Intrauterine movement of the early conceptus in barren and postpartum mares

The equine embryonic vesicle has been shown to be highly mobile prior to day 15, moving from one horn to the other many times per day. In Experiment 1, intrauterine mobility patterns of the vesicle were compared between barren and postpartum mares on days 12, 13, or 14, using an ultrasound instrument. Location of the vesicle (left horn, right horn, body) was determined every five minutes during six two-hour trials in each group. Averaged over all trials, the vesicle moved from one horn to the other 1.1 times per two-hour trial. There were no significant differences between barren and postpartum mares in the mean number of times the vesicle changed its location or in the amount of time the vesicle spent in the left versus right horn. In postpartum mares, the number of location changes and the time spent in a horn were not different between the formerly gravid horn and the nongravid horn. The reported frequent attachment of the vesicle to the formerly nongravid horn was not, therefore, attributable to a difference in the extent of mobility or the amount of time spent in the nongravid horn during the period of high intrauterine mobility. In Experiment 2, the rate of movement of the embryonic vesicle within the uterine body on days 12 through 14 was estimated to average 3.4 mm/min (range, 0-14 mm/min), based on fixed points of reference (cranial end of cervix, uterine cysts). Using time-lapse photography at one-minute intervals, a 14-day embryonic vesicle was monitored as it approached a cyst in the lumen of the uterine body. The vesicle encroached upon the cyst, forming an indentiation in the vesicle. It then moved over the top of the cyst to the other side and continued moving in the same direction.     

Effect of reproductive status on twinning and on side of ovulation and embryo attachment in mares

Brood-farm records were used to test several hypotheses concerning twinning and inequalities in the side of ovulation and embryo attachment. Ovulation occurred more frequently (P<0.05) from the left ovary (61% versus 39%) in maiden mares, but with equal frequency from either ovary in lactating and barren mares. The embryo attached more often (P<0.05) to the left horn in lactating mares (60%) and to the right horn in barren (59%) and maiden (67%) mares. Double ovulations and twin embryos were diagnosed more frequently (P<0.05) in barren mares (11% and 6%, respectively) than in lactating mares (5% and 1%). Pregnancy rates for double ovulations were affected (P<0.01) by the length of the interval between the two ovulations (0 days, 83%; 2 days, 87%; 4 days, 67%; 6 days, 54%; 8 days or more, 38%). Pregnancy rates were higher (P<0.01) for double ovulations 0 or 2 days apart (84%) than for single ovulations (54%). Twins were diagnosed more frequently (P<0.05) when double ovulations were two or more days apart (9 32 ) than when the ovulations were synchronous (0 19 ). These results support the conclusion that an embryo-reduction mechanism exists in mares for the elimination of excess embryos and indicate that the mechanism loses its effectiveness when the embryos originate from asynchronous ovulations.     

Effects of reproductive status and management on cortisol secretion and fertility of oestrous horse mares

Stressful events may contribute to low reproductive efficiency due to glucocorticoid-mediated inhibition of hormone secretion in a variety of species. We therefore investigated effects of stress related to management of mares around artificial insemination on secretion of cortisol and fertility parameters. To avoid further disturbance of mares by frequent blood sampling, faecal cortisol metabolites (fCM) were determined instead (sample collection at 8-h intervals). A total of 50 mares (16 maiden, 17 barren, 12 foaling, 5 teaching mares) were included in the study. Mares were brought to the AI centre in vans or trailers (driving time between 30 min and 5 h). Teaching mares were housed in the clinic and had therefore not to be transported. Mares were inseminated either with fresh/cooled-shipped or frozen semen. Rectal palpations and ultrasound examinations were performed at 24- to 48-h intervals, in animals inseminated with frozen semen at 6-h intervals during the last 48 h before ovulation. In maiden, barren and foaling mares, fCM concentrations in faeces tended to be higher than in teaching mares at all times after arrival at the AI centre. At 24 and 48 h after arrival, fCM concentrations in maiden mares were significantly higher than in teaching mares (24h: maiden mares 12.3+/-3.1 ng/g, barren mares 8.5+/-1.2 ng/g, foaling mares 11.0+/-2.4 ng/g, teaching mares 3.8+/-0.6 ng/g, p<0.05). The time from arrival at the AI centre to detection of ovulation did not differ among the different groups of mares and was 4.5+/-0.4, 5.0+/-0.5, 3.8+/-0.5 and 5.6+/-0.9 days in maiden, barren, foaling and teaching mares, respectively (n.s.). Pregnancy rates were 53, 53, 55 and 60%, respectively (n.s.). The time from arrival at the AI centre to detection of ovulation was 4.4+/-0.3 days and 4.9+/-0.3 days in mares inseminated with fresh/shipped (n=39) or frozen semen (n=11; n.s.), respectively. The frequency of follicular checks influenced fCM secretion and was statistically significant at 16 h before ovulation (fresh/shipped semen: fCM 6.9+/-0.7 ng/g faeces, frozen semen: fCM 16.9+/-5.2 ng/g faeces, p<0.01). In the mare, gynaecological examinations seem to act as stressors and may increase cortisol secretion. However, this does not negatively influence fertility and in animals familiar with that procedure fCM concentrations are not elevated.     

Characterization of intrauterine mobility of the early equine conceptus

Intrauterine mobility patterns of the embryonic vesicle were characterized on Days 9 to 17 after ovulation in pony mares using real-time ultrasonography (n=5 or 7 mares per day). The location of the vesicle was determined by dividing the uterus into right horn, left horn, and body. Each uterine horn was further divided into three approximately equal portions (cranial third, middle third, caudal third), yielding seven segments (body plus three portions of each horn). Location of the vesicle within the uterus was recorded every five minutes for two consecutive hours (25 location determinations per trial). The number of times the vesicle was found in the uterine body versus one of the uterine horns was greater for the body on Day 9 (15.2 vs 9.8; not significant) and Day 10 (17.3 vs 7.7 P<0.05) and greater (P<0.05) for the horns on Days 12 (7.3 vs 17.7) through 17 (0.0 vs 25.0). Averaged over all days, when the vesicle was in one of the uterine horns it was present 56% of the time in the caudal third, 30% of the time in the middle third, and 14% of the time in the cranial third. Mobility was determined by the number of times the vesicle changed locations during successive examinations. On Day 9, the mean number of location changes per trial was minimal (horn to horn, 0.2; body to horn or vice versa, 1.8; between two segments, 4.2). The extent of mobility increased on Day 10 and reached an apparent plateau from Day 11 to Day 14. The mean number of location changes per trial during the plateau was as follows: horn to horn, 1.6; body to horn or vice versa, 5.6; between two segments, 10.7. Fixation (cessation of mobility) occurred in one of the horns in 5 7 mares on Day 15 and in 7 7 mares by Day 16. Mobility was present on the earliest day the embryonic vesicle was detected (Day 9), but Days 11 to 14 were characterized as the days of maximum mobility.     

Fixation and orientation of the early equine conceptus

Fixation and orientation of the conceptus within the uterine lumen of 40 barren mares were examined by ultrasound daily on days 11-21 and at three-day intervals thereafter until day 48. The growth curve of the in situ conceptus had a distinct plateau between days 17-24, as determined by measurements of the width and area of conceptuses on the ultrasound images. The vesicle expanded at an average daily rate of 3-4 mm before the plateau and 2-3 mm after the plateau. Dramatic changes occurred in the shape of conceptus. The predominant shapes were approximately as follows: days 11-16, spherical; day 17, oblong; days 18-21, triangular; and days 24-48, irregular. The embryo was detected in some mares on day 20 and in most mares by day 21. When first detected, the embryo was always on the ventral aspect of the vesicle, opposite to the mesometrial attachment. The embryo gradually moved toward the mesometrial attachment over days 21-36 in association with the growth of the allantois beneath the embryo. It was hypothesized that: 1) vesicle fixation (cessation of mobility) was due to increasing uterine tone with impingement of the endometrial folds upon the vesicle, and 2) vesicle orientation was due to greater strength of the yolk sac wall at the embryonal pole coupled with greater impingement upon the vesicle by the dorsal uterine wall than by the ventral wall.     

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.     

Mobility of twin embryonic vesicles in mares

The patterns of intrauterine mobility and fixation of multiple embryos were studied by ultrasonography in 33 mares with twins, six mares with more than two embryos, and 18 mares with singletons. For both single and multiple embryos, the embryonic vesicles showed a preference for the uterine body on days 11 (57% in body) and 12 (58%) and for the uterine horns on days 13 (40% in body), 14 (20%), 15 (15%), and 16 (1%). The preference for the uterine body was characteristic of vesicles that were 3 to 9 mm in diameter. Based on the number of individual embryos which were in different locations between two successive daily examinations, fixation (cessation of mobility) occurred for 97% of the embryos by day 16 and for all embryos by day 18. For 33 mares with twins, fixation involved one uterine horn in 23 mares and both horns in 10 mares (significantly different from equality). Location determinations were made every five minutes during two-hour trials on days 12, 13, or 14 in nine mares with singletons and ten mares with twins. Individual embryos of twin sets had mobility patterns similar to those of singletons. Summed over singletons and twins, the vesicles moved from one horn to another a mean of 0.9 times per two-hour trial (equivalent to 11 times per day). The smaller embryo of twin sets on the average spent more time in the uterine body, but this finding was attributed to their smaller diameter. The observed frequency with which both embryos of twin sets were simultaneously in a given segment of the uterus (28%) was greater (P<0.01) than the expected frequency if each embryo moved independently of the other (18%). Results indicated that 64% of the location changes of twin embryos occurred independently of one another, supporting the hypothesis that the embryonic vesicle plays an active role in its mobility.     

Changes in vascular perfusion of the endometrium in association with changes in location of the embryonic vesicle in mares

The equine embryonic vesicle is mobile on Days 12-14 (Day 0 = ovulation), when it is approximately 9-15 mm in diameter. Movement from one uterine horn to another occurs, on average, approximately 0.5 times per hour. Mobility ceases (fixation) on Days 15-17. Transrectal color Doppler ultrasonography was used to study the relationship of embryo mobility (experiment 1) and fixation (experiment 2) to endometrial vascular perfusion. In experiment 1, mares were bred and examined daily from Day 1 to Day 16 and were assigned, retrospectively, to a group in which an embryo was detected (pregnant mares; n = 16) or not detected (n = 8) by Day 12. Endometrial vascularity (scored 1-4, for none to maximal, respectively) did not differ on Days 1-8 between groups or between the sides with and without the corpus luteum. Endometrial vascularity scores were higher (P < 0.05) on Days 12-16 in both horns of pregnant mares compared to mares with no embryo. In pregnant mares, the scores increased (P < 0.05) between Day 10 and Day 12 in the horn with the embryo and were higher (P < 0.05) than scores in the opposite horn on Days 12-15. In experiment 2, 14 pregnant mares were examined from Day 13 to 6 days after fixation. Endometrial vascularity scores and number of colored pixels per cross-section of endometrium were greater (P < 0.05) in the endometrium surrounding the fixed vesicle than in the middle portion of the horn of fixation. Results supported the hypothesis that transient changes in endometrial vascular perfusion accompany the embryonic vesicle as the vesicle changes location during embryo mobility.     

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.     

Effects of age and altrenogest treatment on conceptus development and secretion of LH, progesterone and eCG in early-pregnant mares

The treatment of early pregnant mares with a history of repeated early embryonic loss with the progestin altrenogest has become routine; however no controlled studies on the efficiency of altrenogest to prevent embryonic losses are available so far. In the present study, we have investigated effects of altrenogest treatment in mares on conceptus development and the secretion of LH, progesterone, and eCG until day 100 of pregnancy. In addition, differences related to age of mares were assessed. Mares were treated with altrenogest (0.044 mg/kg per os once daily) or sunflower oil (10 ml per os once daily) from day 6 to day 100 after ovulation. Blood samples for analysis of LH, progesterone, and eCG were collected. The size of the embryonic vesicle and embryo/fetus was determined by ultrasound. No difference in the per cycle pregnancy rate between altrenogest-treated (75%) and sunflower oil-treated mares (74%) was detected (n.s.). A significant effect of age but not of altrenogest treatment on mean diameter of the embryonic vesicle was found between days 12 and 22 of pregnancy (e.g. day 15: control, 4-8 years: 22.9 ± 1.0 mm, >8 years: 22.0 ± 1.7 mm, altrenogest, 4-8 years: 26.1 ± 2.0 mm, >8 years: 20.4 ± 1.0 mm, P < 0.05). A significant effect of age and treatment on size of the embryo proper between days 30 and 45 was detected (P < 0.05). In the control group but not in the altrenogest group, size of the embryo proper respective fetus was negatively correlated with age of the mares (day 30: r = −0.834, P < 0.05; day 35: r = −0.506, P < 0.05). Plasma concentrations of LH and progesterone were neither effected by age nor by treatment of mares, but significant effects of age and altrenogest treatment on eCG concentrations between days 40 and 130 were detected (P < 0.05). The present study demonstrates for the first time a positive influence of altrenogest-treatment on a retarded development of the embryo respective fetus around the beginning of placentation in mares older than 8 years.     

Twinning in mares: A survey of veterinarians and analyses of theriogenology records

Responses of 22 veterinarians to a questionnaire and the records of three brood-mare farms were examined to obtain information on twinning. The incidence rates of multiple ovulations on the three farms were 9%, 11%, and 22%. The multiple ovulation rate was reduced 42-67% in foaling mares compared to barren and maiden mares. Multiple ovulations were significantly more frequent in Thoroughbreds (19%) than in Quarter Horses (9%) and Appaloosas (8%). Both the questionnaire and the farm records indicated a high degree of repeatability of multiple ovulations and twin pregnancies within mares and within certain family lines. The likelihood of multiple ovulations was approximately doubled when the preceding cycle also had multiple ovulations. On two of the farms, breeding was withheld or postponed until after the first ovulation when multiple follicles were present. There were no significant differences in overall reproductive efficiency (pregnancy and foaling rates) among the three farms and the incidence of observed twin abortions or births was low on all three farms (0.4, 0.2, and 0%, respectively).     

Transrectal color Doppler sonography of the A. uterina in cyclic mares

Color Doppler ultrasound was used transrectally in 6 mares to locate both the left and right Aa. uterinae and to obtain flow velocity waveforms at defined times (Days 0, 5, 10, 15 and 20) during 4 estrous cycles. Blood flow reflected by the resistance index (RI) was determined for both arteries on 120 occasions. As there was no significant difference and a high correlation in the RI values between the left and right arteries (paired Student's t-test, correlation coefficient r > 0.94; P < 0.05), the average RI value was used for subsequent analyses. There were correlations between RI values, mares and day of estrous cycle (P < 0.0001). The mean RI was higher (P < 0.05) in the 2 multiparous mares (age, 12 to 13 yr) than in the 4 younger maiden mares (age, 6 to 10 yr). During the estrous cycle mean RI values on Day 0 (day of ovulation) and Day 10 were higher (P < 0.05) than on Days 5, 15 and 20, whereas between estrous cycles within mares no differences (P > 0.05) could be measured. The results suggest that transrectal Color Doppler sonography is a noninvasive method for examining differences in impedance to uterine blood flow between different mares and cycle periods.     

Relationships between uterine culture, cytology and pregnancy rates in a Thoroughbred practice

Endometrial cytology and culture specimens (n=2123) were collected concurrently with a guarded uterine culture instrument from 970 mares (738 barren, 1230 foaling and 155 maiden mares) during three breeding seasons (2001-2004). Results were compared to the 28-d pregnancy rate for the cycle from which the samples were taken. Cytological smears were evaluated for inflammation at x100 and graded as: not inflammatory (0-2 neutrophils/field), moderate inflammation (2-5 neutrophils/field), severe inflammation (>5 neutrophils/field), or hypocellular (scant epithelial cells and no neutrophils). Uterine culture swabs were plated within 6h, incubated for 72 h and results determined at 24, 48, and 72 h. Approximately, 20% (n=423) cytology samples were positive for inflammation (>2 neutrophils), whereas approximately 11% (n=231) of cultures had microorganisms recovered. A majority (64%) of the positive cultures (147/231) had inflammation on cytology smears. Streptococcus equi subsp. zooepidemicus was associated with more positive cytology results than coliforms (P<0.01). Mares with positive cytology or culture had lower pregnancy rates than mares with normal findings (P<0.01). Lowest pregnancy rates were recorded for mares with severe endometrial inflammation (21%, versus moderate inflammation 48%). Isolation of a microorganism from mares with endometrial inflammation was not associated with a further reduction in pregnancy rates. In barren, foaling and maiden mares, cytology was positive in 28, 17, and 5%, respectively, and culture was positive in 12.2, 11.1, and 3.2%. Foaling and maiden mares had higher pregnancy rates than barren mares (62, 69, and 44%, respectively, P<0.001). In conclusion, a positive cytology was twice as common as a positive culture, and isolation of microorganisms was associated with reduced pregnancy rates, even in the apparent absence of inflammation.     

Equine fetal kinetics: Allantoic-fluid shifts and uterine-horn closures

Uterine filling by the conceptus and uterine constrictions and allantoic-fluid shifts after filling were studied by daily ultrasound examinations on Days 40 to 74 in 10 mares. Allantoic fluid was first detected at the extremities of the uterus on the following days: 1) tip of umbilical-cord horn, Day 60.0 +/-1.9 (mean +/-SEM); 2) tip of noncord horn, Day 64.8 +/-1.3; and 3) near cervix, Day 48.5 +/-1.3. Transient uterine constrictions with expulsion of allantoic fluid were detected in 37% of 271 examinations. Other end points were studied by weekly ultrasound examinations from Day 40 to term. Height of cross-sections of the fetal body increased (P<0.01) progressively over Monthes 2 to 8, whereas the height of placental fluid minus fetal body decreased (P<0.05) after Month 3. An increasing (P<0.05) frequency of examinations with a reclosed uterine horn occurred between Months 3 and 4. The frequency of reclosed noncord horns continued to increase (P<0.05) after Month 4 and reached 96% at Month 7. The frequency of reclosure of cord horns plateaued (no significant differences) at 54% over Months 4 to 7 and then rapidly decreased (P<0.05). Both uterine horns were closed during the examination that preceded the permanent entry of the fetal hind limbs into the cord horn in all of 9 mares in which this temporal relationship was studied. After entry of the fetal hind limbs, the cord horn remained constricted upon the limbs until at least Month 10. The results provide rationale for the following hypotheses: 1) The gradual decrease in fetal mobility (location and presentation changes) previously reported for Months 4 to 8 is associated with growth of the fetus and a concomitant decrease in volume of allantoic fluid and number of open uterine segments; 2) Closure of both uterine horns near mid-pregnancy plays a role in final selection of cranial fetal presentation followed by entry of the fetal hind limbs into the cord horn.     

Mobility of the conceptus and uterine contractions in the mare

Location of the embryonic vesicle within the uterus of mares was recorded every. five minutes for two consecutive hours (25 location determinations per trial) in three experiments. In Experiment 1 (n=7), the number of location changes among nine uterine segments (three body segments and three segments for each horn) was greater (P<0.05) on Day 13 than on Day 10. The vesicle was located in the body more frequently (P<0.05) and tended (P<0.1) to move to a more caudal position more frequently on Day 10 than on Day 13. Fixation occurred on Day 15 in four of seven mares and on Day 16 in the remaining three mares. The number of location changes was not significantly different between two days prior to fixation and one day prior to fixation. In Experiment 2, the effect of clenbuterol, a B₂ sympathomimetic blocker of uterine contractions, was studied on Days 12 or 13 of pregnancy. Location changes occurred less frequently (P<0.05) in treated mares (n=9) than in controls (n=10), indicating involvement of uterine contractions in the mobility of the embryonic vesicle. In Experiment 3, when the initial direction of location changes was caudal within a horn and cranial within the uterine body, the vesicle was more likely (P<0.05) to continue moving in the same direction than in the opposite direction. However, when the direction within a horn was cranial, the next location change was as likely to be in the opposite direction as in the same direction (not significantly different from equality). When the direction within the uterine body was caudal, the next location change was more likely (P<0.05) to be in the opposite direction.     

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.     

Effects of day of estrous cycle, time of day, luteolysis, and embryo on uterine contractility in mares

One-minute continuous ultrasonic scans of longitudinal sections of the uterine body were videotaped, and contractility scores (1 to 5, minimal to maximal contractility) were assigned without knowledge of mare identity, day of the estrous cycle or pregnancy status. Contractility was assessed, and plasma progesterone concentrations were determined for each of 3 daily examinations (at 0800, 1600 and 2400 hours) from Day 9 to Day 19 (Day 0 = day of ovulation). For both the nonbred (n=11) and pregnant (n=11) mares, there was no effect of hour of scan on the extent of uterine contractility. When data for the nonbred mares were normalized to the onset of luteolysis (defined for each mare as the first >/=25% decrease in plasma progesterone concentrations between successive samples), there was an abrupt increase (P<0.05) in contractility 24 hours prior to the onset of luteolysis. Contractility was also assessed daily in 20 nonbred and 27 pregnant mares from Day 0 to Day 17. For the nonbred mares, a biphasic profile in contractility occurred during the estrous cycle as indicated by the following significant changes: a decrease between Days 0 and 2, an increase between Days 2 and 4, a plateau between Days 4 and 7, a decrease between Days 7 and 11, an increase between Days 11 and 13, and a decrease between Days 14 and 16. For pregnant mares, contractility increased (P<0.05) prior to the late-diestrous increase for nonbred mares. In addition, a significant reduction in contractility was detected on Day 5 in these mares compared with that in the nonbred mares. Contractility in the uterine body in 7 mares was assessed every 5 minutes after departure of the embryonic vesicle from the uterine body. Levels of contractility in the uterine body were lower (P<0.05) 55 minutes after the vesicle had exited the body than 相似文献   

Equine fetal kinetics: entry and retention of fetal hind limbs in a uterine horn

Transrectal ultrasonic examinations were made in 31 pregnant pony mares once a week during Months 6 to 11. Each uterine horn was divided into 3 approximately equal segments (caudal, middle, cranial). The percentage of examinations with cranial fetal presentation increased (P<0.05) progressively from 58% at Month 6 to 99% at Month 9 and was followed in all mares by entry of the fetal hind limbs into one uterine horn. The mean number of uterinehorn segments with limb parts increased (P<0.05) between each set of consecutive months from Month 6 to Month 10. Initially (Months 7 and 8), retraction of limbs after entry into the caudal and middle segments of the horn was common (31% incidence). The mean day of final entry of the limbs without detection of subsequent retraction was Day 230 +/- 2.2. Both uterine horns were closed during the examination preceding final entry of the hind limbs into one horn in 25 of 29 (86%) mares. The limbs reached the cranial segment in most examinations by Months 9 and 10 (73% and 98%). The cross-sectional height, as seen on the ultrasound screen, of both uterine horns increased (P<0.05) progressively during Months 7 to 10. Between Months 10 and 11, the height of the horn containing the limbs decreased (P<0.05); this result was attributable to a flattening of the horn and thinning (P<0.05) of the horn wall above a hoof and metatarsal bone. Apparent placental fluid (nonechogenic areas >5 mm in height) between the hind limbs and the cornual wall was detected in 0, 10, 25, and 63% (P<0.01) of examinations for Months 8 to 11, respectively. Results indicated that entry of the fetal hind limbs into a uterine horn was initially tentative and became final during a mean of Month 8. The apposition between the cornual wall and limbs was close during Months 7 to 11. By Month 11, the fetal-limb horn became flatter and thin-walled and usually contained placental fluid.     

Transrectal Doppler sonography of uterine blood flow during early pregnancy in mares

Transrectal color Doppler sonography was used for the noninvasive investigation of uterine blood flow in five mares. Both the left and right uterine arteries were scanned to obtain blood flow velocity waveforms during two consecutive estrous cycles and two early pregnancies in each mare. Blood flow was expressed as the time-averaged maximum velocity (TAMV) and the resistance index (RI). In all pregnancies the embryonic vesicle could be detected for the first time on Day 11 (day of ovulation: Day 0). No differences in mean TAMV and RI values of both uterine arteries were observed in comparison to the corresponding days of the estrous cycle until Day 11 of pregnancy (P>0.05). From Day 11 onwards, mean TAMV values were higher and mean RI values lower in pregnant mares than in cyclic mares (P<0.05). During the estrous cycle TAMV and RI values did not differ between the right and left uterine arteries (P>0.05). From Days 15 to 29 of pregnancy, TAMV values were consistently higher and RI values lower in the uterine artery ipsilateral to the conceptus and they had a more distinct rise and decline, respectively, compared to the contralateral uterine artery (P<0.05). The variance component estimates for the effect of mare on TAMV and RI values during pregnancy were 60 and 53%, respectively, and for the effect of day of pregnancy, they were 29 and 34%, respectively (P<0.0001). Within mares there were no significant differences between the two pregnancies with regard to blood flow (P>0.05). The results show that uterine blood supply increases in mares during the second week of pregnancy compared to cyclic mares. Furthermore there are individual variations in blood flow between mares.     

Ultrasonic anatomy of equine ovaries

A linear-array ultrasound scanner with a 5-MHz transducer was evaluated for studying follicular and luteal status in mares, and the ultrasonic properties of equine ovaries were characterized. Follicular diameters were estimated in vivo and after removing and slicing six ovaries. Correlation coefficients between the two kinds of determinations were 0.91 for number of follicles >/=2 mm in diameter and 0.95 for diameter of largest follicle. The ovaries of five mares were examined daily until all mares had been examined from three days before an ovulation to three days after the next ovulation. There was a significant difference among days for diameter of largest follicle and second largest follicle and for number of follicles 2-5 mm, 16-20 mm, and >20 mm. Differences seemed to be caused by the presence of many 2- to 5-mm follicles during early diestrus, initiation of growth of large follicles at mid-cycle, selective accelerated growth of an ovulatory follicle beginning five days before ovulation, and regression of large nonovulatory follicles a few days before ovulation. In one of the five mares, the corpus luteum was identified throughout the interovulatory interval, and the corresponding corpus albicans was identified for three days after the second ovulation. In the other four mares, the corpus luteum was last identified an average of 16 days after ovulation or five days before the next ovulation. In a blind study, the location of the corpus luteum (left or right ovary) as determined by ultrasonography agreed with a previous determination of side of ovulation by palpation in 88% of 40 mares on days 0-14. In the remaining 12% and in all of 12 estrous mares, the location was recorded as uncertain. The ultrasound instrument was judged effective for monitoring and evaluating follicles and corpora lutea.