Maintenance of the corpus luteum after uterine transfer of trophoblastic vesicles to cyclic cows and ewes

One or two trophoblastic vesicles (0.4-2 mm diam.) from cow (Day 14) or ewe (Day 11-13) embryos without their disc were transferred, after culture for 24 h, into recipients. Each vesicle was transferred into the uterine horn ipsilateral to the CL by the cervical route in heifers and surgically in ewes on Day 12 of the oestrous cycle. In cows, daily measurements of plasma progesterone concentrations and checks for return to oestrus showed that the CL was maintained in 8 out of 12 recipients. These 8 cows had 25- to 37-day cycles while 4 recipient heifers returned to oestrus normally. Three recipients with an extended cycle were slaughtered. The dissected uterus showed that trophoblastic vesicles had developed in the uterine horns. In ewes, the serum progesterone curve, determined in each recipient, showed that the CL was maintained in 7 out of 12 recipients. These 7 ewes had 20- to 54-day cycles and the other 5 ewes had a normal cycle of 15-19 days comparable to that of 17.0 +/- 0.5 days for the 6 control ewes. Whenever the CL was maintained, high blood progesterone levels were followed by rapid luteolysis. In cattle and sheep, therefore, a trophoblastic vesicle transferred into the uterus can develop in vivo, secreting the embryonic signals when there is no embryonic disc control and transforming the cyclic CL into a CL of pregnancy in about 60% of the cases.(ABSTRACT TRUNCATED AT 250 WORDS)     

Uterine blood flow of cows during the oestrous cycle and early pregnancy: effect of the conceptus on the uterine blood supply.

Blood flow to each uterine horn of cows during the oestrous cycle and early pregnancy was determined daily by use of electromagnetic blood flow probes placed around both middle uterine arteries. The pattern of blood flow to uteri of pregnant and non-pregnant cows was similar until Day 14 after mating or oestrus. Between Days 14 and 18 of pregnancy blood flow to the uterine horn containing the conceptus increased (P less than 0.01) 2- to 3-fold, whereas blood flow to the non-gravid uterine horn in these cows remained constant. No corresponding increase in blood flow to the uterine horn ipsilateral to the ovary bearing the CL was observed in non-pregnant cows during this 4-day period. By Day 19 of pregnancy, blood flow to the gravid uterine horn had returned to a level similar to that observed on Day 13. Blood flow to both uterine horns of pregnant cows remained constant from Days 19 to 25 and then increased to the gravid horn (P less than 0.01) markedly until Day 30 whereas blood flow to the non-gravid horn remained low. Uterine blood flow during the oestrous cycle of non-pregnant cows was positively correlated (P less than 0.01) with systemic concentrations of oestradiol and the ratio of oestradiol (pg/ml) to progesterone (ng/ml). There was no association between oestradiol concentrations and blood flow to the gravid uterine horn. These data indicate local control of uterine blood flow by the bovine conceptus which may function to create optimal conditions for the continuation of pregnancy.     

Ovarian function in Nelore (Bos taurus indicus) cows after post-ovulation hormonal treatments

Maternal recognition of pregnancy in the cow requires successful signaling by the conceptus to block luteolysis. Conceptus growth and function depend on an optimal uterine environment, regulated by luteal progesterone. The objective of this study was to test strategies to optimize luteal function, as well as prevent a dominant follicle from initiating luteolysis. Nelore (Bos taurus indicus) beef cows (n=40) were submitted to a GnRH/PGF(2alpha)/GnRH protocol. Cows that ovulated from a dominant ovarian follicle (ovulation=Day 0) were allocated to receive: no additional treatment (G(C); n=7); 3000IU of hCG on Day 5 (G(hCG); n=5); 5mg of estradiol-17beta on Day 12 (G(E2); n=6); or 3000IU of hCG on Day 5 and 5mg of estradiol-17beta on Day 12 (G(hCG/E2); n=5). Ultrasonographic imaging of the ovaries, assessment of plasma progesterone concentration, and detection of estrus were done daily from Day 5 to the day of subsequent ovulation. Treatment with hCG induced an accessory CL, increased CL volume, and plasma progesterone concentration throughout the luteal phase (P<0.01). Estradiol-17beta induced atresia and recruitment of a new wave of follicular growth; it eliminated a potentially estrogen-active, growing ovarian follicle within the critical period for maternal recognition of pregnancy, but it also hastened luteolysis (Days 16 or 17 vs. Days 18 or 19 in non-treated cows). In conclusion, the approaches tested enhanced luteal function (hCG) and altered ovarian follicular dynamics (estradiol-17beta), but were unable to extend the life-span of the CL in Nelore cows.     

Effect of transfer of one or two in vitro-produced embryos and post-transfer administration of gonadotropin releasing hormone on pregnancy rates of heat-stressed dairy cattle

Pregnancy rates following transfer of an in vitro-produced (IVP) embryo are often lower than those obtained following transfer of an embryo produced by superovulation. The purpose of the current pair of experiments was to examine two strategies for increasing pregnancy rates in heat stressed, dairy recipients receiving an IVP embryo. One method was to transfer two embryos into the uterine horn ipsilateral to the CL, whereas the other method involved injection of GnRH at Day 11 after the anticipated day of ovulation. In Experiment 1, 32 virgin crossbred heifers and 26 lactating crossbred cows were prepared for timed embryo transfer by being subjected to a timed ovulation protocol. Those having a palpable CL were randomly selected to receive one (n = 31 recipients) or two (n = 27 recipients) embryos on Day 7 after anticipated ovulation. At Day 64 of gestation, the pregnancy rate tended to be higher (P = 0.07) for cows than for heifers. Heifers that received one embryo tended to have a higher pregnancy rate than those that received two embryos (41% versus 20%, respectively) while there was no difference in pregnancy rate for cows that received one or two embryos (57% versus 50%, respectively). Pregnancy loss between Day 64 and 127 only occurred for cows that received two embryos (pregnancy rate at Day 127=17%). Between Day 127 and term, one animal (a cow with a single embryo) lost its pregnancy. There was no difference in pregnancy rates at Day 127 or calving rates between cows and heifers, but females that received two embryos had lower Day-127 pregnancy rates and calving rates than females that received one embryo (P < 0.03). Of the females receiving two embryos that calved, 2 of 5 gave birth to twins. For Experiment 2, 87 multiparous, late lactation, nonpregnant Holstein cows were synchronized for timed embryo transfer as in Experiment 1. Cows received a single embryo in the uterine horn ipsilateral to the ovary containing the CL and received either 100 microg GnRH or vehicle at Day 11 after anticipated ovulation (i.e. 4 days after embryo transfer). There was no difference in pregnancy rate for cows that received the GnRH or vehicle treatment (18% versus 17%, respectively). In conclusion, neither unilateral transfer of two embryos nor administration of GnRH at Day 11 after anticipated ovulation improved pregnancy rates of dairy cattle exposed to heat stress.     

Ultrasonic identification of follicular populations and return to estrus in early postpartum dairy cows given intravaginal progesterone for 15 days

In an attempt to program ovarian function in the early post partum period, 52 lactating Holstein cows were injected with 25 mg prostaglandin F(2alpha) (PGF) and given a CIDR device containing 1.9 g progesterone for 15 d starting on Day 25 post partum. Ovarian follicles were measured by ultrasound on 0, 5, 10 and 15 d after insertion and on alternate days after CIDR removal until estrus. Not all cows were devoid of corpora lutea (CL) during the CIDR (11, 9 and 8 cows had a CL on Days 5, 10 and 15, respectively). There was a CL by day interaction (P<0.01) for the number of 10- to 15-mm follicles per cow; the average number of large follicles (>15 mm) was twice greater (0.75 vs 0.37) for those cows not having a CL during the period of CIDR exposure. The average size of the largest follicle increased to a maximum of 19.3 +/- 0.7 mm by 15 d after insertion in cows not having a CL. Plasma estradiol increased for 10 d after insertion, then decreased to the end of the CIDR period. After removal of the CIDR, 34 cows ovulated, eight cows developed ovarian follicular cysts, and eight cows did not ovulated by 14 d. Cows becoming cystic or not ovulating had a declining number of follicles during the CIDR compared with those cows ovulating (P<0.07). The diameter of the largest follicle in cystic cows was equivalent to noncystic cows until removal of the CIDR, but then it increased markedly. Interval to estrus was longer in cows having more 6- to 9-mm follicles on Day 15 (day of CIDR removal). These results demonstrate the existence and maintenance of a large dominant follicle after CIDR insertion and PGF injection which was influenced apparently by the presence of a CL. Furthermore, subsequent reproductive responses after the CIDR treatment was a function of follicular populations prior to withdrawal of the CIDR device. This system may be appropriate for the study of factors regulating follicular growth and fertility in domestic cattle.     

Synchronization and resynchronization of inseminations in lactating dairy cows with the CIDR insert and the Ovsynch protocol

Pregnancy per artificial insemination (AI) was evaluated in dairy cows (Bos taurus) subjected to synchronization and resynchronization for timed AI (TAI). Cows (n = 718) received prostaglandin F_2α (PGF) on Days –38 and –24 (Days 39 and 53 postpartum), gonadotropin-releasing hormone (GnRH) on Day –10, PGF on Day –3, and GnRH and TAI on Day 0. Between Days –10 and –3, cows received a progesterone intravaginal insert (CIDR group) or no CIDR (Control group). Between Days 14 and 23, cows received a CIDR (Resynch CIDR group) or no CIDR (Resynch control group), GnRH on Day 23, with pregnancy diagnosis on Day 30. Cows in estrus (between Days 0 and 30) were re-inseminated at detected estrus (RIDE). Nonpregnant cows received PGF on Day 30 and GnRH and TAI on Day 33. Plasma progesterone was determined to be low or high on Days –24 and –10. Pregnancy rates were evaluated 30 and 55 d after AI. The CIDR insert included in the Presynch-Ovsynch protocol did not increase overall pregnancy per AI for first service (36.1% and 33.6% for CIDR; 34.1% and 28.8% for Control) but did decrease pregnancy loss (7.0% for CIDR and 15.6% for Control). The CIDR insert increased pregnancy per AI in cows with high progesterone at the time the CIDR insert was applied. Administration of a CIDR insert between Days 14 and 23 of the estrous cycle after first service did not increase overall pregnancy per AI to second service (24.7% and 22.7% for Resynch CIDR; 28.6% and 25.3% for Resynch control). For second service, RIDE cows had lower pregnancy rates in the Resynch CIDR group than in the Resynch control group. Cows with a CL (corpus luteum) at Day 30 had higher pregnancy rates in the Resynch CIDR group than those in the Resynch control group.     

Embryo survival in heifers after transfer of an egg to the uterine horn contralateral to the corpus luteum and the effect of treatments with progesterone or hCG on pregnancy rates.

Day 7 eggs (oestrus = Day 0) were surgically transferred singly to the uterine horn contralateral to the CL and heifers were either slaughtered on Day 24-26 (Group 1) or palpated per rectum on Day 42 (Group 2) to determine the presence of a developing conceptus and a maintained corpus luteum. There was a fall in pregnancy rate of the control heifers in Groups 1a (6/10) and 2a (2/10) (P = 0.085). Pregnancy rate was unaffected by progesterone treatments from Day 13 to the day before slaughter in Group 1b (8/10), or to Day 23 in Group 2b (2/10). Two of the conceptuses recovered in Group 1b were developing in the presence of regressed corpora lutea. There was, however, an increase in pregnancy rate in Group 2d (6/10) compared with Group 2a (2/10) when heifers were treated with hCG from Days 13 to 35 (P = 0.085). The results indicated that embryonic death is occurring after Day 24 and suggest that a change in the nature of the embryonic signal may be occurring at this time.     

Side of gestation in dairy heifers affects subsequent sperm transport and pregnancy rates after deep insemination into one uterine horn

Effects of side of previous gestation on sperm transport and pregnancy rates after deep cornual insemination were evaluated in 1686 Friesian cows in their first lactational period. Only single ovulating animals were used. At insemination, semen was deposited deep into the uterine horn ipsilateral or contralateral to the preovulatory follicle. A total of 876 cows (52%) ovulated in the ovary ipsilateral to the postgravid horn, and 810 cows ovulated in the contralateral ovary. Semen was deposited into the previously nongravid uterine horn of 832 cows, and into the gravid horn of 854 cows. The pregnancy rate was higher (P < 0.00001) for semen deposition into the previously nongravid horn (46.6%) than for semen deposition into the gravid horn (35.7%). For inseminations ipsilateral to the side of impending ovulation, pregnancy rates were higher (P = 0.0004) when ovulations occurred on the opposite side to the postgravid horn than on the same side. Pregnancy rates were higher (P = 0.002) for contralateral inseminations when ovulations occurred on the same side to the postgravid horn than on the opposite side; they were higher (P = 0.0001) for total ipsilateral than for total contralateral inseminations. There was no difference between ipsilateral and contralateral inseminations (P = 0.64) when ovulation occurred ipsilateral to the postgravid horn, but pregnancy rates were higher (P < 0.00001) when ipsilateral insemination was carried out into the nonpostgravid horn. Results indicate that the side of gestation in dairy heifers affects subsequent pregnancy rates after deep insemination into one uterine horn, possibly by affecting sperm transport.     

Comparison of synchronization of ovulation with timed insemination and exogenous progesterone as therapeutic strategies for ovarian cysts in lactating dairy cows

The objective of this study was to compare the effectiveness of the Ovsynch and controlled internal drug releasing (CIDR) protocols under commercial conditions for the treatment of cystic ovarian disease in dairy cattle. A total of 401 lactating dairy cows with ovarian cysts were alternatively allocated to two treatment groups on the day of diagnosis. Cows in the Ovsynch group were treated with GnRH on Day 0, PGF2alpha on Day 7, GnRH on Day 9, with timed insemination 16-20 h later. Cows in the CIDR group were treated with a CIDR insert on Day 0 for 7 days; on Day 7, the CIDR was removed, and cows were treated with PGF2alpha. All cows in the CIDR group were observed for estrus and cows exhibiting estrus within 7 days following removal of the CIDR and PGF2alpha administration were inseminated. The outcomes of interest for this experiment were the likelihood to be inseminated, return to cyclicity (determined by a CL on Day 21), conception and pregnancy rates. Data for these variables were analyzed using logistic regression. The percentage of cows inseminated in the Ovsynch and CIDR groups were 82 and 44%, respectively. Cows in the Ovsynch group were 5.8 times more likely to be inseminated than cows in the CIDR group. Cows with a low BCS were 0.48 times less likely to be inseminated than cows with a high BCS. The percentage of cows with a CL on Day 21 for the Ovsynch and CIDR groups was 83 and 79%, respectively (P > 0.05). Cows with a low BCS were 0.49 times less likely to have CL on Day 21 than cows with a high BCS. Conception and pregnancy rates for cows in the Ovsynch group were 18.3 and 14.4%, respectively. Conception and pregnancy rates for cows in the CIDR group were 23.1 and 9.5%, respectively. There was no significant differences between conception or pregnancy rates in cows in both groups. Primiparous cows were 2.6 times more likely to conceive than multiparous cows. In conclusion, the results of this study suggested that fertility was not different between cows with ovarian cysts treated with either the Ovsynch or the CIDR protocols in this dairy herd. In addition, primiparous cows had an increased likelihood for conception compared to multiparous cows, and cows with a low BCS were less likely to be inseminated or have a CL on Day 21, regardless of treatment.     

Luteolytic influence of intrauterine dead embryos in the early pregnant rat

The present investigation was an endeavour to study if annihilation of embryos in the uterus of the rat before the establishment of placental luteotropic functions has any influence on corpus luteal function, and, if there is any, whether it is local or systemic. The responsibility of pregnancy maintenance was imposed on a single ovary by performing unilateral ovariectomy after implantation (on Day 5 postcoitum). The implantation sites in one uterine horn, either ipsilateral or contralateral to the remaining ovary, were selectively destroyed by injecting 0.1 ml of sterile normal saline to that particular horn only, and the peripheral progesterone level and viability of the embryos in the untreated horn, which depended on the functions of the remaining ovary, were examined. Selective killing of embryos in the uterine horn of the ovariectomized side did not exert any influence on the fetal viability in the untreated horn ( nonovariectomized side) and the peripheral progesterone level also remained statistically unaffected. On the contrary, induction of fetal resorptions in the uterine horn of the intact side produced a significant fall in the peripheral level of progesterone and induced resorption of embryos of the ovariectomized side also. The latter could significantly be prevented by simultaneous administration of exogenous progesterone, indicating luteolysis as the major, if not sole, factor responsible for fetal resorption in the untreated horn. The luteolytic effect was attributed neither to saline itself, nor to the distension of the uterine horn caused by saline injection. Luteolytic factors from the dead embryo-bearing horn which act locally on the adjacent ovary only, are discussed.     

Effect of a unilateral or bilateral twin embryo distribution on twinning and embryo survival rate in the cow

Uni- and bilateral twin embryo distributions were effected by the transfer of one embryo on Day 7 to the ipsi- or contralateral uterine horn of previously inseminated heifers (123, Exp. 1) or cows (95, Exp. 2). The embryo transfers were surgical in Exp. 1 and non-surgical in Exp. 2. Transferred and native embryos were distinguished by breed. Embryo survival rate was measured in a proportion (N = 40) of the heifers at Day 53 of gestation and in the remainder of the heifers and all of the cows at term. In the heifers (Exp. 1) overall pregnancy rates of 76% and 75% were recorded after uni- and bilateral twin embryo distributions respectively. Twinning rates of 55% and 60% at Day 53 of gestation and 60% and 60% at term were recorded for uni- and bilateral distributions respectively. In the cows (Exp. 2) calving rates of 61% and 63% and twinning rates of 33% and 38% were recorded following uni- and bilateral twin embryo distributions respectively. When the data from both experiments were combined, overall embryo survival rates were similar for both twin embryo distributions although the ipsilateral transfer of an embryo reduced the survival rate of the native embryo. It is concluded that the confinement of two embryos in one uterine horn on or after Day 7 does not depress pregnancy, twinning or overall survival rate to term.     

Unilateral uteroovarian relationship in pregnant cattle and role of uterine vein

The hypothesis of a unilateral uteroovarian relationship between location of embryos and maintenance of corpora lutea (CL) was tested in superovulated cattle. Ovulations were induced in both ovaries and a uterine horn was isolated subsequent to insemination to produce unilateral pregnancy. The mean weight of CL on day 24 was greater (P<.05) on the gravid side (2580 mg) than on the nongravid side (1200 mg; n=5), supporting the hypothesis. Involvement of the main uterine vein in the unilateral pathway between a gravid horn and the adjacent ovary was demonstrated in an experiment which utilized separation of uterine horns, anastomosis of uterine veins between sides, and insertion of embryos into one side by embryo transfer. Mean weight of CL on day 24 was less (P<.05) when the gravid horn was contralateral to the CL (950 mg; n=3), than when the gravid horn was ipsilateral to the CL (4760 mg) or when the gravid horn was contralateral to the CL and the uterine vein from the contralateral side was anastomosed to the vein on the ipsilateral side (3580 mg; n=3).     

Cytoplasmic oestradiol-binding sites and their relationship to oestradiol content in the endometrium of cattle.

Twenty-three cows and heifers were killed at known times during the oestrous cycle or during the first 35 days of pregnancy. Duplicate cytosol preparations were made from the endometrium of each uterine horn and both the binding-site concentration and the oestradiol level were determined for each sample. During the cycle, the oestradiol concentration was only 0-2 to 1-7% of the concentration of binding sites which varied considerably between Days 19 and 5 (47,665 +/- 7538 sites/cell, mean +/- S.E.M.) and Days 6 to 18 (7060 +/- 444 sites/cell). The concentration of binding sites remained low in pregnant animals (6689 +/- 492), although the oestradiol concentration was high about 20 days after insemination, resulting in almost 14% of the sites being occupied. Five inseminated animals in which no conceptus was found when they were slaughtered 19 to 22 days later had low concentrations of binding sites but two animals had high levels of oestradiol with 13% and 15%, respectively, of their cytoplasmic sites being occupied. It is suggested that these animals had recently lost their conceptuses. Two ovariectomized cows and one non-cyclic animal contained high concentrations of oestradiol-binding sites in the uterine cytoplasm. No significant difference was found between the uterine horn adjacent to the ovary with the CL and the contralateral horn in early pregnancy or during the luteal phase of the oestrous cycle. An animal killed 1 week after parturition contained fourfold more sites in the involuting horn than in the opposite horn. It is suggested that progesterone plays a major role in regulating oestrogen-induced replacement of cytoplasmic binding sites.     

Effect of the regressing corpus luteum of pregnancy on ovarian folliculogenesis after parturition in cattle.

In cattle, the first postpartum dominant follicle has a predilection for the ovary contralateral to the previously gravid uterine horn, possibly due to a local inhibitory effect of the regressing corpus luteum of pregnancy in the ipsilateral ovary. The aim of the present study was to test the hypothesis that the regressing corpus luteum of pregnancy suppresses folliculogenesis in the ipsilateral ovary after parturition. Dairy cows were treated with prostaglandin F2alpha between 190 and 220 days of gestation to cause luteolysis without inducing parturition (n = 14) or were untreated controls (n = 32). Follicular growth and function were monitored by daily transrectal ultrasonography and collection of plasma samples for estimation of FSH, estradiol, and progesterone concentrations. The proportion of first dominant follicles in the ipsilateral ovary was similar for treated and control animals (4/14 vs. 8/32), as was the time interval between calving and establishment of a dominant follicle (mean +/- SEM, 10.1 +/- 0.4 vs. 10.7 +/- 0.5 days). Furthermore, no significant effect of treatment on dominant follicle growth or function was found as determined by plasma hormone concentrations. Although greater folliculogenesis was found in the ovary contralateral to the previously gravid uterine horn, once the location of the future first dominant follicle was selected, the timing of events was independent of location. We suggest that the corpus luteum of pregnancy does not have a local effect on postpartum ovarian folliculogenesis and that, instead, an effect of the previously gravid uterine horn shortly after parturition should be considered.     

Embryotoxic effects adjacent and opposite to the early regressing bovine corpus luteum

Early luteal regression in cattle has an embryotoxic effect that is not overcome by replacement with progesterone, but is prevented by removal of the regressing CL. Two experiments were designed to test the null hypothesis that the luteal component of the embryotoxic effect is delivered by a systemic pathway. Beef heifers and cows (n = 39) received two good quality embryos, one placed into each uterine horn on Day 6 or 7 of the estrous cycle. Treated animals (n = 20) received 15 mg of PGF2alpha three times per day from Day 7 (n = 11; Experiment 1) or 5 (n = 9; Experiment 2) through 8; controls (n = 19) received saline. Progestogen replacement therapy (12 mg flurogestone acetate daily, s.c.) was provided from Day 6 (Experiment 1) or 4 (Experiment 2) until ultrasonographic diagnosis of embryo survival on Day 35 after estrus. The effects of treatment, location of the embryo and location by treatment interaction on embryo survival were tested by Chi square. In Experiment 1, there was no significant difference in embryo survival rate between PGF2alpha-treated and control recipients. In Experiment 2, only 6 of 18 embryos survived to Day 35 when transferred to animals treated with PGF2alpha compared to 12 of 18 in control animals (P< 0.05). The survival of embryos did not differ with location (adjacent or opposite to the regressing CL) or location by treatment interaction. Thus no evidence was obtained to support a local effect of the regressing CL. The embryo mortality associated with luteolytic doses of PGF2alpha in cows receiving replacement therapy with progestogen probably involves compounds that either act systemically or are transported via the uterine lumen to the uterine horn contralateral to the regressing CL.     

Effect of heat stress on conceptus and uterine secretion in the bovine

This study examined the effects of heat stress on conceptus secretion of bovine trophoblastic proteins (bTP) and the uterine secretory environment on Day 17 of pregnancy. After mating to fertile bulls, cows were placed in an environmental chamber at 21 degrees C, 45% RH on Day 7 and were assigned to one of the following treatments on Day 8: Control (21 degrees C, 45% RH), Treatment 1 (37 degrees C, 30% RH) and Treatment 2 (37 degrees C, 40% RH). Cows were slaughtered on Day 17 and each uterine horn was flushed separately with physiological saline to recover the conceptus and uterine contents. The wet weight of the conceptus was recorded and uterine flushings were analyzed for quantitative and qualitative protein changes, prostaglandin F and calcium concentrations. Conceptus tissue was cultured in vitro with 100 muCi of [(3)H]-leucine and the polypeptides released into the medium were analyzed by 2D-PAGE followed by fluorography. Heat stress increased rectal temperature of cows and reduced conceptus wet weight. Uterine content of protein and calcium were increased in the uterine horn ipsilateral to the CL of heat-stressed cows. Although uterine protein increased in heat-stressed cows, no qualitative difference was observed in the polypeptides present in the uterine lumen. Conceptus synthesis and release of bTP were enhanced in treated cows. These responses indicate that heat stress between Days 8 to 17 of pregnancy altered the uterine environment as well as growth and secretory activity of the conceptus.     

Prostaglandin E-2 as a potential luteotrophic agent during early pregnancy in cattle

Heifers slaughtered on Day 18/19 of pregnancy had significantly higher (P less than 0.001) concentrations of PGE-2 (measured as its methyl oxime) in uterine flushings than did animals slaughtered on Days 6 or 12 of pregnancy, or on Days 6 or 12 of the oestrous cycle. In addition, concentrations were higher in the uterine horn ipsilateral to the corpus lueum on Days 12 (P less than 0.05) and 18/19 (P less than 0.01) than in the contralateral horn. Incubation of dispersed luteal cells for 3 h with LH (0.1 or 100 ng/ml) and/or PGE-2 (0.01-1000 ng/ml) in vitro showed no differences in basal progesterone production or in the responses to exogenous hormones between pregnant and non-pregnant cattle. However, low doses of PGE-2 (0.01-10 ng/ml) inhibited the stimulation of progesterone secretion by the lower dose of LH. These findings indicate that although PGE-2 can stimulate progesterone synthesis by luteal cells it may also have inhibitory effects, and therefore its role in pregnancy requires further definition.     

Progesterone in uterine and arterial tissue and in jugular and uterine venous plasma of sheep

Concentrations of progesterone in uterine and arterial tissue and in uterine and jugular venous plasma were determined. Blood was collected on Days 4 and 9 postestrus from the jugular vein and the first and last venous branches draining each uterine cornu; uterine tissue and arteries were subsequently collected. Progesterone was greater (p less than 0.05) in the cranial third than in the middle or caudal thirds of the uterine horn adjacent to the corpus luteum (CL)-bearing ovary or in any third of the contralateral horn. Progesterone in uterine arterial segments adjacent to the CL-bearing ovary was higher (p less than 0.05) than in contralateral segments. Progesterone was higher (p less than 0.05) in blood from the first venous branch of the cranial third of the uterine cornu adjacent to the ovary with the CL, than in the last branch of the caudal third, or contralateral horn, or in jugular blood. When oviductal veins were resected on Day 9 postestrus, progesterone in the first vein draining the cranial third of the uterine cornu adjacent to the CL-containing ovary was not different (p greater than 0.05) 48 h after resection than in the same vessel in the opposite horn or in jugular blood. We concluded that progesterone and other ovarian products may be delivered to the uterus locally.     

Unilateral luteotropic effect of uterine venous effluent of a gravid uterine horn in sheep.

The involvement of the main uterine vein in the unilateral maintenance of CL was studied in bilaterally ovulating unilaterally pregnant ewes. Ewes were mated at estrus (Day 0) and bilaterally ovulating ewes were randomized into three groups at surgery on Day 5. In all ewes, the uterine horns were separated through the intercornual area and one was ligated and transected near the internal bifurcation to produce a nongravid horn. One group served as controls (five ewes). In the other two groups the main uterine vein on one side was surgically anastomosed (end to side) to the corresponding vein of the opposite side (gravid side to nongravid side in one group--three ewes, and nongravid side to gravid side in the other--three ewes). Necropsies were done on Day 20. Mean CL weight was less, (P less than .01) on the nongravid side in control ewes than on the gravid side in control ewes or for either side in the other two groups. There were no significant differences among mean weights of CL on the gravid side in control ewes and either side in the other two groups. The CL regressed when the ipsilateral uterine vein contained blood from only the nongravid horn whereas the CL was maintained when the ipsilateral uterine vein contained venous blood from a gravid horn, whether or not it also contained blood from a nongravid horn. Results indicate that the uterine venous effluent from a gravid uterine horn in sheep has a luteotropic effect on the ipsilateral CL.     

Luteal function,largest follicle,and fertility in postpartum dairy cows treated with 14dCIDR-PGF2α versus 2xPGF2α-Ovsynch for timed AI

A method for timed artificial insemination (AI) that is used for beef cows, beef heifers, and dairy heifers employs progesterone-releasing inserts, such as the controlled internal drug release (CIDR; Zoetis, New York, NY, USA) that are left in place for 14 days. The 14-day CIDR treatment is a method of presynchronization that ensures that cattle are in the late luteal phase of the estrous cycle when PGF_2α is administered before timed AI. The objective of this study was to test the effectiveness of the 14dCIDR-PGF_2α program in postpartum dairy cows by comparing it with the traditional “Presynch-Ovsynch” (2xPGF_2α-Ovsynch) program. The 14dCIDR-PGF_2α cows (n = 132) were treated with a CIDR insert on Day 0 for 14 days. At 19 days after CIDR removal (Day 33), the cows were treated with a luteolytic dose of PGF_2α, 56 hours later were treated with an ovulatory dose of GnRH (Day 35), and 16 hours later were inseminated. The 2xPGF_2α-Ovsynch cows were treated with a luteolytic dose of PGF_2α on Day 0 and again on Day 14. At 12 days after the second PGF_2α treatment (Day 26), the cows were treated with GnRH. At 7 days after GnRH, the cows were treated with PGF_2α (Day 33), then 56 hours later treated with GnRH (Day 35), and then 16 hours later were inseminated. There was no effect of treatment or treatment by parity interaction on pregnancies per AI (P/AI) when pregnancy diagnosis was performed on Day 32 (115/263; 43.7%) or Days 60 to 90 (99/263; 37.6%) after insemination. There was an effect of parity (P < 0.05) on P/AI because primiparous cows had lesser P/AI (35/98; 35.7%) than multiparous cows (80/165; 48.5%) on Day 32. Cows observed in estrus after the presynchronization step (within 5 days after CIDR removal or within 5 days after the second PGF_2α treatment) had greater P/AI than those not observed in estrus (55/103; 53.4% vs. 60/160; 37.5%; observed vs. not observed; P < 0.01; d 32 pregnancy diagnosis). When progesterone data were examined in a subset of cows (n = 208), 55.3% of cows had a “prototypical” response to treatment (i.e., the cow had an estrous cycle that was synchronized by the presynchronization treatment and then the cow responded appropriately to the subsequent PGF_2α and GnRH treatments before timed AI). Collectively, cows with a prototypical response to either treatment had 52.2% P/AI that was greater (P < 0.001) than the P/AI for cows that had a nonprototypical response (19%) (P/AI determined at 60–90 days of pregnancy). In conclusion, we did not detect a difference in P/AI when postpartum dairy cows were treated with 14dCIDR-PGF_2α or 2xPGF2α-Ovsynch before timed AI. The primary limitation to the success of either program was the failure of the cow to respond appropriately to the sequence of treatments.