Effects of Zeranol upon luteal maintenance and fetal development in peripubertal gilts

Eighty gilts were utilized to determine whether zeranol implants could maintain hCG-induced corpora lutea (CL) in peripubertal gilts and to examine the effects of a Zeranol implant on fetal development. Crossbred gilts (171+/-0.3 days of age, 109.1+1.4 kg) were blocked by weight and ancestry to control (n=40) or treatment (n=40) groups. To induce ovulation and CL maintenance, treated gilts received 500 IU of hCG i.m. and a Zeranol ear implant (Ralgro, 36 mg; day 0). All gilts were checked once daily for estrus with a mature boar from days 3-58 of the experiment. On day 42, treated gilts received two 10 mg injections of Lutalyse (PGF(2)alpha) spaced 6 h apart. Treated gilts not displaying estrus within 7 days of PGF(2)alpha received two additional 10 mg of PGF(2)alpha spaced 6 h apart on day 49. On days 44-58, gilts detected in estrus were inseminated twice, 24 h apart with pooled semen via AI. Blood samples were obtained on days 0, 7, 18 and 42 and analyzed for serum progesterone (P(4)). Bred gilts were slaughtered on days 58-62 of gestation. Ovulation, as determined by serum concentrations of P(4) on day 7 of the experiment, was induced by hCG in 79.5% of treated gilts. Zeranol implants, however, failed to increase (P>0.05) the proportion of gilts available for breeding (treated, 21/39; control, 18/40). Of gilts inseminated on days 44-58, 16/21 treated gilts and 16/18 control gilts were pregnant at slaughter on days 58-62 of gestation. Number of fetuses (7.5 versus 12), fetal weight (83 versus 121 g), fetal length (117 versus 132 mm) and fetal survival (45% versus 78%) were reduced (P<0.001) by Zeranol implants. These data indicate that treatment of peripubertal gilts with a 36 mg Zeranol implant did not increase the proportion of gilts available for breeding while causing deleterious effects upon the fetuses.     

Mixing gilts in early pregnancy does not affect embryo survival

There is general acceptance that mixing sows during the first 3 weeks of gestation is detrimental to embryo development and survival. However, there is a paucity of data describing the influence of group housing and remixing during the first 14 days of gestation on pregnancy outcomes. Using 96 purebred maternal (Large White)/terminal (Duroc) line gilts, the current study determined the effects of regrouping, and the timing of regrouping, during the pre-implantation period on embryo mortality. The study was conducted in 2 blocks, with 12 gilts allocated to each of 4 treatments in each block. At 175 days of age, the combination of PG600 and 20 min of daily physical boar contact was used to stimulate puberty, with boar contact resuming 12 days after first detection of oestrus and gilts receiving two artificial inseminations (AIs), 24 h apart, at their second oestrus. After their first AI gilts were allocated to one of four treatment groups (n=12 gilts/treatment). Gilts in one treatment group were housed individually in stalls (STALL). The remaining gilts continued to be housed in their pre-AI groups and were either not remixed (NOMIX), or remixed to form new groups on day 3/4 (RMIXD3/4) or day 8/9 (RMIXD8/9) of gestation (day 0=day of first detection of second oestrus and first insemination). Group-housed gilts were housed in groups of 6, with a space allowance of 2.4 m2/gilt. All gilts were fed once a day (2.2 kg/gilt). Reproductive tracts were collected on day 26.6+/-0.13 of gestation, and the number of corpora lutea (CL) and viable embryos counted. Pregnancy rate was similar across all treatments, averaging 94.5% across the four treatment groups. The number of embryos present on day 26 of gestation was unaffected by housing treatments (P>0.05); gilts in the STALL, NOMIX, RMIXD3/4 and RMIXD8/9 groups possessed 13.2+/-0.67, 12.9+/-0.66, 14.1+/-0.46 and 13.8+/-0.57 embryos, respectively. Similarly, embryo survival rates were 0.91+/-0.04, 0.85+/-0.04, 0.91+/-0.02 and 0.87+/-0.05 for the STALL, NOMIX, RMIXD3.4 and RMIXD8/9 groups, respectively (P>0.05). In conclusion, the current data indicate that individually housing gilts immediately after their first AI does not improve embryo survival. There also appear to be no adverse effects on embryo development or survival when group-housed, mated gilts are remixed during the first 10 days of gestation.     

Steroidogenic acute regulatory protein expression is decreased in the adrenal gland of the growth-restricted sheep fetus during late gestation

Functional development of the adrenal cortex is critical for fetal maturation and postnatal survival. In the present study, we have determined the developmental profile of expression of the mRNA and protein of an essential cholesterol-transporting protein, steroidogenic acute regulatory protein (StAR), in the adrenal of the sheep fetus. We have also investigated the effect of placental restriction (PR) on the expression of StAR mRNA and protein in the growth-restricted fetus. Adrenal glands were collected from fetal sheep at 82-91 days (n = 10), 125-133 days (n = 10), and 140-144 days (n = 9) and from PR fetuses at 141-145 days gestation (n = 9) (term = 147 +/- 3 days gestation). The adrenal StAR mRNA:18S rRNA increased (P < 0.05) between 125 days (7.44 +/- 1.61) and 141-144 days gestation (13.76 +/- 1.88). There was also a 13-fold increase (P < 0.05) in the amount of adrenal StAR protein between 133 and 144 days gestation in these fetuses. However, the amount of StAR protein (6.9 +/- 1.7 arbitrary densitometric units [AU]/microg adrenal protein) in the adrenal of the growth-restricted fetal sheep was significantly reduced, when compared with the expression of StAR protein (17.1 +/- 1.9 AU/microg adrenal protein) in adrenals from the age-matched control group. In summary, there is a developmental increase in the expression of StAR mRNA and protein in the fetal sheep adrenal during the prepartum period when adrenal growth and steroidogenesis is dependent on ACTH stimulation. We have found that, while the level of expression of StAR protein is decreased in the adrenal gland of the growth-restricted fetus during late gestation, this does not impair adrenal steroidogenesis. Our data also suggest that the stimulation of adrenal growth and steroidogenesis in the growth-restricted fetus may not be ACTH dependent.     

The extent and timing of prenatal loss in gilts

The potential litter size of gilts that is based on the ovulation rate is much higher than the actual litter size, which depends on the fertilization rate and subsequent prenatal mortality. Prenatal mortality is divided into embryonic mortality (before Day 30) and fetal mortality (after Day 30). Prenatal loss includes both fertilization failure and prenatal mortality. Crossbred gilts (n = 149) were bred at the first observed estrus after being exposed to the boar at 200 days of age. Time of the first insemination after estrus detection was determined by measurement of vaginal conductivity using a Walsmeta meter. A second insemination was administered either 8 or 16 hours later. Artificial insemination with fresh semen (0 to 3 days old) was used throughout the experiment. Gilts were slaughtered on Day 3 (n = 26), Day 10 (n = 42), Day 30 of gestation (n = 45) or they were allowed to farrow (n = 36). Gilts slaughtered on Day 3 were used to estimate the fertilization rate. Gilts slaughtered on Day 10 and Day 30 were used to calculate embryonic mortality, while fetal mortality was calculated from the gilts that farrowed. The mean (+/-SEM) number of corpora lutea (CL) was 13.15+/-0.46, 13.36+/-0.37 and 12.97+/-0.39 for gilts slaughtered at Days 3, 10 and 30, respectively (P>0.05), and the mean (+/-SEM) number of normal embryos recovered was 11.12+/-0.69, 9.46+/-0.55 and 9.33+/-0.58, respectively. Litter size at parturition was 9.10+/-0.54. There was a significant difference between the number of normal embryos on Day 3 and Day 30 (P=0.05) and also between the number of normal embryos at Day 3 and the number of piglets at term. Ninety percent of the ova were recovered at Day 3. The fertilization rate was calculated either 1) assuming that unrecovered ova had a similar fertilization rate as the recovered ova (FRER=94.5+/-2.0%) or 2) assuming that unrecovered ova were unfertilized (FROR=84.5+/-2.5%). It was concluded that FRER was a more accurate estimation of the fertilization rate. Based on this fertilization rate, embryonic mortality between Day 3 and Day 10 was 20.8+/-8.3%, with an additional 12.5+/-7.1% loss between Day 10 and Day 30, when all gilts were included (P = 0.308). Thus the total prenatal loss, including fertilization failure, up to Day 10 was 26.3% and to Day 30 it was 38.8%. Fetal mortality was 2.2%, giving a total prenatal mortality (excluding fertilization failure) of 35.5% and a prenatal loss of 41%. Most of the prenatal loss was due to embryonic mortality. In those gilts that remained pregnant most of the embryonic loss occurred before Day 10 (19.0+/-6.3%; P=0.003). There was no further loss between Day 10 and 30 of pregnancy. There was a significant difference between the loss from Day 3 to Day 10 compared with the loss from Day 10 to Day 30 (P=0.05); therefore, most of the embryonic loss in pregnant gilts occurred before Day 10. Since fetal mortality was 3.2+/-6.3%, most of the prenatal loss was due to embryonic mortality.     

Effect of chlortetracycline supplementation during prebreeding and early gestation on age at puberty, ovulation rate, embryo survival and fetal development in gilts

A total of 166 crossbred gilts weighing approximately 87 +/- 1 kg was limit-fed (2.5 kg/d) a corn-soybean meal gestation diet containing either 0 or 220 ppm of chlortetracycline (CTC) from 157 +/- 1 d of age until 15 d after breeding. These gilts were slaughtered at 31 +/- 1 or 71 d +/- 1 d of gestation for evaluation of reproductive performance. Age (190 +/- 3 d vs 195 +/- 3 d) and body weights (106 +/- 2 kg vs 106 +/- 2 kg) at puberty were similar for control and CTC-fed gilts, respectively. Although not significant (P > 0.05), ovulation rate was higher in CTC-fed than in control gilts as assessed at both 31 d (14.2 +/- 0.7 vs 12.9 +/- 0.9, P = 0.31) and 71 d (13.9 +/- 0.6 vs 12.4 +/- 0.5, P = 0.10) of gestation. There was an increase (P = 0.04) in the number of live embryos for CTC-fed gilts at 31 d (12.1 +/- 0.7 vs 9.7 +/- 0.7) but not at 71 d (10.0 +/- 1.1 vs 9.6 +/- 1.0) of gestation. The mean uterine length, placental length, placental weight, fetal length, fetal weight, and allantoic fluid volumes were similar between the control and CTC-fed gilts. Results indicated that feeding CTC during prebreeding and early gestation did not influence the proportion or age of gilts at puberty. However, CTC feeding may have influenced a trend to-ward an increased ovulation rate and increased number of live embryos in gilts.     

Effects of leptin on fetal plasma adrenocorticotropic hormone and cortisol concentrations and the timing of parturition in the sheep

We investigated whether leptin can suppress the prepartum activation of the fetal hypothalamus-pituitary-adrenal (HPA) axis and delay the timing of parturition in the sheep. First, we investigated the effects of a 4-day intravascular infusion of recombinant ovine leptin (n = 7) or saline (n = 6) on fetal plasma adrenocorticotropic hormone (ACTH) and cortisol concentrations, starting from 136 days gestation (i.e., at the onset of the prepartum activation of the fetal HPA axis. The effects of a continuous intrafetal infusion of leptin (n = 7) or saline (n = 5) from 144 days gestation on fetal plasma ACTH and cortisol concentrations and the timing of delivery were also determined in a separate study. There was an increase in fetal plasma ACTH (P < 0.01) and cortisol (P < 0.001) concentrations when saline was infused between 136-137 and 140-141 days gestation. Plasma ACTH and cortisol concentrations did not rise, however, when leptin was infused during this period of gestation. When leptin was infused after 144 days gestation, there was no effect of a 4- to 5-fold increase in circulating leptin on fetal ACTH concentrations. In contrast, leptin infusion from 144 days gestation suppressed (P < 0.05) fetal plasma cortisol concentrations by around 40% between 90 and 42 h before delivery. There was no difference, however, in the length of gestation between the saline- and leptin-infused groups (saline infused, 150.2 +/- 0.5 days; leptin infused, 149.8 +/- 1.0 days). In saline-infused fetuses, there was a significant negative relationship between the plasma concentrations of cortisol (y) and leptin (x) between 138 and 146 days gestation (y = 81.4 - 7.7x, r = 0.38, P < 0.005). This study provides evidence for an endocrine negative feedback loop between leptin and the HPA axis in fetal life.     

Development of the pituitary-adrenal axis in chronically cannulated ovine fetuses

In the intact, unstressed ovine fetus, both plasma immunoreactive adrenocorticotrophin (ACTH) and blood cortisol concentrations increased after 121 days gestation. The mean ACTH and cortisol concentrations in intact fetuses of 90-121, 122-135 and 136-144 days gestation were for ACTH 20.4 +/- 3.9 (50) (mean +/- SEM, n), 30.2 +/- 5.6 (26) and 56.0 +/- 6.3 pg/ml (37) respectively, and for cortisol 0.07 +/- 0.01 (24), 0.17 +/- 0.03 (21) and 0.64 +/- 0.13 microgram/100 ml (15), respectively. After 121 days ACTH and cortisol concentrations were correlated positively. Cortisol infused into intact or adrenalectomized fetuses and corticosterone infused into adrenalectomized fetuses suppressed fetal plasma ACTH concentrations. In summary, ACTH and cortisol increase concomitantly after 122 days, so that it is highly probable that ACTH is the trophic stimulus for fetal adrenal maturation. The suppression of ACTH by cortisol and corticosterone suggests that these are the natural feedback regulators. It is proposed that while the mechanism for cortisol feedback may exist early in gestation, it is not until after 121 days that feedback control of ACTH becomes evident and physiologically important.     

Influence of the endometrium, protease inhibitors and freezing on antiviral activity of proteins secreted by pig conceptuses

In Exp. 1, only medium from cultures containing conceptus tissue had antiviral activity (P less than 0.05). Addition of Day-15 pregnant endometrium or Day-14 cyclic uterine flush proteins to cultures containing 200 mg conceptus tissue decreased antiviral activity (conceptus x endometrial protein interaction, P less than 0.06). Effects of endometrium (-54%) and uterine flush proteins (-40%) on antiviral activity of conceptus cultures did not differ from each other (P greater than 0.10). In Exp. 2, antiviral activity was only detected in cultures containing conceptus tissue (P less than 0.06). The amount of antiviral activity in cultures of Day-15 conceptus tissue was not influenced differently (P greater than 0.10) by culture in medium conditioned by endometrium from Day 10 or Day 12 of pregnancy. However, antiviral activity was undetectable in medium conditioned by endometrium from one of the Day-12 gilts. In Exp. 3, antiviral activity was present in medium from only 1 of 3 cultures from Day-12 gilts when assayed unfrozen. Antiviral activity was lower (P less than 0.01) in cultures of conceptuses from Day 12 than Day 14 of pregnancy; however, antiviral activity increased quadratically (P less than 0.05) when cultures contained 0, 0.01, 0.1 and 1.0 units/ml aprotinin, respectively. Freezing and thawing culture medium did not reduce (P greater than 0.10) antiviral activity compared to medium assayed unfrozen (1438 vs 1354 units/ml, respectively). These results suggest a regulatory influence of the endometrium on secretion of antiviral proteins by pig conceptuses in vitro.     

Embryo survival and conceptus growth after reciprocal embryo transfer between Chinese Meishan and Landrace x Large White gilts

Embryos were transferred between Meishan and Landrace x Large White (control) gilts on Day 4 or 5 to establish approximately equal numbers of all four possible combinations of donor breed and recipient breed. The breed of the donor gilt significantly (P less than 0.01) affected embryo survival with 44.5% of transferred Meishan embryos and 69.6% of transferred control embryos surviving to Day 30 +/- 1. There was no influence of the breed of the recipient gilt on the proportion of embryos which survived. These differences in embryo survival between the two breeds could not be explained by differences in (1) the number of embryos transferred, (2) the stage of development of the embryos transferred, (3) the interval between ovulation and transfer or (4) the degree of asynchrony between donor and recipient gilt. On Day 30 +/- 1 embryos from control donors developed into longer fetuses (P less than 0.01) with larger allantoic sacs (P less than 0.05) than did embryos from Meishan donors. Fetuses in control recipients were longer (P less than 0.01), heavier (P less than 0.001) and had larger allantoic sacs (P less than 0.05) than fetuses occupying Meishan uteri. The interaction between breed of donor gilt and breed of recipient gilt did not significantly affect conceptus growth. These results suggest that Meishan pig embryos may be less tolerant to routine embryo transfer procedures than those of control gilts, that the genotype of the dam does not affect the proportion of embryos surviving to Day 30 +/- 1, and that both fetal and maternal factors affect conceptus growth.     

Changes in pituitary responses to synthetic ovine corticotrophin releasing factor in fetal sheep

The rise in cortisol in fetal sheep during late pregnancy has been related to increased responsiveness of the adrenal to ACTH. Most reports have suggested that plasma ACTH concentrations rise coincident with or after the prepartum increase in cortisol. To reexamine the relationship of cortisol with basal immunoreactive ACTH (IR-ACTH) throughout the last 40 days of pregnancy and to determine changes in fetal pituitary responsiveness during this time, we measured basal and synthetic ovine corticotrophin-releasing factor (oCRF) (10 ng-10 micrograms) induced rises in ACTH and cortisol in fetal sheep at days 110-115, 125-130, and 135-140 of pregnancy. The fetuses were catheterized on day 105-120 and entered spontaneous labour at greater than 140 days. Basal IR-ACTH (picograms per millilitre +/- SEM) rose from 16.7 +/- 2.9 pg/mL at day 110-115 to 34.8 +/- 8.7 pg/mL at day 141-145. There was a significant effect of time on basal ACTH concentrations with a mean increase of approximately 5 pg ACTH per millilitre of plasma per 5-day sampling interval. Plasma cortisol changed gradually between day 110 and 125 of gestation and then more rapidly to term. At day 110-115 of gestation there was no significant change in plasma ACTH after 10 or 100 ng oCRF, but there was a significant increase in ACTH after 1 microgram of oCRF. Plasma cortisol did not change after any CRF injection. The change in IR-ACTH after oCRF at day 125-130 of gestation was significantly greater than that at day 110-115. Plasma cortisol concentrations were elevated following 1- and 10-micrograms injections of oCRF.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of adrenocorticotropin stimulation on cortisol dynamics of pregnant gilts and their fetuses: implications for prenatal stress studies

The effect of adrenocorticotropic hormone (ACTH) administration on plasma cortisol concentrations was determined in pregnant gilts and their fetuses. In a first experiment, 100 IU ACTH (Synacthen Depot) was administered intramuscularly to the gilts every second day from Days 49 to 75 of gestation. ACTH injections were carried out at 08:00 h and, thereafter, 10 blood samples were taken within the following 8h via jugular catheters. Blood samples were analysed for plasma cortisol concentrations, and results were compared with values from animals which were treated with physiological saline and untreated animals (blood sampling only). The values for plasma cortisol concentrations increased until 3h after ACTH applications to a mean maximum level of 276.5+/-17.2 nmol/l in the whole 4-week stimulation period. Plasma cortisol levels did not return to pre-treatment values within the 8 h post-injection. No differences in cortisol levels were found between the physiological saline and untreated control, and no habituation of the adrenocortical response to ACTH was found during the 4-week stimulation period. In a second experiment, 100 IU ACTH were administered to pregnant gilts at gestation Day 65. After 3 h, fetuses were recovered under general anaesthesia and blood samples were taken from the umbilical vein, artery, and, after decapitation, from periphery. Application of ACTH to the sows significantly increased their plasma cortisol concentrations (P<0.001), and also increased plasma cortisol concentrations in peripheral blood samples from the fetuses (P=0.09) and in the umbilical vein (P<0.001) and artery (P<0.01), respectively. Plasma ACTH concentrations did not differ in fetuses from ACTH-treated or control sows. The results show that in gilts the adrenocortical response to an exogenous application of Synacthen Depot is consistent over time during mid-gestation. Furthermore, cortisol but not ACTH levels were increased in fetuses from ACTH-treated sows, indicating that maternal cortisol can cross the placenta during mid-gestation. The stimulation of maternal cortisol release through exogenous ACTH with subsequent elevation of fetal cortisol levels is, therefore, a useful approach for studying effects of elevated maternal glucocorticoids in prenatal stress studies in pigs.     

Onset of secretion of proteins with antiviral activity by pig conceptuses

In Exp. 1, antiviral activity was detected in Day-15 pregnant uterine flushings (6222 +/- 2167 units/ml) and in conceptus culture medium collected at 0, 1, 2, 4, 8, 16, 24, 32, 40, and 48 h (95, 375, 650, 1216, 1600, 2100, 2017, 2083, 3500 and 5000 units/ml, respectively; R2 = 0.81, P less than 0.01; y = 190.0 + 252.7x - 11.2x2 + 0.2x3. In Exp. 2, antiviral activity of Day-15 conceptus culture medium was reduced 99% after boiling for 20 min (P less than 0.01) and, after 18 h dialysis (6000-8000 Mr cut-off), 100% of the activity was in the retentate. In Exp. 3, antiviral activity was not detected in cultures of conceptuses from Days 10 and 11 and activity was maximal for Day 14 and Day 15 conceptuses (2100 and 2083 units/ml, respectively). Effects of day were best described by a quadratic regression equation (y = 17,652 - 3263x + 150x2; R2 = 0.55, P less than 0.01). In Exp. 4, changes in antiviral activity detected in uterine flushings from pregnant gilts on Days 8, 10, 11, 12, 14 and 15 (1.3, 0, 6.7, 63.3, 580 and 1663 units/ml, respectively) were described by the equation y = -20,743 + 6189x - 606x2 + 20x3 (R2 = 0.85, P less than 0.01). In Exp. 5, low antiviral activities (5-30 units/ml) were detected in all plasma samples collected from the uterine artery and uterine vein of pregnant and cyclic gilts, but values were not significantly influenced by pregnancy status, day or site of collection.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of parturition in swine with prostaglandin F(2)alpha, estradiol benzoate and oxytocin

Pregnant sows and gilts were administered either 0, 2.5, 5, 10 or 20 mg prostaglandin F(2)alpha (PGF(2)alpha) intramuscularly on Day 112 or 113 of gestation at 0800 h in an effort to induce parturition. The average interval from PGF(2)alpha injection to farrowing was 55.1 +/- 5.7, 29.4 +/- 3.1, 32.1 +/- 4.6, 27.8 +/- 1.8 and 26.9 +/- 1.1 h for 0, 2.5, 5, 10 and 20 mg, respectively. All PGF(2)alpha treatments increased (P < 0.01) over controls the number of sows farrowing 23 to 33 h after injection. The average gestation length was significantly shorter in treated gilts; however, no detrimental effect on pig performance or pig survivability was observed. A second trial evaluated the effect of a 10-mg dose of PGF(2)alpha on the induction of parturition in sows in order to obtain a majority of sows farrowing within normal working hours (0700 to 1700 h). The interval from injection to farrowing was decreased (P < 0.05) by PGF(2)alpha treatment (66.2 +/- 5.3 vs 28.1 +/- 2.2 h). Fifty-seven percent (P < 0.05) of PGF(2)alpha-treated sows farrowed between 0700 and 1700 h as compared to 13.6% for control sows. A third trial was conducted to examine a sequential treatment of PGF(2)alpha and oxytocin to control the time of parturition more precisely. Sows receiving only 10 mg of PGF(2)alpha farrowed on an average 31.1 +/- 1.4 h after injection. The injection of 40 IU oxytocin 24 to 28 h after PGF(2)alpha decreased (P < 0.05) the interval from PGF(2)alpha to farrowing (28.1 +/- 0.9 h). The addition of oxytocin increased (P < 0.05) the number of sows farrowing within 3 h of injection (33 vs 86% for PGF(2)alpha and PGF(2)alpha + oxytocin treatments, respectively). A fourth trial was designed to determine if the addition of exogenous estradiol benzoate (EB) to a sequential treatment of PGF(2)alpha and oxytocin would improve the predictability and synchronization of the induced parturition. Sows were assigned to receive either saline, 10 mg PGF(2)alpha + 40 IU oxytocin or 10 mg PGF(2)alpha + 5 mg EB + 40 IU oxytocin. The addition of EB reduced (P < 0.01) the variance in the interval from oxytocin to farrowing and added precision to the predicted time of induced parturition.     

The effect of labour on uterine blood flow in the pregnant ewe.

The effect of labour on cardiac output and uterine blood flow was measured in pregnant ewes at a mean gestation of 124 days using radioactive microspheres labelled with 169Yb and 85Sr. Labour was induced by a continuous infusion of ACTH into the foetal circulation. Cardiac ouput measured before ACTH infusion in seven ewes was 5234 +/- 175-9 ml./min (mean +/- S.E.) and total uterine blood flow was 732 +/- 57-9 ml./min (mean +/- S.E.). Measurements during labour in six ewes showed a significant increase in cardiac output to 6175 +/- 149-6 ml./min (P less than 0-005) but no significant change in uterine blood flow. However, the partition of blood flow was altered; thus myometrial flow increased by 67% from 114 +/- 15-4 ml./min to 190 +/- 13-2 ml./min (P less than 0-005) while placental blood flow decreased, although not significantly, from 618 +/- 55-9 ml./min to 575 +/- 40-7 ml./min. Similar changes were observed in one ewe in spontaneous labour at term and in another ewe receiving an infusion of 4 mg oestradiol 17beta over a 24 hr period. It is concluded that labour is not associated with any major alternation in total uterine blood flow although myometrial blood flow is increased. It is not known whether this is due to the rise in circulating oestrogens which occurs prior to parturition in the ewe, or to other factors such as the work of uterine muscle during labour.     

The value of urine osmolality as an index of stress in the ovine fetus

In ovine fetuses, during 100-130 days of gestation, urine osmolalities less than 175 mosmol/kg water were associated with plasma immunoreactive adrenocorticotrophin (ACTH) concentrations below 40 pg/ml in 40/41 samples. In 18/29 fetuses with urine osmolalities greater than 175 mosmol/kg water plasma ACTH was significantly elevated. In 38 samples of fetal blood there was a significant correlation between plasma ADH and ACTH concentrations. By least squares regression the equation to the line was [ACTH] = 5.06 + 3.70 [ADH] (r = 0.62, P less than 0.001). In 50 samples from fetuses of gestational ages 100-140 days, with urine osmolalities of 302 +/- 86 mosmol/kg (mean +/- SD) the blood pH, pO2 and pCO2 values were not significantly different from those in 50 samples from fetuses with urine osmolalities of 125 +/- 22 mosmol/kg. It is proposed that the measurement of fetal urine osmolality provides a good index of fetal stress. A fetus with a urine osmolality less than 175 mosmol/kg is almost invariably in the optimum, unstressed condition.     

Effects of estrogen and prostaglandin on progesterone-delayed farrowing

Effects of estradiol benzoate and prostaglandin F(2alpha) (PGF(2alpha)) on concentrations of progesterone and estrogen in serum and the percentage of live births were determined in 21 gilts treated with exogenous progesterone in late gestation. All gilts received progesterone (25mg s.c. four times daily) from Days 108 through 113 of gestation. Gilts receiving no other treatments (controls) had elevated levels of progesterone through 1800 h on Day 114 (29.2 +/- 11.4 ng/ml) and farrowed at 115.6 +/- 0.3 d of gestation with a relatively low percentage of live births (66.8 +/- 17.3). Gilts treated with PGF(2alpha) administered at 0600 h on Day 114 had less (P<0.01) progesterone by 1800 h (7.0 +/- 1.3 ng/ml) relative to that of the controls, but they had similar gestation lengths (115.5 +/- 0.3) and percentages of live births (50.0 +/- 16.2). Administration of estradiol benzoate (10 mg) to gilts at 0600 h on Day 114 did not reduce progesterone on Day 114 or the gestation length relative to that of the control gilts, but it did increase (P<0.05) the percentage of live births (100%).     

Endometrial surface and secretory alterations associated with embryonic mortality in gilts administered estradiol valerate on days 9 and 10 of gestation

Administration of estrogen to gilts on Days 9 and 10 of pregnancy results in total embryonic loss by Day 18. The present study examined changes in the uterine endometrial surface and secretion during conceptus attachment in control and estrogen-treated (Days 9 and 10) pregnant gilts. Gilts were unilaterally hysterectomized on either Days 12 and 14 or Days 16 and 18 of gestation. Uterine horns were flushed with saline and conceptuses were evaluated. Intact conceptuses were recovered from all control gilts, whereas estrogen-treated gilts contained normal intact conceptuses only on Day 12 of gestation. Antiviral activity, which reflects conceptus viability, was reduced (p less than 0.01) in uterine flushings after Day 14 in estrogen-treated gilts. Culture of endometrial explants with [3H]glucosamine revealed several glycoproteins that are synthesized during the period of conceptus attachment; however, no difference in glycoprotein synthesis between treatment groups was detected by analysis with two-dimensional PAGE and fluorography. Analyses of the uterine epithelium by scanning and transmission electron microscopy demonstrated that estrogen administration caused an alteration in the uterine surface, a thinning of the uterine epithelial glycocalyx, and a reduction of cationic ferritin binding to the microvilli of the uterine epithelium. Results indicate that conceptus mortality after early administration of estrogen is associated with alterations in the uterine endometrial surface during the period of conceptus attachment in the pig.     

Impact of a novel inactivated PRRS virus vaccine on virus replication and virus-induced pathology in fetal implantation sites and fetuses upon challenge

Preventing congenital infection is important for the control of porcine reproductive and respiratory syndrome (PRRS). Recently, in our laboratory, an inactivated porcine reproductive and respiratory syndrome virus (PRRSV) vaccine has been developed. Promising results in young pigs encouraged us to test the vaccine potency to prevent congenital infection. In the present study, the performance of this experimental inactivated vaccine was investigated in pregnant gilts. An advanced protocol was used to test the PRRSV vaccine efficacy. This protocol is based on recent insights in the pathogenesis of congenital PRRSV infections. Three gilts were vaccinated with an experimental PRRSV 07V63 inactivated vaccine at 27, 55, and 83 days of gestation. Three unvaccinated gilts were included as controls. At 90 days of gestation, all animals were intranasally inoculated with 10⁵ tissue culture infectious dose 50 (TCID₅₀) of PRRSV 07V63. Twenty days postchallenge animals were euthanized and sampled. The vaccinated gilts quickly developed virus neutralizing (VN) antibodies starting from 3 to 7 days postchallenge (1.0 to 5.0 log₂). In contrast, the unvaccinated gilts remained negative for VN antibodies after challenge. The vaccinated gilts had shorter viremia than the control gilts. Gross pathology (mummification) was observed in 8% of the fetuses from vaccinated gilts and in 15% of the fetuses from unvaccinated gilts. The number of fetuses with severe microscopic lesions in the fetal implantation sites (a focal detachment of the trophoblast from the uterine epithelium; a focal, multifocal, or full degeneration of the fetal placenta) was lower in the vaccinated (19%) versus unvaccinated (45%) gilts (P < 0.05). The number of PRRS-positive cells in the fetal placentae was higher in unvaccinated versus vaccinated gilts (P < 0.05). In contrast, the number of PRRS-positive cells in the myometrium/endometrium was higher in vaccinated versus unvaccinated gilts (P < 0.05). Fifty-seven percent of the fetuses from the vaccinated gilts and 75% of the fetuses from the unvaccinated gilts were PRRSV-positive. In conclusion, implementation of the novel experimental inactivated PRRSV vaccine primed the VN antibody response and slightly reduced the duration of viremia in gilts. It also reduced the number of virus-positive fetuses and improved the fetal survival, but was not able to fully prevent congenital PRRSV infection. The reduction of fetal infection and pathology is most probably attributable to the vaccine-mediated decrease of PRRSV transfer from the endometrium to the fetal placenta.     

Effect of recombinant alpha interferons on fertility and interestrous interval in sheep

In Experiment 1, 12 unmated cyclic ewes received twice-daily intrauterine injections on Days 12 to 14 of one of the following treatments: 1) ovine conceptus secretory proteins (oCSP) containing 25 mug of ovine trophoblast protein-1 (oTP-1) as determined by RIA; 2) 25 or 50 mug recombinant human interferon alpha1 (rhlFN); or 3) 1500 ug of serum proteins (oSP) from a Day-16 pregnant ewe (estrus = Day 0) per uterine horn. Ewes receiving oCSP had longer interestrous intervals (27 +/- 2 days; P<0.05) than ewes receiving oSP (17 +/- 2 days). Ewes receiving either dose of rhlFN had an interestrous interval of 16 +/- 2 days which did not differ (P>0.10) from that of oSP-treated ewes. In Experiment 2, 59 normally cycling ewes, mated on Day 0, received twice-daily intramuscular injections of either 2 mg recombinant bovine interferon alpha1 (rblFN) or placebo on Days 12 to 15 post estrus. On Day 16, pregnancy was confirmed by flushing a morphologically normal conceptus from the uterus. Pregnancy rates for rblFN-treated (80%) and placebo-treated (62%) ewes were not different (P>0.10). Uterine flushings and conceptus-conditioned medium were assayed for oTP-1. Total oTP-1 in conceptus-conditioned culture medium was higher (P<0.02) when conceptuses were from placebo-treated (104 +/- 14 mug/conceptus) than from rblFN-treated (56 +/- 12 mug/conceptus) ewes; while total oTP-1 in uterine flushings was similar (P>0.10) for placebo-treated (132 +/- 15 mug/conceptus) and rblFN-treated (147 +/- 17 mug/conceptus) ewes. The interval from mating to subsequent estrus following conceptus removal was 31 +/- 1 and 28 +/- 1 days for pregnant ewes treated with rblFN and placebo, respectively. Interestrous intervals for nonpregnant ewes were longer (P<0.02) for rblFN-treated (27 +/- 3 days) than for placebo-treated (18 +/- 2 days) ewes.     

Influence of embryonic and maternal genotype on gestational events in the mouse

Mice with high and low prenatal survival were used to study the influence of maternal and embryonic genotype on the timing of implantation, conceptus growth and gestation length. Mice selected for large litter size (Line S1) or rapid post-weaning weight gain (Line G) showed implantation was delayed and gestation prolonged in mice with low prenatal survival (Line G). Reciprocal transfer of Line-S1 and -G embryos to pseudopregnant recipients indicated that conceptus growth was influenced by maternal as well as embryonic genes, at least until mid-pregnancy. In contrast, fetal genotype had a major effect on the length of gestation.