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Intrauterine movement of the early conceptus in barren and postpartum mares
THERIOCENOLOGY INTKAUTERINE MOVEMENT OF THE EARLY CONCEPTUS IN BARREN AND POSTPARTUM MARES
O.J.
Ginther
Department of Veterinary Science University of Wisconsin-Madison Madison, Wisconsin 53706
Received
for publication: Accepted:
October 3, 1983 February 24, 1984
ABSTRACT 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 In postpartum time the vesicle spent in the left versus right horn. 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 In Experiment 2, the during the period of high intrauterine mobility. 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, O-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 indentation in the vesicle. It then moved over the top of the cyst to the other side and continued moving in the same direction.
Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and by an equine research fund Animals, administered by the University of Wisconsin Foundation. facilities, supplies, and equipment were provided by Equiculture, Inc., Cross Plains, Wisconsin. The authors thank Mr. Fred A. Chavez and Mr. Owen Parker, Fischer Imaging Corp., Schiller Park, Illinois, for Technical their advice and cooperation and for the use of the Vetscan. assistance was provided by Debbie Edwards, Matthew Ginther, Anita Ginther, and Julie Lawrence.
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THERIOGENOLOGY INTRODUCTION Ovulation, and therefore entry of the blastocyst into the uterus, occurred with equal frequency on the left and right sides in barren and postpartum mares, but with greater frequency (63%) on the left side in maiden mares (1). Kegardless of the side of entry into the uterus, the embryonic vesicle attached more frequently in the right uterine horn in Imaiden mares (67%) and barren mares (59%). The incidence of attachment in the right horn was greater in maiden mares than in barren mares. In occurred more frequently in the left horn postpartum mares, attachment The greater frequency of left-side attachment in postpartum (60%; 132). mares has been attributed (2) to a preference for attachment to the formerly nongravid horn (3,4,5), since mares that were classified as barren or maiden during the previous pregnancy have a higher incidence of right-side attachment. The frequent attachment in the uterine horn opposite the side of ovulation did not involve simple, one-way transuterine migration. Instead, transuterine movement occurred frequently at intervals of less than two to four hours between days 11 and 15 (1). Mobility then began to decrease in association with intrauterine fixation of the conceptus so that movement was no longer detected after day 16 (6). In the initial study (l), vesicle mobility was monitored by an ultrasound instrument every two to four hours, and the location was recorded as Mobility within horns was not studied and left or right horn. identification of the uterine body as a location was not attempted. Subsequent work with the ultrasound instrument, however, indicated that the uterine body and cervix could be identified (7). mobility patterns of the embryonic In Experiment 1, intrauterine vesicle were compared between barren and postpartum mares. The objective was to determine whether differences in mobility within the uterine horns on days 12 through 14 could account for preferred attachment to the left horn or to the formerly nongravid horn. In Experiment 2, the possibility was evaluated of studying mobility in more detail by arbitrarily dividing each uterine horn into segments or by using fixed reference points (cranial end of cervix, uterine cysts). Through the use of the fixed reference points, the rate of movement of the embryonic vesicle within the uterine body was estimated. MATERIALS
AND METHODS
The mares were primarily of Quarter Horse or Appaloosa breeding. The barren mares were pregnant the previous year but were aborted at three to four months as part of another project. In the postpartum mares, the ovulation that resulted in pregnancy occurred 10 to 50 days The day of ovulation was determined by daily ultraafter parturition. sound examination supplemented when indicated by rectal palpation (8). Mares were bred by natural mating and were examined by ultrasound for the presence of an embryonic vesicle on days 12 through 14 after ovulation as described (1,6). Ultrasonic Imaging Corp.,
634
examinations were done with a Fischer Schiller Park, Illinois). The Vetscan
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Vetscan (Fischer is a sequential
1984 VOL. 21 NO. 4
THERIOGENOLOGY linear-array scanner that produces a real-time, B-mode image. It was equipped with a ~-MHZ transducer designed for insertion into the rectum of horses. The uterine body was examined in longitudinal planes as the transducer was being inserted into the rectum. The transducer was moved slightly from side to side so that the entire width of the body was examined. When the corpus-cornual junction was reached, the transducer was moved laterally along one uterine horn so that the horn was examined in transverse planes. The horn was then re-examined as the transducer was returned toward the midline. The opposite horn was similarly examined. The uterine body was scanned again as the probe was being removed. Photographic images were made with a 35-mm camera attachment using Plus-X Panchromatic film (Eastman Kodak Co., Rochester, New York). Experiment 1. Six trial periods on days 12, 13, or 14 of pregnancy in four horses were used for each reproductive status (barren and postpartum). In the postpartum mares, the formerly gravid horn was defined as the one that contained the fetus at term and was selected on the basis of larger diameter of the uterine horn at 5 to 14 days after parturition. Each trial was two hours in length and consisted of 25 determinations (one every five minutes) of the intrauterine location of the embryonic vesicle. The five-minute interval was because a preliminary study in which the vesicle was continuously observed indicated that the vesicle usually remained in a segment for longer than five minutes (1). The principal locations were left uterine horn, right uterine horn, or uterine body. In addition, each uterine horn was divided into three approximately equal segments (cranial, middle, caudal). When an embryonic vesicle was found in a horn, the transducer was moved from the vesicle towards each end of the horn; the appropriate segment was identified by estimating the relative distance between the vesicle and each end. Factorial analyses of variance ( 2 x 2) were used to examine the data for differences between barren and postpartum mares in the mean number of changes in location per two-hour trial and in the number of determinations in which the vesicle was in a given location. Experiment 2. points and The study on using fixed reference estimating rate of movement of the embryonic vesicle w a s done with three mares (one barren and two postpartum) from Experiment 1 and three additional mares (two barren and one postpartum). The additional postpartum mare was selected because of the presence of a cystic complex on The largest cyst was 26 mm wide the ventral aspect of the uterine body. and was estimated by ultrasound to be 60 mm from the cranial end of the cervix and 50 mm from the corpus-cornual junction. The cervix was used as a reference point to calculate the rate of movement of the vesicle within the uterine body for seven series of determinations in six mares. Mares in which the ultrasound image of the The distance from vesicle to cervix was well defined were selected. cervix was measured every five minutes while the vesicle was in the body. In four series in two mares with a cyst in the uterine body, the rate of movement of the vesicle was determined by measuring the distance from the vesicle to the nearest end of the cyst or to the cranial end of the cervix. The mean rate of movement was calculated in millimeters of The movement per minute averaged over all five-minute observations.
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THERIOGENOLOGY distance traversed between two consecutive determinations was used in the calculations without regard to the nature of the movement between determinations (e.g., changes in direction) or during the previous interval. In two mares, the vesicle was also observed continuously for 15 and 16 minutes, and its location was recorded once each minute. During the day-14 observation period in the mare with the large uterine cyst, the vesicle approached the cyst with both the cyst and vesicle in the same longitudinal plane. The vesicle was observed continuously to determine the outcome of the interaction between the vesicle and cyst. Time-lapse photography at one-minute intervals was used to document the result. In two mares, each uterine horn was divided into three segments as in Experiment 1. In one of the mares the uterine body was also divided into three approximately equal segments by estimating the distance from the corpus-cornual junction to the cranial end of the cervix. For illustrative purposes, the results for the two mares were plotted on a uterine diagram, indicating the length of time the vesicle spent in each segment. RESULTS Experiment 1. Averaged over the 12 two-hour trials, the number of location changesper two hours was as follows: 1) from one horn to another, 1.1; 2) from a horn to the body or vice versa, 3.2; and 3) from one of the seven locations (body plus three segments of each horn) to another, 8.8. There were no differences between barren and postpartum mares on days 12 through 14 in the number of times per two-hour trial in which the embryonic vesicle was found in the left versus right uterine horn (no significant main effects or interaction; Table 1). The right horn was the formerly gravid horn in all of the postpartum mares. The number of determinations in which the vesicle was found in the uterine body versus either horn was greater (P
636
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THERIOGENOLOGY
TABLE 1.
Mean (+SEM) number of location changes and number of times per two-hour trial that the embryonic vesicle was in a given location of the uterus in barren and postpartum mares.a
Reproductive statusC End point
Barren
Postpartum
Number of location changes One horn to another Horn to body or Among seven locations vice-Eersa
1.3 to.2 3.8 il.1 9.5 +l.O
0.8 20.2 2.5 20.9 8.0 il.0
9.5 +1.4 8.2 il.6 17.7 21.4
13.0 t1.8 8.8 i2.6 21.8 +1.4
7.3 +1.2
3.2 21.4
Number of times vesicle was in: A uterine horn Left horn Right horn Either horn Uterine body
aLocation determinations were made euery five minutes during Six trial each two-hour trial (25 determinations/2 hours). periods in four mres on days 12, 13, or 14 for each reproductive status. The right horn was the formerly gravid horn 7:n ai!1 postpartum mares. buterine
body and cranial,
middle,
and caudal one-third
of each
horn.
‘There wan no significant difference between barren and postpartum was in the uterine groups for any end point, except the vesicZe body more often fPcO.05) in barren mzres than in postpartum mares.
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TABLE
2.
Rate of movement bodya.
of the embryonic
vesicle
within
Rate Reference point
No. mares
Five-min
intervals
between
No. series
No. intervals
the uterine
of movement
Per interval
(mm)
Per minute Mean Range
determinations
Cervix
(Group
1)
4
5
27
17.3
3.5
o-14
Cervix
(Group
2)b
2
2
7
22.7
4.5
o-12
-2
-4
-24
14.5 ---
2.9
o-9
8
11
58
16.8
3.4
o-14
31
6.7
6.7
O-30
cyst TOTALS One-min
interval
Cervix
between
(Group
2)b
determinations 2
2
aLocation detemninationswere made on days 12, 13, or 14. b
638
Group 2 intervals were from determinationsmade every minute. The data for the five-minute intervalswere obtained. by using the intervalsbetween every fifth determination.
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THERIOGENOLOGY
Mare
15
C
0 5.10 .~.,..,..,,~,,,,,.,,. ILPI
ha:0 I I
0
45.50 )b
25.&zLt!
IO
20
$0
40
50
60
7-O
80
90
160
1;o
mm from cervix /p
UTERINE BODY -/
pigum 1. DiagMmmatic profiles showing the location of the embryonic vesicle in the uterine body at eack sequential determination in three rapes. The first location determination was made at time 0, and sequential detemtinations tiere mde every minute (mares A and BI or The cranial end of tke cervix ms used as every five minutes lnrare Cl. the point of reference. RM = right middle (vesicle in middle segment of right horn); LP = left posterior.
?4ovementof a day-24 vesicZe away from tke cervix skc6Ii-z FQurS2. at one-minute intervals. Tke cranial end of the cervix is the echogenic (white) area on the right, and the vesicle is tke noneckogenic (black), spherical area sham within the uterine body (gray area delineated Zorsatly and ventrally by a brigkt white line).
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-cm F+JWe3. Photognzphstaken at five-minute intervals to show movement of a day-12 vesicle in the uterine body using a cystic complex and the cervix as referencepoints. The number in the Lower-right corner of each image is the number of minutes from beginning of the The cyst was approximately50 mm from the corpus-cornual sequence. junction and 60 mm from the cervix. At the first Zocation determination (min:O), the embryonic vesicle (upper central portion of image) is near the caudal end of the cyst. The location at each subsequentdeter10 mm caudd to cyst; 10 minutes, 5 mination was as follows: 5 minutes, mm caudal to cyst; 15 minutes, 53 mm caudal to cyst (not shown) and 7 mm cranial to cervix (white area to the right of the vesicle);20 minutes, 8 mm cranial to cyst; 25 minutes, in caudal portion of left horn.
640
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PQure4. Sequentialphotographssho&ng movement of a day-14 vesicle over a cyst (same mare as in Figure 31. The number in tower right corner of each image is the number of minutes from the beginning of the sequence. At the initial determination(min:Ol,the vesicle uas in the caudal portion of the left horn. Tke cyst is skoun (upper central image) on the ventral aspect of the uterine body with its cranial edge located 50 runfrom tke corpus-cornualjunction. The relationshipof the vesicle to the cyst at each sequentialdetermination was as follows: 5 minutes, approachingcyst: 6 minutes, beginning to encroach; 7 minutes, beginning to move over the top; 8 minutes, on top; 9 minutes, moving down the other side; 10 minutes, moving away; 11 minutes, continuingto move atiay.
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piguw 5. Sequential segments of the uterus in every five minutes for two number of minutes that the depicted on the right, the into segments.
location of embryonic vesicle in various two mares. Location determinations were made The numbers at each position are the hours. vesicle spent in each segment. Iq the mZre uterine body as well as the horns 13as divided
The number of minutes the vesicle spent in a given location (Figure 4). of the uterus for the two mares in which each uterine horn and the uterine body were divided into segments are shown diagrammatically (Figure 5). DISCUSSION The high rate of intraluminal mobility of the embryonic vesicle on The vesicles moved from one horn to days 12 through 14 was confirmed. another an average of 1.1 times per two-hour trial. Assuming the twohour period was representative for a 24-hour day, the vesicles moved from one horn to another an average of 13 times per day. No differences were detected in mobility patterns of the vesicle that could account for preferential fixation in-the right horn in barren mares and the left Furthermore, no difference was found in the horn in postpartum mares. amount of time the vesicle spent in the gravid versus the nongravid horn The days studied (days 12 through 14) preceded the in postpartum mares. days that fixation of the vesicle has been found (1) to occur (days 15 Although conclusions must be guarded because of the small through 17).
642
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THERIOGENOLOGY number of mares, it appears that selection of the horn in which fixation will occur is not a function of mobility patterns or the amount of time the vesicle spends in a horn prior to day 15. These results are consistent with the hypothesis (2) that the vesicle usually becomes fixed in the horn that offers the most intraluminal resistance to mobility after the conceptus reaches a critical diameter on days 15 through 17. In other words, resistance to mobility of the expanding vesicle, and therefore the probability of fixation, is greater in the right horn in maiden mares; disproportionate hypertrophy of the two horns during pregnancy reduces the extent of the inequality in resistance in barren mares and changes the direction of this inequality in postpartum mares. The finding that the vesicle was present in the body more often in the barren mares (29% of the determinations) than in the postpartum mares (13%) was unexpected and no interpretation is offered. Direct measurements of the rate of movement of the vesicle were limited to the uterine body since the body, but not the horns, was viewed in longitudinal planes. In addition, the cervix provided a conThe average movevenient point of reference for [measuring distances. ment rate was 3.4 mm/minute; however, the rate was highly variable, ranging from 0 to 70 mm between five-minute determinations and 0 to 30 mm between one-minute determinations. Rapid point-to-point movement was also noted in two mares which were being monitored continuously but which were not part of either experiment. In these mares, the vesicle moved from a point 5 mm and 27 mm cranial to the cervix, respectively, to the caudal portion of the left horn in approximately two minutes. The rate of movement was approximately 45 and 30 mm/min for the two mares. Rapid Imovement seemed to occur more often in the middle onethird of the uterine body (Figure 1). Changes in direction or remaining in place for prolonged periods of time were not noted to occur in the middle one-third but occurred frequently in the caudal one-third. Altnough this observation requires confirmation, the body may turn in a ventral direction in the caudal portion (9), resulting in additional Sometimes the vesicle progressed in a given resistance to movement. direction until an extremity (cervix, tip of a horn) was reached, whereas at other times reversals in direction occurred in other areas (Figures 1 and 5). Passage of the vesicle from one horn to the other without traversing the length of the uterine body occurred frequently. In the vesicles that were observed continuously, there appeared to be some Imovement back and forth, but with an overall progression in a given direction. This probably accounted for the greater rate of movement when determindtions were made every minute (6.7 mm/min) than when the same data were examined every five minutes (4.5 mm/min). The mechanisms involved in the intrauterine mobility of the It is likely, however, that uterine embryonic vesicle are not known. contractions serve as the propulsive force. Expansion and contraction of the larger vesicles (day 14) were observed in the uterine body (compare the image at five minutes with the image at 11 minutes in Such contractions occurred every 5 to 14 seconds during two Figure 4). of the vesicle also observed series in two mares. However, contraction occurred under pressure when the transducer was deliberately pushed down Although the periodic contractions described against the uterine body.
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THERIOGENOLOGY above seemed to be due to local uterine forces rather than external pressures (e.g., pressure from transducer, movement of intestines), more critical methodology will be needed to establish the existence and cause of periodic contraction and expansion of the vesicles. The sequential recordings which showed the movement of an embryonic vesicle over a cyst (Figure 4), however, indicate that the vesicle is sometimes subjected to In addition, ultrasonographic studies considerable propulsive force. (7) indicated that the endometrial folds are in close contact, so that The vesicle apparently must be forced through the lumen is obliterated. The longitudinal orientation of the folds (9) may be the folds. important in this regard. Although the propulsive force may come from the uterine myometrium, the vesicle itself may stimulate the appropriate The principal rationale for this untested uterine contractions. hypothesis is the limited observations (1) that many of the movements of a set of twin vesicles appeared to occur independently of each other. REFERENCES
1.
Ginther, O.J. Theriogenology
Mobility
-19:603-611
of the early (1983).
equine
conceptus.
2.
Ginther, O.J. Effect of reproductive status on twinning and on side of ovulation and embryo attachment in mares. Theriogenology 20:383-395 (1983). -
3.
Contralateral implantation in mares Feo, J.C.S.A. Vet. Rec. 106:368 (1980). post partum oestrus.
4.
Allen, W.E. and Newcombe, J.R. Relationship between early pregnancy site in consecutive gestations in mares. Equine (1981). -13:51-52
mated
5.
Transuterine migration of the Pascoe, R.R. between day 42 and parturition. J. Reprod. 446 (1979).
6.
Fixation and orientation of the early Ginther, O.J. Theriogenology 19:613-623 (1983). conceptus. -
7.
Ginther, O.J. of the equine
8.
Ginther, ovaries.
9.
Reproductive Biology of the Mare: Ginther, O.J. Equiservices, 4343 Garfoot Road, Cross Aspects. 1979, pp. 4 and 21.
644
during
Vet.
J.
fetus in the mare Fert., Suppl. -32:441equine
and Pierson, R.A. Ultrasonic anatomy and pathology Theriogenology g:505-516 (1984). uterus.
Ultrasonic O.J. and Pierson, R.A. Theriogenology (1984). -21:471-483
anatomy
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of equine
Basic and Applied Plains, Wisconsin,
1984 VOL. 21 NO. 4
O.J.
Ginther
Department of Veterinary Science University of Wisconsin-Madison Madison, Wisconsin 53706
Received
for publication: Accepted:
October 3, 1983 February 24, 1984
ABSTRACT 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 In postpartum time the vesicle spent in the left versus right horn. 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 In Experiment 2, the during the period of high intrauterine mobility. 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, O-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 indentation in the vesicle. It then moved over the top of the cyst to the other side and continued moving in the same direction.
Supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and by an equine research fund Animals, administered by the University of Wisconsin Foundation. facilities, supplies, and equipment were provided by Equiculture, Inc., Cross Plains, Wisconsin. The authors thank Mr. Fred A. Chavez and Mr. Owen Parker, Fischer Imaging Corp., Schiller Park, Illinois, for Technical their advice and cooperation and for the use of the Vetscan. assistance was provided by Debbie Edwards, Matthew Ginther, Anita Ginther, and Julie Lawrence.
APRIL 1984 VOL. 21 NO. 4
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THERIOGENOLOGY INTRODUCTION Ovulation, and therefore entry of the blastocyst into the uterus, occurred with equal frequency on the left and right sides in barren and postpartum mares, but with greater frequency (63%) on the left side in maiden mares (1). Kegardless of the side of entry into the uterus, the embryonic vesicle attached more frequently in the right uterine horn in Imaiden mares (67%) and barren mares (59%). The incidence of attachment in the right horn was greater in maiden mares than in barren mares. In occurred more frequently in the left horn postpartum mares, attachment The greater frequency of left-side attachment in postpartum (60%; 132). mares has been attributed (2) to a preference for attachment to the formerly nongravid horn (3,4,5), since mares that were classified as barren or maiden during the previous pregnancy have a higher incidence of right-side attachment. The frequent attachment in the uterine horn opposite the side of ovulation did not involve simple, one-way transuterine migration. Instead, transuterine movement occurred frequently at intervals of less than two to four hours between days 11 and 15 (1). Mobility then began to decrease in association with intrauterine fixation of the conceptus so that movement was no longer detected after day 16 (6). In the initial study (l), vesicle mobility was monitored by an ultrasound instrument every two to four hours, and the location was recorded as Mobility within horns was not studied and left or right horn. identification of the uterine body as a location was not attempted. Subsequent work with the ultrasound instrument, however, indicated that the uterine body and cervix could be identified (7). mobility patterns of the embryonic In Experiment 1, intrauterine vesicle were compared between barren and postpartum mares. The objective was to determine whether differences in mobility within the uterine horns on days 12 through 14 could account for preferred attachment to the left horn or to the formerly nongravid horn. In Experiment 2, the possibility was evaluated of studying mobility in more detail by arbitrarily dividing each uterine horn into segments or by using fixed reference points (cranial end of cervix, uterine cysts). Through the use of the fixed reference points, the rate of movement of the embryonic vesicle within the uterine body was estimated. MATERIALS
AND METHODS
The mares were primarily of Quarter Horse or Appaloosa breeding. The barren mares were pregnant the previous year but were aborted at three to four months as part of another project. In the postpartum mares, the ovulation that resulted in pregnancy occurred 10 to 50 days The day of ovulation was determined by daily ultraafter parturition. sound examination supplemented when indicated by rectal palpation (8). Mares were bred by natural mating and were examined by ultrasound for the presence of an embryonic vesicle on days 12 through 14 after ovulation as described (1,6). Ultrasonic Imaging Corp.,
634
examinations were done with a Fischer Schiller Park, Illinois). The Vetscan
APRIL
Vetscan (Fischer is a sequential
1984 VOL. 21 NO. 4
THERIOGENOLOGY linear-array scanner that produces a real-time, B-mode image. It was equipped with a ~-MHZ transducer designed for insertion into the rectum of horses. The uterine body was examined in longitudinal planes as the transducer was being inserted into the rectum. The transducer was moved slightly from side to side so that the entire width of the body was examined. When the corpus-cornual junction was reached, the transducer was moved laterally along one uterine horn so that the horn was examined in transverse planes. The horn was then re-examined as the transducer was returned toward the midline. The opposite horn was similarly examined. The uterine body was scanned again as the probe was being removed. Photographic images were made with a 35-mm camera attachment using Plus-X Panchromatic film (Eastman Kodak Co., Rochester, New York). Experiment 1. Six trial periods on days 12, 13, or 14 of pregnancy in four horses were used for each reproductive status (barren and postpartum). In the postpartum mares, the formerly gravid horn was defined as the one that contained the fetus at term and was selected on the basis of larger diameter of the uterine horn at 5 to 14 days after parturition. Each trial was two hours in length and consisted of 25 determinations (one every five minutes) of the intrauterine location of the embryonic vesicle. The five-minute interval was because a preliminary study in which the vesicle was continuously observed indicated that the vesicle usually remained in a segment for longer than five minutes (1). The principal locations were left uterine horn, right uterine horn, or uterine body. In addition, each uterine horn was divided into three approximately equal segments (cranial, middle, caudal). When an embryonic vesicle was found in a horn, the transducer was moved from the vesicle towards each end of the horn; the appropriate segment was identified by estimating the relative distance between the vesicle and each end. Factorial analyses of variance ( 2 x 2) were used to examine the data for differences between barren and postpartum mares in the mean number of changes in location per two-hour trial and in the number of determinations in which the vesicle was in a given location. Experiment 2. points and The study on using fixed reference estimating rate of movement of the embryonic vesicle w a s done with three mares (one barren and two postpartum) from Experiment 1 and three additional mares (two barren and one postpartum). The additional postpartum mare was selected because of the presence of a cystic complex on The largest cyst was 26 mm wide the ventral aspect of the uterine body. and was estimated by ultrasound to be 60 mm from the cranial end of the cervix and 50 mm from the corpus-cornual junction. The cervix was used as a reference point to calculate the rate of movement of the vesicle within the uterine body for seven series of determinations in six mares. Mares in which the ultrasound image of the The distance from vesicle to cervix was well defined were selected. cervix was measured every five minutes while the vesicle was in the body. In four series in two mares with a cyst in the uterine body, the rate of movement of the vesicle was determined by measuring the distance from the vesicle to the nearest end of the cyst or to the cranial end of the cervix. The mean rate of movement was calculated in millimeters of The movement per minute averaged over all five-minute observations.
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THERIOGENOLOGY distance traversed between two consecutive determinations was used in the calculations without regard to the nature of the movement between determinations (e.g., changes in direction) or during the previous interval. In two mares, the vesicle was also observed continuously for 15 and 16 minutes, and its location was recorded once each minute. During the day-14 observation period in the mare with the large uterine cyst, the vesicle approached the cyst with both the cyst and vesicle in the same longitudinal plane. The vesicle was observed continuously to determine the outcome of the interaction between the vesicle and cyst. Time-lapse photography at one-minute intervals was used to document the result. In two mares, each uterine horn was divided into three segments as in Experiment 1. In one of the mares the uterine body was also divided into three approximately equal segments by estimating the distance from the corpus-cornual junction to the cranial end of the cervix. For illustrative purposes, the results for the two mares were plotted on a uterine diagram, indicating the length of time the vesicle spent in each segment. RESULTS Experiment 1. Averaged over the 12 two-hour trials, the number of location changesper two hours was as follows: 1) from one horn to another, 1.1; 2) from a horn to the body or vice versa, 3.2; and 3) from one of the seven locations (body plus three segments of each horn) to another, 8.8. There were no differences between barren and postpartum mares on days 12 through 14 in the number of times per two-hour trial in which the embryonic vesicle was found in the left versus right uterine horn (no significant main effects or interaction; Table 1). The right horn was the formerly gravid horn in all of the postpartum mares. The number of determinations in which the vesicle was found in the uterine body versus either horn was greater (P
636
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TABLE 1.
Mean (+SEM) number of location changes and number of times per two-hour trial that the embryonic vesicle was in a given location of the uterus in barren and postpartum mares.a
Reproductive statusC End point
Barren
Postpartum
Number of location changes One horn to another Horn to body or Among seven locations vice-Eersa
1.3 to.2 3.8 il.1 9.5 +l.O
0.8 20.2 2.5 20.9 8.0 il.0
9.5 +1.4 8.2 il.6 17.7 21.4
13.0 t1.8 8.8 i2.6 21.8 +1.4
7.3 +1.2
3.2 21.4
Number of times vesicle was in: A uterine horn Left horn Right horn Either horn Uterine body
aLocation determinations were made euery five minutes during Six trial each two-hour trial (25 determinations/2 hours). periods in four mres on days 12, 13, or 14 for each reproductive status. The right horn was the formerly gravid horn 7:n ai!1 postpartum mares. buterine
body and cranial,
middle,
and caudal one-third
of each
horn.
‘There wan no significant difference between barren and postpartum was in the uterine groups for any end point, except the vesicZe body more often fPcO.05) in barren mzres than in postpartum mares.
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THERIOGENOLOGY
TABLE
2.
Rate of movement bodya.
of the embryonic
vesicle
within
Rate Reference point
No. mares
Five-min
intervals
between
No. series
No. intervals
the uterine
of movement
Per interval
(mm)
Per minute Mean Range
determinations
Cervix
(Group
1)
4
5
27
17.3
3.5
o-14
Cervix
(Group
2)b
2
2
7
22.7
4.5
o-12
-2
-4
-24
14.5 ---
2.9
o-9
8
11
58
16.8
3.4
o-14
31
6.7
6.7
O-30
cyst TOTALS One-min
interval
Cervix
between
(Group
2)b
determinations 2
2
aLocation detemninationswere made on days 12, 13, or 14. b
638
Group 2 intervals were from determinationsmade every minute. The data for the five-minute intervalswere obtained. by using the intervalsbetween every fifth determination.
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1984 VOL. 21 NO. 4
THERIOGENOLOGY
Mare
15
C
0 5.10 .~.,..,..,,~,,,,,.,,. ILPI
ha:0 I I
0
45.50 )b
25.&zLt!
IO
20
$0
40
50
60
7-O
80
90
160
1;o
mm from cervix /p
UTERINE BODY -/
pigum 1. DiagMmmatic profiles showing the location of the embryonic vesicle in the uterine body at eack sequential determination in three rapes. The first location determination was made at time 0, and sequential detemtinations tiere mde every minute (mares A and BI or The cranial end of tke cervix ms used as every five minutes lnrare Cl. the point of reference. RM = right middle (vesicle in middle segment of right horn); LP = left posterior.
?4ovementof a day-24 vesicZe away from tke cervix skc6Ii-z FQurS2. at one-minute intervals. Tke cranial end of the cervix is the echogenic (white) area on the right, and the vesicle is tke noneckogenic (black), spherical area sham within the uterine body (gray area delineated Zorsatly and ventrally by a brigkt white line).
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1984 VOL.
21 NO. 4
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THERIOGENOLOGY
-cm F+JWe3. Photognzphstaken at five-minute intervals to show movement of a day-12 vesicle in the uterine body using a cystic complex and the cervix as referencepoints. The number in the Lower-right corner of each image is the number of minutes from beginning of the The cyst was approximately50 mm from the corpus-cornual sequence. junction and 60 mm from the cervix. At the first Zocation determination (min:O), the embryonic vesicle (upper central portion of image) is near the caudal end of the cyst. The location at each subsequentdeter10 mm caudd to cyst; 10 minutes, 5 mination was as follows: 5 minutes, mm caudal to cyst; 15 minutes, 53 mm caudal to cyst (not shown) and 7 mm cranial to cervix (white area to the right of the vesicle);20 minutes, 8 mm cranial to cyst; 25 minutes, in caudal portion of left horn.
640
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1984 VOL. 21 NO. 4
THERIOGENOLOGY
PQure4. Sequentialphotographssho&ng movement of a day-14 vesicle over a cyst (same mare as in Figure 31. The number in tower right corner of each image is the number of minutes from the beginning of the sequence. At the initial determination(min:Ol,the vesicle uas in the caudal portion of the left horn. Tke cyst is skoun (upper central image) on the ventral aspect of the uterine body with its cranial edge located 50 runfrom tke corpus-cornualjunction. The relationshipof the vesicle to the cyst at each sequentialdetermination was as follows: 5 minutes, approachingcyst: 6 minutes, beginning to encroach; 7 minutes, beginning to move over the top; 8 minutes, on top; 9 minutes, moving down the other side; 10 minutes, moving away; 11 minutes, continuingto move atiay.
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1984 VOL. 21 NO. 4
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THERIOGENOLOGY
piguw 5. Sequential segments of the uterus in every five minutes for two number of minutes that the depicted on the right, the into segments.
location of embryonic vesicle in various two mares. Location determinations were made The numbers at each position are the hours. vesicle spent in each segment. Iq the mZre uterine body as well as the horns 13as divided
The number of minutes the vesicle spent in a given location (Figure 4). of the uterus for the two mares in which each uterine horn and the uterine body were divided into segments are shown diagrammatically (Figure 5). DISCUSSION The high rate of intraluminal mobility of the embryonic vesicle on The vesicles moved from one horn to days 12 through 14 was confirmed. another an average of 1.1 times per two-hour trial. Assuming the twohour period was representative for a 24-hour day, the vesicles moved from one horn to another an average of 13 times per day. No differences were detected in mobility patterns of the vesicle that could account for preferential fixation in-the right horn in barren mares and the left Furthermore, no difference was found in the horn in postpartum mares. amount of time the vesicle spent in the gravid versus the nongravid horn The days studied (days 12 through 14) preceded the in postpartum mares. days that fixation of the vesicle has been found (1) to occur (days 15 Although conclusions must be guarded because of the small through 17).
642
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1984 VOL. 21 NO. 4
THERIOGENOLOGY number of mares, it appears that selection of the horn in which fixation will occur is not a function of mobility patterns or the amount of time the vesicle spends in a horn prior to day 15. These results are consistent with the hypothesis (2) that the vesicle usually becomes fixed in the horn that offers the most intraluminal resistance to mobility after the conceptus reaches a critical diameter on days 15 through 17. In other words, resistance to mobility of the expanding vesicle, and therefore the probability of fixation, is greater in the right horn in maiden mares; disproportionate hypertrophy of the two horns during pregnancy reduces the extent of the inequality in resistance in barren mares and changes the direction of this inequality in postpartum mares. The finding that the vesicle was present in the body more often in the barren mares (29% of the determinations) than in the postpartum mares (13%) was unexpected and no interpretation is offered. Direct measurements of the rate of movement of the vesicle were limited to the uterine body since the body, but not the horns, was viewed in longitudinal planes. In addition, the cervix provided a conThe average movevenient point of reference for [measuring distances. ment rate was 3.4 mm/minute; however, the rate was highly variable, ranging from 0 to 70 mm between five-minute determinations and 0 to 30 mm between one-minute determinations. Rapid point-to-point movement was also noted in two mares which were being monitored continuously but which were not part of either experiment. In these mares, the vesicle moved from a point 5 mm and 27 mm cranial to the cervix, respectively, to the caudal portion of the left horn in approximately two minutes. The rate of movement was approximately 45 and 30 mm/min for the two mares. Rapid Imovement seemed to occur more often in the middle onethird of the uterine body (Figure 1). Changes in direction or remaining in place for prolonged periods of time were not noted to occur in the middle one-third but occurred frequently in the caudal one-third. Altnough this observation requires confirmation, the body may turn in a ventral direction in the caudal portion (9), resulting in additional Sometimes the vesicle progressed in a given resistance to movement. direction until an extremity (cervix, tip of a horn) was reached, whereas at other times reversals in direction occurred in other areas (Figures 1 and 5). Passage of the vesicle from one horn to the other without traversing the length of the uterine body occurred frequently. In the vesicles that were observed continuously, there appeared to be some Imovement back and forth, but with an overall progression in a given direction. This probably accounted for the greater rate of movement when determindtions were made every minute (6.7 mm/min) than when the same data were examined every five minutes (4.5 mm/min). The mechanisms involved in the intrauterine mobility of the It is likely, however, that uterine embryonic vesicle are not known. contractions serve as the propulsive force. Expansion and contraction of the larger vesicles (day 14) were observed in the uterine body (compare the image at five minutes with the image at 11 minutes in Such contractions occurred every 5 to 14 seconds during two Figure 4). of the vesicle also observed series in two mares. However, contraction occurred under pressure when the transducer was deliberately pushed down Although the periodic contractions described against the uterine body.
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1984 VOL. 21 NO. 4
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THERIOGENOLOGY above seemed to be due to local uterine forces rather than external pressures (e.g., pressure from transducer, movement of intestines), more critical methodology will be needed to establish the existence and cause of periodic contraction and expansion of the vesicles. The sequential recordings which showed the movement of an embryonic vesicle over a cyst (Figure 4), however, indicate that the vesicle is sometimes subjected to In addition, ultrasonographic studies considerable propulsive force. (7) indicated that the endometrial folds are in close contact, so that The vesicle apparently must be forced through the lumen is obliterated. The longitudinal orientation of the folds (9) may be the folds. important in this regard. Although the propulsive force may come from the uterine myometrium, the vesicle itself may stimulate the appropriate The principal rationale for this untested uterine contractions. hypothesis is the limited observations (1) that many of the movements of a set of twin vesicles appeared to occur independently of each other. REFERENCES
1.
Ginther, O.J. Theriogenology
Mobility
-19:603-611
of the early (1983).
equine
conceptus.
2.
Ginther, O.J. Effect of reproductive status on twinning and on side of ovulation and embryo attachment in mares. Theriogenology 20:383-395 (1983). -
3.
Contralateral implantation in mares Feo, J.C.S.A. Vet. Rec. 106:368 (1980). post partum oestrus.
4.
Allen, W.E. and Newcombe, J.R. Relationship between early pregnancy site in consecutive gestations in mares. Equine (1981). -13:51-52
mated
5.
Transuterine migration of the Pascoe, R.R. between day 42 and parturition. J. Reprod. 446 (1979).
6.
Fixation and orientation of the early Ginther, O.J. Theriogenology 19:613-623 (1983). conceptus. -
7.
Ginther, O.J. of the equine
8.
Ginther, ovaries.
9.
Reproductive Biology of the Mare: Ginther, O.J. Equiservices, 4343 Garfoot Road, Cross Aspects. 1979, pp. 4 and 21.
644
during
Vet.
J.
fetus in the mare Fert., Suppl. -32:441equine
and Pierson, R.A. Ultrasonic anatomy and pathology Theriogenology g:505-516 (1984). uterus.
Ultrasonic O.J. and Pierson, R.A. Theriogenology (1984). -21:471-483
anatomy
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