Chemical properties of bovine cervical mucus during normal estrus and estrus induced by progesterone and/or PGF2alpha

Ninety-two Friesian cows were used to determine the chemical properties of cervical mucus during normal estrus and estrus induced by progesterone (P4)-releasing intravaginal devices (PRID) and/or prostaglandin F2alpha. The animals were assigned to 4 groups (no treatment, a PRID for 12 days plus injection of 1000 IU PMSG at the removal of PRID, a double i.m. injection of PGF2alpha 11 days apart, or PRID for 7 days plus an im injection of PGF2alpha 24 h before the removal of PRID). A number of cows with normal estrus exhibited three consecutive estrous cycles after delivery. Cows that had not shown estrus for 3 months after delivery had their ovaries palpated twice at 10-day intervals, to determine their ovarian activity. Then PRID and/or PGF2alpha was administered in cows that had a palpable corpus luteum in one of the two palpations (cyclic cows). A double artificial insemination (AI) was performed to the cows of the three induced-estrus groups, while the cows with normal estrus received only one AI. Cervical mucus samples were collected from all cows 5 to 30 min before the first AI. Additionally, samples of cervical mucus were collected from 20 cows during their first estrus after the induced one. The results are summarized as follows: 1) The biochemical properties of cervical mucus in the first three estrus periods after delivery were similar. 2) These properties were similar both in normal estrus after delivery and in the first estrus after an induced one. 3) Glucose and fructose concentrations for normal estrus were similar to those for induced estrus groups. 4) Total protein and cholesterol concentrations were significantly lower (P < 0.001) in normal than in induced estrus, while no difference was found among the induced estrus groups. 5) Pregnancy rates of the cows did not differ significantly among the normal and the induced-estrus groups. 6) The percentages of cows in the induced-estrus groups that produced cervical mucus with total protein and cholesterol concentrations similar to those for the normal estrus groups was very low.     

Regulation of estrus and ovulation in mares with progesterone or progesterone and estradiol biodegradable microspheres with or without PGF2alpha

A single injection of a microsphere preparation, designed to deliver 1.25 gm progesterone and 100 mg estradiol-17beta at a controlled rate, for a duration of 12 to 14 days, produces accurate control of estrus and fertile ovulations in mares. Theatment is followed by PGF(2)alpha injection 14 days after steroid injection. The objectives of the present study were to determine whether estradiol added to the progesterone treatment or PGF(2)alpha administered at the end of the steroid treatment regimen, would improve synchronization of estrus and ovulation. A total of 45 cyclic horse mares was randomly assigned to 1 of 5 treatment groups as follows: Group 1 (control, n=9) sterile microsphere vehicle + sterile PGF(2)alpha vehicle 14 days after treatment with microsphere vehicle; Group 2 (n=9) progesterone and estradiol microspheres + PGF(2)alpha 14 days after treatment with microspheres; Group 3 (n=9) progesterone and estradiol microspheres + PGF(2)alpha vehicle 14 days after treatment with microspheres; Group 4 (n=9) progesterone + PGF(2)alpha 14 days after treatment with microspheres; and Group 5 (n=9) progesterone + PGF(2)alpha vehicle 14 days after treatment with microspheres. Addition of estradiol (P<0.05) or PGF(2)alpha (P<0.05) to the treatment regimen increased synchronization efficary by reducing variation in days to ovulation. All treatments significantly reduced variation in days to estrus compared with that of the controls; however, mares in the progesterone groups had an increased incidence of silent or shortened estrous behavior (<- 2 days) following treatment. Estradiol added to the treatment regimen increased (P<0.05) the number of mares with post treatment estrus > 2 days in duration compared with mares treated with progesterone (78 vs 33%, respectively). Therefore, estradiol and PGF(2)alpha each appear to reduce variation in days to ovulation while estradiol seems to promote better expression of posttreatment estrous behavior.     

Reproductive performance of lactating dairy cows following estrus synchronization regimens with PGF2alpha and progesterone

The objective of this study was to evaluate the reproductive performance of lactating cows in seasonal dairy herds after estrus synchronization with PGF2alpha (PG) with or without supplementation with progesterone (P4). In Trial 1, synchronized cows (S1; n = 521) were compared with untreated control cows (C; n = 518) in 5 herds. Estrus of cows in the S1 group was synchronized with 2 treatments of PG (Lutalyse) 13 d apart. The breeding season started 2 d after the second PG. Cows were first bred by AI for 7 wk and then herd sires were used. Compared with C cows, estrus synchronization in the treated cows reduced the conception rate to first AI (61.1 vs 70.5%; P < 0.01) and the intervals from start of the breeding season to conception for cows conceiving to AI (11.0 vs 14.6 d; P < 0.05) or to both AI and natural mating (16.5 vs 18.4 d; P < 0.05). There was no effect on conception rate to second AI (68.8%), on pregnancy rate by Day 24 (72.3%) or Day 49 (86.3%) of the breeding season, or on the percentage of cows not pregnant at end of the breeding season (5.0%). In Trial 2, effects of P4 supplementation before the second PG on reproductive performance were evaluated in 4 herds. Estrus of each cyclic cow was synchronized with PG as in Trial 1. Half of the cows in each herd were treated with an intravaginal P4 device (CIDR) for 5 d before the second PG (S2+P4, n = 608), whereas the remaining half received no CIDR treatment (S2, n = 593). Compared with S2 cows, P4 treatment increased the estrous response rate to the second PG (89.6 vs 82.9%; P < 0.01), the conception rate to first AI (65.1 vs 59.7%; P = 0.07), the pregnancy rate by Day 6 of the breeding season (59.3 vs 49.0%; P < 0.001), and reduced the intervals from start of the breeding season to conception for cows conceiving to AI (8.6 vs 10.4 d; P < 0.10) or to both AI and natural mating (12.7 vs 16.4 d; P < 0.01). Treatment with a used CIDR from Days 16 to 21 after start of breeding to re-synchronize returns to service had no effect on conception rate to first or second AI but may decrease the conception rate to second AI in cows previously treated with CIDR. In conclusion, estrus synchronization with the double PG system can reduce fertility, while P4 supplementation for 5 d before the second PG can improve estrous response and overall reproductive performance. Stage of the estrous cycle at the time of the second PG can affect fertility following synchronization.     

Biosynthesis and catabolism of prostaglandin F2alpha (PGF2alpha) are controlled by progesterone in the rat uterus during pregnancy

Myometrial quiescence is a key factor in all species to accomplish a successful gestation. PGs play a crucial role in mediating parturition events, and their synthesis and metabolism are regulated by cyclooxygenases (COXs) and NAD(+)-dependent 15-hydroxy-PG dehydrogenase (PGDH), respectively. Progesterone (P(4)) is the hormone responsible for maintaining uterine smooth muscle quiescence during pregnancy. In this work, we have studied the effect of P(4) on the activity of COXs and PGDH, the uterine enzymes involved in the biosynthesis and metabolism of prostanoids in the rat. We found that during pregnancy PGF(2alpha) production and also protein levels of COX-1 and COX-2 were decreased. The exogenous administration of P(4) significantly inhibited the uterine production of PGF(2alpha) and also the protein level of COX-2. PGF(2alpha), metabolism was assessed by PGDH activity, which resulted high during pregnancy and increased as a result of P(4) administration. These results indicate that PGs levels were negatively modulated by P(4), which could be exerting its effect by increasing PGs metabolism through stimulation on PGDH activity and an inhibition on COX and that is a major mechanism for maintain uterine quiescence in pregnancy.     

Synchronization of estrus with PGF2 alpha administered 18 days after a progesterone treatment in lactating dairy cows

In a previous study we showed that estrus synchronization with 2 treatments of PGF2 alpha 13 d apart reduced conception rate at the synchronized estrus and that this reduction occurred mainly in cows in the early luteal phase at the second PGF2 alpha treatment. The objective of the present study was to determine the efficacy of a synchronization regimen in which PGF2 alpha was administered during the mid- to late-luteal phase to cows that had previously been synchronized with progesterone. Spring-calving cows from 6 dairy herds were used in this study. On Day -32 (Day 1 = the start of the breeding season), cows that had calved 2 or more weeks ago were randomly assigned to a synchronization (S, n = 732) or control (C, n = 731) group. Cows in Group S were treated with an intravaginal progesterone device (CIDR) for 12 d from Day -32 to Day -20, while those in Group C were left untreated. Similar percentages of cows in Group S (80.6%) and C (82.9%) had cycled by Day -7. The CIDR treatment synchronized the onset of estrus, resulting in 92.9% of cows in estrus being detected within 7 d after CIDR removal. Cows in Group S that had cycled by Day -7 were treated with PGF2 alpha (25 mg, i.m., Lutalyse) on Day -2. Cows in both groups that were anestrous on Day -7 were treated with a combination of progesterone and estradiol benzoate (EB) to induce estrus and ovulation (CIDR and a 10 mg EB capsule on Day -7, CIDR removal on Day -2, and injection of 1 mg EB 48 h after CIDR removal). The PGF2 alpha treatment synchronized the onset of estrus in 87.5% of the cows. Group S and C cows had similar conception rates to first (61.0 vs 58.3%) and second (58.4 vs 60.9%) AI; similar pregnancy rates over the AI period (82.8 vs 79.2%) and over the whole breeding season (91.9 vs 90.6%); and required a similar number of services per pregnancy to AI (1.7 vs 1.8). The interval from the start of the breeding season to conception for cows conceiving to AI or to combined AI and natural mating was shorter (P < 0.001) by 5.7 and 6.2 d, respectively, for the Group S cows. It is concluded that the treatment regimen tested in the present study achieved satisfactory estrus synchronization, had no detrimental effect on fertility at the synchronized estrus, and shortened the interval from start of the breeding season to conception.     

Incidence of premature estrus in lactating dairy cows and conception rates to standing estrus or fixed-time inseminations after synchronization using GnRH and PGF(2alpha).

Fixed-time AI (TAI) after GnRH-PGF(2alpha)-GnRH treatment is a method to achieve pregnancies in dairy herds without estrous detection. However, cows that fail to respond to the initial GnRH may have compromised TAI conception rates due to asynchronous ovarian response. This study documented the percentage of GnRH-treated Holstein cows (n=345) in two herds that displayed estrus at an inopportune time for optimum TAI conception rate (< or =48h post-PGF(2alpha); premature estrus (PE)) and compared conception rates of two TAI protocols in cows that did not display PE. At biweekly herd health exams, cows diagnosed as not pregnant to a previous AI and cows >80 days postpartum with no AI were treated with 100 microg GnRH (day -7) and 25mg PGF(2alpha) (day 0). Cows detected in PE by twice-daily visual observation from day -7 to day 2 were bred by AI 8-12h later. Cows not detected in PE were randomly assigned by parity, body condition score, and postpartum interval to receive either: (1) 100microg GnRH at 48h after PGF(2alpha) and TAI 16 to 18h later (Ovsynch); or (2) TAI at 72h post-PGF(2alpha) and a concurrent 100 microg GnRH injection to those cows not detected in estrus between 48 and 72h post-PGF(2alpha) (modified Ovsynch (MOV)). All hormone injections were im. Twenty percent (68/345) of the cows were detected in estrus before 48 after PGF(2alpha), of which 5% (17/345) were detected in estrus before PGF(2alpha) (< or =day 0). Herd influenced the percentage of cows in the PE group (herd A versus herd B; 25% versus 14%; P<0.05). Conception rates were not affected by treatment (PE versus Ovsynch versus MOV; 32% (21/65) versus 30% (37/125) versus 32% (47/145); P>0.10). However, within MOV-treated cows, conception rates were greater (P<0.05) in cows detected in estrus (46% (23/50)) compared with cows not detected in estrus (25% (24/95)). In conclusion, 20% of GnRH-treated cows displayed PE and necessitates estrous detection during this period if maximal pregnancy rates are to be achieved. Although additional estrous detection is required compared to Ovsynch, reduced cow handling and hormone usage, efficient use of expensive semen through greater conception rates in cows detected in estrus, and comparable TAI conception rates, suggests the MOV protocol may be a cost effective alternative to Ovsynch in many dairy herd reproductive management programs.     

Polyunsaturated fatty acids differentially alter PGF(2alpha) and PGE(2) release from bovine trophoblast and endometrial tissues during short-term culture

Two studies tested the hypothesis that eicosapentaenoic (20:5omega3; EPA), docosahexaenoic acids (22:6omega3; DHA) or linoleic acid (C18:2omega6; LIN) reduced bovine endometrial and trophoblast prostaglandin F(2alpha) (PGF(2alpha)) and prostaglandin E(2) (PGE(2)) release during short-term culture. In Study 1, endometrial tissues were collected from non-lactating, non-pregnant cows and endometrial plus trophoblast tissues from pregnant cows 16 days post-insemination. In Study 2, endometrial and trophoblast tissues were collected on day 17 of pregnancy, from cows synchronised using a double prostaglandin (PG) or Ovagentrade mark synchronisation. Tissues were incubated in medium only (M) or media supplemented with fatty acids: eicosapentaenoic (20:5omega3; EPA), docosahexaenoic acids (22:6omega3; DHA) or linoleic acid (C18:2omega6; LIN). In Study 1, PGE(2) release from 'pregnant' endometria was higher (P=0.094) than from 'non-pregnant' endometria, while PGF(2alpha) concentrations were similar. Fatty acids treatment had no effect on PGF(2alpha) or PGE(2) release from either pregnant or non-pregnant endometria. Individual fatty acid treatments had no effect on the ratio of PGF(2alpha) to PGE(2) from trophoblast tissues, but when the data from the 3 fatty acid treatments were combined (EPA, DHA and LIN treatment groups) the ratio of PGF(2alpha) to PGE(2) was reduced (P=0.026) when compared to medium only. In Study 2, PGE(2) concentrations were higher (P=0.013) from the trophoblast collected from Ovagentrade mark cows as compared to that of the PG synchrony group. When the data from the 3-omega fatty acids were combined (DHA and EPA treatment groups), the 3-omega treatments decreased (P<0.05) PGE(2) biosynthesis from both endometrial and trophoblast tissues from animals synchronised following PG synchrony but not Ovagentrade mark synchrony. Short-term culture with low concentrations of 3-omega fatty acids tended to reduce prostaglandin release from trophoblast collected 16 days after insemination, with the type of synchrony modifying PGE(2) production from the trophoblast tissues collected 17 days after insemination. The ability of exogenous fatty acids to modify embryonic prostaglandin release needs to be examined in the context of supplementing dairy cows with different sources of fats. Synchronisation method altered trophoblast PGE(2) release, highlighting the importance of the hormonal environment in modifying embryonic prostaglandin synthesis and release.     

Effects of prostaglandins E2 and F2alpha (PGE2; PGF2alpha), trilostane,mifepristone, palmitic acid (PA), indomethacin (INDO), ethamoxytriphetol (MER-25), PGE2 + PA,or PGF2alpha + PA on PGE2, PGF2alpha,and progesterone secretion by bovine corpora lutea of mid-pregnancy in vitro

The effects of PGE2, PGF2alpha, trilostane, RU-486, PA, INDO, MER-25, PGE2, or PGF2alpha + PA on secretion of progesterone, PGE2, or PGF2alpha by bovine corpora lutea (CL) of mid-pregnancy in vitro for 4 and 8 hr was examined. Secretion of PGE2 and PGF2alpha increased with time in culture (P < or = 0.05). PGE2 and PGE2 + PA increased (P < or = 0.05) secretion of progesterone at 4 and 8 h, progesterone secretion was increased (P < or = 0.05) at 4 h; but not at 8 h (P > or = 0.05) by trilostane, mifepristone, PGF2alpha and PGF2alpha + PA, and was decreased at 8 h by PGF2alpha and PGF2alpha + PA. Indomethacin decreased (P < or = 0.05) secretion of PGE2, PGF2alpha, and progesterone at 4 and 8 h. Trilostane, PA, PGF2alpha, RU-486 and PGF2alpha + PA increased (P < or = 0.05) PGE2 at 4 h only. Palmitic acid decreased (P < or = 0.05) PGF2alpha at 4 h, while trilostane, RU-486, or MER-25 did not affect (P < or = 0.05) PGE2 of PGF2alpha secretion. It is concluded that PGE2 of luteal tissue origin is the luteotropin at mid-pregnancy in cows. Also, it is suggested that PA may alter progesterone secretion by affecting the inter conversion of PGE2 and PGF2alpha.     

Synchronization of estrus in embryo transfer recipients after using a combination of PRID or CIDR-B plus PGF2alpha

The use of CIDR-B or PRID in combination with prostaglandin F2alpha (PGF2alpha) for synchronizing estrus in embryo transfer recipients was evaluated in 2 experiments. In Experiment 1, virgin heifers (n=263) were synchronized using either a PRID (including estradiol benzoate capsule) or a CIDR-B in a combined program in which devices were inserted on Day 1, an injection of prostaglandin was given on Day 6, and devices were withdrawn on Day 7. The interval from device removal to the onset of estrus was significantly shorter for CIDR-B than for PRID-treated animals (50.44 vs 55.50 hours; P<0.003). The CIDR-B treatment resulted in a similar degree of synchrony to the PRID treatment (74.0 vs 70.4%; P=0.68). InExperiment 2, cows (n=95) and heifers (n=93) were allocated at random to be synchronized using a PRID (excluding estradiol benzoate capsule) plus PGF2alpha or a CIDR-B device plus PGF2alpha. The devices were inserted on Day 1, an injection of prostaglandin was given on Day 10 and the devices were removed on Day 12. Estrus was observed earlier following the CIDR-B treatment (43.50 vs 47.04 hours; P=0.01), but the degree of synchrony was similar (76.2 vs 76.3%; P>0.10) for the CIDR-B and PRID-treated animals. In both experiments, there were no significant differences in the proportions of animals observed in estrus, selected as embryo transfer recipients, or which achieved pregnancy consequent on embryo transfer between those synchronized using CIDR-B or PRID regimens. We conclude that the CIDR-B is a suitable device for synchronizing estrus in embryo transfer recipients.     

Effect of stage of the estrous cycle on interval to estrus after PGF(2alpha) in beef cattle

Effect of stage of the estrous cycle at the time of prostaglandin F(2alpha) (PGF(2alpha)) injection on subsequent reproductive events in beef females was studied in four trials involving 194 animals. Cycling animals were given two injections of 25 mg PGF(2alpha) 11 days apart or, in some cases, the interval was altered to allow the second injection to fall on a specific day of the cycle. Day of estrous cycle at time of the second injection was determined by estrous detection. Interval from the second PGF(2alpha) injection to the onset of estrus (interval to estrus) was shorter (P<.01) in heifers than in cows. Both cows and heifers injected on days 5 to 9 (early cycle) had a shorter (P<.01) interval to estrus (estrus = day 0) than did those injected on days 10 to 15 (late cycle). Conception rate was lower (P<.05) for early-cycle heifers than for late-cycle heifers inseminated by appointment at 80 hours. There was no significant difference in conception rate of early-or late-cycle heifers or cows inseminated according to estrous detection or early- or late-cycle cows inseminated at 80 hours. Progesterone concentrations in blood samples collected in heifers at 4-hour intervals after the second PGF(2alpha) injection on either day 7 or day 14 declined linearly (P<.05) through 36 hours. Day of the estrous cycle at PGF(2alpha) injection had no effect on rate of progesterone decline, even though heifers injected on day 7 had a shorter (P<.05) interval to estrus. All animals whose cycle length was not affected by the second PGF(2alpha) injection were treated on days 5 through 8 of the cycle, indicating that PGF(2alpha) was less effective in regressing the corpus luteum between days 4 and 9 of the cycle than later in the cycle.     

Low semen dose intracornual insemination of cows at fixed time after PGF2alpha treatment or at spontaneous estrus

The numbers of spermatozoa per insemination and the site of semen deposition in the uterine horn appear to interact to influence pregnancy rate. In two experiments, the effect of a single low dose (2 x 10(6) spermatozoa) intracornual insemination (LD-ICI) on bovine pregnancy rate was compared with that of intracornual (SD-ICI) and conventional (SD-AI) inseminations of 40 x 10(6) spermatozoa. In Experiment 1, 157 cows were treated twice with PGF(2)alpha at a 14-day interval and inseminated at a fixed time (80-82 h) after the second PGF(2)alpha injection using LD-ICI (n=44), SD-ICI (n=61) or SD-AI (n=52). In LD-ICI and SD-ICI groups, semen was deposited in the horn ipsilateral to the ovulatory follicle close to the utero-tubal junction (LD-ICI-UTJ, n=33 and SD-ICI-UTJ, n=41) or in the middle part of the horn (LD-ICI-MH, n=11 and SD-ICI-MH, n=20). Pregnancy rates after LD-ICI-UTJ, LD-ICI-MH, SD-ICI-UTJ and SD-ICI-MH were 27%, 27%, 39% and 35%, respectively (P>0.05). The total pregnancy rate after LD-ICI (27%) did not differ (P>0.05) from that after SD-ICI (37%) or SD-AI (34%). In Experiment 2 (field trial), 362 cows were allotted, at spontaneous estrus, to LD-ICI-UTJ (n=86), LD-ICI-MH (n=97) or SD-AI (n=179). Pregnancy rates after LD-ICI and SD-AI were 47% and 45%, respectively (P>0.05). After LD-ICI-UTJ, the pregnancy rate (54%) did not differ significantly (P>0.05) to that obtained after LD-ICI-MH (41%) and after SD-AI (45%). The results of the study show that the single intracornual insemination of cows with 2 x 10(6) spermatozoa at fixed time, 80-82 h after the second PGF(2)alpha injection or at spontaneous estrus resulted in similar pregnancy percentage as intracornual and conventional inseminations with 40 x 10(6) spermatozoa per semen dose. With intracornual insemination using low or standard dose of spermatozoa, the pregnancy rates were not significantly affected by the exact site of semen deposition in the uterine horn, near the utero-tubal junction or in the middle part.     

Effect of one spontaneous estrus cycle (after synchronization with PGF2alpha) on reproductive performance in dairy cows

The objective of the study was to analyze the effect of a spontaneous estrus cycle after synchronization of estrus with prostaglandin F2alpha (PGF2alpha) in dairy cows on the degree of synchronization and reproductive performance. We assigned 557 Holstein cows to two treatment groups. In Group 1 estrus was synchronized by two treatments with 25 mg of Dinoprost-Trometamol in 14-day intervals. Cows were treated 27 to 33 days postpartum (dpp) and 41 to 47 dpp, respectively. Cows in Group 2 were treated with 25 mg of Dinoprost-Trometamol three times in 14-day intervals, starting at 34 to 40 dpp. The second and third injections were administered at 48 to 54 dpp and 62 to 68 dpp, respectively. All cows were inseminated on observed estrus after a voluntary waiting period of 65 days post partum. Thus cows in Group 1 were inseminated on spontaneous estrus and cows in Group 2 on induced estrus. Cows not inseminated at 80 days post partum were palpated per rectum and treated according to a predefined protocol. Herd reproductive performance measures did not differ significantly between groups. The proportion of cows with low serum progesterone levels was significantly higher 3 days after synchronization than 24 days after synchronization (97% vs 39%). The first-service conception rate was 34.8% in Group 1 and 30.7% in Group 2 (P > 0.05). Days open were 113.5 in Group 1 and 110.9 in Group 2 (P > 0.05). It is concluded that postponing artificial insemination for one spontaneous estrus cycle after synchronization decreased the degree of synchronization. This procedure, however, had no effect on herd reproductive performance compared to insemination on first observed estrus after synchronization.     

Estrous behavior and the estrus-to-ovulation interval in Nelore cattle (Bos indicus) with natural estrus or estrus induced with prostaglandin F2 alpha or norgestomet and estradiol valerate

Estrous behavior and the estrus-to-ovulation interval are essential for estimating the best time to artificially inseminate cattle. Because these parameters are not well characterized in the Nelore breed (Bos indicus), the main purpose of the this study was to determine the estrus-to-ovulation interval in Nelore heifers and cows with natural estrus or with estrus induced by treatments with PGF2 alpha or norgestomet and estradiol valerate (NEV). The cows and heifers were observed continuously (24 h a day) to determine the onset of estrus and to study estrous behavior in the cows. Ten hours after the start of estrus the ovaries were scanned every 2 h by ultrasonography to monitor the dominant follicle until ovulation. Blood samples were collected periodically to determine progesterone levels by RIA. Administration of PGF2 alpha (2 injections, 11 days apart) did not induce estrus in most Nelore females in spite of the presence of functional CL, indicated by progesterone concentrations above 6.0 ng/ml in 25 of 28 animals. Treatment with NEV induced high sexual receptivity in cows (10/11), but only 66% ovulated. Cows with natural or induced estrus exhibited behavioral estrus of 10.9 +/- 1.4 h, and ovulation occurred 26.6 +/- 0.44 h (n = 26) after the onset of estrus. In most of the cows (53.8%) estrus began at night (between 1801 and 600 h), and 34.6% it started and finished during the night. It is concluded that in Nelore females ovulation occurs approximately 26 h after the onset of estrus. Additionally, estrous behavior is shorter than in European breeds, and there is a high incidence of estrus at night, which makes it difficult to detect and, consequently, impairs Al in Nelore cattle. The observation that a high percentage of Nelore females with an active CL did not respond to usual dosages of PGF2 alpha warrants further investigation.     

Synchronization of estrus in suckled postpartum beef cows with melengestrol acetate and PGF2alpha

A total of 402 two suckled postpartum beef cows at 2 locations (CSU and ECRC) were utilized in 3 trials to evaluate the effectiveness of a combination melengestrol acetate (MGA)-PGF2alpha estrus synchronization system in spring-calving cows. The cows were allocated by days post partum, body condition score (1 = emaciated; 9 = obese), sire breed, and dam age at the beginning of treatment to 1 of 2 treatments within location and trial: MGA-PGF2alpha (0.5 mg MGA/head/d for 14 d with 25 mg of PGF2alpha injected 17 d after MGA withdrawal), and unsynchronized controls. All cows were observed for estrus at 12-h intervals for at least 5 d post injection. Cows observed in standing estrus were inseminated 12 to 18 h later. There was a location effect on response to treatment that was attributed to differences in body condition score between locations so data were analyzed within a location. Body condition score at the CSU location was 5.7 compared with 4.0 at the ECRC location. The CSU MGA-PGF2alpha treated cows had higher (P < 0.05) 5-day estrus and 5-d pregnancy rates (78.6 and 61.0%, respectively) than the CSU controls (11.1 and 6.9%, respectively). Similar results for 5-d estrus and pregnancy rates but of decreased magnitude were also observed for the ECRC MGA-PGF2alpha treated (31.6 and 21.4%, respectively) cows compared with that of the ECRC controls (11.9 and 8.5%, respectively). The CSU MGA-PGF2alpha treated cows had higher (P < 0.05) 25- and 60-d pregnancy rates (82.5 and 94.8%) than the CSU controls (65.3 and 87.5%). The 25- and 60-d pregnancy rates were similar between the ECRC MGA-PGF2alpha treated cows and ECRC control cows. The MGA-PGF2alpha estrus synchronization system appears to contribute to pregnancy early in the breeding season in postpartum beef cows, although its effectiveness is limited by cow body condition.     

Trilostane but not prostaglandin F2alpha (PGF2alpha) or cortisol aborts 90-day-pregnant lutectomized sheep

Ewes were lutectomized and treatments were started 72 h later. Pregnant ewes were treated with vehicle; prostaglandin F2alpha (PGF2alpha); cortisol (C); trilostane (TR), a 3beta-hydroxy-steroid dehydrogenase inhibitor; PGF2alpha + C; TR + PGF2alpha; TR + C, or TR + PGF2 + C. TR, TR + PGF2alpha, TR + C, and TR + PGF2alpha + C aborted (P < or = 0.05) all ewes receiving TR. One ewe treated with PGF2alpha aborted (P > or = 0.05). The average time to abortion of TR-treated ewes was 50.8 h (P < or = 0.05) after initiation of treatments. All aborted ewes had retained placentas (P < or = 0.05) except one ewe in the TR + PGF2alpha, treatment group. TR was given every 12 h starting at 72 h postlutectomy until 96 h postlutectomy. TR reduced (P < or = 0.05) progesterone. Estradiol-17beta was increased (P < or = 0.05) 2 h after the first two TR treatments and declined 2 h later and was followed by a sustained increase (P < or = 0.05) in estradiol-17beta, which was coincident with the onset of abortions. Estradiol-17beta was increased (P < or = 0.05) by PGF2alpha but did not decrease (P > or = 0.05) placental secretion of progesterone. It is concluded that TR but not PGF2alpha is an abortifacient in 90-day-pregnant lutectomized ewes and that abortion occurs only when there is a decrease in circulating progesterone and an increase in circulating estradiol-17beta.     

Prostaglandin F2alpha (PGF2alpha) and prolactin secretion in rats.

Plasma prolactin and F-prostaglandins (PGF) were measured anesthetized male Sprague-Dawley rats before and at 15, 30, 45 and 60 minutes following i.v. injection of either PGF2alpha (4 mg/kg), chlorpromazine, 1 mg/kg or chlorpormazine (1 mg/kg) after pretreatment with i.p. indomethacin (2 mg/kg). Following PGF2alpha administration, plasma prolactin levels increased significantly only at 15 and 30 minutes in spite of extremely high PGF levels throughout 60 minutes. Besides the expected rise in plasma prolactin, chlorpromazine caused a transient but statistically significant increase in PGF. Indomethacin blocked the chlorpormazine-induced PGF rise but not prolactin increase. Animals stressed with ether anesthesia showed elevation of plasma prolactin, which was not blocked by indomethacin although PGF concentration fell. Theese results indicate that PGF2alpha can stimulate prolactin release. This effect does not appear to be physiologic since very high PGF levels are required. Furthermore, blockade of prostaglandin synthesis by indomethacin does not prevent the release of prolactin in response to chlorpormazine or stress. Our findings do not support a possible role of PGFs as intermediaries in prolactin release. However, it is possible that PGFs may work through other mechanisms not investigated in our study.