Embryonic migration relative to maternal recognition of pregnancy in sheep

Twenty-five crossbred ewes were utilized to examine the timing of embryonic migration relative to maternal recognition of pregnancy. These ewes also were utilized to examine whether ovine embryos synthesized estradiol-17 beta in association with embryonic elongation and intrauterine migration. Embryos were flushed on d 11 through 15 from hemiovariectomized ewes. Recovery of embryos from the uterine horn contralateral to the remaining ovary indicated that migration had occurred. Ewes subsequently were returned with rams to determine their interestrous interval. Recovered embryos were classified morphologically, their length determined and individually incubated. Changes in estradiol within the medium were determined after a 6-h incubation. Embryo migration began on d 14 (P less than .05); on consecutive days from 11 through 15, 0, 0, 0, 60 and 100% of ewes examined, respectively, had an embryo in the contralateral horn. Extended estrous cycles (greater than 20 d) were observed in 0, 0, 40, 80 and 100% of ewes examined (P less than .05) following removal of embryos on d 11 through 15 of the cycle. Ovine embryos were longer (P less than .05) on d 14 (4.8 +/- 1.1 cm length, mean +/- SE) compared with d 13 (.2 +/- .1 cm) and increased further (P less than .05) on d 15 (7.8 +/- 1.1 cm). Incidence of intrauterine migration was correlated with embryonic length (r = .83; P less than .01) and estradiol synthesis (r = .77; P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Intrauterine migration of the porcine embryo: coordination of bead migration with estradiol

Forty crossbred gilts were used in three experiments to examine the effects of estradiol on embryo migration. Small, spherical beads of Silastic glue containing either cholesterol or estradiol-17 beta were used to mimic embryo migration. In the first experiment, 10 cholesterol- and 10 estradiol-impregnated beads were injected into the tip of the uterine horns, either on the same side (n = 5) or opposite from each other (n = 5). The second experiment consisted of a localized release of cholesterol or estradiol and observing migration of cholesterol-containing beads inserted 10 cm anterior and posterior to this site (n = 5). In the third experiment, 10 cholesterol-impregnated beads were injected into either the tip or base of one uterine horn. Additionally, these gilts were exposed to vehicle or exogenous estradiol in a 2 X 2 factorial arrangement of treatments (n = 5). Results of these experiments indicated that cholesterol-impregnated beads migrated further (P less than .05) when adjacent to estradiol-containing beads than when in an opposite uterine horn. Localized release of estradiol failed to induce movement of beads away from the site of steroid release. Finally, beads inserted at the base of the uterus moved anteriorly following treatment of gilts with estradiol. We suggest from these experiments that the porcine uterine horn cannot discriminate between estradiol- and cholesterol-releasing beads and, further, lacks a coordinated ability to displace adjacent beads. A site-dose dependent mechanism(s) of estrogenic induction of migration may exist such that porcine embryos become bilaterally intermixed following posterior, then anterior, waves of uterine contractions.     

Secretory function of the ovine uterus: effects of gestation and steroid replacement therapy

In Exp. 1, changes in uterine fluid content of protein, calcium and prostaglandin F2 alpha (PGF) were examined between d 30 to 144 of gestation. Volume of uterine fluid (mean +/- SE) in the nongravid uterine horn of unilaterally pregnant ewes increased (P less than .05) between d 30 (8 +/- 1 ml) and d 144 (749 +/- 46 ml) of gestation. Protein concentration and total protein in uterine fluid also increased (P less than .05) between d 30 (2.3 +/- .4 mg/ml; 19 +/- 7 mg) and d 144 (23.5 +/- 3.3 mg/ml; 17.4 +/- 2.0 g). Total recoverable calcium (mg) in secretions increased from .1 mg (d 30) to over 1.4 g (d 144) due to day of gestation effects (P less than .05). Total PGF also increased (P less than .01) from 7 ng on d 30 to 15.7 g on d 144. In Exp. II, ovariectomized (OVX) ewes were treated with either corn oil, estrone (E), progesterone (P) or P+E (PE) for 30 d. Treatment with P or PE increased calcium concentration and content (P less than .01) in secretions, but differences in uterine fluid volumes and concentrations of protein and PGF were not significant. Treatment of OVX ewes with P stimulated (P less than .05) in vitro synthesis of secretory proteins by endometrium, whereas treatment with E enhanced release of unlabeled proteins (P less than .05). The major endometrial secretory proteins were identified in allantoic fluids from d 60 to term and were detected along the mesenchymal border of the chorioallantois using immunohistochemistry. Results from this study indicate that P may be a primary hormone regulating accumulation of fluid, protein, calcium and specific endometrial proteins in the uterine lumen during gestation, and that uterine milk proteins gain access to the fetal-placental unit.     

Uterine influences on the formation of subnormal corpora lutea in seasonally anestrous ewes

The hypothesis that subnormal luteal function after induced ovulation in anestrous ewes was the result of uterine influences exerted during the periovulatory period was tested. Crossbred ewes (n = 27) in seasonal anestrus were induced to ovulate by administration of 12 doses of 250 ng of LHRH at 2-h intervals, followed immediately by a bolus injection of LHRH (250 micrograms; d 0). Ewes were unilaterally hysterectomized on either d -3 (PRELHRH) or 2 (POSTLHRH). Daily blood samples were collected and assayed for progesterone (P4) and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). All ewes were slaughtered on d 10, and corpora lutea (CL) were collected, weighed, and assayed for concentration of P4. All ewes that ovulated exclusively in the ovary ipsilateral to the remaining uterine horn had a transient increase in plasma P4 of 2 to 3 d (short luteal phase). In ewes with at least one CL in the isolated ovary, elevated plasma P4 was maintained after hysterectomy but was consistently lower (P less than .05) in POSTLHRH ewes than in PRELHRH ewes. Concentrations of PGFM did not differ between treatments. The CL ipsilateral to the remaining uterine horn weighted less (P less than .01) and contained less P4 (P less than .01) than contralateral CL. These data confirm the hypothesis that premature regression of subnormal CL is uterine-dependent in a local fashion. Presence of the uterus during the follicular and(or) early luteal phase inhibited subsequent luteal function in seasonally anestrous ewes.     

Suppressive action of gonadotropin-releasing hormone and luteinizing hormone on function of the developing ovine corpus luteum

Experiments were conducted to examine the effects of exogenous GnRH and LH on serum concentrations of progesterone (P4) in the ewe. Ewes in Exp. 1 and 2 were laparotomized on d 2 of an estrous cycle and ewes with corpora lutea (CL) in both ovaries were unilaterally ovariectomized. Ewes with CL in one ovary only were not ovariectomized. While they were anesthetized, ewes (n = 5) were injected with 25 micrograms GnRH (Exp. 1) or 50 ng GnRH (Exp. 2) into the artery supplying the ovary bearing the CL. Control ewes (n = 5 in each experiment) were injected similarly with saline. In Exp. 3, six ewes were injected i.v. (jugular) on d 2 with 100 micrograms oLH (t = 0) and 50 micrograms oLH at 15, 30 and 45 min; six control ewes were injected similarly with saline. Jugular blood was collected from all ewes at frequent intervals after treatment for LH analysis and on alternate days of the cycle through d 10 or 11 for P4 analysis. Treatment with 25 micrograms GnRH increased serum concentrations of LH at 15, 30, 45 and 60 min postinjection (P less than .001) and reduced serum concentrations of P4 on d 7 through 11 (treatment x day interaction; P less than .05). Injection with 50 ng GnRH caused a slight increase in serum concentrations of LH at 15 min but had no effect on serum concentrations of P4.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uterine blood flow during early pregnancy in ewes: interaction between the conceptus and the ovary bearing the corpus luteum

To determine if a transient increase in uterine blood flow (BF) and estradiol-17 beta (E2 beta) secretion occurs during maternal recognition of pregnancy in ewes (as previously observed for sows and cows), 40 nonpregnant (NP) ewes were assigned in equal numbers to surgery on d 9, 11, 13 or 15 postestrus (d 0 = day of estrus). For 20 NP ewes (five/day), each uterine horn (UH) was flushed with saline and uterine flushings (UF) collected. For the remaining 20 ewes, BF was determined for each UH using electromagnetic transducers, and samples of uterine arterial (UA) and uterine venous (UV) blood were obtained from each UH. After an intervening cycle, each ewe was mated, subjected to surgery on the same day postmating as during her previous nonmated cycle, and BF measurements and UA and UV samples were obtained. In addition, each UH of pregnant (P) ewes was flushed and the location of conceptuses was determined. Concentrations of E2 beta and progesterone (P4) in UA and E2 beta in UV and UF were determined by radioimmunoassay. For NP ewes, BF (ml/min) was not different for UH ipsilateral or contralateral to the ovary bearing the corpus luteum (CL), and did not differ across days, averaging 6.5 +/- .4. For P ewes, BF to UH contralateral to the ovary bearing the CL on all days and BF to UH ipsilateral to ovaries bearing CL on d 9 was similar to BF of either UH of NP ewes, averaging 6.8 +/- .6. On d 11, 13 and 15 of pregnancy, BF to UH ipsilateral to the ovary bearing CL was elevated (P less than .01) twofold (13.3 +/- .9).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of progesterone supplementation on pregnancy and embryo survival in ewes

Two hundred eighteen ewes were used in experiments 1) to develop a progesterone supplementation regimen capable of sustaining serum concentrations of progesterone at about 2.0 ng/ml for a period of 50 d (Exp. 1) and 2) to determine the effects of progesterone supplementation (d 6 to 50 after mating) on pregnancy and embryo survival rates in mated ewes (Exp. 2). In ovariectomized ewes in Exp. 1, s.c. administration of four cylindrical (9.5 x 60 mm) silastic implants, containing 20% (1.1 g) progesterone by weight, sustained mean serum concentrations of progesterone of 1.9 +/- .07 ng/ml compared with 1.03 +/- .05 ng/ml in ewes bearing two implants. In Exp. 2 each ewe (n = 159) was mated to two fertile rams at a spontaneous estrus (d 0) during mid-breeding season. Mean ovulation rate, determined on a subgroup of 46 ewes, was 1.45 +/- .05. On d 6, ewes were assigned randomly to control (two implants containing no progesterone) or progesterone-treated (four implants similar to those used in Exp. 1) groups. From d 7 to 50 after mating, progesterone concentrations in serum were greater (P less than .001) in progesterone-treated (four implants similar to those used in Exp. 1) groups. From d 7 to 50 after mating, progesterone concentrations in serum were greater (P less than .001) in progesterone-treated (3.50 +/- .06) than in control (2.65 +/- .05) ewes. Pregnancy rates (86% and 83%) and calculated embryo survival rates (77% and 78%) were similar (P greater than .05) for the control and progesterone-treated groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Attempts to overcome the anti-fertility effect of intrauterine plastic spirals in the ewe

A study was conducted to determine whether the antifertilization of intrauterine devices in ewes could be overcome by the use of hormones or drugs that either stimulate or inhibit uterine motility. 44 parous, western ewes were unilaterally ovariectomized, and a plastic spiral was inserted into the uterine horn opposite the remaining ovary. Spirals were immediately removed from 5 ewes. At the time of mating, 2 weeks to 3 months post surgery, sham-operated and spiral control ewes were injected with saline solution. Ewes with spirals were injected with either estradiol, epinephrine, oxytocin, oxytocin and acetylcholine, or oxytocin, acetylcholine, and physostigmine. Other ewes with spirals were laparotomized, and either the uterus was massaged or the cervical lumen was cleaned. 3 days postmating, 8 ova recovered from 5 sham-operated ewes were all cleaved, with a mean of 90 accessory sperm in the zonae pellucidae. 3 of 12 ova recovered from 8 spiral control ewes were cleaved. Only 1 of 40 ova recovered from 28 treated ewes was cleaved. Accessory sperm were not found in either cleaved or uncleaved ova from any spiral ewe. None of the treatments overcame the antifertilization effect of the spiral.     

Hormonal regulation of oxytocin-induced prostaglandin F(2alpha) secretion by the bovine and ovine uterus in vivo

In long-term ovariectomized ewes and cows, endometrial oxytocin receptors rest at relatively high levels but oxytocin is unable to induce prostaglandin F(2alpha) release. A series of studies were carried out to investigate the roles of physiological levels of progesterone and estradiol in "activating" these receptors in terms of permitting oxytocin-induced prostaglandin F(2alpha) release. In long-term ovariectomized cows, treatment with progesterone, but not estradiol, resulted in the induction of responsiveness to oxytocin. This responsiveness appeared within 2 d of progesterone treatment, reached a maximum by 6 d and was maintained to Day 18. In ovariectomized ewes, while estradiol treatment did induce temporary responsiveness to oxytocin after 3 d of treatment, treatment with progesterone was required to induce sustained responsiveness that appeared by Day 9 of treatment and was maintained to Day 12. Measurement of endometrial receptors for oxytocin revealed a significant decline in oxytocin receptors by Day 6 of progesterone treatment when responsiveness to oxytocin was maximal, demonstrating that receptor concentrations were not a limiting factor. The most likely mechanism by which progesterone treatment induces responsiveness to oxytocin may be through the up regulation of post receptor signaling pathways and/or enzymes involved in prostaglandin synthesis.     

Characterization of ovine follicles destined to form subfunctional corpora lutea

A study was done to test whether ovulatory follicles destined to form subfunctional corpora lutea differed from normal ovulatory follicles in steroidogenic function. Twenty-five ewes were treated with prostaglandin F2 alpha on d 11 of the estrous cycle, then unilaterally ovariectomized before (n = 13) or after (n = 12) the surge of luteinizing hormone (LH) at the induced estrus to collect "control" follicles, which would have produced normal corpora lutea. In 15 ewes, the second ovary was removed 63 to 84 h later to collect "treated" follicles before (n = 7) or after (n = 8) the second expected surge of LH. Five ewes (control) were allowed to ovulate from the remaining ovary at first estrus and another five (treated) at the second estrus (3 to 4 d later). Treated ewes had lower serum progesterone than control ewes during the ensuing cycle (P less than .05). Treated follicles contained less estradiol in the theca (4.4 +/- .6 vs 10.0 +/- 2.5 ng; P less than .05), less androstenedione (.1 +/- .1 vs 1.0 +/- .2 ng) and estradiol (.5 +/- .1 vs 2.9 +/- 2.2 ng) in the granulosa (P less than .05) and less progesterone in the follicular fluid (.8 +/- .4 vs 3.3 +/- .8 ng; P less than .05) than control follicles, when removed before the surge of LH. Follicles removed after the surge of LH did not differ. In conclusion, ovulatory follicles with low steroidogenic function became corpora lutea that secreted lower-than-normal quantities of progesterone.     

Ovarian follicular changes after weaning in sows.

Three experiments investigated ovarian follicular development in sows whose litters were weaned at 28 to 31 d of lactation. Unilateral ovariectomy near the time of weaning was used to assess early follicular characteristics and to identify those sows that would not return to estrus within 10 d after weaning. This allowed segregation of and exclusion from the study those sows that had a prolonged interval from weaning to first estrus. In Exp. 1, 82 and 72% of the large follicles that were marked at 48 or 72 h after weaning (10 sows per time point) were subsequently identified as corpora lutea. In Exp. 2, sows (seven to nine per time point) were unilaterally ovariectomized at 0, 6, 12, 18, 24, or 48 h after weaning, and follicular fluid was evaluated for changes in steroid concentrations. Progesterone concentrations in fluid from medium-sized (4 to 6 mm) follicles increased by 6 h after weaning and then declined through 24 h concomitant with increases in testosterone and estradiol. For Exp. 3, follicular fluid and granulosa cells from individual follicles were obtained from sows (seven to nine per time point) at 0, 6, and 24 h after weaning. In follicular fluid, insulin-like growth factor I (IGF-I) concentrations were not correlated (P greater than .05) with concentrations of progesterone, testosterone, or estradiol, or with granulosa cell production of estradiol during culture in androstenedione-supplemented medium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Patterns of late embryonic and fetal mortality and association with several factors in sheep

Embryonic and fetal mortality reduce lambing rates and litter sizes, thus contributing to economic losses in the sheep industry. In the current study, the timing of late embryonic and fetal loss in ewes and the factors with which these losses were associated were examined. Ewes lambing and lambs born were compared with pregnancy diagnosis and counts of embryos by ultrasonography near d 25, 45, 65, or 85 of gestation. Approximately 19.9% of the ewes experienced late embryonic loss, fetal loss, or both; and 21.2% of the embryos or fetuses were lost from d 25 to term. Potential offspring were lost throughout gestation; 3.7% of embryos from d 25 to 45, 4.3% of fetuses from d 45 to 65, 3.3% from d 65 to 85, and 11.5% from d 85 to parturition; thus, approximately 3 to 4% of the potential offspring were lost for each 20-d period of pregnancy beyond d 25. A greater proportion of ewes lost one (36.7%) rather than all (20.5% single; 3.8% multiple) embryos or fetuses. The patterns of loss were similar in ewes mated during the anestrous season and the transitional period and did not vary with service period within breeding season or method of synchronization of estrus. Late embryonic or fetal losses were not related to the temperature-humidity index. Maternal serum collected near d 25, 45, 65, or 85 of gestation was assayed for concentrations of progesterone, estradiol-17beta , and vascular endothelial growth factor (VEGF). The proportions of embryos or fetuses lost were associated with breed type (P < 0.05), as were concentrations of progesterone (P < 0.01), estradiol (P < 0.05), and VEGF (P < 0.01). The relationships of loss or retention of pregnancy to hormonal variables at the 4 stages studied were limited. Complete and partial losses increased rapidly as maternal progesterone at d 25 decreased below 2 ng/mL (P < 0.05). Survival of fetuses within a litter from d 25 to 65 was greater for ewes with medium concentrations of VEGF near d 25 and from d 65 to parturition was greater for ewes with high concentrations of VEGF near d 45 (P < 0.05). In summary, late embryonic or fetal losses occurred from d 25 throughout gestation and varied with breed type and with concentrations of progesterone in maternal serum on d 25.     

Growth hormone at breeding modifies conceptus development and postnatal growth in sheep

Experiments were performed to determine the effects of components of the GH-IGF axis on conceptus development and postnatal growth in sheep. In Exp. 1, ewes received one of the following treatments: 1) sustained release GH at breeding, 2) sustained release GH at breeding and estradiol-17beta at d 5 and 6, 3) only estradiol-17beta at d 5 and 6, or 4) no treatment. Uteri were flushed on d 7, and flushings were analyzed for content of IGF-I. A single injection of sustained-release bovine GH at breeding increased IGF-I content in uterine luminal flushings compared with control ewes (P < 0.05). Treatment with estradiol-17beta on d 5 and 6 after breeding did not alter IGF-I content compared with control ewes, and it blocked the effect of GH on uterine luminal IGF-I content. In Exp. 2, sustained release GH or no treatment was administered at breeding, and gravid uteri were collected at d 25, 80, or 140 of gestation. On d 80, GH-treated ewes had smaller chorioallantoic weights (P < 0.05) and tended to have more efficient placentae (fetal weight/total placental weight; P = 0.052), with a higher percentage of placental weight as cotyledons (P = 0.068) compared with control ewes. In Exp. 3, ewes were treated with or without sustained release GH at progesterone withdrawal. Lambs from GH-treated ewes were heavier at birth (P < 0.05). Lambs from GH-treated ewes reared as singles, but not lambs reared as multiples, were heavier at 30, 60 (P < 0.05), and 75 d (P = 0.075) of age than lambs from control ewes. In conclusion, ewes treated with sustained-release GH at breeding developed smaller, more efficient placentas, and had larger lambs at birth.     

Effect of prostaglandin F2 alpha, phenylephrine and ergonovine on uterine contractions in the ewe

Two experiments were conducted to determine the effect of prostaglandin F2 alpha (PGF2 alpha), phenylephrine and ergonovine on uterine contractions. In the first experiment, ewes were bilaterally ovariectomized, and a strain gauge force transducer was sutured to the serosa of one uterine horn. Each ewe was treated sc with 2 micrograms of estradiol-17 beta daily to prevent regression of the uterus. Beginning at least 5 d after ovariectomy, four dose levels of PGF2 alpha, phenylephrine and methoxamine were given by im injection and ergonovine was given by im or iv injection. Phenylephrine, methoxamine and ergonovine are alpha-adrenoceptor agonists. Uterine activity was recorded by physiograph for 30 min before and 90 min after treatment. Tracing were analyzed for 20-min periods before treatment and 4 to 24 min and 50 to 70 min after treatment. In Exp. 2, transducers were attached to uteri of intact ewes at d 10 to 12 of an estrous cycle. During subsequent estrus, one or two dose levels of PGF2 alpha, phenylephrine and ergonovine were given by im injection and uterine activity recorded. In Exp. 1, PGF2 alpha and phenylephrine increased (P less than .05 or .01) the number of amplitude of contractions at both 4 to 24 and 50 to 70 min. Ergonovine given im increased the number of contractions. In intact estrous ewes, PGF2 alpha increased the number and amplitude of contractions at 4 to 24 min, phenylephrine increased the number and amplitude at both 4 to 24 and 50 to 70 min, and ergonovine increased the number slightly but significantly at 4 to 24 min.(ABSTRACT TRUNCATED AT 250 WORDS)     

Adequacy of main uterine vein and the ovarian artery in the local venoarterial pathway for uterine-induced luteolysis in ewes.

The local uteroovarian pathway for uterine-induced luteolysis was studied in 34 ewes. Bilaterally ovulating ewes were used to study the role of the main uterine vein (uterine branch of uteroovarian vein) and unilaterally ovulating ewes were used to study the role of the ovarianartery. Surgical operation was done on day 7, 8, or 9 of diestrus and ewes were necropsied on day 20. In 4 bilaterally ovulating control ewes (unilaterally hysterectomized), mean weight of corpus luteum (CL) was less (P smaller than 0.05) on the side of the intact uterine horn (55 mg) than on the side of unilateral hysterectomy (548 mg). In 4 treated ewes (unilaterally hysterectomized and with surgical anastomosis of uterine vein from the intact side to the hysterectomized side), mean weight of CL on the hysterectomized side (153 mg) was less (P smaller than 0.05) than on the uterine-intact side (391 mg). The mean weight of CL on the hysterectomized side in the treated group was not significantly different from that of the uterine-intact side in the control group. Unilaterally ovulating ewes were randomized into 5 groups: (1) controls which were uterine intact, (2) controls in which a unilateral hysterectomy was done ipsilateral to CL, (3) unilateral hysterectomy done ipsilateral to CL and anastomosis of the ovarian branch of the ovarian artery on the uterine-intact side to the ovarian branch of the ovarian artery on the hysterectomized side, (4) controls in which unilateral hysterectomy was done contralateral to CL and the ovarian vascular pedicle on the uterine-intact side was isolated, and (5) unilateral hysterectomy done contralateral to CL, isolation of ovarian vascular pedicle on the uterine-intact side, and anastomosis of the ovarian branch of the ovarian artery on the unilaterally hysterectomized side to the ovarian branch of the ovarian artery on the uterine-intact side. Mean weight of CL was less (P smaller than 0.05) in groups 1 (56 mg), 3 (40 mg), and 4 (120 mg) than in groups 2 (408 mg) or 5 (473 mg). The mean weight of CL was not significantly different among groups 1, 3, and 4 or between groups 2 and 5. Results demonstrate that the local luteolytic effect of the uterus in ewes involves a venoarterial pathway and indicate that the main uterine vein is an adequate uterine outlet and the ovarian artery is an adequate ovarian inlet for the venoarterial pathway without the necessity of other possible concomitant local routes.     

Effects of melatonin and progesterone administered to ewes in spring and summer

Melatonin (MEL) was evaluated for effects on LH, prolactin (PRL) and fertility in spring (Exp. 1, 2) and summer (Exp. 3 to 5). In Exp. 1, 17 ovariectomized ewes bearing estradiol implants were fed 3 mg MEL or vehicle for 44 d beginning May 1. Melatonin decreased (P less than .001) PRL levels but had no effect on LH secretion and response to GnRH. In Exp. 2, 12 ewes each received a 40-d MEL ear implant or a sham implant on March 31. Progesterone-releasing pessaries (CIDR) were applied for 12 d and were withdrawn concomitant with ram joining on May 7. Neither treatment stimulated follicular development or induced estrus or ovulation. Exp. 3 and 4 were contemporary 2 x 2 factorial trials with 24 ewes at each of two locations. Melatonin implants were administered on June 29 and CIDR on July 22. The CIDR were removed and rams (Exp. 3, vasectomized; Exp. 4, fertile) were joined on August 3. Days from introduction of rams to estrus were reduced (P less than .05) by CIDR but not by MEL. All ewes lambed in Exp. 4, and days to estrus and conception were reduced (P less than .001) by CIDR but not by MEL. Exp. 5 was designed like Exp. 4 except that MEL implants were inserted June 20 and rams were joined August 8. Intervals from introduction of rams to estrus were reduced (P less than .01) by both MEL and CIDR treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Interrelationships among conceptus size, uterine protein secretion, fetal erythropoiesis, and uterine capacity

The interrelationships among d-11 conceptus size, d-105 placental weight, placental efficiency (the ability of the placenta to support fetal growth and development), fetal erythropoiesis, and uterine capacity were examined in 1/2 Meishan, 1/2 White crossbred gilts that were unilaterally ovariohysterectomized at 90 to 100 d of age. In Exp. 1, gilts were mated after at least one normal estrous cycle and then slaughtered at 105 d of gestation and number of fetuses and CL, placental weights, fetal weights, hematocrits, fetal plasma iron, and fetal plasma folate were measured. In Exp. 2, gilts were mated and plasma progesterone was measured on d 2 and 3 of gestation. On d 11, the length of the remaining uterine horn was recorded and the uterine horn was flushed with minimal essential medium. Number of CL, conceptus number, conceptus diameters, and total uterine flush retinol-binding protein (tRBP), acid phosphatase (tAP), and folate-binding protein (tFBP) were measured. Gilts were mated again and slaughtered at 105 d of pregnancy and the same traits measured in Group 1 were recorded. Plasma progesterone concentrations on d 2 and 3 were correlated with average conceptus diameter on d 11 (r = 0.60, P < 0.01, for each day). In contrast, tRBP (r = 0.49, P < 0.01), tAP (r = 0.53, P < 0.01), and tFBP (r = 0.51, P < 0.01) in uterine flushings on d 11 were only correlated with d-3 plasma progesterone concentrations. No correlations between d-11 average conceptus diameter or d-11 uterine length with d-105 uterine capacity were observed. Uterine capacity was negatively correlated with placental weight, fetal weight and fetal hematocrit (r = -0.36, P < 0.01; r = -0.44, P < 0.01; r = -0.32, P < 0.01; respectively). Hematocrits were correlated with fetal plasma iron (r = 0.50, P < 0.01) and folates (r = 0.44, P < 0.01). Hematocrit, plasma iron, and plasma folate were each correlated with residual fetal weights after adjusting for placental weight (a measure of placental efficiency), and accounted for 11% of the variation in this trait. These data suggest that conceptus diameter and uterine protein secretion on d 11 may be influenced by the onset of progesterone secretion by the CL, but do not support an influence of conceptus growth during early pregnancy on uterine capacity. These results also suggest that reducing placental and fetal weights will likely result in increased uterine capacity.     

胚胎移植试验羊群发情规律的研究

为了有效提高绵羊体细胞克隆和转基因等研究工作的效率,缩短胚胎移植试验羊群中空怀个体的利用周期间隔,试验对采用不同移植方法的胚胎移植受体及供体绵羊进行了移植前后的发情规律研究。结果表明:采用自制孕激素海绵栓和进口阴道孕激素释放装置(CIDR)对绵羊进行同期发情处理时发情率均接近90%,且92%以上的个体发情起始时间均集中在撤栓后24～48 h。在胚胎移植试验结束后,未参加胚胎移植个体和子宫角法未移植受体第2情期发情起始时间主要集中在上次发情后的14～20 d,而输卵管法未移植受体和输卵管法冲卵供体的发情时间则比较分散,呈现明显延后状态。未参加胚胎移植个体和子宫角法未移植受体人工授精后的受胎率接近往年羊场的平均水平,输卵管法未移植受体的受胎率略有下降,且输卵管法冲卵供体的受胎率明显降低。     

Estradiol-17 beta-oxytocin-induced cervical dilation in sheep: application to transcervical embryo transfer.

Experiments were conducted to determine whether exogenous estradiol-17beta (E2) and oxytocin (OT) can be used to improve transcervical (TC) embryo transfer (ET) procedures for sheep. Our concerns that the E2-OT treatment may alter luteal function prompted Exp. 1, in which 32 ewes were assigned to treatments in a 2x2 factorial array. On d 7 after onset of estrus, ewes received i.v. either 100 microg of E2 or diluent; 12 h later, ewes received i.v. either 400 USP units of OT or saline. To monitor luteal function, progesterone was measured in jugular blood collected from d 7 to 18. The treatments did not affect progesterone concentrations. Two trials were conducted in Exp. 2. In Trial 1, ewes were assigned to one of three treatments: TC transfer with E2-OT treatment to dilate the cervix, laparoscopic ET with E2-OT treatment, or laparoscopic ET with an equivalent diluent that did not dilate the cervix. In Trial 2, ewes were assigned to treatments in a 2x2 factorial array: TC or laparoscopic ET on d 6; E2-OT treatment for cervical dilation or diluents on d 6. Transferred embryos were recovered on d 12 in Trial 1 and d 14 in Trial 2, evaluated morphologically for development, and scored. Treatments did not affect the percentage of transferred embryos recovered. However, mode of transfer decreased (P<.01) the mean embryo development score. The E2-OT treatment increased (P<.01) the development score of embryos transferred transcervically, indicating that cervical dilation may improve the chances of embryos surviving after TC transfer. In conclusion, E2-OT treatment did not affect luteal function, and the E2-OT treatment can be used to enhance the success of TC embryo transfer in sheep.     

Effect of initial length of uterus per embryo on fetal survival and development in the pig

Influence of initial length of uterus available to each embryo on its subsequent survival and development was determined by systematic restriction of the length available to each potential embryo. Fifty-seven pregnant crossbred gilts were laparotomized at d 3 of gestation, length of uterine horns was measured in situ and corpora lutea (CL) were counted. In Exp. 1, uterine space available to each potential embryo was restricted by ligating one uterine horn 5 cm from the tip per CL. Uteri were examined at d 20, 25 or 50. In Exp. 2, one uterine horn was ligated on d 3 at 10, 20 or 30 cm from the tip per CL and uteri were examined at d 50. Embryos in the restricted section (RS) had a specific mean uterine length available to each potential embryo of 5, 10, 20 or 30 cm. Embryos in the nonrestricted section (NRS) had a variable mean uterine length available to each potential embryo of 44 +/- 4 cm. When embryos were restricted to 5 cm, the proportion of surviving fetuses at d 20, 25 and 50 was 61, 12 and 8%, respectively, whereas in combined NRS it was 82%. When the uterus was examined at d 50 after restricting embryos to 10, 20 or 30 cm/CL, 25, 33 and 52% of fetuses survived; in combined NRS survival was 71%. Each fetus surviving to d 50 in RS was associated with 36 cm of initial uterine length but fetal survival was not associated with number of CL. In RS, 59% were female fetuses and in NRS 50% were females.(ABSTRACT TRUNCATED AT 250 WORDS)