Contractility of the ovarian vascular bed during the oestrous cycle and early pregnancy in gilts

The vasoconstrictor activity of the ovarian vascular bed in vitro was investigated during the oestrous cycle and early pregnancy. Gilts were killed during the follicular phase (Days 20 to +1; N = 5) or luteal phase (Days 11 to 13; N = 4) of the oestrous cycle, or on Day 13 of pregnancy (N = 5). Immediately before death, a sample of vena cava blood was obtained for determination of progesterone and oestrogen (oestrone and oestradiol-17 beta) concentrations. One ovary was removed, cannulated, perfused in vitro, and subjected to 10-min infusions of saline (vehicle control) and noradrenaline. Vasoconstriction was provoked by electrical stimulation at the end of each infusion. Ovaries from luteal-phase gilts exhibited greater (P less than 0.01) vasoconstriction than did ovaries from follicular-phase and pregnant gilts at the end of saline and noradrenaline infusions. The oestrogen to progesterone ratio was less (P less than 0.01) for luteal-phase and pregnant than for follicular-phase gilts. Vasoconstriction was negatively correlated (r = -0.99, P less than 0.01) with the oestrogen to progesterone ratio in systemic blood of gilts during the oestrous cycle but not during early pregnancy (r = +0.39, P greater than 0.10), possibly due to an effect of the conceptuses.     

Effect of intrauterine application of oestradiol-17 beta and prostaglandin E-2 on the porcine oestrous cycle and uterine endocrinology.

Silastic beads were inserted into the uterine lumen on Day 10 after oestrus. Gilts received beads containing oestradiol-17 beta only, oestradiol benzoate, or oestradiol-17 beta+prostaglandin (PG) E-2. Oestrous cycles were slightly longer in treated than in untreated pigs (20.2 +/- 0.4 days), and durations were 22.6 +/- 1.3, 26.2 +/- 1.7 and 23.2 +/- 1.8 days for oestradiol-17 beta, oestradiol benzoate and oestradiol-17 beta+PGE-2 treatments, respectively (P greater than 0.05). Thus, PGE-2 and an oestrogen such as oestradiol benzoate that persist for a longer period cannot prolong the cycle more than oestradiol-17 beta alone. Additional cyclic gilts underwent similar treatments with beads containing oestradiol-17 beta, oestradiol-17 beta+PGE-2 or cholesterol, and cannulation of one utero-ovarian vein on Day 10. Blood samples were collected from the catheter every 15 min from 08:00 until 11:00 h and from 20:00 until 23:00 h for 5 consecutive days starting the day after surgery and peripheral plasma samples were also collected daily. On Day 16, beads containing oestradiol-17 beta were surrounded by endometrial folds whereas cholesterol beads were free. Concentrations of plasma progesterone did not vary significantly from Days 11 to 16 in gilts treated with oestradiol-17 beta or oestradiol-17 beta+PGE-2, but decreased in cholesterol-treated gilts. Concentrations of plasma oestrone and oestradiol-17 beta were more than ten times higher in gilts treated with oestradiol-17 beta or oestradiol-17 beta+PGE-2 than in cholesterol-treated gilts on the day after bead insertion, but decreased rapidly to values comparable to those in cholesterol-treated gilts by Day 14. In contrast, concentrations of oestrone sulphate remained high until Day 16. Concentrations of PGE-2 in the utero-ovarian vein plasma did not differ (P greater than 0.05) between treatments but those of PGF-2 alpha were higher (P less than 0.004) in gilts treated with cholesterol than in those treated with oestradiol-17 beta or oestradiol-17 beta+PGE-2. It is postulated that insufficient oestradiol-17 beta is released by the beads toward the end of a 'recognition period' to prolong the cycle for more than 3-6 days.     

Effect of asynchronous superinduction on embryo survival and range of blastocyst development in swine

The importance of uniform development of blastocysts was examined by comparing the effects of asynchronous superinduction (Day 6 embryos into Day 7 pregnant recipients and Day 7 embryos into Day 6 pregnant recipients) on the range of embryo development at Days 12 and 13 to subsequent survival to Day 30. Twenty gilts were used to produce five Day 7 recipients that received Day 6 embryos and five Day 6 recipients that received Day 7 embryos. Embryos from the Day 7 and Day 6 recipients were examined 6 days later. Recovered embryos ranged morphologically from spherical to filamentous blastocysts. This range of embryos was within the limits of that previously observed for naturally mated sows. However, recovered blastocysts from the Day 6 embryos transferred into Day 7 recipients were morphologically more variable and proportionately less developed than the blastocysts from the Day 7 embryos transferred into Day 6 recipients. Forty additional gilts were subsequently utilized to generate 20 recipients (10 recipients per transfer group) that were examined on Day 30. More Day 7 embryos transferred into Day 6 recipients survived (p less than 0.05) than Day 6 embryos transferred into Day 7 recipients. These experiments suggested that greater variation in early development of embryos, within litters, subsequently resulted in greater mortality of embryos.     

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)     

Effect of intrauterine infusion of Escherichia coli on hormonal patterns in gilts during the oestrous cycle

The aim of this study was to determine the effect of intrauterine Escherichia coli infusion on the patterns of plasma LH, prolactin, progesterone, androstenedione, testosterone, oestrone, oestradiol-17beta, cortisol and 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) in gilts during the oestrous cycle. On day 4 of the oestrous cycle (day 0), 25 mL of saline or 25 mL of Escherichia coli suspension, containing 10(7) colony forming units x mL(-1), was infused once into the each uterine horn in group I or II respectively. The control gilts developed a new oestrous cycle at the expected time but not bacteria-treated. Endometritis and vaginal discharge developed in all gilts after Escherichia coli infusion. The administration of Escherichia coli resulted in a reduction of plasma levels of LH, prolactin, oestrone and oestradiol-17beta (P < 0.05-0.001), mainly on days 15-18 after treatment (expected perioestrous period). During this time, the plasma androstenedione level was elevated (P < 0.05-0.001) after bacteria infusion. In the gilts receiving bacteria, progesterone concentration decreased from day 8 after treatment and was low until the end of the study (P < 0.05-0.001). On days 8-12 after bacteria administration, the level of PGFM was higher (P < 0.001) than that found in the control group. These results suggest that the developing inflammatory process of the endometrium in gilts following Escherichia coli infusion significantly affects the pituitary-ovarian axis function as well as prostaglandin production leading to anoestrus.     

Direct effects of oestradiol-17 beta and prostaglandin E-2 in protecting pig corpora lutea from a luteolytic dose of prostaglandin F-2 alpha

Implants containing vehicle or oestradiol-17 beta (10 mg) were placed into pairs of corpora lutea (CL) with and without prostaglandin F-2 alpha (PGF-2 alpha) (100 micrograms) on Day 11 and CL were collected on Day 19, in cyclic gilts (Exp. 1). The results demonstrated that CL implanted with PGF-2 alpha with or without oestradiol-17 beta had a markedly lower (P less than 0.01) weight (mg) and progesterone concentration (ng/mg) than CL with vehicle-or oestradiol-17 beta-implanted or unimplanted CL, which were similar (149 and 7.2 vs. 304 and 49.6, respectively). In Exp. 2, CL implanted with vehicle, oestradiol-17 beta or PGE-2 remained fully functional until Day 19, whereas CL implanted with oestradiol-17 beta +/- PGF-2 alpha and PGE-2 + PGF-2 alpha exhibited lower (P less than 0.05) weight and progesterone concentrations; CL implanted with PGE-2 + PGF-2 alpha were heavier (P less than 0.05) and tended (P less than 0.10) to have greater progesterone concentrations than CL implanted with oestradiol-17 beta + PGF-2 alpha. In Exp. 3, a dose-dependent (P less than 0.05) effect of PGE-2 on preventing regression induced by PGF-2 alpha was observed on Day 19. These data demonstrate a direct effect of PGE-2, but not of oestradiol-17 beta in protecting the CL against luteolysis induced by PGF-2 alpha.     

Influence of sexual maturity of donor on in vivo survival of transferred porcine embryos.

A study was conducted to determine whether embryos recovered from first-estrous (pubertal) and second-estrous gilts differed in survival when transferred to first- or third-estrous recipients. Embryos were recovered surgically from first- and second-estrous donors 48-72 h postmating and 6-10 normal embryos/zygotes (1-4 cells) were transferred to oviducts (3-5 embryos/ampulla) of nonmated synchronous first- (n = 40) or third- (n = 15) estrous recipients. Blood samples were collected from the jugular vein of recipient gilts on Days 3, 12, and 30 of gestation and the sera were analyzed for progesterone and free (unconjugated) estrogens by use of radioimmunoassays. Recipient gilts were subsequently slaughtered between Days 30 and 40 to assess embryonic losses. Mean number of ovulations was lower among first-estrous vs. third-estrous recipients (8.9 +/- 0.7 vs. 11.4 +/- 0.7; p < 0.05). Percentage of recipients that maintained pregnancy was similar between first- and third-estrous gilts (67.5 vs. 60.0%) and recovery of total conceptuses (normal and degenerating) resulting from transfer of one-cell- and cleavage-stage embryos did not differ among first- vs. third-estrous gilts (76.1 vs. 78.2%). Similarly, percentage of viable fetuses in first-estrous gilts that were pregnant from transfer of one-cell- and cleavage-stage embryos was not different from that of third-estrous gilts (69.3 vs. 75.6%). Percentages of total conceptuses and viable fetuses in first- and third-estrous gilts that were recipients of cleavage-stage embryos only also did not differ (p > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cleavage of pig embryos after labeling with fluorescent dyes

In studies on embryonic development, treated and control ova could be co-mixed before transfer to recipients if nontoxic labels for ova were available. These experiments were conducted to determine whether pig ova would continue to cleave after being stained with the fluorochromes tetramethylrhodamine isothiocyanate (TRITC) and fluorescein isothiocyanate (FITC). In the first experiment, pig ova stained with TRITC and unstained control ova were transferred into opposite oviducts of recipient gilts. In the second experiment, ova stained with TRITC and ova stained with FITC were transferred into opposite oviducts of recipient gilts. Embryos were recovered 96 h after transfer (Day 6; Day 0 = onset of estrus), the presence of fluorescence was determined, and the number of nuclei per embryo was assessed. Stained ova retained sufficient fluorochrome to permit detection until the zonae pellucidae were shed. Development of embryos stained with TRITC was equal to that of unstained control embryos. However, development of embryos stained with FITC appeared slightly retarded in comparison to that of TRITC-stained embryos. These findings demonstrate the efficacy of the fluorescent staining technique for pig ova during the first six days of pregnancy.     

Acid phosphatase and leucine aminopeptidase activity in the uterine flushings of non-pregnant and pregnant gilts

The activities of uteroferrin, measured as acid phosphatase (AP), and an aminoacylpeptidase (AA) were measured in uterine flushings collected from gilts on Days 6, 8, 10, 12, 14, 15, 16 and 18 of the oestrous cycle and pregnancy (N = 37). Changes in AP (P less than 0.05) were associated with day for both specific and total AP in non-pregnant and pregnant gilts. For pregnant and non-pregnant gilts, AP activity was greatest between Days 14 and 16 and then decreased to Day 18. The AA specific activity increased (P less than 0.01) between Days 10 and 12 of the oestrous cycle and pregnancy, but neither effects of pregnancy nor day by pregnancy status interaction were detected. The AA total activity was greater for pregnant gilts (P less than 0.01). These data suggest an inhibitory effect of oestrogens of blastocyst origin on synthesis and/or secretion of uteroferrin, but not AA.     

Regulation of gene expression and cellular localization of prostaglandin synthase by oestrogen and progesterone in the ovine uterus

Expression of the gene for prostaglandin synthase (PGS) was examined in whole endometrial tissue derived from ewes during the oestrous cycle (Days 4-14), on Day 15 of pregnancy and following ovariectomy and treatment with ovarian steroid hormones. Whilst no significant differences were seen in PGS mRNA concentrations analysed by Northern blot analysis in endometrial tissue during the oestrous cycle or in early pregnancy, treatment of ovariectomized (OVX) ewes with oestradiol-17 beta markedly reduced endometrial PGS mRNA concentration. There was no difference in PGS mRNA concentration in ewes treated with progesterone, either alone or in conjunction with oestrogen, from that in OVX controls. In contrast, differences in immunolocalization of PGS observed in uterine tissue from OVX-steroid-treated ewes were much more marked and reflected similar changes seen previously in the immunocytochemical distribution of endometrial PGS during the oestrous cycle. In OVX ewes and those treated with oestrogen, immunocytochemical staining for PGS was seen in stromal cells, but little immunoreactive PGS was located in the endometrial epithelial cells. However, in ewes treated with progesterone alone or with oestrogen plus progesterone, PGS was found in luminal and glandular epithelial cells and in stromal cells. Intensity of immunostaining for PGS in endothelial cells and myometrium did not differ between the treatments. Thus, whilst oestrogen lowers PGS mRNA in the endometrium, presumably in stroma, it may also increase the stability of the enzyme itself in the stromal cells. Although oestradiol-17 beta has no effect on PGS in endometrial epithelium, progesterone stimulates the production of PGS in endometrial epithelial cells without altering the overall abundance of PGS mRNA in the endometrium as a whole. Conceptus-induced changes in PGF-2 alpha release by ovine endometrium would not appear to be mediated via effects on PGS gene expression or protein synthesis.     

Effect of centchroman on tubal transport and preimplantation embryonic development in rats

A single oral administration of centchroman (1.25 mg/kg) to adult female rats within 24 h of mating induced slight acceleration in the rate of transport of embryos through the oviducts. The compound did not seem to produce any deleterious effect on preimplantation embryonic development since well organized and apparently normal embryos were collected from the genital tract up to Day 12 of pregnancy. The recovery rate of embryos from centchroman-treated rats was, however, significantly reduced after Day 4 of pregnancy. There was some stimulation in the rate of cleavage of embryos and morula to blastocyst transformation, but retardation in the shedding of the zona pellucida. The rate of blastocyst formation was not altered when 6-8-cell embryos collected from the oviducts of control rats were transferred to the uteri of control or centchroman-treated females. A delay in zona shedding was observed in the centchroman-treated recipients.     

Development and survival of pig blastocysts after oestrogen administration on day 9 or days 9 and 10 of pregnancy

In Exp. 1, administration of 5 mg oestradiol valerate i.m. to pregnant gilts on Days 9 or 9 and 10 advanced the uterine secretion of calcium, protein, and acid phosphatase as demonstrated by levels recovered in the uterine flushings of females unilaterally hysterectomized on Day 11. Upon removal of the remaining uterine horn on Day 12, protein and acid phosphatase increased while Ca2+ decreased in oestradiol-treated gilts as did PGF. In contrast, a 4-fold increase in recoverable Ca2+ occurred from Days 11 to 12 in control gilts. Recoverable oestradiol-17 beta was increased in all 3 groups on Day 12 and plasmin inhibitor concentration increased in oestradiol-treated gilts. Two-dimensional PAGE demonstrated the appearance of a group of very acidic polypeptides in oestradiol-treated gilts. Blastocysts recovered from the second uterine horn had undergone elongation to the filamentous morphology in all 3 groups. In Exp. 2, oestradiol valerate was administered to pregnant gilts on Day 9 or Days 9 and 10 followed by total hysterectomy on Day 16. No differences in recoverable Ca2+ or protein were found, but acid phosphatase was decreased by 75% after oestradiol treatment. Recoverable oestradiol was decreased in oestradiol-treated gilts while PGF and plasmin inhibitor concentrations were unaffected. Compared with the control gilts, blastocysts recovered from oestradiol-treated gilts were fragmented and degenerating on Day 16. PAGE demonstrated greatly intensified staining of the group of acidic polypeptides in oestradiol-treated gilts. These results indicate that oestradiol treatment on Day 9 of pregnancy advances uterine secretory response, but that blastocyst elongation can occur in this uterine environment and in the presence of declining intraluminal Ca2+ levels.(ABSTRACT TRUNCATED AT 250 WORDS)     

Transfer of vitrified blastocysts from one or two superovulated Large White Hyperprolific donors to Meishan recipients: reproductive parameters at Day 30 of pregnancy

The present study was designed to determine the effect of pooling embryos from two donors on the reproductive success of transfer of vitrified/warmed porcine blastocysts. Intact blastocysts were collected from superovulated Large White Hyperprolific gilts (n = 24) on Days 5-5.5 after artificial insemination. Embryos were recovered by flushing the uterine horns, and unhatched blastocysts were selected. Vitrification and warming were performed as described by Berthelot et al. [Cryobiology 41(2000) 116]. To evaluate in vitro development, 37 vitrified/warmed blastocysts were cultured, non-vitrified embryos (n = 48) were used as controls. Embryo transfers were conducted in asynchronous (-24 h) Meishan gilts (n = 20). Twenty vitrified/warmed blastocysts were surgically transferred into one uterine horn. Ten recipients received embryos from one donor (Group 1) and the other 10 transfers were performed with mixed embryos from two donors (Group 2). Pregnancy was assessed ultrasonographically at Day 25 after estrus and recipients were slaughtered at Day 30 after transfer. In vitro survival rate of the vitrified/warmed blastocysts was lower (P < 0.01) than that from control embryos (73.0% versus 93.7%). The pregnancy rate for Group 1 (70%) was not different (P > 0.05) than that from Group 2 (90%). No significant differences were detected between Groups 1 and 2 for in vivo embryo development (number fetuses/transferred embryos in pregnant recipients) or in vivo embryo survival (number viable fetuses/transferred embryos in pregnant recipients). However, the in vivo efficiency (number viable fetuses/total transferred embryos) was higher (P < 0.05) when transfers were performed with embryos from two donors (19.5% versus 30.5%). These results indicate that pooling embryos from two donors increases the in vivo efficiency after transfer of vitrified/warmed porcine blastocysts.     

Peripheral plasma prolactin concentrations during oestrous cycles in different types of primitive gilt

Plasma prolactin concentrations were determined by radioimmunoassay during oestrous cycles and around the time of oestrus in different types of primitive gilts: Vietnamese, Zlotnicka and wild-boar X domestic pig hybrids. The animals were bled without stress from an indwelling arterial catheter. The following results were obtained: (1) in all gilts the main prolactin peak was observed at Day 15 or 16 of the oestrous cycle; (2) Vietnamese and hybrid gilts showed a second smaller prolactin surge after (Day 2) or before (Day 17) oestrus; (3) base levels of prolactin during the oestrous cycle were 14.8 +/- 0.93 ng/ml (Vietnamese gilts), 13.2 +/- 1.05 ng/ml (Zlotnicka gilts) and 15.6 +/- 2.01 ng/ml (hybrid gilts). The 15-16-day prolactin peaks reached maximum values of 36.4, 43.4 and 56.5 ng/ml respectively.     

Effect of oestrous cycle and early pregnancy on uterine production and expression of immune regulatory factors in gilts

This study was undertaken to characterize uterine immune factors involved in the establishment of pregnancy in gilts. Thirty crossbred Yorkshire-Landrace gilts of similar age and weight were observed twice a day for oestrous behaviour with intact boars. On the day of first standing oestrus (Day 0) and 12h later, 15 gilts were inseminated with pooled semen from Duroc boars of proven fertility. Pregnant gilts were slaughtered either on Days 10, 15 or 25 of gestation (n=5 per day). The other 15 gilts were not inseminated and were slaughtered on either Days 0, 10 or 15 of the oestrous cycle (n=5 per day). Immediately after slaughter, endometrial tissue samples from the mesometrial side were removed for gene expression using RNase protection assay and in situ hybridization methodologies. The other uterine horn was flushed with 20 ml of PBS to collect the uterine fluid. In pregnant gilts, endometrial interleukin (IL)-6 mRNA expression was higher on Day 15 than on Days 10 and 25 (P<0.01 and P<0.1, respectively). On Day 15, IL-6 expression was also significantly higher (P<0.01) in pregnant gilts than in cyclic gilts. In both pregnant and cyclic gilts, transforming growth factor (TGF)-beta2 in uterine fluid was significantly higher (P<0.0001) on Day 15 than on Day 10. At the gene expression level, TGF-beta2 also increased between Days 10 and 15 in both cyclic and pregnant gilts but differences were not significant. On Day 15, concentrations of interferon-gamma and prostaglandin E(2) (PGE(2)) in uterine fluid were markedly higher (P<0.001) in pregnant gilts than in cyclic gilts, whereas the total amount of TGF-beta2 in uterine fluid and its endometrial expression were approximately 70% higher although this increase was not significant. Finally, tumour-necrosis factor-alpha and granulocyte-macrophage/colony-stimulating factor mRNA expressions were undetectable in all endometrial samples. In conclusion, production and/or expression of uterine TGF-beta2, IL-6 and PGE(2) increased during the embryonic attachment period and are coincidental with embryonic interferon-gamma production.     

Effect of porcine conceptus secretory proteins on interestrous interval and uterine secretion of prostaglandins

Porcine conceptus secretory proteins (pCSP) were obtained from medium in which pig conceptuses, collected on Day 15 of pregnancy, were cultured for 30 h. Culture medium was pooled, dialyzed, and concentrated by Amicon ultrafiltration for intrauterine infusion. Serum proteins (SP) were obtained from blood collected from a Day 15 pregnant gilt and diluted for intrauterine infusion. Catheters were placed into both uterine horns and the inferior vena cava of cyclic (Day 8) gilts. Single blood samples were collected at 0800 h on Days 9, 10, and 11. On Day 11, all gilts received 1 mg estradiol-17 beta (E2) i.m. at 0800 h. Protein infusions commenced on Day 12 and continued through Day 15, twice daily at 0800 h and 2000 h. Protein infusions per uterine horn were (1) 4.0 mg pCSP + 4.0 mg SP (pCSP, 4 gilts) and (2) 8.0 mg SP (SP, 4 gilts). Blood samples were collected every 15 min on Days 12 through 17 between 0805 h and 1100 h. Single blood samples were collected at 0800 h after Day 17 until gilts exhibited estrus. Concentrations of prostaglandin (PG) E, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), and progesterone (P4) were measured by specific radioimmunoassays. Interestrous intervals for pCSP-treated (18.2 days) and SP-treated (18.0 days) gilts were not different (SEM = 0.8 days) and temporal changes in concentrations of P4 in plasma did not differ between pCSP-treated (29.2 ng/ml) and SP-treated (31.2 ng/ml) gilts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine pattern and external oestrous symptoms at second and fourth oestrus in gilts

The peripheral blood plasma levels of LH, oestradiol-17β and progesterone were recorded during the second and fourth pro-oestrous—oestrous periods in six crossbred (Swedish Landrace X Swedish Yorkshire) gilts. The relationships between hormonal levels, external heat signs and ovarian function were studied.Blood samples were taken every third hour during the pro-oestrous—oestrous periods and during this time the heat detection was performed when blood was collected, otherwise twice daily. The ovaries were inspected by laparoscopy after the first, second and fourth oestrus. The gilts were slaughtered after the fifth oestrus and the genital organs examined.In the five gilts showing five successive regular heats the duration of the second pro-oestrus (reddening and swelling of the vulva) was significantly longer (56.4 ± 5.3 h) than that of the fourth (23.4 ± 6.3 h). The oestrus (standing reflex) duration did not differ, being 51.6 ± 5.4 h for the second and 52.2 ± 9.3 h for the fourth oestrus. The mean oestradiol-17β level was significantly increased during the fourth pro-oestrous—oestrous period (43.9 ± 0.75 pmol) as compared to the second (37.8 ± 0.73 pmol). The LH level was also significantly higher during the fourth (1.61 ± 0.08 μg/l) than during the second pro-oestrous—oestrous period (1.25 ± 0.08 μg/l). There was, however, no difference in the duration of elevated oestradiol levels (> 30 pmol/l). In spite of the higher oestradiol-17β levels, the duration of the external heat signs was reduced during the fourth pro-oestrus when compared to the second. This phenomenon might be explained by a change in susceptibility of vulvar hormonal receptor mechanisms.The sixth gilt displayed three normal heats, but failed to show standing reflex and to ovulate thereafter. The hormonal patterns were normal during the second pro-oestrous—oestrous period. At the expected fourth heat there was a rise of oestradiol but no preovulatory LH peak occurred.     

Effects of media NaCl concentration and osmolarity on the culture of early-stage porcine embryos and the viability of embryos cultured in a selected superior medium

One- and 2-cell porcine embryos were obtained from oviductal flushes and cultured for 96 hours in media with varied osmolarity that resulted from alterations in NaCl and sorbitol content. The viability of experimental embryos cultured to advanced stages was determined by comparison with that of the controls, noncultured embryos transferred to recipient gilts. The data suggest that variation in embryonic development in the experimental media is related to the NaCl concentration rather than to osmolarity. Increased NaCl concentration impairs development of the embryos to the advanced morula/blastocyst stages (P<0.001). There was no difference in the pregnancy rate between the recipients of cultured (45%) and noncultured (57%) embryos on Day 25. There was, however, a higher embryonic survival rate (P<0.05) within the control gilts.     

Attainment of puberty in female pigs: Clinical appearance and patterns of progesterone,oestradiol-17β and LH

The object of the study was to investigate the clinical and endocrine patterns of progesterone, oestradiol-17β and LH during the peripubertal period in female pigs. Crossbred gilts were penned in groups at an age of 10–12 weeks and boars were kept in adjacent pens during the entire experimental period. Daily oestrous checks started at 4.5 months of age and the gilts were slaughtered after their third heat. At the age of 4.5–5 months a permanent catheter was inserted in the cephalic vein and blood samples were collected from the gilts once daily until either the first or second oestrus. In three gilts hourly blood samples were taken during their first and second oestrus, beginning at early pro-oestrus.The gilts showed their first oestrus at the average age of 183 days. No corpora lutea from earlier ovulations were observed in gilts laparoscoped after their first detected oestrus. During the 30-day period before first oestrus the mean daily progesterone levels varied between 32 and 329 pmol/l. The average levels of oestradiol-17β varied between 15.6 and 30.8 pmol/l. There was no tendency for the oestradiol-17β level to rise before onset of first pro-oestrus. The average levels of LH varied between 0.15 and 0.94 μg/l. The statistical analyses revealed no significant relationship between the level of the hormones studied and onset of first oestrus. The mean progesterone levels during the first and second oestrous cycles were almost identical, however. Oestradiol-17β increased gradually during pro-oestrus, reaching maximum levels before onset of oestrus and thereafter decreasing sharply to values around 30 pmol/l. The oestradiol-17β levels were higher at the second than at the first pro-oestrous period. The concentrations of plasma LH rose sharply with declining plasma levels of oestradiol-17β. The duration of elevated plasma LH levels (> 1 μg/l) was, on average, 26 h and the LH levels were higher during the first oestrus than during the second oestrus. The first rise in progesterone was observed 11–29 h after the LH levels had decreased to concentrations below 1 μg/l.     

Intrauterine migration of the porcine embryo: influence of estradiol-17 beta and histamine

The role of estradiol-17 beta (E2) in migration of the porcine embryo was examined (Experiment 1) by observing the distribution of Silastic (polydimethyl siloxane, Medical Adhesive Silicone Type A, Dow Corning) beads impregnated with cholesterol or E2 (n=5 gilts per treatment) after 5 days in utero (Day 12 of the estrous cycle, Day 0=1st day of estrus). Beads impregnated with E2 migrated farther (P less than 0.05) than those impregnated with cholesterol. Twenty additional gilts and sows were used to determine if histamine was involved with intrauterine migration (Experiment 2). On Day 6 of gestation the tip of each uterine horn was exposed and the subserosa of each of 5 gilts was injected with either vehicle, 8 mg of cromolyn sodium (an inhibitor of histamine release) or 8 mg of cromolyn sodium plus 1 mg of histamine. Four days later (Day 10), the excised uterus was examined for migration of embryos. An additional group of 5 gilts received 8 mg of cromolyn sodium on Days 6 and 10 and were examined on Day 12. Results from the second experiment demonstrated that cromolyn sodium treatment alone restricted (P less than 0.05) Day 10 embryos to the tip of the uterine horn but by Day 12 embryos had overcome this restriction. Injection of histamine overcame the inhibitory effects of cromolyn sodium and restored migration of Day 10 embryos. These experiments suggest that both E2 and histamine are involved in intrauterine migration of the porcine embryo. The extent to which these hormones might be interrelated during migration is not fully understood at this time.