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 progesterone impregnated vaginal sponges and PMSG administration on estrus synchronization in mares

Estrus synchronization trials with mares were carried out using progesterone impregnated vaginal sponges and pregnant mare serum gonadotropin (PMSG) injections. In Phase 1, 10 non-pregnant, non-lactating mares were administered 1 g progesterone via vaginal sponges (5 x 6 cm) without regard to stage of estrous cycle. Sponges were replaced on day 7 of trial for an additional seven days. On day 12, PMSG (1000 IU, IM) was administered to five mares (Group A); five control mares (Group B) received no injections. There was no difference (P>.05) in estrus synchronization between Group A and Group B. Total sponge retention was 75%. In Phase 2, 11 non-pregnant, non-lactating mares were administered 2 g progesterone via vaginal sponges (10 x 6 cm) without regard to stage of estrous cycle. Sponges were replaced on day 7 of trial for an additional seven days. Estrus behavior was exhibited in 54.5% of mares by day 19. Total sponge retention was 95.4%. There was no difference (P>.05) in estrus synchronization or sponge retention between Phase 1 and Phase 2. The larger Phase 2 sponges showed less (P<.01) posterior movement within the vagina than the smaller Phase 1 sponges.     

Concentration of prostaglandins F in uterine venous plasma of anesthetized mares during the estrous cycle and early pregnancy

Prostaglandins F were quantitated by radioimmunoassay in uterine venous plasma of anesthetized mares on day 7 of estrus, days 2, 6, 10, 14 or 18 of diestrus and days 10, 14 or 18 of pregnancy. The PGF concentration was greater (P<.01) at day 14 of diestrus than at all other days studied. The concentrations at days 10 and 18 of diestrus and at days 10, 14 and 18 of pregnancy were greater (P<.05) than at day 7 of estrus and days 2 and 6 of diestrus. PGF concentrations at days 10 and 14 were greater (P<.01) for diestrous than for pregnant mares.     

Factors affecting the success of surgical and nonsurgical equine embryo transfer

Nonsurgical embryo recovery was attempted from light-horse and draft mares. Embryo recovery rates were not affected (P>.05) by technician or stallion but were lower (P<.05) from draft mares (44%) than light-horse mares (67%). Sham transfer of embryos on day 8 post-ovulation did not (P>.05) increase the number of mares returning to estrus by 22 days post-ovulation. Method of embryo transfer greatly affected pregnancy rates. Embryos transferred surgically during March–June resulted in 0 of 12 pregnancies versus 13 of 25 pregnancies obtained during July–September, This strongly suggests a seasonal influence on pregnancy rates. Technician influenced (P<.05) the success of nonsurgical transfer (46.2% vs. 7.7%). In addition, protection of the insemination rod with a sheath (guarded method) appeared to provide some advantage over an unguarded method of nonsurgical transfer (54% vs. 23%). Lastly, a preliminary experiment was conducted to evaluate transfer of embryos via flank incision. Four of 5 embryos transferred by this method resulted in a pregnancy at 50 days post estrus.     

The effect of GnRH on induction of follicular development and ovulation in anovulatory and ovulatory mares

The effects of estradiol cypionate (ECP) and GnRH injections were tested on mares during January and February. Sixteen mares were blocked on their ovarian status and equally allotted to two groups. Group one received daily injections of 500 μg ECP (im) for 14 days followed by a 21 day period of twice daily injections of 200 μg GnRH (im). Group two received the carrier vehicle.Mean length of diestrus of ovulatory mares was 14.3 ± 1.6 days and 17.8 ± 3.5 days for treated and control groups respectively. Corresponding estrus lengths were 8.0 ± 1.4 days and 6.3 ± 2.1 days. Plasma LH levels, number of follicles < 20 mm, number of follicles > 20 mm and diameter of the largest follicle in ovulatory mares were not significantly affected by treatment with ECP or GnRH.Anovulatory mares treated with ECP and GnRH exhibited estrus more frequently (54% and 70% of the time) than sham injected controls (17% and 15% of the time). Plasma LH levels were significantly elevated (P<.05) in anovulatory mares treated with GnRH. Also more follicles < 20 mm (P<.09) were detected on the ovaries of GnRH treated mares than on those of control mares. Effects of the treatment were transient since LH levels and ovarian activity were similar in both mare groups after cessation of treatment.     

Effects of repeated daily injections of prostaglandin F2α on ovaries in mares

In experiment 1, seven groups of pony mares (2 or 3/group) were given either no injections (controls), or 5(5X) or 10(10X) daily subcutaneous (SC) injections of 1.25 mg PGF_2α beginning on days 1, 7 or 13 post-ovulation. Compared to controls (24.5 days), the interovulatory interval was longer (P<.05) for day 7, 10X (33.5 days) and day 13, 10X mares (49.0 days) but was not different for the remaining groups. In experiment 2, nine groups of pony mares (4/group) were given either no injections (controls) or 1(1X) or 10(10X) daily SC injections of 1.25 mg PGF_2α beginning on day 2 of estrus or on days 1, 7 or 13 post-ovulation. Compared to controls (25.0 days), the interovulatory interval was longer (P<.05) for day 13 post-ovulation, 10X mares (40.0 days) and shorter (P<.05) for day 1 post-ovulation, 10X mares (14.5 days). The interovulatory interval for the remaining groups was not different (P>.05) from that for controls. In day 13 post-ovulation, 10X mares, the longer interovulatory interval did not appear to be related to a depression in either peripheral LH concentration (no effect of treatment on LH) or on follicular development (no effect of treatment on diameter of largest follicle). This suggests that circulating levels of gonadotropins were adequate for ovarian follicular development and ovulation and the effect of repeated daily injections of PGF_2α in preventing ovulation was likely exerted at the ovarian level directly on the follicle.     

Vaginal pH during estrus in mares

Vaginal hydrogen ion concentration of Saddlebred mares was measured throughout the behavioral estrous period. The mean pH on the day of ovulation was significantly (P=<.01) lower than on all other tested days of estrus. Follicular development and vaginal pH values in pony mares at time of slaughter were highly correlated. A significant decrease in vaginal pH values, determined through a series of carefully monitored measurements during estrus, was found to be characteristic and indicative of ovulation.     

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.     

Effects of cervical dilation and intrauterine infusions on the timing of oviductal transport of equine embryos

Equine embryos spend 5 to 6 d in the oviduct before entering the uterus as expanded blastocysts, and cannot be consistently collected nonsurgically until Day 7. Technologies such as cryopreservation and embryo splitting, which are most successful with embryos at the morula or early blastocyst stage, have not been used in mares because equine morulae and early blastocysts are located in the oviduct and cannot be recovered nonsurgically. These experiments test the hypothesis that transport of equine embryos through the oviduct can be hastened by cervical dilation or by acute, sterile endometritis induced by intrauterine oyster glycogen treatment. Cervical dilation with or without intrauterine infusion of 0.5 ml PBS on Day 4 did not appear to hasten the transport of embryos into the uterus since Day 5 uterine embryo recovery rates were not higher (P > 0.1) for mares with cervical dilation or cervical dilation plus PBS infusion vs mares receiving no treatments (0 of 5 and 0 of 5 vs 0 of 10, respectively). Intrauterine infusions of 40 ml of 1% oyster glycogen or 40 ml of PBS on Day 3 did not appear to hasten the transport of embryos into the uterus since Day 5 uterine embryo recovery rates were not higher (P > 0.1) for oyster glycogen- or PBS-treated vs untreated mares (2 of 12 and 3 of 11 vs 0 of 10, respectively). Cervical and uterine treatments on Day 3 or Day 4 and uterine lavages on Day 5 decreased (P < 0.05) Days 11 to Day 15 pregnancy rates compared with that of untreated mares. Day 11 to Day 15 pregnancy rates were 1 of 5 for mares with Day 4 cervical dilation and Day 5 uterine lavage, 1 of 5 for mares with Day 4 PBS infusion and Day 5 uterine lavage, 2 of 12 for mares with Day 3 oyster glycogen infusion and Day 5 uterine lavage, and 3 of 11 for mares with Day 3 PBS infusion and Day 5 uterine lavage vs 7 of 10 for mares that received no treatment or lavage. Cervical and uterine manipulations on Day 3 or 4 and uterine lavage on Day 5 appeared to decrease pregnancy rates by Days 11 to 15. The results of these experiments do not support the hypothesis that cervical dilation or uterine infusion hasten oviductal transport, since neither cervical manipulation nor transcervical infusion of oyster glycogen or PBS into the uterus significantly hastened the rate of embryo transport into the uterus.     

Day of cycle affects changes in equine intrauterine pressure in response to teasing

Oxytocin is released in response to teasing during both estrus and diestrus in mares, and at least during estrus, teasing results in an increase in electromyographic activity in the uterus. Exogenous oxytocin causes an increase in intrauterine pressure and prior studies have shown that this response is correlated to the day of the estrous cycle. To determine if teasing causes an increase in intrauterine pressure and if this response varies by day of the cycle, intrauterine pressure was measured while mares were teased with a stallion 2 days before ovulation, on the day ovulation was detected and 2 days after ovulation. A significant increase in intrauterine pressure was observed in response to teasing both 2 days before ovulation and on the day of ovulation, when plasma concentrations of progesterone were low. No significant increase in intrauterine pressure was observed in response to teasing 2 days after ovulation when progesterone concentrations were elevated. Management practices that include teasing or stallion exposure may be beneficial in stimulating uterine clearance mechanisms in mares during the preovulatory period.     

Body condition during pregnancy and lactation and reproductive efficiency of mares

In Experiment I, 32 mares were equally allotted to the following treatments: mares fed to A) high body condition from 90 days prepartum to foaling and maintained in high body condition to 90 days postpartum, B) high body condition from 90 days prepartum to foaling and allowed to lose body condition to 90 days postpartum, C) lose body condition from 90 days prepartum to foaling and maintained in low body condition to 90 days postpartum, and D) lose body condition from 90 days prepartum to foaling and allowed to gain weight after foaling to attain a high level of body condition by 90 days postpartum. After three cycles, pregnancy rate at 30 days postovulation was lower (P<0.05) in C mares (50%) than in those in the other three groups (100%). Maintenance of pregnancy to 90 days was also reduced (P<0.05) in C mares (25%) when compared with A, D (both 100%) and B mares (88%). Foal growth to 90 days of age was similar in all treatments. In Experiment II, 927 mares were evaluated for body condition and monitored for reproductive performance. Pregnancy rate was lower (P<0.05) and number of cycles/conception was higher (P<0.05) for barren and maiden mares entering the breeding season in thin condition and for pregnant mares foaling in thin condition (condition score less than 5.0) when compared with mares with a higher level of condition. Also, onset of estrus and ovulation appeared to be delayed in barren and maiden mares entering the breeding season in thin condition. Breeding efficiency was enhanced in mares entering the breeding season or foaling at a condition of 5.0 or above. Initial excess stores of body fat enhanced fertility. There were no detrimental effects of excess body fat stored in late gestation.     

Effects of oral treatment with N-acetylcysteine on the viscosity of intrauterine mucus and endometrial function in estrous mares

Persistent breeding-induced endometritis is ranked as the third most common medical problem in the adult mare and leads to enormous economic loss in horse breeding. In mares suffering from persistent breeding-induced endometritis, increased amounts of intrauterine (i.u.) fluid or viscous mucus in estrus or after breeding may act as a barrier for sperm and can contribute to low fertility. Current therapies of these mares aim to eliminate i.u. fluid and mucus by uterine lavage and/or administration of ecbolic drugs. Recently, i.u. administration of N-acetylcysteine (NAC) has been shown to support therapy in mares with endometritis. It was the objective of the present study to investigate effects of an oral administration of NAC on the viscosity of i.u. fluid in estrous mares. It was hypothesized that oral treatment with NAC reduces the viscosity of i.u. fluid and has a positive effect on the inflammatory response of the endometrium. Mares (n = 12) were included in the study as soon as estrus was detected (ovarian follicle >3.0 cm and endometrial edema), which was defined as Day 1. They were randomly assigned to a treatment (10 mg/kg NAC on Days 1-4) or a control group (no treatment). On days 1 and 5 i.u. mucus was collected and its rheologic properties were accessed. On Day 5, endometrial biopsies were obtained and evaluated for integrity of the luminal epithelium, number of polymorphonuclear neutrophils (PMN), staining for cyclooxygenase 2 (COX2), staining with Kiel 67 antigen (Ki-67), lectins and periodic acid Schiff (PAS). In the treatment group, viscosity of i.u. mucus increased significantly between Days 1 and 5 (P < 0.05), while no differences were found in control mares (n.s.). At no time were significant differences between treated and control mares seen. Integrity of epithelium was not affected. After NAC treatment the mean number of PMN in endometrial biopsies was significantly lower compared to mares of the control group (1.9 ± 0.3 vs. 4.8 ± 0.4; P < 0.05). Nuclear immunostaining for COX2 was significantly lower after NAC treatment compared to control mares (P < 0.05). Score for PAS and Alcain staining of mucus in deep uterine glands differed significantly between groups (both P < 0.05). We conclude that oral NAC treatment does not reduce viscosity of uterine mucus but has an antiinflammatory effect on the equine endometrium.     

Physical properties of bovine cervical mucus during normal and induced (progesterone and/or PGF2alpha) estrus

Ninety two Friesian cows were used to determine physical properties of cervical mucus collected during normal estrus and estrus induced. Estrus was induced using either progesterone (P4) releasing intravaginal devices (PRID) and/or prostaglandin F2alpha (PGF2alpha). The animals were assigned to 4 groups (no treatment, a PRID for 12 days plus an injection of 1000 IU PMSG at the removal of the PRID, a double injection of 3 mL PGF2alpha 11 days apart, and a PRID for 7 days plus an injection of PGF2alpha 24 h before the removal of PRID). A number of cows with normal estrus exhibited three consecutive estrus cycles after calving. Cows that had not shown estrus for three months after calving had their reproductive system palpated twice at 10-day intervals, to determine their ovarian activity. Then PRID and/or PGF2alpha was administered to cows that were found to have a palpable corpus luteum in one of two palpations (cycling cows). The cows of the three induced estrous groups were artificially inseminated (AI) twice, while those with normal estrus received only a single AI. Cervical mucus samples were collected from all cows 5 to 30 min before the first AI. Additionally, samples of cervical mucus were collected from 20 cows at their first estrus after the induced estrus. The results are summarized as follows: 1) The physical properties of cervical mucus were similar in the first three normal consecutive estrus cycles after calving. 2) The physical properties of cervical mucus in normal estrus after calving were similar to those in the first estrus after an induced estrus. 3) The pH values for normal estrus were similar to those for induced estrus. 4) Viscosity of cervical mucus in the normal estrous group was significantly lower than that in the induced estrus. Furthermore, significant differences were noticed among the three induced estrous groups. 5) Spinnbarkeit, crystallization and receptivity of cervical mucus (penetration test) were significantly higher in the normal estrous group than in the induced estrous groups, while no difference was detected among induced estrus groups. 6) Pregnancy rates in the normal estrus group were the same as in the induced estrus groups. 7) The percentages of cows in the induced estrous groups that produced cervical mucus with similar viscosity, spinnbarkeit and receptivity (penetration test) characteristics as the normal estrus group, was very low.     

Chemical properties of bovine cervical mucus during normal estrus and estrus induced by progesterone and/or PGF2alpha

Ninety-two Friesian cows were used to determine the chemical properties of cervical mucus during normal estrus and estrus induced by progesterone (P4)-releasing intravaginal devices (PRID) and/or prostaglandin F2alpha. The animals were assigned to 4 groups (no treatment, a PRID for 12 days plus injection of 1000 IU PMSG at the removal of PRID, a double i.m. injection of PGF2alpha 11 days apart, or PRID for 7 days plus an im injection of PGF2alpha 24 h before the removal of PRID). A number of cows with normal estrus exhibited three consecutive estrous cycles after delivery. Cows that had not shown estrus for 3 months after delivery had their ovaries palpated twice at 10-day intervals, to determine their ovarian activity. Then PRID and/or PGF2alpha was administered in cows that had a palpable corpus luteum in one of the two palpations (cyclic cows). A double artificial insemination (AI) was performed to the cows of the three induced-estrus groups, while the cows with normal estrus received only one AI. Cervical mucus samples were collected from all cows 5 to 30 min before the first AI. Additionally, samples of cervical mucus were collected from 20 cows during their first estrus after the induced one. The results are summarized as follows: 1) The biochemical properties of cervical mucus in the first three estrus periods after delivery were similar. 2) These properties were similar both in normal estrus after delivery and in the first estrus after an induced one. 3) Glucose and fructose concentrations for normal estrus were similar to those for induced estrus groups. 4) Total protein and cholesterol concentrations were significantly lower (P < 0.001) in normal than in induced estrus, while no difference was found among the induced estrus groups. 5) Pregnancy rates of the cows did not differ significantly among the normal and the induced-estrus groups. 6) The percentages of cows in the induced-estrus groups that produced cervical mucus with total protein and cholesterol concentrations similar to those for the normal estrus groups was very low.     

Assessing the usefulness of prostaglandin E2 (Cervidil) for transcervical artificial insemination in ewes

The underlying theme of this study involved the evaluation of the dilatory effects of prostaglandin E₂ on the ovine cervix and thus the assessment of its potential applicability to transcervical artificial insemination (TCAI) in ewes. A novel method of prostaglandin E₂ administration (controlled slow-release vaginal inserts) was examined, and the practical implications of this approach including cervical penetrability and posttreatment pregnancy rates were evaluated. The Guelph method of TCAI was performed during the seasonal anestrus (n = 40) and the breeding season (n = 40) on multiparous Rideau Arcott × Polled Dorset ewes, with or without the pretreatment with Cervidil (for a duration of 12 hours or 24 hours before TCAI). Cervical penetration rates averaged 82.5% (66 of 80), and they varied neither (P > 0.05) between the two seasons nor between Cervidil-treated ewes and their respective controls. Cervidil priming significantly reduced the total time required for TCAI during the breeding season in comparison with controls (54 vs. 98 seconds), especially after the 24-hour exposure (38 vs. 108 seconds). The time taken to traverse the uterine cervix was negatively correlated (P < 0.05) with the breed (percentage of Rideau Arcott genotype) and lifetime lamb production in seasonally anestrous ewes. Four out of 36 (11%) successfully penetrated ewes in the breeding season (three ewes allocated to the 12-hour control group and one ewe that had received Cervidil for 12 hours) became pregnant and carried the lambs to term. Vaginal mucus impedance at TCAI was significantly and positively correlated with the total time required to complete the procedure in cyclic ewes, and the negative correlation between vaginal mucus impedance and total time values at the time of controlled intravaginal drug release device removal approached to significance in anestrous ewes. The present results indicate a moderate benefit of using Cervidil for inducing cervical dilation before TCAI in ewes, mainly in the breeding season. The specific reason(s) for impaired fertility after the TCAI using frozen–thawed ram semen remains to be elucidated.     

The effects of cervical dilation on plasma PGFM, progesterone and the duration of luteal function in diestrous mares

Transcervical diagnostic techniques may alter the length of the equine estrous cycle and affect subsequent luteal function. Therefore, nine mares were used to determine the effect of cervical dilation on plasma 13, 14-dihydro, 15-keto-prostaglandin F(2) (PGFM), progesterone (P(4)) and posttreatment duration of luteal function. Mares were given a daily score of 0 to 4 based on sexual receptivity. Five days following the end of receptivity, mares were randomly assigned to one of three, 3 x 3 latin squares. Control mares received no cervical dilation. Cervically stimulated mares recieved cervical dilation for 60 sec. Cervically stimulated plus inhibitor mares were dilated similarly to cervically stimulated mares, but received a prostaglandin synthetase inhibitor 30 min prior to treatment. Each mare completed all three treatments in three consecutive estrous cycles. Plasma PGFM and P(4) were determined by RIA. Plasma PGFM was lower (P<0.05) in cervically stimulated plus inhibitor than control and cervically stimulated mares. In addition, plasma P(4) was lower (P<0.10) in cervically stimulated plus inhibitor than in control and cervically stimulated mares. Luteal function following treatments did not differ. These data indicate that neither plasma PGFM and P(4) nor the duration of luteal function were affected by cervical dilation. However, administration of a prostaglandin synthetase inhibitor prior to cervical dilation decreased plasma PGFM and P(4) concentrations.     

Effect of exogenous gonadal steroids and pregnancy on uterine luminal prostaglandin F in mares

Two experiments were conducted to assess the effect of exogenous hormone treatment on uterine luminal prostaglandin F (PGF). In the first experiment ovariectomized pony mares received either corn oil (21 days, n = 3), estradiol valerate (21 days, n = 3), progesterone (21 days, n = 3) or estradiol valerate (7 days) followed by progesterone (14 days, n = 4). Progesterone treated mares had higher (P<.01) uterine luminal PGF compared with all other groups, and no differences were detected between other treatment comparisons. In Experiment II, uterine fluid was collected from 4 ovariectomized horse mares before and after treatment with estradiol valerate (7 days) followed by progesterone (50 days). Pretreatment uterine luminal PGF levels were lower (P<.001) than post-treatment levels (.03 vs 76.80 ng/ml). In a third experiment PGF was measured in uterine fluid of pony mares on days 8, 12, 14, 16, 18 and 20 of the estrous cycle and pregnancy. In nonpregnant mares a day effect P<.03) was observed in which uterine fluid PGF increased during the late luteal phase and declined thereafter. In contrast, no day effect was observed in pregnant animals and uterine luminal PGF was lower (P<.001) than in cycling animals. These studies indicate that exogenous progesterone administration results in a large increase in uterine luminal PGF, whereas, pregnancy results in suppression. Taken collectively with previous work from our laboratory, these results suggest that while the endometrium of pregnant mares is capable of producing large amounts of PGF, the presence of a conceptus impedes its synthesis and/or release which allows for luteal maintenance.     

Postpartum reproductive performance in the multiparous mare fed to obesity

Twenty multiparous Quarter Horse mares were assigned to one of two treatment groups at 40 to 75 d of pregnancy. Group 1 was the control group and the mares were fed to maintain a moderate degree of body fat (condition score 5.5 to 7). Group 2 was the obese group and the mares were fed to achieve (prepartum) and then maintain (post partum) an extremely high degree of body fat (condition score 9). Estrous intensity was evaluated using subjective teasing scores ranging from 0 (rejection) to 4 (maximum receptivity). Mares were artificially inseminated beginning with the second postpartum ovulatory cycle; the study was terminated after 63 d of pregnancy. Duration of estrus, maximum teasing score and the number of mares exhibiting overt estrus (teasing score > 2) did not differ between treatment groups during the first and second postpartum ovulatory cycles. The intervals from foaling to first cycle ovulation, foaling to second cycle ovulation, and first to second cycle ovulation were also similar between treatment groups. All mares in both treatment groups conceived and maintained pregnancy. The first cycle conception rate and the number of cycles per conception did not differ between treatment groups. A high degree of body fat produced by overfeeding during gestation did not adversely affect postpartum reproductive performance in the multiparous mare.     

The reproductive cycle of the crab-eating macaque (Macaca fascicularis)

Characteristic changes in the menstrual cycle of the crab-eating macaque were evaluated. Cyclical changes in type and abundance of exfoliated cells in vaginal smears as well as the ferning pattern of cervical mucus were observed. These indices were useful in predicting approximate ovulation time. The cyclical changes in sexual skin swelling and/or coloration were detected only in adolescent females. Micro-sections from ovaries of autopsied animals revealed large Graafian follicle formations often rupturing by day fourteen of the cycle. Length of the menstrual cycle ranged from 26–38 days with a modal value of 28 days.This research has been supported by Ford Foundation Grant No. 710-0287.     

Antiluteogenic effects of serial prostaglandin F2α administration in cycling mares

A single dose of PGF2α does not consistently induce luteolysis in the equine CL until at least 5 days after ovulation, leading to the erroneous assumption that the early CL is refractory to the luteolytic effects of PGF2α. We hypothesized that serial administration of PGF2α in early diestrus would induce a return to estrus similar to mares treated with a single injection in mid-diestrus, and fertility of the induced estrus would not differ. The objectives of the study were to evaluate the effects of the 2 approaches as reflected by: (1) concentrations of plasma progesterone; (2) interovulatory and treatment-to-ovulation intervals; (3) the proportion of mares pregnant after artificial insemination. The study consisted of a balanced crossover design in which 10 reproductively normal Quarter Horse Mares were exposed to 2 treatments on 2 consecutive reproductive cycles. At detected ovulation (Day 0), mares were randomly allotted to 1 of 2 treatment groups: I, mid-diestrus treatment, administration of a single 10-mg dose of dinoprost tromethamine (PGF2α) im on Day 10; II, early diestrus treatment, administration of 10-mg PGF2α im twice daily on Days 0, 1, and 2 and once daily on Days 3 and 4. Mares in estrus and with a follicle 35 mm or greater in diameter were artificially inseminated with at least 2 billion motile sperm from a fertile stallion. Pregnancy was defined as detection of a growing embryonic vesicle on 2 consecutive examinations approximately 14 days after ovulation. Serial plasma samples were collected throughout the study period, and concentration of plasma progesterone was determined by RIA. A mixed-model ANOVA for repeated measures was used to analyze hormonal data. Interovulatory and treatment-to-ovulation intervals were compared by a paired t test and fertility by a McNemar chi-square analysis. All mares in group I underwent luteolysis after PGF2α administration denoted by mean (±SD) concentration of plasma progesterone of 0.25 ± 0.21 ng/mL detected 2 days after treatment. In group II, mean concentration of plasma progesterone remained below 1.0 ng/mL during treatment and until the onset of the next estrus. The mean interovulatory interval in group I was 18.5 ± 2.0 days compared with 13.1 ± 3.7 days in group II (P < 0.01). Treatment-to-ovulation intervals were 8.5 ± 2.0 days and 13.1 ± 3.7 days for groups I and II, respectively (P < 0.05). In both groups, 9 of 10 mares were pregnant (P = 1.0). Serial PGF2α administration beginning at ovulation consistently prevented luteal function in 10 of 10 mares in the present study without adversely affecting pregnancy rate of post-treatment cycles.