Unilateral uteroovarian relationship in pregnant cattle and role of uterine vein

The hypothesis of a unilateral uteroovarian relationship between location of embryos and maintenance of corpora lutea (CL) was tested in superovulated cattle. Ovulations were induced in both ovaries and a uterine horn was isolated subsequent to insemination to produce unilateral pregnancy. The mean weight of CL on day 24 was greater (P<.05) on the gravid side (2580 mg) than on the nongravid side (1200 mg; n=5), supporting the hypothesis. Involvement of the main uterine vein in the unilateral pathway between a gravid horn and the adjacent ovary was demonstrated in an experiment which utilized separation of uterine horns, anastomosis of uterine veins between sides, and insertion of embryos into one side by embryo transfer. Mean weight of CL on day 24 was less (P<.05) when the gravid horn was contralateral to the CL (950 mg; n=3), than when the gravid horn was ipsilateral to the CL (4760 mg) or when the gravid horn was contralateral to the CL and the uterine vein from the contralateral side was anastomosed to the vein on the ipsilateral side (3580 mg; n=3).     

Side of gestation in dairy heifers affects subsequent sperm transport and pregnancy rates after deep insemination into one uterine horn

Effects of side of previous gestation on sperm transport and pregnancy rates after deep cornual insemination were evaluated in 1686 Friesian cows in their first lactational period. Only single ovulating animals were used. At insemination, semen was deposited deep into the uterine horn ipsilateral or contralateral to the preovulatory follicle. A total of 876 cows (52%) ovulated in the ovary ipsilateral to the postgravid horn, and 810 cows ovulated in the contralateral ovary. Semen was deposited into the previously nongravid uterine horn of 832 cows, and into the gravid horn of 854 cows. The pregnancy rate was higher (P < 0.00001) for semen deposition into the previously nongravid horn (46.6%) than for semen deposition into the gravid horn (35.7%). For inseminations ipsilateral to the side of impending ovulation, pregnancy rates were higher (P = 0.0004) when ovulations occurred on the opposite side to the postgravid horn than on the same side. Pregnancy rates were higher (P = 0.002) for contralateral inseminations when ovulations occurred on the same side to the postgravid horn than on the opposite side; they were higher (P = 0.0001) for total ipsilateral than for total contralateral inseminations. There was no difference between ipsilateral and contralateral inseminations (P = 0.64) when ovulation occurred ipsilateral to the postgravid horn, but pregnancy rates were higher (P < 0.00001) when ipsilateral insemination was carried out into the nonpostgravid horn. Results indicate that the side of gestation in dairy heifers affects subsequent pregnancy rates after deep insemination into one uterine horn, possibly by affecting sperm transport.     

Embryonic survival in the uterus of ewes inseminated at the uterotubal junction on Day 32 post partum

Experiments were conducted to determine 1) if pregnancy initiated on Day 32 post partum would be maintained until lambing, 2) if there is a difference in the ability of the previously gravid or nongravid uterine horn to maintain pregnancy, and 3) if season has an effect on embryo loss. Estrus was induced in ewes on Day 32 post partum. At estrus, ewes were inseminated surgically at the uterotubal junction and assigned to the following groups: 1) inseminated at estrus and laparotomized on Day 3 to collect embryos for determination of fertilization rate (C), 2) inseminated in the previously gravid uterine horn (PG), 3) inseminated in the previously nongravid uterine horn (NG), and 4) inseminated when both horns were previously gravid (BG). Ewes pregnant in the PG, NG and BG groups were allowed to lamb. Conception rate in Group C at embryo collection was 70%. Embryo loss, based on concentrations of progesterone at Day 18 post insemination, was 43, 19 and 18% in the BG, NG and PG group, respectively. The high embryo loss in Group BG occurred only during the breeding season. Only 24% of the ewes that had been inseminated lambed. This was due to the prepartum loss of embryos and fetuses (47, 48 and 33% in Group BG, NG and PG, respectively. In conclusion, the detrimental effects of the uterus on embryo survival was evident within 18 d post insemination in Group BG (breeding season), and embryo loss prior to lambing was high in all the treatment groups (both seasons).     

Uterine blood flow of cows during the oestrous cycle and early pregnancy: effect of the conceptus on the uterine blood supply.

Blood flow to each uterine horn of cows during the oestrous cycle and early pregnancy was determined daily by use of electromagnetic blood flow probes placed around both middle uterine arteries. The pattern of blood flow to uteri of pregnant and non-pregnant cows was similar until Day 14 after mating or oestrus. Between Days 14 and 18 of pregnancy blood flow to the uterine horn containing the conceptus increased (P less than 0.01) 2- to 3-fold, whereas blood flow to the non-gravid uterine horn in these cows remained constant. No corresponding increase in blood flow to the uterine horn ipsilateral to the ovary bearing the CL was observed in non-pregnant cows during this 4-day period. By Day 19 of pregnancy, blood flow to the gravid uterine horn had returned to a level similar to that observed on Day 13. Blood flow to both uterine horns of pregnant cows remained constant from Days 19 to 25 and then increased to the gravid horn (P less than 0.01) markedly until Day 30 whereas blood flow to the non-gravid horn remained low. Uterine blood flow during the oestrous cycle of non-pregnant cows was positively correlated (P less than 0.01) with systemic concentrations of oestradiol and the ratio of oestradiol (pg/ml) to progesterone (ng/ml). There was no association between oestradiol concentrations and blood flow to the gravid uterine horn. These data indicate local control of uterine blood flow by the bovine conceptus which may function to create optimal conditions for the continuation of pregnancy.     

Progesterone in uterine and arterial tissue and in jugular and uterine venous plasma of sheep

Concentrations of progesterone in uterine and arterial tissue and in uterine and jugular venous plasma were determined. Blood was collected on Days 4 and 9 postestrus from the jugular vein and the first and last venous branches draining each uterine cornu; uterine tissue and arteries were subsequently collected. Progesterone was greater (p less than 0.05) in the cranial third than in the middle or caudal thirds of the uterine horn adjacent to the corpus luteum (CL)-bearing ovary or in any third of the contralateral horn. Progesterone in uterine arterial segments adjacent to the CL-bearing ovary was higher (p less than 0.05) than in contralateral segments. Progesterone was higher (p less than 0.05) in blood from the first venous branch of the cranial third of the uterine cornu adjacent to the ovary with the CL, than in the last branch of the caudal third, or contralateral horn, or in jugular blood. When oviductal veins were resected on Day 9 postestrus, progesterone in the first vein draining the cranial third of the uterine cornu adjacent to the CL-containing ovary was not different (p greater than 0.05) 48 h after resection than in the same vessel in the opposite horn or in jugular blood. We concluded that progesterone and other ovarian products may be delivered to the uterus locally.     

Progesterone and placentation increase secreted phosphoprotein one (SPP1 or osteopontin) in uterine glands and stroma for histotrophic and hematotrophic support of ovine pregnancy

Secreted phosphoprotein one (SPP1, osteopontin) may regulate conceptus implantation and placentation. We investigated effects of progesterone (P(4)) and the conceptus on expression and localization of SPP1 in the ovine uterus. Steady-state levels of SPP1 mRNA in the endometrium of unilaterally pregnant ewes did not differ significantly between nongravid and gravid horns within their respective days of pregnancy; however, levels did increase as pregnancy progressed. SPP1 mRNA was detectable in the glandular epithelium (GE) of both nongravid and gravid horns via in situ hybridization. SPP1 protein was localized to the apical surface of the luminal epithelium of both nongravid and gravid uterine horns. Gravid horns exhibited extensive stromal SPP1 on Days 40 through 120, whereas SPP1 was markedly lower in the stroma of nongravid uterine horns through Day 80 of pregnancy. By Day 120, stromal expression of SPP1 between nongravid and gravid horns was similar. Long-term P(4) treatment of ovariectomized ewes induced SPP1 in the uterine stroma and GE. A bioactive 45-kDa SPP1 fragment was purified from uterine secretions and promoted ovine trophectoderm cell attachment in vitro. Interestingly, increased stromal cell expression of SPP1 was positively associated with vascularization as assessed by von Willebrand factor staining. Finally, ovine uterine artery endothelial cells produced SPP1 during outgrowth into three-dimensional collagen matrices in an in vitro model system that recapitulates angiogenesis. Collectively, P(4) induces and the conceptus further stimulates SPP1 in uterine GE and stroma, where SPP1 likely influences histotrophic and hematotrophic support of conceptus development.     

Maintenance of the corpus luteum after uterine transfer of trophoblastic vesicles to cyclic cows and ewes

One or two trophoblastic vesicles (0.4-2 mm diam.) from cow (Day 14) or ewe (Day 11-13) embryos without their disc were transferred, after culture for 24 h, into recipients. Each vesicle was transferred into the uterine horn ipsilateral to the CL by the cervical route in heifers and surgically in ewes on Day 12 of the oestrous cycle. In cows, daily measurements of plasma progesterone concentrations and checks for return to oestrus showed that the CL was maintained in 8 out of 12 recipients. These 8 cows had 25- to 37-day cycles while 4 recipient heifers returned to oestrus normally. Three recipients with an extended cycle were slaughtered. The dissected uterus showed that trophoblastic vesicles had developed in the uterine horns. In ewes, the serum progesterone curve, determined in each recipient, showed that the CL was maintained in 7 out of 12 recipients. These 7 ewes had 20- to 54-day cycles and the other 5 ewes had a normal cycle of 15-19 days comparable to that of 17.0 +/- 0.5 days for the 6 control ewes. Whenever the CL was maintained, high blood progesterone levels were followed by rapid luteolysis. In cattle and sheep, therefore, a trophoblastic vesicle transferred into the uterus can develop in vivo, secreting the embryonic signals when there is no embryonic disc control and transforming the cyclic CL into a CL of pregnancy in about 60% of the cases.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of intrauterine administration of estradiol on postpartum uterine involution in cattle

In cattle, the first postpartum dominant follicle has a predilection for the ovary contralateral to the previously gravid uterine horn. However, the presence of an estradiol-secreting dominant follicle in the ipsilateral ovary is a marker of subsequent fertility, possibly due to a localized effect of ovarian estradiol on uterine involution. The present study tested the hypothesis that estradiol increases the rate of uterine involution when administered into the previously gravid uterine horn around the expected time of selection of the first postpartum dominant follicle. Dairy cows were treated with 10 mg estradiol benzoate (n=15) or saline (n=14) administered through the cervix into the previously gravid uterine horn lumen on Days 7 and 10 postpartum. Uterine involution was monitored by daily transrectal ultrasonography and estimation of peripheral plasma concentrations of PGFM and acute phase proteins, while ovarian function was monitored by ultrasonography and measurement of plasma hormone concentrations. There was no effect of estradiol treatment on the diameter of the previously gravid or nongravid uterine horns, nor on the plasma concentrations of PGFM or acute phase proteins. However, cows in which the first postpartum dominant follicle ovulated during the study period had a smaller diameter of the previously gravid (P<0.01) or nongravid uterine horns (P<0.001) compared with cows in which the follicle regressed. Thus, our hypothesis was not proven, and the opposite pathway of utero-ovarian signaling may be more important during the postpartum period.     

Ovine trophoblast protein-1 and bovine trophoblast protein-1 are present as specific components of uterine flushings of pregnant ewes and cows

A rabbit antiserum raised against ovine trophoblast protein-1 (oTP-1) was used to stain Western blots of the protein components from the uterine flushings of pregnant ewes (n = 61), non-bred cyclic ewes (n = 22), bred-but-nonpregnant ewes (n = 36), pregnant cows (n = 34), and bred-but-nonpregnant cows (n = 15). Nonpregnant animals were defined as ones from which no embryo was recovered. Uterine flushings of pregnant ewes contained oTP-1 between Days 14 and 24 of pregnancy, but not at Day 12. All of the cyclic ewes and 34 of 36 bred ewes, judged as nonpregnant, tested negatively for the presence of oTP-1. With one exception, oTP-1 was not detected in the nongravid uterine horns of pregnant ewes in which the conceptus had been confined to one uterine horn. Bovine trophoblast protein-1 (bTP-1), which cross-reacts immunologically with oTP-1, was also detectable specifically in the uterine flushings of pregnant cows when anti-oTP-1 antiserum was used. The urine (n = 14) and certival mucus (n = 20) samples of all the pregnant ewes tested were free of any detectable oTP-1. Thus, a useful pregnancy test for ewes based on oTP-1 release into these fluids seems unlikely. Results of this study show that oTP-1 and bTP-1 are pregnancy-specific proteins that are secreted into the uterine lumen where they possibly exert a local response.     

Growth and microvascular development of the uterus during early pregnancy in ewes.

Growth and microvascular development of the uterus were evaluated for ewes on Days 12, 18, 24, and 30 after mating (3-4 ewes/day; Day 0 = day of mating) in two experiments. In experiment 1, fresh weight and dry weight of gravid uterine horns were increased on Days 24 and 30 after mating, whereas those of nongravid uterine horns were elevated only on Day 30. The increased fresh and dry weights of gravid uterine horns on Day 24 were associated with uterine hyperplasia (increased DNA content). Increased fresh and dry weights of gravid uterine horns on Day 30, however, were associated with hypertrophy (increased RNA:DNA and protein:DNA ratios) of uterine tissues. In experiment 2, vascularity of endometrial tissues was elevated on Days 24 and 30 after mating. In addition, dramatic changes in uterine architecture (increased lumenal diameter and decreased endometrial thickness) and in uterine microvascular development (increased abundance of large microvessels and development of a subepithelial capillary plexus) were observed by Day 24 after mating. Characterization of the patterns of uterine growth and microvascular development will enable us to further define the role of previously reported uterine and conceptus-derived growth and angiogenic factors during early pregnancy.     

Adaptations to reduction of endometrial surface available for placental development in sheep

On Day 5 of pregnancy, before the blastocyst migrates to the uterus, one uterine horn was ligated to restrict the trophoblast to the lumen ipsilateral to the corpus luteum. The numbers of placentomes (caruncles and cotyledons) were reduced by half, but neither at 120 nor at 140 days of pregnancy (term 147 days) did the weights of placentae and fetuses of treated ewes differ significantly from those of control ewes. Amongst uterus-ligated animals prepared for chronic study, the rate of uterine blood flow (electromagnetic flow transducer, ml/min) to the pregnant horn was higher than in control ewes, as was the concentration of progestagens in maternal peripheral blood. There may be a compensatory response that causes hypertrophy of placentomes and that increases blood flow to the uterine horn containing placental tissue.     

Effect of intrauterine administration of oestradiol on postpartum uterine bacterial infection in cattle

After parturition fewer first dominant follicles are selected in the ovary ipsilateral to the previously gravid uterine horn in cattle. However, the presence of a large oestradiol-secreting follicle in the ipsilateral ovary is a predictor of fertility, possibly due to a localised effect of oestradiol which increases the rate of elimination of the ubiquitous uterine bacterial contamination that occurs after calving. The present study tested the hypothesis that oestradiol reduces uterine bacterial contamination when administered into the uterine lumen around the expected time for selection of the first postpartum dominant follicle. Animals were infused with saline (n=15) or 10mg oestradiol benzoate (n=15) into the previously gravid uterine horn on Days 7 and 10 postpartum. Peripheral coccygeal blood samples were collected daily and oestradiol concentrations measured by radioimmunoassay (RIA). Uterine lumen swabs were collected 7, 14 and 21 days postpartum for aerobic and anaerobic culture, bacteria were identified and growth scored semi-quantitatively. Plasma oestradiol concentrations were higher for treated animals between Days 7 and 14 (1.4+/-0.1 versus 2.0+/-0.2 pg/ml, P<0.05). Control animals had a similar bacterial growth score on Days 7 and 14, with a lower value on Day 21 (5.7+/-1.0 and 6.1+/-0.7 versus 0.3+/-0.1, P<0.05). However, treated animals had a surprising higher bacterial load on Day 14, than on Days 7 or 21 (7.1+/-0.9 versus 4.0+/-0.6 or 3.6+/-0.6, P<0.05). The increased score was attributable to more pathogens associated with endometritis on Day 14 than Day 7 (5.1+/-1.0 versus 2.5+/-0.5, P<0.05), in particular Prevotella melaninogenicus (1.5+/-0.5 versus 0.7+/-0.2, P<0.05) and Fusobacterium necrophorum (1.5+/-0.4 versus 0.3+/-0.2, P<0.05). In conclusion, administration of oestradiol into the uterine lumen surprisingly increased uterine pathogenic anaerobic bacterial contamination. Thus, it is unlikely that increased fertility associated with a first dominant follicle in the ipsilateral ovary is a consequence of the elimination of bacterial contamination by ovarian oestradiol.     

The effect of oestradiol on postpartum uterine involution in sheep

The present study tested the hypothesis that ovarian oestradiol increases the rate of uterine involution after parturition in sheep. The day after parturition, ewes were randomly assigned as un-operated controls (n=5), or a 3 cm silastic implant containing oestradiol (n=8) or empty (n=7) was sutured within the bursa of the ovary ipsilateral to the previously gravid uterine horn. Blood samples were collected daily for measurement of PGFM and acute phase proteins until 17 days postpartum when the ewes were slaughtered and the genital tract was collected. There was no consistent effect of treatment group on uterine involution determined by the collagen density, dry matter content, width, length, or weight of the genital tract. Furthermore, there was no evidence of a localised effect of oestradiol on involution as there were no significant differences between the previously gravid and non-gravid uterine horns. However, oestradiol-treated ewes had lower plasma concentrations of 15-keto-13,14-dihydro-prostaglandin F2alpha (P<0.01), alpha1-acid glycoprotein (P<0.05) and ceruloplasmin (P<0.001); but, not haptoglobin. These observations could reflect a direct effect of oestradiol on inflammatory mediator synthesis or secretion because, in the absence of parallel physical measurements, it is unlikely that these observations reflect a beneficial effect of treatment on uterine health.     

Effect of undernutrition on the distribution of progesterone in the uterus of ewes during the luteal phase of the estrous cycle

The effect of undernutrition on ovarian and uterine venous progesterone concentrations and endometrial progesterone content on Days 5 and 10 of the estrous cycle were studied. Forty ewes were synchronized using progestagen pessaries. At pessary withdrawal, the ewes were fed diets to provide either 1.5 or 0.5 times the daily maintenance requirement (Group H, n = 20 and Group L, n = 20, respectively). Ewes fed the low nutrition diet (Group L) had higher mean peripheral progesterone concentrations than those fed the high plane diet (Group H; P < 0.05) but lower endometrial progesterone content on Day 5 (P < 0.05). Neither ovarian nor uterine venous levels were affected by nutrition on either Day 5 or 10. Progesterone concentrations in blood samples collected ipsilateral to ovaries bearing a corpus luteum (CL) were higher than in the contralateral samples (P < 0.001). It is concluded that undernutrition can produce a reduction of endometrial content of progesterone the first week after mating. Since no differences in ovarian venous concentrations were observed, it remains to be shown whether this variation is due to other variables, such as the population of endometrial progesterone receptors or other nonhormonal factors.     

Effect of administration of eCG to postpartum cows on folliculogenesis in the ovary ipsilateral to the previously gravid uterine horn and uterine involution

This study tested the hypothesis that increased oestradiol secretion by large follicles in the ovary ipsilateral to the previously gravid uterine horn has a local effect to increase the rate of uterine involution. Cows were administered an i.m. water placebo (n = 19), 250 iu equine chorionic gonadotrophin (eCG) (n = 18) or 750 iu eCG (n = 20) 14 days post partum (day 0). Transrectal ultrasonography at the time of treatment and 2, 4 and 6 days later monitored uterine horn diameter and ovarian structures. Blood samples collected contemporaneously were assayed for 15-keto-13, 14-dihydro-prostaglandin F(2alpha) and oestradiol concentration. For control cows, accumulated diameter of the largest follicle in the ovary ipsilateral to the previously gravid uterine horn, compared with the contralateral ovary, was smaller on day 0 (P < 0.05) and days 2, 4 and 6 (P < 0.001). There were no significant differences in the eCG-treated animals. There were 12, 8 and 11 cows with a plasma oestradiol concentration < 1 pg ml(-1) on day 0 in the control, 250 and 750 iu eCG treatment groups, respectively. For control cows, the peripheral oestradiol concentrations were higher on day 6 compared with days 0, 2 and 4 (P < 0.05); for cows treated with 250 iu eCG, concentrations were higher on days 4 and 6 compared with day 0 (P < 0.05); and for cows treated with 750 iu eCG, concentrations were higher on days 2 and 4 compared with day 0 (P < 0.01). Treatment with eCG, or the presence of a follicle > 8 mm in diameter in the ovary ipsilateral to the previously gravid uterine horn, did not affect the rate of uterine involution or plasma 15-keto-13,14-dihydro-prostaglandin F(2alpha) concentration. In conclusion, administration of eCG to increase follicular growth and oestradiol production overcame the inhibition of follicular growth in the ovary ipsilateral to the previously gravid uterine horn, but did not affect uterine involution.     

Effects of postparturient uterine lavage on uterine involution in the mare

Eighteen postparturient mares were used to evaluate effects of uterine lavage on uterine involution. Mares were randomly assigned to one of three treatment groups: Group 1 (seven mares), no lavage; Group 2 (five mares), lavage on Day 3 post partum; and Group 3 (six mares), lavage on Days 3, 4, and 5 post partum. Five liters sterile physiologic saline, prewarmed to 42 degrees C, were used for each lavage. Transrectal ultrasound examination of the reproductive tract was performed on Day 11 post partum to detect the presence of free fluid in the uterine lumen, to estimate the cross-sectional diameter of the uterine horns and body, and to determine if ovulation had occurred. Endometrial biopsies were also taken on Day 11 post partum to evaluate endometrial histologic characteristics. Lavage had no effect (P>0.05) on diameter of the uterine body or previously gravid uterine horn, presence of fluid in the uterine lumen, or number of mares which had ovulated by Day 11 post partum. Histologic characteristics of the endometrium (height of luminal epithelium, gland depth, relative gland vclume, and inflammatory-cell score) were not affected by treatment (P>0.05). Postpartum uterine lavage did not significantly affect uterine involution by the parameters measured in normal-foaling mares at Day 11 post partum.     

Effects of the fetal-placental unit on uterine prostaglandin levels at term in the pregnant rat

Uterine prostaglandins (PGs) increase markedly at term in the pregnant rat. To assess the contribution of the fetal-placental unit (FPU) on uterine tissue and uterine venous blood PG concentrations, each uterine horn of 14 unilaterally pregnant rats at day 21 of pregnancy were compared. In addition, 7 bilaterally pregnant rats were studied. Uterine tissue and uterine venous plasma PGF, PGE, 6-Keto-PGF1 (6KF) and thromboxane B2 (TxB2) and systemic plasma progesterone, estradiol and estrone were determined by radioimmunoassay. Uterine concentrations of PGs (ng/mg DNA) were always greater on the pregnant side of unilaterally pregnant rats (p less than .05) although the PGF levels were elevated to a lesser extent than were PGE, TxB2 or 6KF. However, no differences were detected between uterine tissue from the pregnant side of unilaterally pregnant compared to bilaterally pregnant rats. In addition, no differences were found in uterine venous plasma PGs adjacent or opposite the pregnant uterine horn and in systemic plasma progesterone, estradiol and estrone levels in unilaterally vs bilaterally pregnant rats. These data suggest that the presence of the FPU is associated with an increased capacity of uterine tissue to produce PGE, TxB2 and 6KF, and to a lesser degree PGF, and thus may contribute to the increase in uterine PGs periparturition.     

Effect of heat stress on conceptus and uterine secretion in the bovine

This study examined the effects of heat stress on conceptus secretion of bovine trophoblastic proteins (bTP) and the uterine secretory environment on Day 17 of pregnancy. After mating to fertile bulls, cows were placed in an environmental chamber at 21 degrees C, 45% RH on Day 7 and were assigned to one of the following treatments on Day 8: Control (21 degrees C, 45% RH), Treatment 1 (37 degrees C, 30% RH) and Treatment 2 (37 degrees C, 40% RH). Cows were slaughtered on Day 17 and each uterine horn was flushed separately with physiological saline to recover the conceptus and uterine contents. The wet weight of the conceptus was recorded and uterine flushings were analyzed for quantitative and qualitative protein changes, prostaglandin F and calcium concentrations. Conceptus tissue was cultured in vitro with 100 muCi of [(3)H]-leucine and the polypeptides released into the medium were analyzed by 2D-PAGE followed by fluorography. Heat stress increased rectal temperature of cows and reduced conceptus wet weight. Uterine content of protein and calcium were increased in the uterine horn ipsilateral to the CL of heat-stressed cows. Although uterine protein increased in heat-stressed cows, no qualitative difference was observed in the polypeptides present in the uterine lumen. Conceptus synthesis and release of bTP were enhanced in treated cows. These responses indicate that heat stress between Days 8 to 17 of pregnancy altered the uterine environment as well as growth and secretory activity of the conceptus.     

Ability of induced corpora lutea to maintain pregnancy from the third month of gestation to term in cattle

The local relationship between the pregnant uterine horn and the CL during maternal recognition of pregnancy is well-documented. It continues beyond that time; pregnancies were maintained in lutectomized cows when CL were induced on the ovary ipsilateral, but not contralateral, to the uterine horn of pregnancy during Days 28-53. This study evaluated factors affecting maintenance of pregnancy by CL induced after Day 53, in lutectomized cows that had received exogenous progesterone from Day 29 to 15 days after induction of a CL. Twenty-four suckled beef cows were lutectomized on Day 29 of gestation; pregnancy was maintained with progesterone from two controlled internal drug releasing (CIDR) inserts, exchanged every 5 days. Beginning on Day 53, ovaries and viability of pregnancy were evaluated by ultrasonography every 5 days. When a follicle >or=10 mm in diameter was present ipsilateral to the fetus, each cow received 1,000 IU of hCG. Following induction of a CL (20 of 24), progesterone was reduced to a single CIDR for 5 days, then removed. Retention of pregnancy was confirmed by rectal palpation and calving. Cows with induced CL maintained pregnancy to term, including four with the CL contralateral to the fetus. Three cows failed to form normal CL by Day 98 and lost pregnancy after removal of exogenous progesterone. One cow that did not respond to hCG lost pregnancy during exogenous progesterone. In conclusion, CL induced after Day 53 maintained pregnancy to term, even when induced contralateral to the pregnant uterine horn.     

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.