Effects of a new injectable short-term release deslorelin in foal-heat mares

Mares treated with subcutaneous deslorelin implants on the first postpartum estrus early in the breeding season had significant reductions in the number of large follicles at early pregnancy examinations and delayed return to estrus (in mares that failed to become pregnant); these adverse effects were attributed to a prolonged release of the drug from the implant. In 2003, an injectable short-term release (<24 h) deslorelin product became available. The objective of this study was to determine if this product would hasten ovulation in early foaling first postpartum estrus mares without reducing the number of large follicles at early pregnancy examination (14-15 days postovulation). Beginning 5-6 days postpartum, first postpartum estrus (foal-heat) mares were teased daily and examined thrice weekly (Tuesday, Thursday and Saturday) by transrectal ultrasonography. Mares in estrus with a follicle > or = 34 mm diameter on Tuesdays or Thursdays were alternately assigned to: Treatment 1, n = 17; 1.5 mg injectable short-term release deslorelin, or Treatment 2, n = 16; Control (no treatment). The schedule allowed accurate determination of the number of mares ovulating within 2 days of treatment (i.e., ovulations detected on Thursday or Saturday). Mares were mated on the day of treatment and at 2-day intervals until either ovulation was confirmed or until behavioral estrus ceased. Transrectal ultrasonography was done 14-15 days after ovulation to assess ovarian follicles and pregnancy status. Fewer covers were required and more mares ovulated within 2 days of treatment in deslorelin-treated versus Control mares (P < 0.01). Pregnancy rates were normal (69%) in deslorelin-treated mares. The number of large follicles 14-15 days after ovulation did not differ between deslorelin-treated and Control mares (P > 0.10), suggesting follicular suppression did not occur with this formulation of deslorelin.     

Removal of deslorelin (Ovuplant) implant 48 h after administration results in normal interovulatory intervals in mares

Deslorelin implants, approved for use in inducing ovulation in mares, have been associated with prolonged interovulatory intervals in some mares. Administration of prostaglandins in the diestrous period, following a deslorelin-induced ovulation, has been reported to increase the incidence of delayed ovulations. The goals of the present study were: (1) to determine the percentage of mares given deslorelin that experience delayed ovulations with or without subsequent prostaglandin treatment, and (2) to determine if removal of the implant 48 h after administration would effect the interval to subsequent ovulation. We considered interovulatory intervals to be prolonged if they were greater than the mean +/- 2 standard deviation (S.D.) of the control group in study 1 and the hCG group in study 2. In study 1, we retrospectively reviewed reproduction records for 278 mares. We either allowed the mare to ovulate spontaneously or induced ovulation using deslorelin acetate implants or hCG. We administered prostaglandin intramuscularly, 5-9 days after ovulation in selected mares in each group. A higher percentage of mares which were induced to ovulate with deslorelin and given prostaglandins had a prolonged interovulatory interval (23.5%; n = 16), as compared to deslorelin-treated mares that did not receive prostaglandins (11.1%; n = 5). In study 2, we induced ovulation in mares with hCG (n = 47), a subcutaneous deslorelin implant via an implanting device provided by the manufacturer (n = 28), or a deslorelin implant via an incision in the neck (n = 43) and we removed the implant 48 h after administration. We administered prostaglandin to all mares 5-9 days after ovulation. In study 2, mares from which the implant was removed had a normal ovulation rate and none had a prolonged interval to ovulation. Administration of prostaglandin after deslorelin treatment was associated with a longer interval from luteolysis to ovulation than that found in mares not treated with deslorelin. Prostaglandin administration during diestrus may have exacerbated the increased interval to ovulation in deslorelin-treated mares. We hypothesize that prolonged secretion of deslorelin from the implant was responsible for the extended interovulatory intervals.     

Acceleration and Timing of Fertile Ovulation in Cyclic Mares with a Deslorelin Implant

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 pregnancy rate at 18 (±3) and 38 (±3) days were recorded, as were systemic side effects and local reactions at the implantation sites. Pregnancies resulting from breedings during the treatment estrus and/or from breedings during the next estrus were followed and the early and late pregnancy loss rate, the number of pregnancies going to term and of live–born foals was recorded. Mean follicle diameter at treatment was not significantly different between the deslorelin and placebo treatment group with 41.6 mm and 40.8 mm, respectively. Treatment with deslorelin STI reduced the time interval to Ovulation significantly from 69.5±25.48 h to 42.7±12.35 h (p<0.001). The percentage of mares having ovulated within 48 h rose from 26.3% to 95.0%, respectively, for placebo and deslorelin STI (p<0.001). As a consequence, the duration of estrus in days and the percent of animals requiring more than 1 breeding were significantly reduced in deslorelin treated animals from 5.4 days to 4.6 days, and from 55.6% to 5.0%, respectively (p=0.009 and =0.001). The percent of mares pregnant from breedings at the treatment estrus (65.0% versus 44.4%) or the next estrus (83.3% versus 92.3%) was satisfactory and similar for deslorelin and placebo treated mares (p>0.005), and in 70.0% and 66.7% of these once or twice bred mares did pregnancies go to term and live foals were born. kw|Keywords|k]GnRH     

Induction of ovulation during the postpartum period in the thoroughbred mare with a prostaglandin analogue,Synchrocept™

Breeding of mares at the foal heat is desirable, but the low pregnancy rate and the not infrequent occurrence of subsequent anestrus are a deterrent. A PGF_2a analogue, Synchrocept^? (prostalene), as a single 2 mg subcutaneous injection was used to induce ovulation, either during the corpus luteum phase subsequent to a foal heat (test group 1) or at a fixed interval of 20 days from parturition (test group 2) in mares that also had a foal heat. Mares with no signs of a foal heat were treated 20 days postpartum (test group 3). A total of 80, mostly Thoroughbred, mares were treated in more than 15 breeding centers in Northern Germany between mid-January and mid-May 1975. At the same locations and over the same time periods, 60 control mares (control group 1) were bred at the foal heat and 40 additional control mares (control group 2) were bred later than 25 days postpartum.In groups 1 and 2, treatment induced estrus in 95% of the mares and in group 3 estrus was induced in 68% of the mares. Of these animals, 92% were bred and 81% conceived on the average 28 days after parturition. The number of services per conception in mares treated was 25% lower (2.5) than in controls (3.2). Synchrocept acted as a luteolysin, but seems also to have induced heat and estrus in animals with plasma progesterone levels below 1 ng/ml, as has been reported previously. Neither mares nor foals showed detectable clinical signs of drug intolerance.     

Evaluation of three equine FSH superovulation protocols in mares

Superovulation could potentially increase embryo recovery for immediate transfer or cryopreservation. The objectives were to evaluate the effect of pretreatment with progesterone and estradiol (P+E) on follicular response to eFSH and compare doses of eFSH and ovulatory agents on follicular development and ovulation in mares. In Experiment 1, 40 mares were assigned to one of four treatment groups. Group 1 consisted of untreated controls. Group 2 mares were administered eFSH without pretreatment with P+E. Group 3 mares were administered P+E for 10 days starting in mid-diestrus followed by eFSH therapy. Group 4 mares were administered P+E for 10 days followed by eFSH therapy. All treated mares were administered 12.5mg eFSH twice daily and prostaglandins were given on the second day of eFSH therapy. Mares were bred with fresh semen the day of hCG administration and with cooled semen the following day. The numbers of preovulatory follicles and ovulations were lower for mares treated with P+E prior to eFSH treatment. Pretreatment with P+E in estrus also resulted in a lower embryo recovery rate per ovulation compared to the other two eFSH treatment groups. In Experiment 2, two doses of eFSH (12.5 and 6.25mg) and two ovulation-inducing agents (hCG and deslorelin) were evaluated. The number of preovulatory follicles was greater for mares given 12.5mg of eFSH compared to mares given 6.25mg. Number of ovulations was greatest for mares given 12.5mg of eFSH twice daily followed by administration of hCG. Embryo recovery per flush was similar among treatment groups, but the percent of embryos per ovulation was higher for mares given the low dose of eFSH. In summary, there was no advantage to giving P+E prior to eFSH treatment. In addition, even though the lower dose of eFSH resulted in fewer ovulations, embryo recovery per flush and embryo recovery per ovulation were similar or better for those given the lower dose of eFSH.     

Effect of dose of GnRH analog on ovulation in mares

Proper timing of insemination for optimal conception is accomplished by frequent palpations per rectum, by ultrasonography of the preovulatory follicle and/or by treatment with hCG or GnRH. Sustained release of GnRH from implants has been shown to hasten ovulation. Therefore, 2 studies were conducted to evaluate the efficacy of a GnRH analog, deslorelin, for hastening ovulation in nonlactating cyclic mares. The GnRH implant was 2.3 x 3.7 mm and released deslorelin for 2 to 3 days. In Experiment 1, 60 nonlactating, cycling mares were assigned to 1 of 5 doses: 0, 1.2, 1.7, 2.2 and 2.7 mg per implant. Mares were assigned sequentially on the first day of estrus (Day 1). Ovaries were examined per rectum and with ultrasonography every 12 h until ovulation. Once the mares obtained a follicle >30 mm, they were injected subcutaneously with a GnRH implant. The mares were inseminated every other day during estrus with semen from 1 of 3 stallions. Pregnancy was determined with ultrasonography. Experiment 2, 40 nonlactating, cyclic mares were assigned to 1 of 5 treatments (same treatments as in Experiment 1). Data were obtained on interval to ovulation, duration of estrus and pregnancy rates at 12, 18 and 35 d after ovulation. Time to ovulation was shorter (P<0.05) in GnRH-treated mares than in control mares in the Experiment 1. Mean time to ovulation was 68, 49, 48, 47, 44 h in Experiment 1, and 91, 66, 58, 46, 58 h in Experiment 2 for mares given 0, 1.2, 1.7, 2.2 and 2.7 mg/mare in the 2 trials. Averaged for both experiments, the proportion of mares ovulating within 48 h of treatment was 40, 75, 85, 90 and 90% for 0, 1.2, 1.7, 2.2 and 2.7 mg/mare. For both experiments, there was no effect of GnRH on pregnancy rate. In summary, a subcutaneous implant containing GnRH analog induced ovulation in most mares by 48 h of injection, and there was no advantage of doses higher than 2.2 mg/mare.     

Efficacy of a prostaglandin analogue in reproduction in the cycling mare.

A prostaglandin F analogue caused luteolysis in normal cycling non-lactating mares, and lactating mares (treated after the foal estrus). Effective doses ranged from 1.0 to 4.0mg given as a single subcutaneous injection 8–10 days after ovulation. A dose of 0.5mg was ineffective, hence the dose-response relationship was steep, indicative of a quantal type of response. Mares usually returned to estrus within 2–4 days and ovulated by 7 days after treatment. Mares bred naturally or by artificial insemination at the induced estrus and ovulation were fertile. The compound was without side-effects, and hence should be of value in manipulating the estrous cycle of the mare.     

Chronobiological characterization of the first estrous cycle in Brasileiro de Hipismo mares during the postpartum period

This study was conducted on 32 mares during the first 30 d of the postpartum period to characterize the first estrous cycle, assessing ovarian cyclicity by determining plasma progesterone concentration and by transrectal palpation. The total pregnancy rate of the breeding season was 81.25%. The present results show that the incidence of estrus occurring at the beginning of the breeding season were early, long and anovulatory. The mares that did not become pregnant ovulated on average 14.5 d post partum, and those that became pregnant ovulated at 19.6 d post partum (P<0.05). On the basis of clinical and hormonal data, we divided the animals into 4 groups, all presenting signs of estrus: Group 1, animals that did not ovulate (n=7) and that presented basal P(4) levels (0.01-2.34 ng/ml) during the first 30 postpartum days; Group 2, animals that ovulated and did not become pregnant (n=13); Group 3, animals that ovulated and became pregnant (n=8). Maximal P(4) levels ranged from 4.40 to 13.50 ng/ml (Group 2) and from 3.70 to 20.50 ng/ml (Group 3). Group 4 were animals that presented high plasma P(4) levels before any clinical sign of ovulation (n=3). The absence of pregnancy could not be attributed to a failure of the corpus luteum, since the groups of mares that became pregnant exhibited similar plasma P(4) levels as the group of nonpregnant mares. Our findings demonstrated that mares exhibited differences in the timing of the first postpartum estrus, the duration of the first postpartum estrus and the timing of the first postpartum ovulation according to the month of the breeding season in which foaling occurs under tropical conditions. Furthermore, our results indicate that the foal heat may be used since its utilization did not affect the total pregnancy rate of the breeding season.     

The effects of prostalene and alfaprostol as uterine myotonics, and the effect on postpartum pregnancy rate in the mare following daily treatment with prostalene

The effects of oxytocin and two prostaglandin (PG) F(2)alpha analogues, prostalene and alfaprostol, on uterine pressure in the mare were measured using balloon-tipped catheters connected to pressure transducers. The PGF(2)alpha analogues caused increased uterine pressure beginning 7 to 15 min postinjection and persisting for the duration of each 60 min recording session. Forty postpartum mares of light-horse breed were used to evaluate the effects of prostalene on postpartum pregnancy rate. Eighteen mares were injected by aseptic technique subcutaneously with 1 mg prostalene twice daily, beginning on the day of foaling (Day 0) and continuing for 10 consecutive days (Day 10) or until the mare was first bred at foal heat. Twenty-two postpartum mares were injected with 1.0 ml sterile saline by the same technique as the controls. Of treated mares, 76.9% were diagnosed pregnant after breeding versus 44.4% of the control mares (P = 0.07). Of treated mares, 66.7% bred at their second postpartum estrus became pregnant versus 28.6% of control mares (P = 0.03). Prostalene, given at 1 mg twice daily for 10 d postpartum, produced an increased pregnancy rate after both foal heat and second postpartum estrus breedings in the mare.     

Management and fertility of mares bred with frozen semen.

Semen quality, mare status and mare management during estrus will have the greatest impact on pregnancy rates when breeding mares with frozen semen. If semen quality is not optimal, mare selection and reproductive management are crucial in determining the outcome. In addition to mare selection, client communication is a key factor in a frozen semen program. Old maiden mares and problem mares should be monitored for normal cyclicity and all, except young maidens, should have at least a uterine culture and cytology performed. Mares with positive bacterial cultures and cytologies should be treated at least three consecutive days when in estrus with the proper antibiotic. With frozen semen, timing the ovulation is highly desirable in order to reduce the interval between breeding and ovulation. The use of ovulation inducing agents such as human chorionic gonadotropin (hCG) or the GnRH analogue, deslorelin, are critical components to accurately time the insemination with frozen semen. Most hCG treated mares ovulate 48h post-treatment (12-72h) while most deslorelin (Ovuplant) treated mares ovulate 36-42h post-treatment. However, mares bred more than once during the breeding cycle appear to have a slight but consistent increase in pregnancy rate compared to mares bred only once pre- or post-ovulation. In addition, the "capacitation-like" changes inflicted on the sperm during the process of freezing and thawing appear to be responsible for the shorter longevity of cryopreserved sperm. Therefore, breeding closer to ovulation should increase the fertility for most stallions with frozen semen. Recent evidence would suggest that breeding close to the uterotubal junction increases the sperm numbers in the oviduct increasing the chances of pregnancy. Post-breeding examinations aid in determining ovulation and uterine fluid accumulations so that post-breeding therapies can be instituted if needed. Average pregnancy rates per cycle of mares bred with frozen semen are between 30 and 40% with a wide range between sires. Stallion and mare status are major factors in determining the success of frozen semen inseminations. Pregnancy rates are lower for barren and old maiden mares as well as those mares treated for uterine infections during the same cycle of the insemination. To maximize fertility with frozen semen, a careful selection of the stallions and mares, with proper client communication is critical. Dedication and commitment of mare owner and inseminator will have the most significant impact on the pregnancy rates.     

Effect of hCG administration on day 7 of the estrous cycle on follicular dynamics and cycle length in cows

The use of hCG in cattle at breeding or at different times after breeding has been associated with extension in estrous cycle length among cows that do not become pregnant. The objective of this study was to determine whether the increase in estrous cycle length observed in hCG-treated cows that fail to become pregnant is due to changes in ovarian follicular dynamics. Twelve nonbred lactating cows were randomly assigned either to receive hCG on Day 7 of the cycle (Day 0 = day of estrus, n = 6) or to serve as controls (n = 6). Ultrasound scanning was conducted daily from Day 0 until the onset of the next ovulation to monitor follicular and corpus luteum (CL) dynamics. Blood samples were collected for progesterone analysis at each ultrasound session. Ovulation of the Day 7 follicle occurred in all 6 hCG-treated cows. The time of emergence of the second-wave of follicular growth was advanced in hCG-treated cows but was not statistically different (P > 0.05) from that of the control cows (10.8 +/- 0.3 vs 12.7 +/- 1.4 d). The mean diameter of the second-wave dominant follicle from Days 15 to 18 was not different (P > 0.05) between the treatment groups. However, the second-wave dominant follicle had a slower growth rate (0.8 vs 1.3 mm/d) among cows treated with hCG compared with that of the controls. The second-wave dominant follicle was the ovulatory follicle in 5 control cows, but only in 3 hCG-treated cows. The dominant follicle from the third wave ovulated in 1 control and in 3 hCG-treated cows. The lifespan of the spontaneous CL and the time to low progesterone levels (< 1 ng/ml) were not different between the control and hCG-treated cows. These results suggest an altered follicular dynamic but no extension in estrous cycle length when hCG is administered on Day 7 of the cycle in postpartum cows.     

Progesterone and estradiol in biodegradable microspheres for control of estrus and ovulation in mares

Progesterone and estradiol 17-beta in poly (DL-lactide) microspheres were used to control estrus and ovulation in mares after luteolysis was induced by prostaglandin F(2)infinity. Mares were given a single intramuscular injection of biodegradable poly (DL-lactide) microspheres, 1 day following prostaglandin treatment, containing no hormones (control), 0.625 g progesterone and 50 mg estradiol (low dose), 1.25 g progesterone and 100 mg estradiol (medium dose), or 1.875 g progesterone and 150 mg estradiol (high dose; n=15 mares per group). Mares treated with the low dose had significantly longer intervals (P<0.05) to estrus and ovulation than the control mares; however, low dose mares had shorter intervals (P<0.05) to estrus than high dose mares and shorter intervals to ovulation than medium and high dose mares. Regression analysis indicated that the medium dose was sufficient for maximizing interval to ovulation while the high dose maximized interval to estrus. All groups of mares exhibited similar (P>0.05) post-treatment estrus lengths. A clinical response scoring system based on synchrony of both estrus and ovulation within a treatment group was also used to measure the effectiveness of treatments on control of estrus and ovulation. Clinical response scores did not differ (P>0.05) among treatment groups. Mares were randomly assigned for insemination at the beginning of the first post-treatment estrus. Rates for embryo recovery performed by uterine lavage 7 days post-ovulation did not differ (P>0.05) among groups. Concentrations of serum progesterone increased in mares receiving progesterone and estradiol microspheres. At 10 to 14 days post-injection of microspheres, progesterone concentrations were higher (P<0.05) and remained above 1 ng/ml in the mares receiving the high dose. Progesterone concentrations were also higher (P<0.05) on Days -3 to -1 (Day 0 = day of post-treatment ovulation) in mares receiving the high dose when compared to control mares. Gonadotropin concentrations were suppressed (P<0.05) in the medium and high dose groups.     

The effect of postpartum uterine lavage on foal heat pregnancy rate

Mares (n = 37) were treated on Days 2 and 4 post partum with a uterine lavage of 10 l of warm, sterile NaCl (0.9%) solution. Endometrial cytology and culture were performed on Day 7. Mares were bred on the first postpartum estrus by artificial insemination. Pregnancy rates were determined by ultrasound examination at Day 16 post ovulation. No differences were noted in degree of uterine inflammation or presence of uterine bacteria at Day 7 post partum between treated (n = 18) and control (n = 19) mares. Pregnancy rates at the first postpartum estrus for treated mares (55.5%) was not statistically different from that of control mares (68.4%). No advantage was noted in the use of intrauterine lavage with 10 l of warm sterile NaCl (0.9%) at Days 2 and 4 post partum as a means of improving foal heat pregnancy rate.     

Use of deslorelin short-term implants to induce ovulation in cycling mares during three consecutive estrous cycles

Alternatives to human chorionic gonadotropin (hCG) for inducing ovulation in cycling mares over several consecutive cycles were explored. Placebo, one, three or five short-term implants each containing 2.2 mg of gonadotropin-releasing hormone (GnRH) analogue (deslorelin) were administered to cycling mares after identification of a follicle over 30 mm. Mares were treated over three consecutive cycles, and artificially inseminated during the third cycle only. Serum was assayed for concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and progesterone during each cycle. All deslorelin doses decreased the interval to ovulation (4.0 days, 2.6 days, 2.4 days and 2.0 days), increased the proportion of mares ovulating within 48 h (20.0%, 83.3%, 73.3% and 85.7%), and decreased the diameter of the largest follicle at ovulation (45.8 mm, 38.0 mm, 41.0 mm and 37.2 mm) for the placebo, 2.2 mg, 6.6 mg and 11.0 mg groups, respectively (P < 0.05). The interovulatory interval was lengthened in the 11.0 mg group compared with all other groups (21.2 days, 21.8 days, 26.4 days and 32.7 days for the placebo, 2.2 mg, 6.6 mg and 11.0 mg groups, respectively, P < 0.05). No differences (P > 0.05) were detected in serum concentrations of progesterone or pregnancy rate among the groups. Cycle number had no effect (P > 0.05) on the reproductive parameters or serum concentrations of progesterone. Concentrations of LH were higher in Cycle 3 in the 6.6 mg and 11.0 mg groups, and FSH concentrations were decreased in Cycles 2 and 3 in treated mares. Deslorelin was efficacious for inducing ovulation in cycling mares with no diminished activity over three consecutive cycles. However, ovarian suppression and changes in serum concentrations of gonadotropins were noted at higher doses.     

Sexual behavior following introduction of a stallion into a group of mares

A rested stallion was introduced daily for 30 days into each of three herds of 20 mares. Observations of sexual and mating behavior were made for one hour. The stallion remained with a herd until another stallion was introduced the following day. Other mares were isolated from stallions and were bred by artificial insemination. The diameter or growth rate of the preovulatory follicle for the six days preceding ovulation and the length of the interovulatory interval for mares which did not become pregnant were not affected significantly by the presence of a stallion. The number of breedings per hour of observation (2.4 ±0.2) and the length of the interval from introduction of a stallion into the herd of mares to first breeding (12 ±1 min) were significantly different among stallions, but the length of the interval between breedings (17 ±2 min) was not. The mean number of breedings per stallion per hour was not affected significantly by the number of posturing (estrous) mares. The number of times that the stallion rebred the same mare when more than one mare postured during the observation hour (49%) was greater (P<0.01) than what would be expected to occur by chance (30%). The hypothesis that breeding occurs preferentially in those estrous mares that are closest to ovulation was not supported, except for significantly lower breeding activity in posturing mares on days 8 and 7 before ovulation and on days 0 (day of ovulation) and ?1 (26% bred) than on days 6 to 1 (52%).     

Reproductive hormone secretions in pony mares subsequent to ovulation control during late winter

Beginning in December, pony mares were placed under a schedule of increasing light. Starting in February, onset of estrus was checked by daily teasing with a stallion. Mares were randomly assigned to one of three treatments (6 mares per group) administered in March. Treatments were: Group I — 75 mg progesterone injected intramuscularly every day for 10 days in combination with a 1.25 mg injection of PGF₂α on day 7 of progesterone treatment and a 2,000 IU injection of HCG on day 2 of estrus; Group II — a norgestomet ear implant inserted for 10 days in combination with 1.25 mg PGF₂α given 7 days after insertion and 2,000 IU HCG administered on day 2 of estrus; and Group III — same as II except that 2 mg of GnRH rather than HCG were administered on day 2 of estrus. Blood plasma for radioimmunoassay of progesterone, LH and estradiol was collected from the first day of treatment until 14 days after the end of estrus. Also in March, 6 mares were bled daily from the first day of estrus until subsequent estrus or day 21 (control estrus). Although estrus was detected in all mares, 14 of 18 mares ovulated subsequent to treatments and four of the six control estrus mares ovulated. Only among HCG treated mares was the ovulation rate higher (P < .05) than it was in the control estrus group. The interval from last progesterone injection or norgestomet implant removal to estrus did not differ between treatment groups. Concentrations of estradiol and LH were increased for several days around the time of ovulation and tended to be positively correlated with each other. In the mares that did not ovulate, concentrations of LH and estradiol appeared to be lower than in mares that ovulated. In summary, progestins in combination with PGF₂α and increasing light will synchronize estrus in mares during late winter and HCG will hasten ovulation in some mares.     

Control of estrus in the lactating postpartum mare with fluprostenol (ICI-81,008)

During the 1976 breeding season 68 mares (56 Thoroughbred and 12 Quarter Horse) were allotted to 4 treatment groups. On day 7, 8 or 9 post-ovulation or day 6, 7 or 8 after foal heat each of 28 mares was injected intramuscularly with 250 μg of the prostaglandin analogue ICI-81,008 (generic name fluprostenol). In the second group, 32 mares were bred at foal heat. Group 3 consisted of 9 mares, which were passed at foal heat and bred at the second postpartum estrus. In group four, 12 of the mares which had failed to conceive at foal heat were bred at the second estrus. Twenty-four prostaglandin treated mares returned to estrus 4.2±.4 days post-injection. The interestrual interval was shorter (P<.05) for prostaglandin treated mares (11.4±.6 days) than for previously mated second heat control mares (19.2±2.3). Also, the interval between parturition and second estrus was decreased (P<.05) in treated mares (24.5±.8 days) compared to group three (32.8±2.5 days). Duration of the second postpartum estrus was similar for both treated and control mares. Plasma progesterone levels in prostaglandin treated mares as determined by RIA were 7.5±.5 and 6.9±.5 ng/ml before treatment and at l hour post-injection, then dropped precipitously to near undetectable levels at 48 hours after injection. Pregnancy rate at 45 days was significantly higher (P<.05) in prostaglandin treated mares (78%) as compared to foal heat mares (48%) and mares which were passed at foal heat and bred at the second postpartum estrus (44%).     

Effect of intrauterine treatment with prostaglandin E2 prior to insemination of mares in the uterine horn or body

Two trials were conducted to investigate the effects of intrauterine infusion of PGE2 and uterine horn insemination on pregnancy rates in mares achieved by breeding with a suboptimal number of normal spermatozoa. Estrus was synchronized and mares were teased daily with a stallion to detect estrus. Mares in estrus were examined by transrectal palpation and ultrasonography to monitor follicular status. On the first day a 35-mm diameter follicle was present, hCG (1500 IU, iv) was administered and the mares were bred the next day. Mares (Trial 1, n = 34; Trial 2, n = 28) were inseminated with 25 million total spermatozoa from either a stallion with good semen quality (Trial 1) or poor semen quality (Trial 2). In each trial, mares were assigned to 1 of 4 treatment groups as follows: Group PGE-HI - infusion of 0.25 mg PGE2 into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the proximal end of the same uterine horn; Group PGE-BI - infusion of 0.25 mg PGE2 into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the uterine body; Group SAL-HI - infusion of 1 mL sterile saline into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the proximal end of the same uterine horn; or Group SAL-BI - infusion of 1 mL sterile saline into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the uterine body. After breeding, mares were examined daily by transrectal ultrasonography to confirm ovulation, and were re-examined 14 to 16 d after ovulation for pregnancy status. Data were analyzed by Chi-square. Overall pregnancy rates were 59% for stallion 1 and 29% for stallion 2. Group pregnancy rates did not differ for mares bred by either stallion (P > 0.10). Pregnancy rates were not altered by horn insemination for either stallion (P > 0.10). Intrauterine infusion of PGE2 improved pregnancy rate in mares bred by the stallion with good quality semen (P < 0.05), but did not alter pregnancy rate in mares bred by the stallion with poor quality semen (P > 0.10). Further research is warranted to determine if intrauterine infusion of PGE2 will enhance spermatozoal colonization of the oviduct and pregnancy rates in mares, and if PGE-treatment will improve pregnancy rates achieved by subfertile stallions.     

Strategies to improve the ovarian response to equine pituitary extract in cyclic mares

Equine pituitary extract (EPE) has been reported to induce heightened follicular development in mares, but the response is inconsistent and lower than results obtained in ruminants undergoing standard superovulatory protocols. Three separate experiments were conducted to improve the ovarian response to EPE by evaluating: (1) effect of increasing the frequency or dose of EPE treatment; (2) use of a potent gonadotropin-releasing hormone agonist (GnRH-a) prior to EPE stimulation; (3) administration of EPE twice daily in successively decreasing doses. In the first experiment, 50 mares were randomly assigned to one of four treatment groups. Mares received (1) 25 mg EPE once daily; (2) 50 mg EPE once daily; (3) 12.5 mg EPE twice daily; or (4) 25 mg EPE twice daily. All mares began EPE treatment 5 days after detection of ovulation and received a single dose of cloprostenol sodium 7 days postovulation. EPE was discontinued once half of a cohort of follicles reached a diameter of >35 mm and hCG was administered. Mares receiving 50 mg of EPE once daily developed a greater number (P = 0.008) of preovulatory follicles than the remaining groups of EPE-treated mares, and more (P = 0.06) ovulations were detected for mares receiving 25 mg EPE twice daily compared to those receiving either 25 mg EPE once daily and 12.5 mg EPE twice daily. Embryo recovery per mare was greater (P = 0.05) in the mares that received 12.5 mg EPE twice daily than those that received 25 mg EPE once daily. In Experiment 2, 20 randomly selected mares received either 25 mg EPE twice daily beginning 5 days after a spontaneous ovulation, or two doses of a GnRH-a agonist upon detection of a follicle >35 mm and 25 mg EPE twice daily beginning 5 days after ovulation. Twenty-four hours after administration of hCG, oocytes were recovered by transvaginal aspiration from all follicles >35 mm. No differences were observed between groups in the numbers of preovulatory follicles generated (P = 0.54) and oocytes recovered (P = 0.40) per mare. In Experiment 3, 18 mares were randomly assigned to one of two treatment groups. Then, 6-11 days after ovulation, mares were administered a dose of PGF2, and concomitantly began twice-daily treatments with EPE given in successively declining doses, or a dose of PGF2alpha, but no EPE treatment. Mares administered EPE developed a higher (P = 0.0004) number of follicles > or = 35 mm, experienced more (P = 0.02) ovulations, and yielded a greater (P = 0.0006) number of embryos than untreated mares. In summary, doubling the dose of EPE generated a greater ovarian response, while increasing the frequency of treatment, but not necessarily the dose, improved embryo collection. Additionally, pretreatment with a GnRH-a prior to ovarian stimulation did not enhance the response to EPE or oocyte recovery rates.     

The influence of energy intake and percentage of body fat on the reproductive performance of nonpregnant mares

Sixty mares in transition from winter anestrus to normal cyclicity were assigned to a 3 x 2 factorial experiment to determine the effect of energy intake and percentage of body fat on the interval to first ovulation. The factors were 1) percentage of body fat--thin (<11.5), good (11.5 to 15), or fat (>15); and 2) energy intake--maintenance (100% of National Research Council (NRC) digestible energy requirement for maintenance) or high energy (150% of NRC digestible energy requirement for maintenance). Percentage of body fat was estimated by ultrasonographic scanning of rump fat thickness. Energy treatments began on April 2 and ended on June 4. Mares were teased daily with a stallion and their ovaries were palpated per rectum daily or every third day. A high energy intake was effective in hastening ovulation for mares in the thin group (P < 0.05) but not for mares in the moderate or fat groups. Mares in the fat group had a shorter (P < 0.05) interval from April 2 to ovulation (26.4 +/- 4.2 d) than those in the good or high energy-thin groups (48.7 +/- 2.8 and 49.1 +/- 4.2 d, respectively). Duration of the initial estrus was shorter (P < 0.05) for mares in the fat group (16.2 +/- 5.7 d) compared with mares in the good group (34.7 +/- 3.9 d) and tended (P<0.12) to be shorter than mares in the high energy-thin group (29.0 +/- 5.7 d).