Cyclic Gilts Research Articles

Maternal recognition of pregnancy in swine. I. Minimal requirement for exogenous estradiol-17 beta to induce either short or long pseudopregnancy in cycling gilts.

Five experiments were conducted to determine the minimal requirement for estradiol-17 beta (E2) injections to induce either short pseudopregnancy (SPP) or long pseudopregnancy (LPP) in cycling gilts. In experiments 1 through 5, E2 was injected i.m. on combinations of days between 11 and 25 days postestrus. Exogenous E2 on Days 12 and 13 or on Days 12 through 19 was optimal for induction of SPP or LPP, respectively. The duration of E2-induced diestrus was clearly demarcated between SPP (n = 73, duration 23-35 days) and LPP (n = 23, duration > 50 days). A sixth experiment was conducted to determine the minimum dose of intrauterine E2 required to induce SPP, and these gilts received intrauterine infusions of 0, 4, 40, or 400 micrograms E2 per 24 h on Days 12 and 13 postestrus. Pseudopregnancy was induced in 0 of 12, 1 of 4, 1 of 11, and 4 of 7 gilts in the treatment groups, respectively. These data suggest that uterine exposure alone is not sufficient to induce SPP. The present results indicate that the optimal signal for inducing LPP in unmated cycling gilts, and perhaps also for maternal recognition of pregnancy in mated gilts, may occur in two phases with continuous exposure to E2 being required from Day 12 to Days 17-19.

Effect of chronic treatment with a GnRH agonist (Goserelin) on LH secretion and early pregnancy in gilts

A slow release implant containing the gonadotrophin-releasing hormone (GnRH) analogue Goserelin acetate (D-Ser[Bu t] 6, Azgly-NH 2 10) a for GnRH receptor down-regulation in the pituitary was used in gilts, to determine what effects elimination of episodic luteinising hormone (LH) peaks may have on progesterone secretion in the oestrus cycle and in early pregnancy, and on the establishment and maintenance of pregnancies. Groups of non-mated and mated gilts were implanted with the GnRH agonist on day of oestrus (Day 0) and on Days 0, 14, 21 and 29 of pregnancy. The GnRH implant caused increased plasma LH concentrations for 38 h with a peak occurring 14 h post treatment, after which there was a prolonged period during which episodic LH release was abolished. A transient increase in progesterone concentration followed GnRH implant insertion and a steep decline on the day of abortion or the 2 days preceding it was seen in the majority of GnRH agonist treated gilts. In the cyclic gilts, the implant did not alter the pattern of progesterone secretion. In all gilts implanted before Day 29, pregnancy failed. However, in 50% of the gilts implanted on Day 29, pregnancy was maintained. In conclusion, these results indicate that episodic LH peaks play an important role in the establishment of pregnancy and are essential for the maintenance of pregnancy before Day 29.

Transforming growth factor-α in uterine luminal fluid of pregnant and cycling gilts from day 10 to 18

Energy efficient buildings need to take advantage of any renewable energy available. An opaque ventilated façade (OVF) is a kind of façade that absorbs solar energy and transfers it to the ventilation system. This way, the sensible ventilation load of the heating system can be reduced in the winter season. The energy saving of this system depends strongly on the weather variables, mainly solar radiation on the façade, ambient temperature and wind speed. In order to find the most convenient locations where the best OVF efficiency can be obtained, its performance has to be studied along a complete season. For this purpose in this study a sensitivity analysis with the most important weather variables was carried out and the energy saving values in 12 locations in Spain in the winter were evaluated using a numerical model previously validated with experimental data. The results showed that although the most influential weather variable was solar radiation, a combination of high temperatures and low wind speeds can also lead to important energy saving values. It was found that the most convenient locations for installing an OVF were those with low and medium winter severity climates, namely, in the southern and coastal regions of Spain (zones A3, B3, B4, C3 and C4).

Relationship between phosphoinositide hydrolysis and prostaglandin F 2α secretion in vitro from endometrium of cyclic pigs on day 15 postestrus

The mechanism for the luteolytic release of prostaglandin (PG)F 2α in swine is not known. This study examined the potential role of oxytocin (OT)-induced phosphoinositide (PI) hydrolysis in promoting PGF 2α secretion in vitro from the endometrium of cyclic gilts on Day 15 postestrus. In Experiment 1, endometrial PI hydrolysis was increased (P < 0.05) by 100 nM OT and was increased quadratically (P < 0.05) by LiCl, but was not affected by the LiCI × OT interaction (P > 0.30). PI hydrolysis was maximal at 50 mM LiCl and declined at 100 mM LiCl. In Experiment 2, endometrial PI hydrolysis and PGF 2α secretion were similarly increased (P < 0.01) by 0, 0.1, 1, 10, and 100 nM OT in a dose-dependent manner. In Experiment 3, the linear increase in PI hydrolysis occurring 0, 3, 5, 10, and 20 min after treatment was greater (P = 0.01) for tissue treated with 100 nM OT than for the tissue treated with 0 nM OT. The quadratic increase (P < 0.05) in PGF 2α secretion occurring 0, 3, 5, 10, and 20 min after treatment was greater (P < 0.05) for tissue treated with 100 nM OT than for the tissue treated with 0 nM OT. In Experiment 4, AIF 4 − (an activator of G P and phospholipase C) similarly increased (P < 0.01) PI hydrolysis and PGF 2α secretion. In Experiment 5, PI hydrolysis (P < 0.01) and PGFZ. secretion (P < 0.05) were increased by 100 nM OT but were not stimulated by cholera toxin (an activator of G s and adenylate cyclase). Cholera toxin also did not enhance PI hydrolysis and PGF 2α secretion in response to 0.1 or 100 nM OT. These results are consistent with the hypothesis that OT may induce PI hydrolysis to stimulate the endometrial secretion of PGF 2α during corpus luteum regression in swine.

Effects of anti-progesterone murine monoclonal antibodies on plasma progesterone concentrations and on anti-mouse reactions in cyclic pigs

The effect of murine anti-progesterone monoclonal antibodies on plasma progesterone levels was studied in cyclic gilts. Intravenous injection of increasing amounts of anti-progesterone antibodies (50–500 mg IgM) resulted in a concomitant rise in levels of antibody-bound progesterone (6–25 ng ml −1). At the same time a significant rise in plasma concentrations of total progesterone (3–21 ng ml −1) was observed immediately after the administration of antibodies. The net effect of progesterone binding by the monoclonal antibody on circulating progesterone levels was significant for the group of animals injected with at least 50 mg of antibody. The effect, however, was relatively small (1–11 ng ml −1) and more or less independent of the quantities of antibody administered. Plasma levels of circulating antibody capable of binding progesterone were still detectable at the end of the experimental period (± 13 days after injection). On the other hand, it appeared that in all animals, except the one injected with the largest quantity (500 mg) of antibody, the concentration of antibody-bound progesterone started to decrease as early as the first day after injection and was below detectable levels within 1 or 2 days. Mechanisms that may control the initial increase in progesterone levels and enable the animals to maintain adequate levels of free progesterone in circulation are discussed. Administration of a minimum dose of 32 mg antibody resulted in an anti-mouse immune response after the first injection, and subsequently in a neutralization of the anti-progesterone monoclonal antibodies immediately after the second injection. When smaller quantities of antibody (≤ 20 mg) were used, anti-mouse antibodies were detected only after the second or third injection.

Local increase of steroid hormone concentrations in blood supplying the uterus and oviduct in anaesthetized and conscious gilts

Sexually mature cycling gilts ( n = 5) with two recorded oestrous cycles were anaesthetized on Day 10 of the oestrous cycle. On both sides of the uterus, catheters were inserted into branches of the uterine artery proximal to the ovary. The tip of each catheter was placed close to, but above anastomoses with ovarian artery branches. This allowed collection of uterine arterial blood mixed with ovarian arterial blood supplying the uterus and oviduct. A third catheter was placed in the jugular vein. Catheters were exteriorized subcutaneously to the backs of the animals for blood sample collection. Simultaneous blood samples were collected as follows: (a) in anaesthetized animals, every 5 min for 1 h immediately after catheters were inserted during surgery, and every 10 min for 2 h, when the surgery was completed; (b) from conscious animals on Day 2 after surgery, every 10 min for 2 h in the morning and every 10 min for 2 h in the afternoon. Blood plasma samples were assayed for progesterone and androstenedione by RIA method. Mean values (±SEM) for progesterone measured in samples collected from branches of the uterine arteries and from the jugular vein in anaesthetized animals were 34 ± 1.25 ng ml −1 and 26 ± 1.31 ng ml −1 of plasma, respectively. In conscious animals the measurements showed 33 ± 0.90 ng ml −1 and 24 ± 0.81 ng ml −1 of plasma, respectively. Plasma concentration of androstenedione in branches of the uterine arteries and from the jugular vein in anaesthetized and conscious animals were 107 ± 5.26 pg ml −1 and 72 ± 5.50 pg ml −1, and 78 ± 4.54 pg ml −1 and 57 ± 3.77 pg ml −1, respectively. It was concluded that counter-current transfer of steroid hormones in ovarian pedicle vasculature on Days 10–11 of the oestrous cycle significantly elevates ( P < 0.0001) the local concentration of steroid hormones in arterial blood supplying the uterus and oviduct (35% for progesterone and 46% for androstenedione).

The Influence of Longtime Active GnRH‐Agonist on Hormonal Level and Follicular Development in Cyclic Gilts

The Influence of Longtime Active GnRH‐Agonist on Hormonal Level and Follicular Development in Cyclic Gilts

Detection of Functional Oxytocin Receptors on Endometrium of Pigs1

Oxytocin (OT) stimulates phosphoinositide (PI) hydrolysis and prostaglandin (PG) F2 alpha secretion from the endometrium of cyclic pigs, but the presence of specific endometrial receptors for OT has not been demonstrated in this species. Two experiments were performed to detect the presence of functional OT receptors on endometrium collected 15 days post estrus from cyclic gilts. OT receptor density and Kd were determined by receptor assay and Scatchard analysis. Hydrolysis of PI (i.e., incorporation of [3H]inositol into total inositol phosphates) and PGF2 alpha secretion were studied with use of incubations of endometrial explants. Concentrations of PGF2 alpha were log-transformed for analysis of variance and are expressed as means +/- standard error of log-transformed data. In experiment 1, mean density and mean Kd of OT receptors on endometrium of gilts were 29.2 +/- 5.54 fmol/mg protein and 1.59 +/- 0.23 nM, respectively. OT receptor density was significantly correlated with the ability of 100 nM OT to stimulate PI hydrolysis (r = 0.83, p < 0.05) and PGF2 alpha secretion (r = 0.87, p < 0.10), but was not highly correlated with receptor Kd (r = -0.08, p = 0.85). In contrast, OT receptor Kd was not highly correlated with OT-stimulated PI hydrolysis (r = -0.19, p = 0.68) or OT-stimulated PGF2 alpha secretion (r = 0.14, p = 0.86). OT-stimulated PI hydrolysis was also significantly correlated (r = 0.80, p < 0.05) with OT-stimulated PGF2 alpha secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the distribution of immune cells in the uteri of prepubertal and cycling gilts

To establish the cellular basis for the local immune response in the porcine uterus, immunohistochemical studies using a panel of monoclonal antibodies to pig leukocytes were conducted on uterine tissues from prepubertal and cycling gilts. In prepubertal uteri, neutrophils were the most predominant cell type, while MHC class II + cells and CD2 + T lymphocytes were also common. At the early-stage of the oestrous cycle, CD2 + T cells were numerous in the endometrium, particularly in the uterine epithelium and subepithelial regions. However, by the mid-stage of the cycle there was a significant and dramatic fall in CD2 + T cells and other lymphocytes expressing the CD4, CD8 and CD1 phenotypes, MHC class II + cells were predominant throughout the endometrium. During late oestrus there was a dramatic infiltration of neutrophils into the subepithelial stroma. A distinct increase in the CD2 + intraepithelial T lymphocyte population was also observed at this stage of the cycle. It was concluded that in the healthy, non-pregnant pig uterus T lymphocytes, macrophages and neutrophils were the prominent leukocyte cell types and their migration and distribution in the uterus was strongly influenced by the oestrous cycle. These immune cells may play an important interactive role in the cyclic cellular changes in both the structure and function of the endometrium. Furthermore, the leukocyte phenotypes found in the porcine endometrium indicate that a local cellular immune response could be elicited.

Immunocytochemical localization and changes in endometrial progestin receptor protein during the porcine oestrous cycle and early pregnancy.

Changes of progesterone receptor (PR) protein and cellular localization in the endometrium were evaluated during the oestrous cycle and early pregnancy of the gilt. During the oestrous cycle, the concentration of total PR protein within the endometrium was highest on Days 0-5 and decreased on Day 10. The endometrial concentration of PR reached a nadir on Day 12 and this level was maintained throughout the remainder of the oestrous cycle (Day 18). In pregnant gilts, the concentration of endometrial PR protein from Day 10 to Day 18 was similar to that in cyclic gilts. Western blot analysis with antiserum specific for the A and B isoforms of PR indicated that porcine endometrium expresses both isoforms of PR. Immunostaining was detectable for both the A and B isoforms of PR from Day 0 to Day 12 of the oestrous cycle. However, no staining was observed on Day 15 and Day 18 of the oestrous cycle or pregnancy Immunocytochemical localization of PR in the endometrium of cyclic gilts and pregnant gilts indicated that there was intense staining for PR in surface epithelium and glandular epithelium during oestrus (Day 0) and on Day 5. However, the staining was less intense on Day 7 and Day 10 of the oestrous cycle and no epithelial staining was observed after Day 12. PRs were present in the stroma and myometrium throughout the oestrous cycle and early pregnancy. The presence of conceptuses during pregnancy did not affect the loss of PR from the uterine epithelium after Day 10 of gestation. Down-regulation of epithelial PR might be one factor involved in the timing of luteolysis during the oestrous cycle as well as conceptus growth and placentation during early pregnancy.

Effects of prolactin on estrogen, cAMP and oxytocin secretion by porcine granulosa cells in vitro.

Granulosa cells were isolated from ovaries (without pre-ovulatory follicles or corpora lutea) of cycling gilts slaughtered at 8 months of age. They were cultured in the presence or absence of exogenous porcine prolactin (1, 10, 1,000, 10,000, or 100,000 pmol/ml medium). The secretion of estrogen, cAMP and oxytocin into the incubation medium was analysed by radioimmunoassay. It was found that prolactin (10, 1,000, 10,000 and 100,000 pmol/ml) inhibited estrogen secretion (p < 0.001) and stimulated cAMP output (p < 0.001, p < 0.001, not significant, and p < 0.01, respectively). Small doses of prolactin (1 and 10 pmol/ml) decreased (p < 0.001, p < 0.05), whilst high doses (1,000, 10,000 and 100,000 pmol/ml) increased (p < 0.001) oxytocin secretion by granulosa cell culture. The data suggest a direct action of prolactin on porcine ovarian cyclic nucleotides, steroid and nonapeptide hormone release.

Cytogenetic evaluation of ova from pubertal and third-estrous gilts.

Cytogenetic characteristics of ova surgically recovered from 19 first-estrous (pubertal) gilts were compared with those from 24 third-estrous gilts. Mean percentage recovery of ova was 82.1 +/- 2.9%. A total of 159 and 203 ova from first- and third-estrous gilts, respectively, were evaluated. Gilts at first and third estrus ovulated more mature ova (metaphase I-II chromosomes visible) than immature ova (germinal vesicle stage through prometaphase stage), but the percentage of immature ova in gilts at first estrus was greater than in those at third estrus (33.1 vs. 24.1%, p < 0.06). Percentage of mature ova with a normal haploid complement of chromosomes was similar in gilts at first and at third estrus (52.7 vs. 47.5%, p > 0.10). Percentage of hyperploid ova did not differ between first- and third-estrous gilts (10.8 vs. 5.9%, respectively); however, estimated frequency of nondisjunction appeared greater for gilts at first than at third estrus (21.6 vs. 11.9%, p < 0.10). These data suggest that ova of first-estrous gilts are inferior in quality compared to those of cyclic gilts.

Expression of c-fos in Porcine Endometrium during the Estrous Cycle and Early Pregnancy1

This study determined the pattern of expression of the c-fos oncogene in endometrium from pregnant and cyclic gilts. A transcript of the expected 2.2-kb size for the c-fos mRNA was detected in porcine endometrium from cyclic and pregnant gilts. Expression of endometrial c-fos mRNA was not different for Days 0, 5, 10, 15, or 18 cyclic or pregnant gilts. However, expression of c-fos mRNA was greater on Day 12 of pregnancy compared to Day 12 of the estrous cycle. Furthermore, expression of c-fos mRNA was related to developmental stages when pig conceptuses secrete estradiol, the primary determinant for maternal recognition of pregnancy. Throughout the estrous cycle and early pregnancy, immunoreactive fos protein was localized to the glandular and surface epithelial cells as well as myometrial cells. Results of this study indicate that endometrial expression of c-fos mRNA increases on Day 12 of pregnancy, coinciding with the establishment of maternal recognition of pregnancy in pigs.

The effect of space restriction during rearing on the attainment of puberty and subsequent reproductive activity of female pigs

Indoor rearing of gilts has been reported to delay the onset of puberty and reduce the expression of regular oestrous cycles in gilts. The possibility that this may be a consequence of insufficient allocation of floor space, i.e. crowding, was investigated in the present study by rearing gilts between 26 and 90 kg at two stocking densities which were based on the pigs' physical dimensions and spatial preferences and represented adequate (uncrowded) or inadequate (crowded) conditions. A total of 35 Large White/Landrace crossbred gilts were housed in groups of six in partially slatted concrete pens with two adjustable sides. Space allocation ( A, m 2) was adjusted weekly and was based on the equation A=k W 0.66 where W represented the mean group liveweight and the value of k was either 0.048 (uncrowded) or 0.025 (crowded). Daily exposure to a mature boar for 20 min day −1 commenced when the mean weight of the gilts reached 90 kg (160.9 days of age) and continued until puberty was reached or until the gilts were 250 days of age. Gilts were transferred to individual stalls in a dry sow house 10–12 days after puberty and mated at their second oestrus following daily heat checks. All mated gilts were slaughtered between 28 and 32 days after mating to determine pregnancy rate and embryonic survival. Although crowding during the 91 day rearing phase significantly reduced growth rate (uncrowded 732.0±14.1, crowded 688.0±14.1; P<0.05), there was no significant effect of treatment on either the proportion of gilts reaching puberty by 250 days of age or the mean age of the gilts at puberty (uncrowded 16 18 , 177.4 days; crowded 15 17 , 179.8 days). Among the gilts which reached puberty, although both the mating and pregnancy rates tended to be lower for the crowded gilts than for the uncrowded animals ( 13 15 vs. 16 16 mated; 9 13 vs. 14 16 pregnant at 28–32 days), and slightly fewer crowded gilts exhibited normal first oestrous cycle lengths ( 7 15 vs. 11 16 ), none of these differences were statistically significant. Neither ovulation rate nor embryonic survival were affected by treatment. These results demonstrate that space restriction which was sufficient to significantly impair growth rates during rearing did not adversely affect puberty attainment in gilts exposed to boars from 160 days of age, nor did it significantly affect subsequent reproductive performance in the limited number of animals used.

Distribution of lectin binding sites in the oviducts of cycling and hormone-treated pigs.

Gamete transport, fertilization, and early embryonic development take place in different regions of the oviduct and under different hormonal conditions. The objective of this study was to use lectins to detect variation in the distribution of glycosylated molecules on the surface of the epithelia that influence these events. Oviducts were collected from gilts on day 1 (estrus) and day 16 (diestrus) of the estrous cycle, and from gilts that were bilaterally ovariectomized on day 4 of the estrous cycle, and were subsequently treated with estradiol valerate (100 micrograms/day), progesterone (200 mg/day), or corn oil vehicle for 11 days. Six biotinylated lectins, Triticum vulgaris (WGA), Arachis hypogaea (PNA), Ulex europeus (UEA-I), Dolichos biflorus (DBA), Ricinus communis (RCA-I), and Canavalia ensiformis (Con A), were used to probe tissue from the isthmus and ampulla using peroxidase-conjugated avidin as the marker. In cyclic gilts, WGA and DBA stained more strongly in the isthmus than the ampulla on both cycle days. Staining with PNA was patchy, but greater on the apical surface of isthmic epithelium on day 16 than day 1. With UEA-I, staining was more intense in the ampulla on day 16 than day 1. Staining by PNA and UEA-I was suppressed in both the ampulla and isthmus with estradiol treatment. DBA staining was suppressed in the isthmus with both estradiol and progesterone treatments. Cilia were labelled by all lectins except WGA and PNA. Thus glycosylation patterns vary in the porcine oviduct with region and hormonal state, reflecting the variety of events that may be influenced.

Effect of ovarian antral follicle cauterization on the interestrus interval of the gilt

The objective of the present study was to determine if destruction of ovarian antral follicles by laser-cauterization affects CL lifespan during the estrous cycle of the gilt. Cyclic gilts were randomly assigned to either SHAM, laser (L) or laser-estradiol (L-E2) treatment groups, with the L-E2 group receiving a 5-mg intramuscular (i.m.) injection of estradiol-17β cypionate at the time of the first surgery. Ovarian antral follicles were laser-cauterized on either Days 12 and 14 (L12) or Days 14 and 17 (L14) of the estrous cycle. In the L12-E2 group, 3 of 4 gilts had extended mean interestrus intervals of more than 22 days compared with 0 of 4, 0 of 6, 0 of 7 and 1 of 5 gilts in the SHAM, L12, L14 and L14-E2 groups, respectively. The L12-E2 gilts had a longer (P<0.05) mean interestrus interval (23.5±1.3 days) than the L12 (20.0±1.1 days), L14 (20.7±1.0 days) and SHAM (20.5±1.3 days). The mean interestrus interval of L14-E2 gilts (21.8±1.2 days) did not differ from those of the L12-E2 group or the L12, L14 and SHAM group gilts. Six additional gilts were injected with 5 mg estradiol cypionate-17β to serve as nonsurgical controls for E2 treatment. Gilts (3 of 3) given an E2 injection on Day 12 had extended mean interestrus interval (26.0±2.6 days), while 2 of 3 gilts injected with E2 on day 14 had extended mean interestrus intervals (27.7±2.1 days). These results indicate that in cyclic gilts destruction of ovarian follicles by laser-cauterization did not affect CL lifespan, and that luteolysis is not dependent on the presence of antral follicles.

Factors contributing to the formation of experimentally-induced ovarian cysts in prepubertal gilts

Manipulation of an ovary during the follicular phase in cycling gilts or prepubertal gilts treated with PMSG and hCG results in formation of cysts on manipulated ovaries and corpora lutea (CL) of normal appearance on nonmanipulated ovaries. In contrast, cysts did not form after manipulation in luteal phase gilts. In the present experiment, daily administration of 50 mg progesterone to prepubertal gilts treated with PMSG and hCG established luteal phase concentrations of progesterone but did not lessen the incidence of manipulated-induced cysts. Number of cysts formed was associated with the number of follicles ≥5 mm at manipulation, which was inversely related to serum concentrations of progesterone. Number of receptors for LH/hCG in follicular tissues did not differ between manipulated and nonmanipulated ovaries but was greater in granulosa (P<.05) and theca (P<.08) from follicles with diameters ≥7 mm compared to 5 and 6 mm. Contents of estradiol, androstenedione, testosterone, progesterone and prostaglandins E 2 and F 2α in follicular fluid, granulosa and theca were not different between follicles ≥5 mm destined to form cysts or CL. Exogenous prostaglandin E 2 or F 2α given during follicular development failed to induce cysts. Profiles of progesterone and estradiol in peripheral serum and duration of luteal phase concentrations of progesterone were not different for gilts with induced cysts and gilts with CL. In conclusion, manipulation of follicles resulted in a failure to ovulate. Subsequent formation of cysts did not result from or result in a loss of steroidogenic function or the ability to bind LH to follicular receptors. These results demonstrate that the mechanism for ovulation is independent of other follicular processes, since ovulation can be disrupted without altering follicular steroidogenesis or subsequent luteinization.

Changes in ovulation rate, uterine capacity, uterine dimensions, and parity effects with selection for litter size in swine.

This study was conducted with random samples of pigs of a line (LS) selected for eight generations for litter size and a randomly selected control line (RS) in the Nebraska Gene Pool population and of crosses of these lines with a Large White-Landrace composite line (I) that was selected for an index of ovulation rate and embryonic survival to 50 d of gestation. Two experiments were done to obtain information on ovulation rate, uterine dimensions, and uterine capacity. In Exp. 1, 103 gilts were slaughtered 9 to 16 d after their second estrus to obtain reproductive tracts for evaluation of ovulation rate and uterine dimensions. In Exp. 2, unilateral hysterectomy-ovariectomy was performed 3 to 10 d after puberty in 109 gilts that were then mated at their next estrus and slaughtered at 93 to 100 d of gestation to recover reproductive tracts for evaluation. Litter size at birth was recorded at first (n = 414), second (n = 159), and third (n = 143) parity of pureline and crossline gilts. The cumulative response to eight generations of selection for litter size pooled over type of cross and parity was 1.21 +/- .38 pigs, in good agreement with the realized response of 1.06 pigs previously estimated for the period of selection. This response was due to an increase of 1.30 +/- .54 eggs in ovulation rate (measured by the number of corpora lutea in cyclic and pregnant gilts) and .66 +/- 1.28 pigs in uterine capacity (measured after unilateral hysterectomy-ovariectomy). No significant changes were found in uterine dimensions in cyclic gilts. Approximately 25% of the increase in litter size could be explained by a reduction in number of mummified pigs at birth, an indication that uterine capacity in late gestation was increased. Estimated differences between lines (gLS - gRS) were not significantly different for pureline and crossline gilts and sows, and no interactions of these estimates with parity were detected. Estimates of heterosis for LS x I and RS x I did not differ significantly, nor were interactions of heterosis with parity significant.

Responsiveness of porcine large and small luteal cells to luteotropic or luteolytic hormones and cell morphologic changes during the estrous cycle and pregnancy.

Isolated porcine luteal cells from d 10 and 15 of the estrous cycle (estrus = d 0) were incubated with or without combinations of FSH (0, 10, 10(2), 10(3) ng), LH (0, 10, 10(3) ng), oxytocin, or prostaglandin F2 alpha (PGF2 alpha) (each at 0, 10, 10(3), and 10(5) pg). Progesterone (P4) content was determined after overnight incubation (0 h) then at 2 and 24 h of incubation. The basal (0 h) P4 production of large cells (LC) from d 10 corpora lutea (CL) was 31-fold higher than that by small cells (SC) at 0 h. The LC and SC from d 10 but not those from d 15, were stimulated to a small extent by LH (P < .05). The FSH inhibited P4 production (P < .05) by SC at 24 h on d 10 and by LC after 2 or 24 h of incubation on d 15. There was no interaction between LH and FSH on P4 production. Oxytocin and PGF2 alpha decreased P4 production by d 15 LC at 2 h of incubation (P < .05) and by d 15 SC after 2 or 24 h of incubation (P < .05 and P < .01). The morphology of cells from CL of the cycle or early or mid pregnancy were examined using scanning and transmission electron microscopy (EM). Freshly isolated LC (using scanning EM) from d 10 contained many microvilli arranged in apparent networks on their membranes, but SC had smooth surfaces and contained only a few microvilli. Internally, LC had more small mitochondria than did SC and a different organization of smooth endoplasmic reticulum (SER). The SC from CL of pregnant (d 30 to 60) gilts contained more mitochondria than SC from CL of cyclic gilts. The results indicate that FSH, oxytocin, and PGF2 alpha can have a direct cellular luteolytic effect in the late luteal phase in pigs. The FSH influenced LC, whereas oxytocin and PGF2 alpha effected a more pronounced decrease in P4 from SC. The lower amount of P4 produced overall by SC may be associated with fewer microvilli, mitochondria, and SER in SC.

Pig membrana granulosa cells prevent resumption of meiosis in cattle oocytes

Membrana granulosa was isolated from healthy large antral follicles of prepubertal or cyclic gilts stimulated with PMSG or PMSG and hCG. Ultrastructural observations revealed that pieces of pig membrana granulosa were associated with the basement membrane. The cattle cumulus-enclosed oocytes (COC) were placed in the rolled pieces of the pig membrana granulosa (PMG). After 8 and 24 hr of coculture with PMG from prepubertal gilts, only 16% and 21% of oocytes underwent GVBD, respectively. PMG from PMSG-stimulated cyclic gilts blocked the resumption of meiosis in all COC. The inhibitory effect of heterologous granulosa cells was fully reversible. When COC were initially incubated for 2 and 4 hr, subsequent culture in PMG prevented GVBD in 100% and 36% of oocytes, respectively. This suggests that functional contact between COC and PMG was established during the first 2 hr of coculture. To follow metabolic cooperation between PMG and COC, PMG was prelabeled with 3H-uridine and cocultured with COC. Autoradiography on semithin sections revealed the intensive passage of 3H-uridine from PMG into the cumulus layer and an oocyte. COC placed in PMG after GVBD (8 and 12 hr of an initial incubation) did not extrude the first polar body. PMG isolated from cyclic gilts after PMSG and hCG stimulation also inhibited GVBD of COC. Since nearly all COC placed in PMG isolated 10 and 12 hr after hCG remained in the GV stage after 24 hr of coculture, the hCG stimulation did not substantially diminish the meiosis inhibiting activity of PMG.(ABSTRACT TRUNCATED AT 250 WORDS)