intervals (i.e., > 25 days) did not differ between mares with follicles < 15 mm diameter (4/8, 50%) and those with follicles > 15 mm diameter (3/11, 27%) at onset of native GnRH treatment (P > 0.10). While concurrent untreated controls were not used in this study, the 79% response rate to twice daily administration of native GnRH is in agreement with other reports using pulsatile or constant infusion as methods of administration, confirming therapy can hasten follicular development and first ovulation of the breeding season. As with previous reports, follicle size at onset of treatment is an important determinant of interval from onset of native GnRH therapy to ovulation. Use of hCG or Ovuplant™ did not enhance ovulatory response in native GnRH treated mares. Use of Ovuplant™ during native GnRH therapy may increase the incidence of post-treatment anestrus in mares not becoming pregnant.     

Effect of Dose of Cloprostenol on the Interval to Ovulation in the Diestrous Mare: A Retrospective Study

Although the ovulatory effects of prostaglandins are well documented in several domestic species including horses, there has been little attention paid to the use of this ovulatory effect for clinical purposes. Mares often grow large follicles during the luteal phase that may or may not ovulate before progesterone levels decline. Clinical observations of administering prostaglandins in diestrous mares with large follicles suggest that there may be a negative correlation between follicular diameter and interval from treatment to ovulation. The objectives of this study were twofold: to investigate the cloprostenol dose rate effect on interval to ovulation and to confirm the negative correlation between follicular diameter and interval to ovulation. The hypothesis tested was that high doses of cloprostenol given in diestrus to mares with larger follicles would induce ovulation more rapidly than in mares given lower doses or with smaller follicles. To test the hypothesis, a total of 1,234 estrous cycles were induced with different doses of cloprostenol (ranging from 8.75 to 625 μg). All mares had at least one follicle of 28 mm or larger. Dominant follicles were followed by transrectal ultrasound examinations every other day until ovulation was detected. There was a significant effect of dose (P < .000) and follicular diameter (P < .000) on the interval from treatment to ovulation. The shortest mean interval (2.4 days) was observed after administration of 625 μg in mares with follicles 36 mm or larger, whereas the longest (4.9 days) occurred after 8.75 μg in follicles of 28 to 31 mm.     

Efficacy of short-term administration of altrenogest to postpone ovulation in mares

Estrogen from a growing follicle stimulates the preovulatory surge of luteinizing hormone (LH) while progesterone (P) is known to suppress LH. The possibility exists that administration of P, in the presence of an ovulatory follicle, would sufficiently suppress LH and, therefore, delay ovulation. The objective of this research was to elucidate the potential for oral administration of altrenogest (17-Allyl-17β-hydroxyestra-4,9,11-trien-3-one) to postpone ovulation of a preovulatory follicle (35 mm) for approximately two days. Fourteen light-horse mares, ranging in age from two to 19 years, were randomly assigned to one of three treatments (A-.044 mg/kg BW altrenogest for two days; B-.088 mg/kg BW altrenogest for two days; and C- no altrenogest). Mares began treatment when a 35-mm or greater follicle was observed via real-time transrectal ultrasonography. Both number of days until ovulation and follicular maintenance differed between treated and control mares. Number of days until ovulation was increased (P<.05) for mares in treatment A when compared with the control mares. Follicular diameter maintenance, a measurement of follicular diameter throughout treatment, also increased (P<.05) for mares in treatment A when compared with the control mares. Mean LH concentration was not different between mares treated with altrenogest at either treatment dose when compared with the control mares. Pregnancy rates and embryonic vesicle size change were also measured to determine potential effects of altrenogest administration. No differences (P>.05) were found in either characteristic.Short-term administration of altrenogest increased the number of days to ovulation. Further study is warranted to prove conclusively that altrenogest increases follicular maintenance, alters the preovulatory LH surge, and has no detrimental effects upon reproductive efficiency.     

Efficacy of altrenogest administration to postpone ovulation and subsequent fertility in mares

A recent report suggested administration of altrenogest during the follicular phase could postpone ovulation. Based on these results, two questions were generated. We first hypothesized that by initiating a altrenogest treatment earlier in the estrous cycle, a greater and/or more consistent delay in ovulation would result. Second, we hypothesized that exposure to elevated progestin concentrations might alter viability of the ovulatory follicle and oocyte. The focus of the first experiment was to determine if initiation of altrenogest treatment at different stages of the estrous cycle would yield a more predictable time to ovulation, whereas the second experiment was designed to determine whether mares receiving altrenogest during estrus had compromised fertility. In the first experiment thirty mares of mixed light breed, ranging in age from 5-15 years, were randomly assigned to one of three groups. The two treated groups received altrenogest (0.088 mg/kg of body weight) for two days once a follicle of 30 or 35 mm in diameter was detected. Control mares were not treated. Mares treated with altrenogest whether initiated at the detection of a 30 or 35 mm follicle demonstrated similar (P>.05) day to ovulation interval when adjusted to 35 mm (5.4 and 5.6 days, respectively). Both treated groups demonstrated a delayed interval (P<.05) when compared to control (3.9 days). Thirty-six mares of similar breed and age, were randomly assigned to two groups for use in the second experiment. All mares were monitored daily via transrectal ultrasonography from the time a 35 mm or greater follicle was detected until ovulation. Treated mares received daily doses of altrenogest (0.088 mg/kg of body weight) for two days once a follicle of 35 mm or greater was detected. Control mares received no treatment. Fertility data were collected from mares inseminated every other day with 500 million motile spermatozoa from one of two stallions with proven fertility. Pregnancy data were collected via transrectal ultrasonography at days 12, 14 and 16 post-ovulation. Ovulation data were collected from 27 control cycles and 26 treated cycles. Contrary to previous reports and Experiment 1, no difference (P=0.35) was noted between groups with respect to days to ovulation. Control mares averaged 4.14 days and treated mares averaged 4.7 days to ovulation from initial detection of a 35 mm follicle. Fertility data were also similar (P=0.8) between control and treated mares (66.6% and 61.5% per cycle, respectively). Interestingly, a greater number (P=0.017) of treated cycles (5/26) resulted in follicular regression than did control cycles (0/27). While these data suggest that this dosage of altrenogest may not postpone ovulation, it did appear related to increased incidence of follicular regression. Fertility was unaffected, however, in those mares that ovulated. Further studies are needed in which initiation at different stages of estrus and different doses of altrenogest are used.     

Ovulation,Pregnancy Rate and Early Embryonic Development in Vernal Transitional Mares Treated with Equine‐ or Porcine‐FSH

The objective of this study was to compare the efficacy of purified equine‐ and porcine‐FSH treatment regimes in mares in early vernal transition. Mares (n = 22) kept under ambient light were examined ultrasonographically per‐rectum, starting January 30th. They were assigned to one of two treatment groups using a sequential alternating treatment design when a follicle ≥ 25 mm was detected. In the eFSH group, mares were treated twice daily with equine‐FSH, and in the pFSH group mares were treated twice daily with porcine‐FSH; treatments were continued until follicle(s) ≥ 35 mm, and 24 h later hCG was administered. Oestrous mares were inseminated with fresh semen and examined for pregnancy on days 11–20 post‐ovulation. In the eFSH group, 11/11 (100%) mares developed follicle(s) ≥ 35 mm, 8/11 (73%) ovulated and 6/8 (75%) conceived. In the pFSH group, 5/11 (45%) developed follicle(s) ≥ 35 mm, 4/11 (36%) ovulated and 3/4 (75%) conceived. Treatment with eFSH resulted in a greater ovarian stimulation; higher number of pre‐ovulatory‐sized follicles, higher number of ovulations and higher number of embryos (p < 0.05). Following ovulation, serum progesterone concentrations were correlated with the number of CLs and supported early embryonic development; maternal recognition of pregnancy occurred in all pregnant mares. We concluded that eFSH can be used to effectively induce follicular growth and ovulation in vernal transitional mares; however, if bred, diagnosis and management of twins’ pregnancies would be required prior to day 16 because of the increased risk of multiple embryos per pregnancy. Conversely, the current pFSH treatment regime cannot be recommended.     

hCG‐Induced Ovulation in Thoroughbred Mares Does Not Affect Corpus luteum Development and Function During Early Pregnancy

Our aim was to compare Corpus luteum (CL) development and blood plasma concentration of progesterone ([P₄]) in thoroughbred mares after spontaneous (Control: C) or human chorionic gonadotrophin (hCG)‐induced ovulation. Lactating mares (C = 12; hCG = 21) were daily teased and mated during second oestrus post‐partum. Treated mares received 2500 IU hCG i.v. at first day of behavioural oestrus when dominant follicular size was >35, ≤42 mm and mated 12–24 h after. Control mares in oestrus were mated with dominant follicular size ≥45 mm. Dominant follicle before ovulation, CL and gestational sac were measured by ultrasound and [P₄] by radioimmunoassay (RIA). Blood sampling and ultrasound CL exams were done at days 1, 2, 3, 4, 8, 12, 16, 20, 25, 30, 35, 40, 45, 60 and 90 after ovulation and gestational sac from day 12 after ovulation in pregnant (P) mares; non‐pregnant (NP) were followed until oestrus returned. Data analyses considered four subgroups: hCG‐P, hCG‐NP, C‐P and C‐NP. Preovulatory follicular size was smaller in hCG mares than in C: 39.2 ± 2.7 mm vs 51.0 ± 1.8 mm (p < 0.0001). All hCG mares ovulated 24–48 h after treatment and presented similar oestrus duration as controls. C. luteum size in P mares showed the same pattern of development through days 4–35, presenting erratic differences during initial establishment. Thus, on days 1 and 3, CL was smaller in hCG‐P (p < 0.05); while in hCG‐NP, CL size was greater than in C‐NP on day three (p = 0.03). Corpus luteum size remained stable until day 90 in hCG‐P mares, while in C‐P a transient and apparently not functional increase was detected on days 40 and 45 (p < 0.05) and the decrease from day 60 onwards, made this difference to disappear. No differences were observed in [P₄] pattern between P, or between NP subgroups, respectively. So, hCG‐induced ovulation does not affect CL development, neither [P₄] during early pregnancy. One cycle pregnancy rate tended to be lower in hCG mares while season pregnancy rates were similar to controls.     

Induction of ovulation and multiple ovulations in seasonally anovulatory and ovulatory mares with an equine pituitary extract

A crude equine pituitary ethanol extract (EE) was used to induce single and miltiple ovulations in seasonally anovulatory pony mares 3-15 years of age. 12 mares were injected daily for 14 days with EE; 6 of the EE-treated mares were also treated with human chorionic gonadotropin (HCG), and 6 control mares received saline vehicle only. In a 2nd experiment designed to determine if EE treatment could induce multiple ovulations in seasonally ovulatory mares, 7 mares were treated during diestrus, 7 mares were treated beginning on Day 1 of estrus, and 7 remained untreated. The results of experiment 1 confirmed that EE treatment can induce ovulation in mares during the anovulatory season, that the timing of ovulation can be improved with HCG, and that ova from induced ovulations are fertilizable. Results of experiment 2 demonstrated that EE treatment can induce follicular activity and multiple ovulations during the ovulatory season.     

Induced abortion with two Prostaglandin F2α analogues in mares: Plasma progesterone changes

Three experiments were conducted to test the abortifacient effects of PGF2α analogues on mares during midgestation (average gestation length 141.5 days). The progesterone concentration was measured by radioimmunoassay. In experiment I, five mares recieved an injection of PGF2α analogue (fluprostenol: 500 μg intramuscularly) and a second injection either at 24, 48, of 72 h. Although the progesterone concentration decreased (P < 0.05) an average of 44 per cent in 24 h, none of the pregnancies were terminated. In experiment 2, beginning at least 10 days after experiment I, the same five mares were given PGF2α analogue as follows: 250 μg intravaginally and 500 μg intramuscularly. The treatment was repeated 48 h later. Progesterone concentrations had not increased since experiment 1 and dit not decrease during the 48 h following either injection. In experiment 3, six mares (average gestation length 162 days) were treated every 6 or 12 h with PGF2α analogue (cloprostenol: 375 μg) until expulsion of the fetus occurred at 47 ± 25 h after the initial injection; the mares received an average of 5 treatments. The progesterone concentration averaged 22 ± 7 ng/ml before the initial PGF2α treatment, decreased (P<0.05) to 8.4 ±2.7 ng/ml by 12 h before expulsion and 1–8 ±0.4 ng/ml 12 h after fetal expulsion. The progesterone concentration remained below 1.0 ng/ml for the next 4 days. However, only one of six mares exhibited estrual behavior after induced abortion.     

Evaluation of Injectable Sustained Release Progestin Formulations for Suppression of Estrus and Ovulation in Mares

Thirty-one mares were used in an experiment to evaluate the effectiveness of three sustained-release injectable formulations of altrenogest and one formulation of medroxyprogesterone acetate (MPA) for long-term suppression of estrus and ovulation. Luteolysis was induced by injection of prostaglandin-F_2α (Lutalyse) on day 0 (6th day after the previous ovulation) and was immediately followed by treatment with 1) no injection (controls; n = 7), 2) 1.5 mL of an altrenogest solution in sustained-release vehicle (LA 150, 1.5 mL; 225 mg altrenogest; n = 6), 3) 3 mL (450 mg altrenogest) of the same solution (n = 6), 4) 500 mg altrenogest in lactide-glycolide microparticles suspended in 7-mL vehicle (MP 500; n = 6), or 5) 1.0 g MPA as a 5-mL suspension. Mares were checked for estrus daily, and their ovaries scanned every other day until a 25-mm or greater follicle was detected, after which they were scanned daily. Control mares returned to estrus an average of 3.9 days after Lutalyse administration; all the single-injection altrenogest formulations increased (P < .05) the days to return to estrus, with the greatest increase occurring in mares receiving MP 500. Return to estrus was not affected by MPA treatment. Time of ovulation was determined by serial ultrasound scans and confirmed by daily plasma luteinizing hormone (LH) and progesterone concentrations. Control mares ovulated an average of 8.8 days after Lutalyse administration. Treatment with 1.5 or 3 mL of LA 150 increased (P < .05) the mean days to ovulation to 16.5 and 21.2 days, respectively; MP 500 increased (P < .05) the days to ovulation to 33.5 days. Administration of MPA did not affect (P > .1) days to ovulation relative to control mares. The MP 500 treatment provided long-term suppression of estrus and ovulation and could prove useful for that purpose. Treatment with the LA 150 solutions provided shorter-term suppression, and a relatively tight grouping of the individual mares around the mean days to ovulation; these one-shot formulations could be useful for synchronizing ovulation in cyclic mares and inducing normal estrous cyclicity in vernal transitional mares exhibiting erratic, anovulatory estrous periods.     

Effect of short-term artificial light and transvaginal progesterone device on first ovulation in late transitional mares

In study I, plasma progesterone concentrations were evaluated in anoestrous mares that received an intravaginal progesterone release device (IPRD) for 10 days. Mares were divided into 3 groups based on the dosage of progesterone (0 g, n=3; 1.38 g, n=5; and 1.9 g, n=5). No statistical differences were found in plasma progesterone concentrations between the two doses tested. In study II, the effects of a protocol based on a short program of artificial light combined with an IPRD containing 1.38 g of progesterone on oestrous behaviour and onset of ovulation were evaluated. IPRDs were inserted into 31 late transitional mares (10 days of treatment). The mares were divided into a control group (n=9, IPRD with 0 g of progesterone) and two treatment groups (T1, n=10, IPRD with 0 g of progesterone and artificial light; T2, n=12, IPRD with 1.38 g of progesterone and artificial light). The percentages of mares in heat within the first 14 days after treatment were 100%, 70%, and 100% in the control, T1, and T2 groups, respectively (P=0.097), and their ovulation rates were 44%, 60%, and 100%, respectively (P≤0.01). In conclusion, a protocol based on artificial light and an IPRD containing 1.38 g of progesterone for 10 days could be considered to advance the first ovulation of the year in late transitional mares, as it ensures a higher rate of ovulation within the first 14 days after treatment.     

Prolonged interovulatory interval and hormonal changes in mares following the use of Ovuplant™ to hasten ovulation

In its first year of commercial availability in the United States, reports from the field indicated that Ovuplant™ (a deslorelin-containing slow-release implant for hastening ovulation in mares) was associated with a delayed return to estrus in mares not becoming pregnant. Supposedly this effect was particularly prevalent in mares subsequently administered PGF_2α to cause luteal regression after embryo collection. The present experiment was conducted 1) to determine if the field observations were repeatable under controlled experimental conditions, and 2) to gather endocrine data that might yield information on the underlying cause(s) of this observation. Twenty-five light horse mares were used. Ovaries of each mare were examined by transrectal ultrasonography daily during estrus until ovulation. Once a follicle >30 mm was detected, the mare received either Ovuplant (treated group; N = 13) at the recommended dosage or a sham injection (controls; N = 12); treatments were administered in a manner to ensure that they were unknown to personnel involved with data collection. On day 7 after ovulation, each mare received a luteolytic injection of PGF_2ð. Mares were examined every other day until return to estrus or development of a 30 mm follicle, at which time daily examination was performed until ovulation. Jugular blood samples were collected daily. Two mares receiving Ovuplant did not return to estrus within 30 days and their data were not included in the statistical analyses; in contrast, no control mare exhibited such an extended interovulatory interval. For all other mares receiving Ovuplant, the interval between the first and second ovulations was longer (P = .0001) than that of control mares by an average of 6.2 days. In addition, plasma LH concentrations were lower (P <.05) in the treated mares on days 0 through 4, 9, 11, 18, and 19 after the first ovulation. Plasma FSH concentrations were also lower (P = .017) in treated mares from days 4 to 11 and on days 6 and 5 prior to the second ovulation (P = .005). Differences in progesterone and estradiol were observed but were less consistent than for LH and FSH. Mares receiving Ovuplant had fewer small (P =.026), medium (P = .003) and large (P = .045) follicles prior to the second ovulation. In conclusion, Ovuplant treatment at the recommended dosage decreased follicular activity after ovulation and increased the interovulatory interval in mares short-cycled with PGF_2ð. These effects appear to be mediated by a hyposecretion of LH and(or) FSH.     

The Effect of Sulpiride Treatment During the Periovulatory Period on Prolactin Concentration and Ovulation in the Mare

Sixteen estrous cycles from 10 cyclic mares were randomly assigned to a control or sulpiride group (n = 8 each). All mares received 1,500 IU of human chorionic gonadotropin (hCG) (hour 0) during estrus with a follicular diameter ≥32 mm. Mares were scanned every 12 hours until ovulation. In the treatment group, beginning at hour 0, each mare received 1.5 mg/kg of sulpiride every 12 hours intra-muscularly until ovulation or formation of a luteinized unruptured follicle (LUF). Concentrations of luteinizing hormone (LH) and prolactin (PRL) were measured by radioimmunoassay. In each group, there were 10 preovulatory follicles for the eight cycles. The ovulation rate (9/10, 90%) was similar in the control and sulpiride groups. Two mares formed an LUF, which was first detected at hours 48 and 72 for the sulpiride and control mares, respectively. The interval from hCG to ovulation was 49.5 ± 11.1 and 43.5 ± 5.8 hours, for the control and sulpiride groups, respectively (P > .5). LH followed the typical preovulatory surge pattern, with no difference between groups (P > .5). Sulpiride administration increased PRL concentration in treated mares at 24 (P < .1), 36, and 48 hours (P < .05) after treatment. In conclusion, sulpiride administration every 12 hours increased PRL concentration in treated mares after 24 hours of the beginning of treatment. However, at this time window and concentration, PRL did not have any effect on ovulation. The control mare that developed an LUF had a PRL concentration similar to other ovulatory control mares (always ≤10 ng/mL).     

Efficacy of Long-Acting Formulations of Estradiol or Progesterone Plus Estradiol on Estrous Synchronization in Broodmares

A preliminary trial was performed to evaluate the ability of sustained release preparations of estradiol-17β or progesterone plus estradiol-17β to synchronize estrus in cyclic mares. Group 1 mares were treated with a 50 mg intramuscular (IM) injection of sustained release estradiol-17β, while group 2 mares were treated with estradiol plus 1.5 g of sustained release progesterone. All mares received an IM injection of 10 mg of prostaglandin-F₂α (PGF₂α) 10 days after steroid treatment. Mares were examined by transrectal ultrasonography on Days 1 and 10 of treatment and then at ≤2 day intervals to monitor follicle size. Once a follicle ≥30 mm diameter and uterine edema were detected, 0.5 mg of the GnRH analog histrelin was administered IM. Mares were examined daily thereafter to detect ovulation. Group 1 mares did not exhibit ovulation synchrony (ovulations occurred 12-22 days after steroid treatment), whereas ovulation synchrony was satisfactory in group 2 mares (interval to ovulation being 20.4 ± 1.5 days, range 17-22 days). Using sustained release preparations of progesterone plus estradiol-17β, with PGF₂α administered on Day 10, could eliminate the need for daily injections of steroid preparations in oil when synchronizing estrus and ovulation.     

The effect of systemic administration of cloprostenol on ovulation in mares treated with a prostaglandin synthetase inhibitor

Prostaglandins (PGs) are essential to trigger the cascade of events that degrade the extracellular matrix of follicles leading to follicular rupture and ovulation. In mares, systemic administration of flunixin meglumine (FM), a PG synthetase inhibitor, blocks ovulation by inducing luteinized unruptured follicles (LUF). In the rat, the administration of PGF(2α) (PGF) and PGE restored ovulation in indomethacin treated animals. The mares were treated with FM 0, 12, 24 and 36 h after human chorionic gonadotrophin (hCG) administration to induce experimentally LUF (n = 15) or were left untreated (controls, n = 5). In addition, 250 μg of cloprostenol were administered intravenously to the mares 33, 35 and 36 h (CLO 33, n = 5) or 48, 49 and 50 h (CLO 48, n = 5) after hCG. One group was treated with FM but not with cloprostenol (FM-control, n = 5). The ovulation rate, follicular diameter and progesterone concentration were compared amongst groups. The ovulation rate at 48 h was higher (p < 0.05) in the controls (100%) than in the FM-control (0%), CLO 33 (0%) or CLO 48 (20%) mares. All but one FM treated mares developed LUF by 48 h after hCG administration. Two LUF collapsed between 48 and 60 h and 72 and 84 h in one mare from FM-control and from the CLO 33 group each, respectively. Progesterone concentration was significantly higher (p < 0.05) in the control mares than in any of the FM treated mares 5, 9 and 13 days after hCG. In conclusion, FM administered during the periovulatory period blocked ovulation in the mares. In contrast, the administration of cloprostenol, a PGF analogue, in the previously FM treated mares failed to restore ovulation.     

Ultrasonographic studies on ovarian dynamics and associated estrus manifestations of jennies under controlled management, Ethiopia

A serial ultrasonographic study was conducted on nine jennies aged 5–15 years from January to April 2008 with the objective of studying ovarian follicular dynamics and estrus manifestations under controlled management. Ovarian follicular activity was determined from the number and size distribution of follicles, length of interovulatory interval (IOI), growth rate of preovulatory follicles, diameter of follicles at the onset of estrus, and incidence of ovulation. Estrus manifestations were characterized using length of estrus and estrous cycle. The mean (±SD) number of follicle detected per ovary was 5.45?±?2.3 (range, 1–16) with sizes ranging from 2.9 to 44 mm. The mean (±SD) size of follicle encountered at the onset of estrus was 25.9?±?3.7 mm (range, 20.9–34.4) while that of the preovulatory follicles at ?1 day before ovulation was 36.81?±?3.78 mm. The mean (±SD) IOI, estrus, and estrous cycle length were 25.4?±?3.6, 7.9?±?2.9, and 24.2?±?7.4 days, respectively. The mean (±SD) growth rate of the preovulatory follicle after the day of divergence was 1.9?±?0.3 mm/day. Serum progesterone profile followed the same patterns of ovarian dynamics with maximum values being detected during midluteal phase. Serum progesterone assay revealed blood progesterone profiles of <1.0 ng/ml during estrus and up to 11 ng/ml during midluteal phase with a pattern following follicular dynamics. Body condition of the study jennies steadily increased and was positively correlated (r?=?0.52, p?<?0.001) with the diameter of the preovulatory follicle. In conclusion, the ultrasonic evaluation has revealed that follicular dynamics of jennies were generally related with body condition which might have been influenced by the type of management.     

Embryo Transfer in Anovulatory Recipient Mares Treated with Estradiol Benzoate and Long-Acting Progesterone

This study aimed to prepare anovulatory mares in anestrus or in the transitional period as embryo recipients. Ninety embryo-recipient mares were divided into two groups (G). G1 (n = 45) comprised animals in anestrus or in the transitional period; these animals were treated for 3 days (D) with 5, 3, and 2 mg of estradiol benzoate (intramuscular) on D0 (day of the donor's ovulation), D1, and D2 (after ovulation), respectively, followed by weekly application of 400 mg of long-acting progesterone (intramuscular) from D3 after ovulation (donor) until the 120th day of gestation. G2 (n = 45) comprised mares with normal estrous cycles. Plasma levels of progesterone (P₄) were measured on days D1, D2, D8, and D14. Sixty percent of the animals in G1 and 71.1% in G2 (P > .05) completed the pregnancy. On D8, there was no difference in P₄ levels between G1 and G2 animals, but there was a difference in P₄ levels on D14 (P < .05). It was concluded that anovulatory mares in anestrus or in the transitional period could be used as embryo recipients. The protocol was efficient and also considered an appropriate alternative to prepare the uterine environment for embryo transfer; long-acting progesterone administration kept P₄ levels high enough to maintain pregnancy until the 120th day and provided recipients during the time of the year when fewer mares were cycling and ovulating.     

Effect of deslorelin acetate on gonadotropin secretion and ovarian follicle development in cycling mares

OBJECTIVE: To evaluate gonadotropin secretion and ovarian function after administration of deslorelin acetate to induce ovulation in mares. DESIGN: Randomized controlled trial. ANIMALS: 16 healthy mares with normal estrous cycles. PROCEDURE: 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) was evaluated 10 days after initial ovulation. RESULTS: Interovulatory intervals of mares treated with deslorelin (mean +/- SD, 25.6 +/- 2.6 days) were longer than those of control mares (22.9 +/- 1.8 days). Diameter of the largest follicle was significantly smaller during 2 days of the diestrous period after ovulation in deslorelin-treated mares than in control mares. Concentrations of follicle-stimulating hormone (FSH) were lower in deslorelin-treated mares on days 5 through 14 than in control mares. Concentrations of luteinizing hormone were not different between groups during most of the cycle. Gonadotropin release in response to administration of GnRH was lower in mares treated with deslorelin acetate than in control mares. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of deslorelin was associated with reduction in circulating concentrations of FSH and gonadotropin response to administration of GnRH during the estrous cycle. Low concentration of FSH in treated mares may lead to delayed follicular development and an increased interovulatory interval.