Supplemental progesterone during early pregnancy exerts divergent responses on embryonic characteristics in sows and gilts

Progesterone (P4) plays a key role in pregnancy establishment and maintenance; during early pregnancy, P4 stimulates the production and release of uterine secretions necessary for conceptus growth prior to implantation; therefore, exogenous P4 supplementation may improve embryo development. This study evaluated the effects of supplementation during early pregnancy with long-acting injectable progesterone or altrenogest on embryonic characteristics of sows and gilts. Thus, a total of 32 sows and 16 gilts were used. On day 6 of pregnancy sows and gilts were allocated to one of the following groups: non-supplemented; supplemented with 20 mg of altrenogest, orally, from days 6 to 12 of pregnancy; supplemented with 2.15 mg/kg of long-acting injectable progesterone on day 6 of pregnancy. Animals were killed on day 28 of pregnancy, and ovulation rate, embryo survival, embryo weight, crown-to-rump length, uterine glandular epithelium and endometrial vascularization were assessed. Treatments had no effect on pregnancy rate, embryo survival or endometrial vascular density (P > 0.05). Non-supplemented gilts presented larger and heavier embryos compared to gilts from supplemented groups (P < 0.05). Sows in the altrenogest group presented larger and heavier embryos compared to non-supplemented sows and sows supplemented with long-acting injectable progesterone. In conclusion, supplementation of sows and gilts with progestagen from day 6 of pregnancy can be used as a means to improve embryo survival without deleterious effects.     

Effects of oestrous synchronization with altrenogest in gilts on endometrial and embryonic characteristics

The use of altrenogest (ALT) supplementation for oestrous synchronization improves subsequent reproductive performance of gilts and sows. However, the causes of this improvement in reproductive performance after ALT treatment are not fully/clearly understood. The objective of this study was to evaluate the effects of ALT supplementation for oestrous synchronization in gilts on the endometrial glands and embryonic development characteristics at 28 days of pregnancy. Pregnant gilts were divided into two experimental treatments: Control (did not receive ALT; n = 9 gilts) and ALT (ALT feeding at 20 mg/day for 18 days; n = 9 gilts). At 28 days of pregnancy, six gilts from each treatment were slaughtered, and reproductive tracts were immediately evaluated. There was no statistical difference (P > 0.05) between treatments regarding ovulation rate, number of embryos, number of vital embryos and number of non-vital embryos. Embryo weight, length and embryonic vesicle weight were lower in ALT treatment compared with Control (P < 0.01), and it was lower in the cervical uterine region compared with apex uterine region, respectively (P < 0.05). Higher values of gland duct area, gland duct perimeter, percentage of the glandular area and total endometrial area were observed in ALT treatment compared with Control (P < 0.05). The use of ALT during 18 days for oestrous synchronization in gilts increased the gland duct area, perimeter and total endometrial area but did not increase the embryo number and embryo size at day 28 of pregnancy.     

Synchronization of oestrus in gilts with altrenogest: effects on ovulation rate and foetal survival

Previous studies have shown that use of altrenogest resulted in a high rate of fertility and increased litter size compared with controls under conditions of practical pig production. The present study was designed to evaluate whether ovulation rate and/or foetal survival were increased by altrenogest using crossbred gilts derived from one herd (n = 227) and introduced in the same piggery over 12 months. Each gilt was allocated to a treated group (n = 103) receiving an individual daily dose of 20 mg of altrenogest for 18 days in its feed or a control group (n = 124) after puberty had been diagnosed, (197 ± 1 day; mean ± SEM). They were inseminated (double AI) at the second induced or natural oestrus. Pregnancy was diagnosed by ultrasonography at Days 22 and 42 post-insemination in the absence of return to oestrus. Pregnant gilts were slaughtered at 48 ± 3 days of pregnancy following the second examination. The number of living and dead foetuses were recorded before uterine contents (foetuses and placentae) were weighed and the number of corpora lutea (CL) per ovary counted.Precise synchronization of oestrus was observed after the end of the progestogen administration, with 93% of the gilts in oestrus by Days 5 to 7. For the controls, the interval from first to second oestrus ranged from 17 to 25 days in 93% of the control gilts. The pregnancy rate was 89.3% for treated gilts and 77.4% for controls (P < 0.05). The ovulation rate was increased by the treatment (15.4 ± 0.3 vs 14.6 ± 0.3; mean ± SEM, P < 0.02). Although the altrenogest group had more foetuses (11.1 vs 10.6), this difference was not significant (P > 0.14). The percent of foetal survival was similar in both groups (64.9%; P > 0.27). The foetal and placental weights differed only between dams and increased with stage of gestation. The increase in litter size through feeding altrenogest was associated with an increased ovulation rate.     

Ultrasonographic characterization of the ovaries in non-pregnant first served sows and gilts

This study was aimed firstly, to examine the ovaries in non-pregnant first served sows and gilts by transcutaneous ultrasonography and secondly, to evaluate the suitability for this procedure to be performed routinely on farms. Two thousand five hundred and twenty-three females on a 1250-sow unit, synchronized with Regumate (gilts only) and/or gonadotropins (sows and gilts) not detected as returned to estrus by daily boar contact prior to scanning were ultrasonographically tested for pregnancy between days 20 and 114 postinsemination (p.i.). Of 256 sows (S) and 130 gilts (G) found to be non-pregnant the ovaries were visualized in 87.1 and 80.0% of them, respectively. Ovarian findings were: corpora lutea (CL); follicles of 2-6mm (F(2-6)); peri-ovulatory ovarian structures (POS; comprising follicles of 7-8mm and corpora haemorrhagica); single cysts (SC); oligocystic ovarian degeneration (OOD) and polycystic ovarian degeneration (POD). Their incidence was: CL>F2-6>POS>POD ( P<0.05 ) in both S and G. POD and SC plus OOD were more frequently in S ( P<0.05 ). The ovarian findings were related to the intervals of regular (days 18-25 p.i. (R1), 38-46 p.i. (R2)) and irregular service returns (days 26-37 p.i. (IR1), 47-114 p.i. (IR2)). Comparison within intervals: CL tended to be more frequently with P<0.05 only at IR2 in S. Comparison among intervals (R1 to IR2): The percentage of females (1) with CL tended to increase (S and G) and (2) with F2-6 plus POS decreased significantly (S; P<0.05 ) or tendentiously (G). SC plus OOD was higher before R2, POD after IR1 (S and G; P<0.05 ). In conclusion, the results indicate a high heterogeneity of ovarian structures in non-pregnant first served sows and gilts up to day 114 after service and suggest CL as an important cause for a delayed and, rather than POD, a failed service return. The results further demonstrate that transcutaneous ultrasonography is an appropriate and recommended method for examining the ovaries on farm in female pigs with reproductive failures.     

Prostaglandin-induced regression of porcine corpora lutea maintained by estrogen

Corpora lutea were marked with suture in 24 crossbred gilts on day 7 to 9 of the estrous cycle (first day of estrus = 0). All gilts were injected with 5 mg of estradiol benzoate (EB) daily from day 10 to 15 to extend the lifespan of corpora lutea, then the gilts were randomly assigned to two groups. On day 20, the 12 gilts of Group 1 were injected with 10 mg PGF_2α, and the 12 gilts of Group 2 were injected with saline. Ovaries were recovered 10 to 13 days after PGF_2α or saline injection. Ten gilts in Group 1 displayed estrus 5 ± 0.7 days after PGF_2α injection, but only two gilts in Group 2 displayed estrus during the experimental period. In gilts that displayed estrus, all marked CL had regressed. Marked CL were still present in all 12 gilts that failed to exhibit estrus during the experimental period. These results show that in the pig, PGF_2α caused regression of CL that were maintained beyond the normal luteal phase of the estrous cycle by EB treatment.     

The influence of embryo presence on prostaglandins synthesis and prostaglandin E2 and F2alpha content in corpora lutea during periimplantation period in the pig

We determined the expression of PGE2 synthase (mPGES-1), PGF synthase (PGFS), carbonyl reductase/prostaglandin 9-ketoreductase (CBR1) genes and the content of PGE2, PGF2alpha in porcine corpora lutea on Days 12-14 of pregnancy and Days 12-14 of the estrous cycle. For this study we used a surgically-generated model in which one of the uterine horns was cut transversely and a part of this horn was detached from the uterine corpus. The expression of mPGES-1, PGFS, and CBR1 genes and mPGES-1/PGFS ratio were significantly higher in corpora lutea of the pregnant gilts compared to the corpora lutea from the parallel ovaries of the cyclic gilts. There was no difference in mPGES-1, PGFS, CBR1 genes expression and mPGES-1/PGFS ratio between corpora lutea ipsi-(CL1) and contralateral (CL2) to the uterine horn with the developing embryos. The highest content of PGE2 was found in CL1 of the pregnant gilts. The PGE2/PGF2alpha ratio was significantly higher in CL1 of the pregnant gilts compared to corpora lutea from parallel ovary of the cyclic gilts. We suggest that the activity of the investigated genes is induced by compounds of embryonic origin which are not distributed only to the ipsilateral ovary but are transported within the mesometrium to both ovaries in a more systemic manner.     

A study of prostaglandin F2α as the luteolysin in swine: V comparison of prostaglandin F, progestins, estrone and estradiol in uterine flushings from pregnant and nonpregnant gilts

Uterine flushings were collected from 38 gilts representing Days 6,8,10,12,14,15,16 and 18 of the estrous cycle and pregnancy. The same group of gilts were represented within each of the respective days of the estrous cycle and pregnancy, i.e., three to six gilts per day per status. Uterine flushings (about 40ml) were assayed for prostaglandin F (PGF), estrone (E₁), estradiol (E₂), progestins (P) and protein. Nonpregnant gilts had higher (P<.01) concentrations of P in uterine flushings than pregnant gilts, but pregnant gilts had higher (P<.01) E₁ and E₂ concentrations. Significant day by status interactions were detected for E₁ (P<.05), but not for E₂ concentrations in uterine flushings. Total recoverable PGF and PGF concentrations in uterine flushings were greater (P<.01) in pregnant than nonpregnant gilts and significant (P<.01) day by status interactions were detected. In nonpregnant gilts, PGF increased between Days 12 and 16, i.e., during the period of corpora lutea (CL) regression. In pregnant gilts, PGF in uterine flushings increased markedly between Days 10 and 18. Total recoverable PGF on Day 18 of the estrous cycle was only 464.5 ± 37.6 ng as compared to 22,688.1 ± 1772.4 ng on Day 18 of pregnancy. Total recoverable protein was also higher (P<.01) in pregnant gilts. These data indicate that PGF synthesis and secretion by the uterine endometrium and/or conceptuses is not inhibited during pregnancy and suggest that PGF is sequestered within the uterine lumen of pregnant gilts, as is the total protein component of endometrial secretions referred to as histotroph.     

Responses to n-3 fatty acid (LCPUFA) supplementation of gestating gilts,and lactating and weaned sows

Feeding n-3 long-chain polyunsaturated fatty acids (LCPUFA) to gilts or sows has shown different responses to litter growth, pre-weaning mortality and subsequent reproductive performance of the sow. Two hypotheses were tested: (1) that feeding a marine oil-based supplement rich in protected n-3 LCPUFAs to gilts in established gestation would improve the growth performance of their litters; and (2) that continued feeding of the supplement during lactation and after weaning would offset the negative effects of lactational catabolism induced, using an established experimental model involving feed restriction of lactating primiparous sows. A total of 117 primiparous sows were pair-matched at day 60 of gestation by weight, and when possible, litter of origin, and were allocated to be either control sows (CON) fed standard gestation and lactation diets, or treated sows (LCPUFA) fed the standard diets supplemented with 84 g/day of a n-3 LCPUFA rich supplement, from day 60 of first gestation, through a 21-day lactation, and until euthanasia at day 30 of their second gestation. All sows were feed restricted during the last 7 days of lactation to induce catabolism, providing a background challenge against which to determine beneficial effects of n-3 LCPUFA supplementation on subsequent reproduction. In the absence of an effect on litter size or birth weight, n-3 LCPUFA tended to improve piglet BW gain from birth until 34 days after weaning (P = 0.06), while increasing pre-weaning mortality (P = 0.05). It did not affect energy utilization by the sow during lactation, thus not improving the catabolic state of the sows. Supplementation from weaning until day 30 of second gestation did not have an effect on embryonic weight, ovulation rate or early embryonic survival, but did increase corpora lutea (CL) weight (P = 0.001). Eicosapentaenoic acid and docosahexaenoic acid (DHA) levels were increased in sow serum and CL (P < 0.001), whereas only DHA levels increased in embryos (P < 0.01). In conclusion, feeding n-3 LCPUFA to gilts tended to improve litter growth, but did not have an effect on overall subsequent reproductive performance.     

Maintenance of pregnancy and levels of progesterone and relaxin in the serum of gilts following a stepwise reduction in the number of corpora lutea

The number of corpora lutea (CL) was reduced in pregnant gilts in a stepwise fashion. Eleven pregnant gilts were unilaterally ovariectomized at Day 30, leaving from 6 to 12 CL on the remaining ovary. At Day 40, the number of CL was again reduced by about half in each gilt and this was repeated on Day 50 until 1 to 3 CL remained. Blood was obtained to determine the level of progesterone in plasma on each day of surgery and 24 h later. Four gilts aborted; one had 1 CL and three had 2 CL. One gilt which had 1 CL resorbed the litter. The six gilts that maintained pregnancy from Day 50 to parturition had 1, 3, 2, 2, 2 and 2 CL, respectively. Gilts pregnant at Day 60 were also bled on that day and at 8-h intervals beginning 2 to 3 days prior to expected parturition at Day 114. At laparotomy on Day 50, gilts had from 3 to 20, nonluteinized follicles ranging from 12 to 20 mm in diameter. Hypertrophy of CL was not detected, nor were accessory CL formed. The level of progesterone in serum dropped significantly 24 h after surgery and rose to levels intermediate to pre- and postsurgery levels 10 days later. Parturition was uneventful and levels of relaxin and progesterone appeared normal.     

Corpus luteum susceptibility to prostaglandin F2α (PGF2α) luteolysis in hysterectomized prepuberal and mature gilts

The susceptibility of induced corpora lutea (CL) of prepuberal gilts and spontaneously formed CL of mature gilts to prostaglandin F_2α (PGF_2α) luteolysis was studied. Prepuberal gilts (120 to 130 days of age) were induced to ovulate with Pregnant Mare Serum Gonadotropin and Human Chorionic Gonadotropin (HCG). The day following HCG was designated as Day 0. Mature gilts which had displayed two or more estrous cycles of 18 to 22 days were used (onset of estrus = Day 0). Gilts were laparotomized on Day 6 to 9, their CL marked with sterile charcoal and totally hysterectomized. On Day 20, gilts were injected IM with either distilled water (DW), 2.5 mg PGF_2α or 5.0 mg PGF_2α. An additional group of prepuberal gilts was injected with 1.25 mg PGF_2α, a dose of PGF_2α equivalent, on a per kilogram body weight basis, to the 2.5 mg PGF_2α dose given to the mature gilts. The percentages of luteal regression on Day 27 to 30 for mature and prepuberal gilts given DW, 2.5 mg PGF_2α and 5.0 mg PGF_2α were 0.0 vs 4.4, 43.5 vs 96.8 and 47.7 vs 91.6, respectively; the percentage of luteal regression for the prepuberal gilts given 1.25 mg PGF_2α was 75.1. These results indicate that induced CL of the prepuberal gilt were more susceptible to PGF_2α luteolysis than spontaneously formed CL of the mature gilt and that pregnancy failure in the prepuberal gilt could be due to increased susceptibility of induced CL to the natural luteolysin.     

Age at puberty, ovulation rate, uterine length, prenatal survival and litter size in Chinese Meishan and Yorkshire females

Studies on the ovulation rate, prenatal survival and litter size of Chinese Meishan pigs have given widely divergent results depending on the extent of inbreeding of the animals, their original genetic diversity, the age and parity, and the conditions of management. To obtain meaningful results, it is necessary to characterize the population under study. The following report characterizes populations of Meishan and Yorkshire of a widely diverse background. First farrowing data were collected on 21 Meishan and 20 Yorkshire gilts. Meishan gilts had 12.4 fully formed piglets and Yorkshire gilts had 7.4 fully formed piglets (P < 0.01). Meishan gilts averaged 1.86 mummified fetuses per litter vs 0.05 per Yorkshire litter (P < 0.01). Yorkshire piglets averaged 1.3 kg body weight at birth vs 0.9 kg for Meishan piglets (P < 0.01). At 47 days of second gestation, 19 Meishan and 12 Yorkshire sows averaged 22.7 and 16.3 corpora lutea (CL), respectively (P < 0.01). Uterine length and number of fetuses were not different (P > 0.40) in the two breeds. Daily estrous detection of 50 Meishan and 34 Yorkshire gilts began at 60 and 120 days of age, respectively. Meishan gilts reached sexual maturity at 95 days of age, which was 105 days earlier than Yorkshire gilts (P < 0.01). Meishan gilts were in estrus nearly 1 day longer than Yorkshire gilts at first, second and third estrus (P < 0.05). No differences in cycle length between breeds were detected for the first or second estrous cycle (P > 0.60). Nineteen Meishan gilts were slaughtered at 51 days of gestation and their reproductive tracts were recovered. The mean number of dissected CL (17.0), number of fetuses (13.1), total uterine length (396 cm), spacing per fetus (29.9 cm), allantoic (124.9 ml) and amniotic (32.2 ml) volumes, crown-rump length (82.8 mm), weight (35.4 g), sex, and direction of each fetus were determined. Chinese Meishan gilts reached puberty much earlier and were in estrus longer than Yorkshire gilts and Meishan sows had more CL than Yorkshire sows.     

Synchronization of estrus and ovulation in sows not conceiving in a scheduled fixed-time insemination program

A field study was conducted to investigate the effectiveness of a treatment with altrenogest, eCG and hCG or the GnRH-analogue D-Phe(6)-LHRH to synchronize estrus and ovulation of sows diagnosed as non-pregnant in order to reintegrate them back into a scheduled fixed-time insemination program. Sows (n=531) diagnosed as non-pregnant by ultrasonography on days 21-35 after insemination were subjected to one of three treatments: (1) 16 mg altrenogest/day/animal orally for 15 days to block follicular growth, followed by injection of 1000 IU eCG intramuscularly (i.m.) 24h after withdrawal of altrenogest to stimulate follicular growth and 500 IU hCG i.m. 78-80 h after eCG to induce ovulation; (2) similar to (1) except that 20mg altrenogest and 800 IU eCG were used and (3) similar to (2) except that 50 microg D-Phe(6)-LHRH was used to induce ovulation. Females were artificially inseminated (AI) twice at 24 and 40 h, respectively, after hCG/D-Phe(6)-LHRH. Success of treatments was checked by ultrasonography of the ovaries. Rates of conception and farrowing (CR, FR), and number of total and live born piglets (TB, LB) were recorded and compared to those of synchronized first served sows. Females had differing ovarian structures prior to treatment. Altrenogest effectively blocked follicular growth in >80% of the females irrespective of dosage, but 16 mg increased the development of polycystic ovarian degeneration. Four to 18% of the females still had corpora lutea after altrenogest. Most females ovulated either between both inseminations or thereafter (P<0.05). Females treated with D-Phe(6)-LHRH tended to ovulate earlier than those injected with hCG. The CR and FR were up to 25% lower for sows diagnosed as non-pregnant than for sows after first service (P<0.05). Among sows diagnosed as non-pregnant the CR was higher in females treated with D-Phe(6)-LHRH (P<0.05). No differences were found in regard to numbers of TB and LB. In conclusion, a treatment with 20mg altrenogest per day per animal, followed by 800 IU eCG and 50 microg the GnRH-analogue D-Phe(6)-LHRH is appropriate to synchronize estrus and ovulation of sows diagnosed as non-pregnant. Whether there might be a need to feed altrenogest for a longer interval of 18 days has to be investigated.     

The effects of post-weaning progestagen treatment (Regumate) of early-weaned primiparous sows on subsequent reproductive performance

This study investigated the effects of feeding the orally active progestagen, altrenogest (Regumate) post-weaning on the subsequent reproductive performance of early weaned sows. Ninety (90) Large White/Landrace first parity sows were randomly assigned to three treatments. Treatment 1 (EW) and treatment 3 (CW) sows were weaned on day 12 and day 24 post-partum, respectively while treatment 2 sows (EW-R) were weaned on day 12 post-partum and received an individual daily dose of 20 mg of Regumate on days 13 to 24 post-partum inclusive. Each sow was mated naturally at least twice at the first post-weaning or post-treatment oestrus and slaughtered on days 25–28 of pregnancy to determine the number of corpora lutea and embryos. Regumate-to-oestrus and weaning-to-oestrus intervals were similar for EW-R and CW sows (6.2 vs. 5.6 days). However, both intervals were significantly shorter (P<0.01) than the weaning-to-oestrus interval of EW sows (7.3 days). An excellent synchronization of oestrus was achieved with Regumate treatment with 97% of treated sows in oestrus within 7 days of Regumate withdrawal compared with 64% for EW sows (P<0.01) and 87% for CW sows (P>0.05). Treatment with Regumate resulted in a significant increase in ovulation rate (16.9 vs. 15.4 and 14.9 for treatments EW-R, EW and CW, respectively; P<0.05) and a non-significant increase in early embryonic survival (77% vs. 68% vs. 68% for treatments EW-R, EW and CW, respectively; P>0.05). These results indicate that Regumate feeding is a potential management tool to alleviate the diminished reproductive performance associated with early weaning regimes since it leads to successful control of oestrus, higher ovulation and embryo survival rates and thus a greater potential litter size.     

Prostaglandin-induced regression of porcine corpora lutea maintained by estrogen.

Corpora lutea were marked with suture in 24 crossbred gilts on day 7 to 9 of the estrous cycle (first day of estrus equals 0). All gilts were injected with 5 mg of estradiol benzoate (EB) daily from day 10 to 15 to extend the lifespan of corpora tutea, then the gilts were randomly assigned to two groups. On day 20, the 12 gilts of Group 1 were injected with 10 mg PGF-2ALPHA, and the 12 gilts of Group 2 were injected with saline. Ovaries were recovered 10 to 13 days after PGF-2ALPHA or saline injection. Ten gilts in Group 1 displayed estrus 5 plus or minus 0.7 days after PGF-2ALPHA injection, but only two gilts in Group 2 displayed estrus during the experimental period. In gilts that displayed estrus, all marked CL had regressed. Marked CL were still present in all 12 gilts that failed to exhibit estrus during the experimental period. These results show that in the pig, PGF-2ALPHA caused regression of CL that were maintained beyond the normal luteal phase of the estrous cycel by EB treatment.     

Passive immunization of the pig against gonadotropin releasing hormone during the follicular phase of the estrous cycle

Three experiments were conducted to determine the effects of passively immunizing pigs against gonadotropin releasing hormone (GnRH) during the follicular phase of the estrous cycle. In Experiment 1, sows were given GnRH antibodies at weaning and they lacked estrogen secretion during the five days immediately after weaning and had delayed returns to estrus. In Experiment 2, gilts passively immunized against GnRH on Day 16 or 17 of the estrous cycle (Day 0 = first day of estrus) had lower (P<0.03) concentrations of estradiol-17beta than control gilts, and they did not exhibited estrus at the expected time (Days 18 to 22). When observed three weeks after passive immunization, control gilts had corpora lutea present on their ovaries, whereas GnRH-immunized gilts had follicles and no corpora lutea. The amount of GnRH antiserum given did not alter (P<0.05) serum concentrations of LH or pulsatile release of LH in sows and gilts. In Experiment 3, prepuberal gilts were given 1,000 IU PMSG at 0 h and GnRH antiserum at 72 and 120 h. This treatment lowered the preovulatory surge of LH and FSH, but it did not alter serum estradiol-17beta concentrations, the proportion of pigs exhibiting estrus, or the ovulation rate. These results indicate that passive immunization of pigs against GnRH before initiation of or during the early part of the follicular phase of the estrous cycle retards follicular development, whereas administration of GnRH antibodies during the latter stages of follicular development does not have an affect. Since the concentration of antibodies was not high enough to alter basal or pulsatile LH secretion, the mechanism of action of the GnRH antiserum may involve a direct ovarian action.     

Inhibition of pregnancy with indomethacin in mature gilts and prepuberal gilts induced to ovulate

Twenty prepuberal (P) gilts, 56.5 +/- 1.1 kg body weight, were induced to ovulate with 1000 IU of pregnant mare's serum gonadotropin followed 72 h later by 500 IU of human chorionic gonadotropin (hCG), and bred by artificial insemination (AI) with 50 ml fresh pooled boar semen the day after hCG treatment (Day 0). Eighteen mature (M) gilts, 120.6 +/- 1.7 kg body weight, were bred by AI each day of estrus using pooled semen from the same boars (onset of estrus = Day 0). One-half of each group was fed the prostaglandin (PG) synthesis inhibitor indomethacin (IND), at 10 mg/kg body weight, or control (C) feed twice daily on Days 10 to 25. Blood samples taken by venipuncture on Days 10, 15, 20 and 25 were quantitated for progesterone (P4) and 13,14-dihydro-15-keto-PGF2 alpha (PGFM) by radioimmunoassay. Ovaries were examined on Day 26. All M-C gilts were pregnant, whereas 3 of 9 M-IND gilts (P less than 0.05) and none of the P gilts (P less than 0.01) were pregnant. Three of the 6 nonpregnant M-IND gilts displayed estrus on Day 21. The 3 remaining M-IND gilts had maintained corpora lutea (CL) on Day 26. Only corpora albicantia were present in P gilts on Day 26. Serum P4 concentrations for M-C gilts, nonpregnant M-IND gilts with maintained CL, and pregnant M-IND gilts were not different. Serum P4 for all nonpregnant gilts in which CL had regressed by Day 25 decreased to less than 5 ng/ml on Day 20.(ABSTRACT TRUNCATED AT 250 WORDS)     

PGE receptor characteristics on porcine luteal cells during the estrous cycle and early pregnancy.

This study examined the affinities and concentrations of prostaglandin E (PGE) receptors on porcine luteal cells during the estrous cycle and early pregnancy. Corpora lutea (CL) were obtained from nonpregnant gilts at days 9 (n = 4), 12 (n = 3), and 14 (n = 6); three gilts possessed red, vascular CL and three gilts had white nonvascular CL) of the estrous cycle, and days 9 (n = 4), 12 (n = 3), 14 (n = 5), and 30 (n = 5) of pregnancy. The CL were dissociated enzymatically to disperse single cells and the red blood cells were removed by elutriation. The luteal cells were assayed for specific PGE binding by displacement analysis with use of [3H] PGE2 and varying concentrations of unlabeled PGE2. The specific binding of [3H] PGE2 to luteal cells decreased (p < 0.05) from days 9 to 14 of the estrous cycle, but only decreased (p < 0.05) from days 9 to 12 of pregnancy. Specific binding was higher (p < 0.05) on day 14 of pregnancy than the comparable stage of the estrous cycle. The affinities of PGE receptors decreased (p < 0.05) only on the luteal cells dissociated from red, vascular CL of day 14 nonpregnant gilts compared with those of other days of the estrous cycle and pregnancy. The number of PGE receptors on porcine luteal cells was similar (p > 0.05) in pregnant and nonpregnant gilts, but decreased (p < 0.05) on days 12-14 postestrus. During early pregnancy, it was evident that high affinity PGE receptors are sustained on porcine luteal cells; however, the role of the PGE receptors in maternal recognition of pregnancy remains speculative.     

Evaluation of systems for collection of porcine zygotes for DNA microinjection and transfer

Crossbred gilts and sows (n=116) were used for the collection of 1-cell zygotes for DNA microinjection and transfer. Retrospectively, estrus synchronization and superovulation schemes were evaluated to assess practicality for zygote collection. Four synchronization and superovulation procedures were used: 1) sows were observed for natural estrous behavior; 1000 IU human chorionic gonadotrophin (hCG) was administered at the onset of estrus (NAT); 2) cyclic gilts were synchronized with 17.6 mg altrenogest (ALT)/day for 15 to 19 days followed by superovulation with 1500 IU pregnant mares serum gonadotropin (PMSG) and 500 IU hCG (LALT); 3) gilts between 11 and 16 days of the estrous cycle received 17.6 mg ALT for 5 to 9 days and PMSG and hCG were used to induce superovulation (SALT); and 4) precocious ovulation was induced in prepubertal gilts with PMSG and hCG (PRE). A total of 505 DNA microinjected embryos transferred into 17 recipients produced 7 litters and 50 piglets, of which 8 were transgenic. The NAT sows had less (P < 0.05) ovarian activity than gilts synchronized and superovulated by all the other procedures. Synchronization treatments with PMSG did not differ (P > 0.05) in the number of corpora hemorrhagica or unovulated follicles, but SALT and PRE treaments had higher ovulation rates than LALT (24.7 +/- 2.9, 24.3 +/- 1.8 vs 11.6 +/- 2.7 ovulations; X +/- SEM). The SALT and PRE treatments yielded 12.3 +/- 2.6 and 17.7 +/- 1.7 zygotes. Successful transgenesis was accomplished with SALT and PRE procedures for estrus synchronization and superovulation.     

Comparison of PGF2α-induced luteolysis in early pregnant and estrogen-treated ‘pseudopregnant’ gilts

Conceptus estrogen clearly plays a major role in luteal maintenance in the pig; however, other conceptus-derived substances or conceptus-induced uterine secretory products appear to have a local luteotrophic/anti-luteolytic effect on the corpora lutea (CL) and likely may play a key role in maternal recognition of pregnancy in the pig. The objective of these studies was to compare PGF₂α-induced luteolysis in estrogen-treated ‘pseudopregnant’ gilts versus pregnant gilts during the period of maternal recognition of pregnancy. In Experiment 1, doses of PGF₂α ranging from 1 to 100 μg were administered via intraluteal silastic implants to pseudopregnant gilts to determine the dose necessary to cause functional (progesterone) and structural (weight) luteal regression similar to that observed during the natural estrous cycle. Luteal sensitivity to this minimally effective luteolytic dose of PGF₂α was then determined for both pseudopregnant and pregnant gilts in Experiment 2. Experiment 3 investigated whether Day 13 porcine conceptus tissue could directly prevent PGF₂α-induced luteolysis at the level of the CL. The minimally effective luteolytic dose of PGF₂α (100 μg) determined in the pseudopregnant pig caused a similar decline in progesterone concentration and weight of CL in pregnant gilts, suggesting that the susceptibility of CL of pregnant and pseudopregnant pigs to PGF₂α is similar. However, luteal weight was greater (P<0.05) for the pregnant gilts than for pseudopregnant gilts, suggesting that estrogen treatment alone cannot mimic the conceptus effects on CL growth and development. Experiment 3 demonstrated that lyophilized Day 13 conceptus tissue implanted directly into individual CL could partially inhibit PGF₂α-induced luteolysis, providing for the first time direct evidence that porcine conceptuses as early as Day 13 contain factors which can directly (i. e. at the level of the CL) prevent luteal regression.