Effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given GnRH

The effects of plasma progesterone concentrations on LH release and ovulation in beef cattle given 100 microg of GnRH im were determined in three experiments. In Experiment 1, heifers were given GnRH 3, 6 or 9 days after ovulation; 8/9, 5/9 and 2/9 ovulated (P<0.02). Mean plasma concentrations of progesterone were lowest (P<0.01) and of LH were highest (P<0.03) in heifers treated 3 days after ovulation. In Experiment 2, heifers received no treatment (Control) or one or two previously used CIDR inserts (Low-P4 and High-P4 groups, respectively) on Day 4 (estrus=Day 0). On Day 5, the Low-P4 group received prostaglandin F(2alpha) (PGF) twice, 12 h apart and on Day 6, all heifers received GnRH. Compared to heifers in the Control and Low-P4 groups, heifers in the High-P4 group had higher (P<0.01) plasma progesterone concentrations on Day 6 (3.0+/-0.3, 3.0+/-0.3 and 5.7+/-0.4 ng/ml, respectively; mean+/-S.E.M.) and a lower (P<0.01) incidence of GnRH-induced ovulation (10/10, 9/10 and 3/10). In Experiment 3, 4-6 days after ovulation, 20 beef heifers and 20 suckled beef cows were given a once-used CIDR, the two largest follicles were ablated, and the cattle were allocated to receive either PGF (repeated 12h later) or no additional treatment (Low-P4 and High-P4, respectively). All cattle received GnRH 6-8 days after follicular ablation. There was no difference between heifers and cows for ovulatory response (77.7 and 78.9%, P<0.9) or the GnRH-induced LH surge (P<0.3). However, the Low-P4 group had a higher (P<0.01) ovulatory response (94.7% versus 61.1%) and a greater LH surge of longer duration (P<0.001). In conclusion, although high plasma progesterone concentrations reduced both GnRH-induced increases in plasma LH concentrations and ovulatory responses in beef cattle, the hypothesis that heifers were more sensitive than cows to the suppressive effects of progesterone was not supported.     

Comparison of estrus induction and subsequent fertility with two different intravaginal devices in ewes during the non-breeding season

Two experiments were conducted to compare the effect of estrus induction by controlled internal drug release (CIDR) and intravaginal cream containing 500 mg progesterone (P cream) in ewes during the non-breeding season. In the first experiment, twenty-four ewes were randomly grouped for two treatments with the different intravaginal devices for 12 days: Group A was the CIDR group and Group B was the P cream group. Blood was collected from all treated ewes, and progesterone (P(4)), estradiol 17-beta (E(2)) and luteinizing hormone (LH) concentrations were measured by enzyme immunoassay. In the second experiment, the conception rates from natural mating, estrus-detected AI (inseminated 12 h after estrus detection), or fixed-time AI (inseminated 42 h after removal of an intravaginal device) in 127 ewes treated with CIDR or P cream were compared. In Experiment 1, the rate of estrus induction and the time of estrus onset after device removal were 91.7% and 36.3 +/- 15.7 h in Group A, and 100% and 35.0 +/- 12.6 h in Group B, respectively. There were no significant differences between the devices. The mean plasma P(4) concentration in Group B was significantly (P < 0.01) lower than Group A between day -9 and day -1 (Day 0: the day of device removal). However, no significant differences were found in the mean E(2) concentrations of the two groups after treatment. The mean time of estrus onset in ewes with an observed LH surge and the time of LH surge after treatment were 23.3 +/- 8.7 h and 30.3 +/- 5.0 h for Group A and 27.6 +/- 6.5 and 26.3 +/- 8.0 h for Group B, respectively, and there were no significant differences. However, a significant difference (P < 0.05) was found in the mean time from the time of estrus onset to LH surge between Group A (6.4 +/- 6.7 h) and Group B (-1.3 +/- 4.1 h). In Experiment 2, the conception rates for natural mating, estrus-detected AI, and fixed-time AI were 55.0, 29.4, and 25.0% for Group A and 40.7, 25.0, and 42.1% for Group B, respectively, and there were no significant differences. These results suggest that the effect of induction of estrus and ovulation and the rate of conception after treatment were comparable to CIDR even though the plasma P(4) concentration of the P cream method tended to be low during the insertion period.     

GnRH treatment at CIDR insertion influences ovarian follicular dynamics in Japanese black cows

Ovarian follicular dynamics and estrous synchronization after Gonadotropin-releasing hormone (GnRH) treatment at Controlled Internal Drug Releasing device (CIDR) insertion were investigated in Japanese Black cows. CIDR was inserted for eight cows at 7 days after estrus. Cows were allocated to either Group A: 8-day CIDR insertion with GnRH treatment on d 0 (n=4, d 0=CIDR insertion) or Group B: 8-day CIDR insertion (n=4). Both groups were injected with prostaglandin F2alpha (PGF2alpha) on d 7. Ultrasonography and blood sampling were performed twice daily. Intensive sampling was performed every 15 min for 8 hr to determine the pulsatile release of LH on d -1, d 5 and d 10. Three of four cows showed intermediate ovulation within 2 days after GnRH treatment during CIDR insertion in Group A, whereas no ovulation was found in Group B. Three of four cows in Group A and all four cows in Group B ovulated after CIDR removal. Plasma progesterone concentrations from d 3 to d 7 in three intermediate ovulatory cows in Group A (8.4 +/- 1.6 ng/ml) was significantly higher than those in Group B (4.1 +/- 1.2 ng/ml; 4 cows) during CIDR insertion (P<0.01). Interval to estrus and ovulation after CIDR removal was observed at 60.0 +/- 12.0 hr and 76.0 +/- 6.9 hr in three cows in Group A, and 75.0 +/- 15.1 hr and 93.0 +/- 20.5 hr in Group B, respectively. There was a significant increase in LH pulse frequency on d 10 compared on d -1 or d 5 in both groups (P<0.05), in addition those on d 10 in Group A tended to be higher than in Group B. As a result, GnRH treatment at CIDR insertion at 7 days after estrus induced intermediate ovulation with formation of corpus luteum (CL) and rather synchronized emergence of ovulatory follicle during CIDR insertion. These induced CL increased plasma progesterone concentrations and contributed to precise synchronization.     

Plasma concentrations of immunoreactive (ir)-inhibin, gonadotropins and steroid hormones during the ovulatory cycle of the duck

The present study was undertaken to determine changes in circulating levels of immunoreactive (ir)-inhibin, FSH, LH, estradiol-17beta, progesterone, and testosterone during the ovulatory cycle of Shao ducks. Serial blood samples were taken from two groups of laying ducks for measurement of ir-inhibin, gonadotropins, and steroid hormones at 2 h intervals for 24 h. Plasma concentrations of ir-inhibin did not change significantly during the ovulatory cycle. The highest level of plasma ir-inhibin was observed 6 h prior to ovulation, which coincided with a decreased level of plasma FSH. One FSH surge was found 12 h after ovulation. Estradiol-17beta, progesterone, and testosterone were also determined during the ovulatory cycle. Two peak values were detected for estradiol-17beta 8 h before ovulation and 4 h after ovulation, while progesterone started to increase 4 h before ovulation and reached a peak at ovulation. The highest level of plasma testosterone was detected around the time of ovulation. These results suggest that inhibin may be involved in the control of FSH secretion during the ovulatory cycle. In addition, both LH and progesterone are of importance in the ovulation process of Shao ducks.     

Estrus synchronization and pregnancy rates in beef cattle given CIDR-B, prostaglandin and estradiol, or GnRH

Two experiments were conducted to determine estrous response and pregnancy rate in beef cattle given a controlled internal drug release (CIDR-B) device plus prostaglandin F2 alpha (PGF) at CIDR-B removal, and estradiol or gonadotropin releasing hormone (GnRH). In Experiment I, crossbred beef heifers received a CIDR-B device and 1 mg estradiol benzoate (EB), plus 100 mg progesterone (E + P group; n = 41), 100 micrograms gonadotropin releasing hormone (GnRH group; n = 42), or no further treatment (Control group; n = 42), on Day 0. On Day 7, CIDR-B devices were removed and heifers were treated with PGF. Heifers in the E + P group were given 1 mg EB, 24 h after PGF, and then inseminated 30 h later. Heifers in the GnRH group were given 100 micrograms GnRH, 54 h after PGF, and concurrently inseminated. Control heifers were inseminated 12 h after onset of estrus. The estrous rate was lower (P < 0.01) in the GnRH group (55%) than in either the E + P (100%) or Control (83%) groups. The mean interval from CIDR-B removal to estrus was shorter (P < 0.01) and less variable (P < 0.01) in the E + P group than in the GnRH or Control groups. Pregnancy rate in the E + P group (76%) was higher (P < 0.01) than in the GnRH (48%) or Control (38%) groups. In Experiment II, 84 cows were treated similarly to the E + P group in Experiment I. Cows received 100 mg progesterone and either 1 mg EB or 5 mg estradiol-17 beta (E-17 beta) on Day 0 and either 1 mg of EB or 1 mg of E-17 beta on Day 8 (24 h after CIDR-B removal), in a 2 x 2 factorial design, and were inseminated 30 h later. There were no differences among groups for estrous rates or conception rates. The mean interval from CIDR-B removal to estrus was 44.2 h, s = 11.2. Conception rates were 67%, 62%, 52%, and 71% in Groups E-17 beta/E-17 beta, E-17 beta/EB, EB/E-17 beta, and EB/EB, respectively. In cattle given a CIDR-B device and estradiol plus progesterone, treatment with either EB or E-17 beta effectively synchronized estrus and resulted in acceptable conception rates to fixed-time artificial insemination.     

Estrous synchronization using an intravaginal progesterone device in combination with gnrh or estradiol benzoate characterized by the initial ovarian conditions in Japanese black cows

Estrous synchronization using a Controlled Internal Drug Releasing device (CIDR) in combination with GnRH or estradiol benzoate (EB) treatment was investigated in Japanese black cows characterized with initial ovarian conditions. A total of 142 cows were allocated to one of four treatments: insertion of CIDR for eight days (Group A: n=34), CIDR with 100 microg of GnRH on d 0 (Group B: n=54, d 0=CIDR insertion), CIDR with GnRH on d 0 and 1 mg of EB on d 10 (Group C: n=20) or CIDR with 2 mg of EB on d 0 and 1 mg of EB on d 9 (Group D: n=34). All cows received 25 mg of PGF(2alpha) on d 7 and blood was collected for progesterone (P4) analysis on d 0, 8, and 21. AI was performed at estrus, but in Group D timed AI was set following a day of EB treatment. Estrus was induced in 141/142 cows, and the majority of which occurred on d 10 and 11 (98 cows, 34 cows). GnRH treatment induced more intermediate ovulation than EB treatment in cows with CL on d 0 (19.0% vs. 0%). Ovulation after CIDR removal was significantly higher in cows with CL on d 0 compared to those without CL (87.0% vs. 71.4%). Group B showed higher conception rates than those combined with Groups C and D where EB was injected after CIDR removal (51.1% vs. 38.9%). Conception had no correlation with either CL existence on d 0 or intermediate ovulation on d 8. P4 concentrations on d 8 were significantly lower compared to those on d 0 or d 21. On d 21 in cows without intermediate ovulation, Group A showed significantly lower P4 concentrations than the other 3 groups. The data suggests that CIDR insertion with PGF(2alpha) treatment is an effective method for estrous synchronization irrespective of initial ovarian conditions, and GnRH treatment at CIDR insertion induces intermediate ovulation and improves the conception rate in Japanese black cows.     

Estrous and ovulatory responses following cervical artificial insemination in Thai-native goats given a new or once-used controlled internal drug release with human chorionic gonadotropin

The study was conducted to compare estrous rate, ovulatory response, plasma progesterone concentrations, and conception rate following cervical artificial insemination in goats given a new or once-used controlled internal drug release (CIDR) device with human chorionic gonadotropin (hCG). Fifty-six Thai-native goats with the average age and body weight of 11 months and 17.3 kg received a 14-day treatment with a new CIDR device (Eazi-Breed^TMCIDR®, Pfizer, NY, USA) or a once-used CIDR device. All goats received a 300-IU injection of hCG (Chorulon®, Intervet International B.V., New Zealand) at the day of CIDR removal to induce ovulation. All goats displaying signs of Estrous behavior were artificially inseminated at 12 h after the onset of estrus with frozen semen. No differences in percentage of estrus and ovulation rates were observed; however, goats that received once-used CIDR devices exhibited shorter (P?P?>?0.05) between treatments during CIDR device insertion and at the time of CIDR removal except on day 4. No significant differences were found in overall conception rates between the treatments. This study indicates that the once-used CIDR device with hCG could be applied to synchronize the estrus and ovulation in small-size Thai-native goats without negative effects on Estrous behavior, ovulatory response, and plasma P4 concentration.     

The effects of administering estradiol benzoate plus progesterone during the growth or static phases of the dominant follicle in CIDR-treated lactating dairy cows

We studied the effects of administering estradiol benzoate (EB) plus progesterone (P4) as part of a CIDR-based protocol during the growth or static phases of dominant follicle development on follicular wave emergence, follicular growth, synchrony of ovulation and pregnancy rate following CIDR withdrawal, treatment with PGF(2alpha) and GnRH, and fixed-time artificial insemination (TAI). Forty-one previously synchronized lactating Holstein dairy cows were randomly allocated to three treatment groups. The control group (n=14) received a CIDR on the third day after ovulation only (Day 0). The two treatment groups were administered CIDRs comprising 2 mg EB and 50 mg P4 either on the third (T1, n=14) or eighth day (T2, n=13) after ovulation (Day 0). All cows received PGF(2alpha) after CIDR removal on Day 7, GnRH on Day 9, and TAI 16 h after GnRH treatment. The proportion of cows with follicular wave emergence within 8 days of treatment differed (P<0.01) among the control (14.3%), T1 (85.7%), and T2 groups (92.9%). However, the mean intervals between treatment and wave emergence were not significantly different. There were significant differences in the diameters of the dominant follicles on Day 7 (P<0.01) and in preovulatory follicles on Day 9 (P<0.01), with the largest follicles observed in the control group and the smallest follicles observed in the T2 group. In contrast, the numbers of cows showing synchronous ovulation after GnRH treatment (92.9 to 100.0%) and pregnancy following TAI (46.2 to 50.0%) were similar between the treatment groups. The results showed that, irrespective of the phase (growth or static) of the dominant follicle, administration of 2 mg EB plus 50 mg P4 to CIDR-treated lactating dairy cows induced consistent follicular wave emergence and development, synchronous ovulation after GnRH administration, and similar pregnancy rates following TAI.     

Effect of subluteal concentrations of progesterone on luteinizing hormone and ovulation in lactating dairy cows

Two experiments were conducted to determine if administration of progesterone within a low, subluteal range (0.1-1.0 ng/mL) blocks the luteinizing hormone (LH) surge (experiments 1 and 2) and ovulation (experiment 2) in lactating dairy cows. In experiment 1, progesterone was administered to cycling, lactating dairy cows during the luteal phase of the estrous cycle using a controlled internal drug release (CIDR) device. CIDRs were pre-incubated in other cows for either 0 (CIDR-0), 14 (CIDR-14) or 28 days (CIDR-28). One group of cows received no CIDRs and served as controls. One day after CIDR insertion, luteolysis was induced by two injections of prostaglandin (PG) F(2alpha) (25 mg) at 12 h intervals. Two days after the first injection, estradiol cypionate (ECP; 3 mg) was injected to induce a LH surge. Concentrations of progesterone after luteolysis were 0.11, 0.45, 0.78 and 1.20 ng/mL for cows treated with no CIDR, CIDR-28, CIDR-14, and CIDR-0, respectively. LH surges were detected in 4/4 controls, 4/5 CIDR-28, 2/5 CIDR-14 and 0/5 CIDR-0 cows following ECP. In experiment 2, progesterone was administered to cycling, lactating, Holstein cows during the luteal phase of the estrous cycle as in experiment 1. Luteolysis was induced as in experiment 1. The occurrence of an endogenous LH surge and ovulation were monitored for 7 days. Concentrations of progesterone after luteolysis were 0.13, 0.30, 0.70 and 1.20 ng/mL for cows treated with no CIDR, CIDR-28, CIDR-14 and CIDR-0, respectively. LH surges and ovulation were detected in 5/5 controls, 3/7 CIDR-28, 0/5 CIDR-14 and 0/5 CIDR-0 cows. It was concluded that low concentrations of progesterone can reduce the ability of either endogenous or exogenous estradiol to induce a preovulatory surge of LH and ovulation.     

Fertility following CIDR based synchronization regimens in anoestrous Nili-Ravi buffaloes

The objective of this study was to compare oestrus expression and fertility rate in used and new controlled internal drug releasing (CIDR) device treated anoestrous buffaloes. Furthermore, to determine the timing of ovulation, and fertility rate in estradiol benzoate (EB) and GnRH-administered CIDR-treated anoestrous Nili-Ravi buffaloes. In experiment 1, buffaloes received either a used CIDR (UCIDR, n = 35) or a new CIDR (NCIDR, n = 36) for 7 day and PGF2α on day 6. Oestrous expression was similar (p > 0.05) between UCIDR (88.5%) and NCIDR (96.6%) buffaloes. The pregnancy rate did not differ (p > 0.05) because of treatment (37.1% in UCIDR vs 36.6% in NCIDR). In experiment 2, buffaloes (n = 55) received CIDR device for 7 days and PGF2α, on day 6 and randomly assigned into three treatment groups: (i) CIDR-EB (n = 17) received EB on day 8, (ii) CIDR-GnRH (n = 18) received GnRH on day 9 and (iii) control (n = 20) received no further treatment. Mean interval from CIDR removal to ovulation in CIDR-EB, CIDR-GnRH and CIDR group were 61.3 ± 0.8, 64.9 ± 1.8 and 65.1 ± 16.7 h, respectively. However, the buffaloes in the CIDR-EB and CIDR-GnRH group had lesser variability in the timing of ovulation compared to control. The pregnancy rate of both CIDR-EB group (58%) and CIDR-GnRH group (61%) were tended to be higher (p < 0.1) than control (30%). In conclusion, compared to NCIDR devices, previously UCIDR devices are equally effective to induce oestrus in anoestrous buffaloes resulting optimal pregnancy rate. Administration of EB and GnRH after CIDR removal results in tighter synchrony (less variability) and improved fertility in anoestrous buffaloes. CIDR based synchronization regimens have great potential in fertility improvement in anoestrous buffaloes.     

Relations between plasma IGF-I concentrations during treatment with CIDR-based or Ovsynch protocol for timed AI and conception in early postpartum Japanese black beef cows

We examined the relations between plasma insulin-like growth factor (IGF) -I concentrations during treatment with CIDR-based or Ovsynch protocol for timed AI and conception and plasma steroid concentrations in early postpartum Japanese Black beef cows. Cows in the control group (Ovsynch; n = 21) underwent Ovsynch protocol (GnRH analogue on Day 0, PGF(2alpha) analogue on Day 7, and GnRH analogue on Day 9), with AI on Day 10, approximately 20 h after the second GnRH treatment. Cows in the Ovsynch+CIDR group (n = 22) received Ovsynch protocol plus a CIDR for 7 days (starting on Day 0). Cows in the further treatment group (EB+CIDR+GnRH; n = 22) received 2 mg of estradiol benzoate (EB) on Day 0 in lieu of the first GnRH treatment, followed by the same treatment as in the Ovsynch+CIDR protocol. Plasma IGF-I concentrations were determined on Days -7, 0, 7, 9 and 17. Conception rates were improved in the CIDR-combined groups (both CIDR-treated groups were combined) relative to Ovsynch group (P < 0.05) for cows with low IGF-I concentrations (<1,000 ng/ml) on Days -7, 0, and 7, but improved conception rate produced by the CIDR-based protocols did not occur in cows with a high IGF-I concentration (> or =1,000 ng/ml). Plasma estradiol-17beta concentrations increased from Day 0 to 7 (P < 0.05) and were unchanged from Day 7 to 9 in the Ovsynch group with low IGF-I concentrations on Day 0, while they were unchanged from Day 0 to 7 and increased from Day 7 to 9 (P < 0.05) in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group. Plasma progesterone concentrations in the Ovsynch group with low IGF-I concentrations on Day 0 were higher on Day 14 than in the Ovsynch group with high IGF-I concentrations on Day 0 and in the CIDR-combined group (P < 0.05). In conclusion, CIDR-based protocols may improve conception relative to Ovsynch in early postpartum beef cows with lower plasma IGF-I concentrations at the start of the protocols. This improvement is probably due to prevention of premature increases of estradiol-17beta and progesterone concentrations, which occurred in cows with low IGF-I concentrations treated with Ovsynch, by the CIDR treatment.     

Dynamic changes in plasma concentrations of gonadotropins, inhibin, estradiol-17beta and progesterone in cows with ultrasound-guided follicular aspiration

To elucidate the effects of ultrasound-guided transvaginal follicular aspiration, plasma concentrations of FSH, LH, inhibin, estradiol-17beta and progesterone, and folliculogenesis were examined in Holstein cows. Four clinically healthy cows with regular estrous cycles were scanned by ultrasound per rectum once a week for 9 weeks before the commencement of follicular aspiration. All visible follicles were divided into 3 categories based on their sizes (2 < or = small < 5 mm; 5 < or = medium < 10 mm, large > or = 10 mm). The follicular aspiration was started at random during the estrous cycle and conducted under epidural anesthesia induced with 5 ml of 2% lidocaine once a week for 6 weeks. The average number of total visible follicles > or = 2 mm in diameter at 7 days after aspiration (21.7 +/- 7.4, n = 24) was similar to that before starting aspiration (26.7 +/- 10.5, n = 36). Plasma inhibin and estradiol-17beta declined and fell to a trough on 1.5 days and returned to pre-aspiration values by 5 days after aspiration. Plasma concentrations of FSH increased and reached peak levels between 1 and 1.5 days after aspirations. Plasma concentrations of LH also increased and reached peak levels between 0.5 and 1.5 days after aspirations. Both plasma FSH and LH had returned to pre-aspiration levels by 5 days after aspirations. Plasma concentrations of progesterone did not change with the follicular aspiration. These results demonstrate that follicular aspiration decreases plasma concentrations of inhibin and estradiol-17beta, which in turn leads to a rise in plasma concentrations of FSH and LH. It is suggested that marked increases in plasma concentrations of FSH and LH after the aspiration stimulate the development and maturation of a new cohort of follicles within one week in cows.     

On the negative feedback regulation of gonadotropins in castrate and intact cattle with comparison of two FSH radioimmunoassays

Two homologous radioimmunoassays for bovine follicle stimulating hormone (bFSH) were utilized in comparing the differential regulation of FSH and luteinizing hormone (LH) in response to ovariectomy or administration of gonadal steroids in cattle. There appeared to be significant LH cross-reactivity in one of the bFSH systems (bFSH-HS-2-17), but not in the other (bFSH-BP3). Concentrations of FSH in plasma measured by these two systems suggested both qualitative and quantitative differences. Following ovariectomy in heifers, LH concentrations in plasma were increased by 7.5 h, while FSH (measured in the bFSH-BP3 system) was not significantly elevated until 18 h. Administration of 200 micrograms of estradiol-17 beta to ovariectomized heifers inhibited levels of FSH in plasma but large doses of testosterone (100 mg), androstenedione (400 mg) and dihydrotestosterone (800 mg) had no effect. Similarly, LH was not affected by the androgens, while estradiol induced LH surges, leading to increased mean LH concentrations. In contrast to the results in heifers, LH concentrations in plasma from steers were inhibited by administration of androgens as well as by estradiol. In steers, FSH (bFSH-BP3) was marginally inhibited by estradiol and not at all by the androgens. Differences in the secretory patterns of FSH and LH also occurred in intact heifers during the estrous cycle. The 72-h period preceding estrus (follicular phase) was characterized by rapidly declining serum progesterone concentrations, followed by concurrent increases in both LH and estradiol. The circulating levels of bFSH (BP3) tended to decline during this interval. Overall, during the estrous cycle, progesterone levels were positively correlated with bFSH-BP3 (r = .37) and negatively correlated with LH (r = -.39). The gonadotropins were not significantly related (r = -.15). These relationships are consistent with the concept that LH controls the final stages of follicular development in cattle and that FSH may exert only a permissive effect.     

Effect of estradiol cypionate and GnRH treatment on plasma estradiol‐17β concentrations,synchronization of ovulation and on pregnancy rates in suckled beef cows treated with FTAI‐based protocols

Two experiments were conducted to evaluate the effect of different ovulation inducers on E‐17β plasma concentrations, synchronized ovulations and pregnancy rates. In Experiment 1, cows received a progesterone intravaginal device (PID) with 1 g of progesterone (P4) plus 2 mg of estradiol benzoate (EB) (day 0). At PID removal (day 8), cows received 0.150 mg of D‐cloprostenol and were randomly assigned to four treatment groups (n = 10/treatment): Group ECP: 1 mg of estradiol cypionate at PID removal, Group EB: 1 mg of EB 24 hr after PID removal, Group GnRH: 10 μg of GnRH 48 hr after PID removal, Group ECP‐GnRH: 1 mg of ECP at PID removal plus 10 μg of GnRH 48 hr later. Ultrasonographic examinations were performed to detect the dominant follicle and ovulation. GnRH‐treated cows ovulated later (p < .05) compared to ECP‐ and ECP+GnRH‐treated cows. There were effects of treatment, time and their interaction on E‐17β concentrations (p < .05). ECP treatment affected plasma E‐17β concentration, which increased earlier and decreased later compared to treatments without ECP. In Experiment 2, cows received (i) ECP: n = 126; (ii) EB: n = 126; (iii) GnRH: n = 136; (iv) ECP+GnRH: n = 139; FTAI was performed 48–50 hr after PID removal. Pregnancy rates did not differ among ovulation inducers (p > .05; ECP: 54.0%, 68/126; EB: 49.2%, 62/126; GnRH: 40.4%, 55/136; ECP+GnRH: 43.9%, 61/139). In conclusion, ECP administration (ECP and ECP+GnRH treatments) affected E‐17β concentrations, determining its earlier increase and later decrease compared to treatments without ECP (EB and GnRH treatments). ECP+GnRH‐treated cows achieved the best distribution of ovulations without affecting pregnancy rates.     

Plasma gonadotropins and ovarian hormones during the estrous cycle in high compared to low ovulation rate gilts

Mature gilts classified by low (12 to 16 corpora lutea [CL], n = 6) or high (17 to 26 CL, n = 5) ovulation rate (OR) were compared for plasma follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone, estradiol-17beta, and inhibin during an estrous cycle. Gilts were checked for estrus at 8-h intervals beginning on d 18. Blood samples were collected at 8-h intervals beginning on d 18 of the third estrous cycle and continued for one complete estrous cycle. Analysis for FSH and LH was performed on samples collected at 8-h intervals and for ovarian hormones on samples collected at 24-h intervals. The data were standardized to the peak of LH at fourth (d 0) and fifth estrus for the follicular phase and analyzed in discrete periods during the periovulatory (-1, 0, +1 d relative to LH peak), early-luteal (d 1 to 5), mid-luteal (d 6 to 10), late-luteal (11 to 15), periluteolytic (-1, 0, +1 d relative to progesterone decline), and follicular (5 d prior to fifth estrus) phases of the estrous cycle. The number of CL during the sampling estrous cycle was greater (P < 0.005) for the high vs low OR gilts (18.8 vs 14.3) and again (P < 0.001) in the cycle subsequent to hormone measurement (20.9 vs 14.7). For high-OR gilts, FSH was greater during the ovulatory period (P = 0.002), the mid- (P < 0.05) and late-luteal phases (P = 0.01), and tended to be elevated during the early-luteal (P = 0.06), but not the luteolytic or follicular periods. LH was greater in high-OR gilts during the ovulatory period (P < 0.005), but not at other periods during the cycle. In high-OR gilts, progesterone was greater in the mid, late, and ovulatory phases (P < 0.005), but not in the follicular, ovulatory, and early-luteal phases. Concentrations of estradiol-17beta were not different between OR groups during the cycle. Inhibin was greater for the high OR group (P < 0.005) during the early, mid, late, luteolytic, and follicular phases (P < 0.001). The duration of the follicular phase (from last baseline estrogen value to the LH peak) was 6.5 +/- 0.5 d and was not affected by OR group. These results indicate that elevated concentrations of both FSH and LH are associated with increased ovulation rate during the ovulatory phase, but that only elevated FSH during much of the luteal phase is associated with increased ovulation rate. Of the ovarian hormones, both inhibin and progesterone are highly related to greater ovulation rates. These findings could aid in understanding how ovulation rate is controlled in pigs.     

Timing of follicular phase events and the postovulatory progesterone rise following synchronisation of oestrus in cows

In cows the timing of both ovulation and the subsequent postovulatory progesterone rise are critical to successful fertilisation and early embryo development. The aim of this study was to determine the degree of variability in the timing of ovulation relative to other follicular phase events and to determine how variations in the timing of follicular phase events contribute to the timing of the postovulatory progesterone rise. Plasma concentrations of progesterone, oestradiol and luteinising hormone (LH) and the timing of oestrus and ovulation were determined following induction of luteolysis were determined in 18 mature, non-lactating Holstein-Friesian cows. Four cows were excluded on the basis of abnormal reproductive function. In the remaining 14 cows oestrus occurred at 57.4+/-4.3h and the LH surge at 54.6+/-4.0h following luteolysis (progesterone <1ngmL(-1)) followed by a fall in circulating oestradiol concentration at 64.6+/-4.4h. Cows ovulated at 88.0+/-4.7h with the postovulatory progesterone rise (to >1ngmL(-1)) occurring 159+/-7.2h after luteolysis. There was considerable variation in the timing of ovulation following luteolysis (range 64-136h) onset of oestrus (range 24-40h) and onset of the LH surge (range 24-44h). Cows were then split on the basis of interval from progesterone fall to progesterone rise giving groups (n=7 per group) with intervals of 180.6+/-6.7 and 138.3+/-5.7h (P<0.001). Between groups, both the intervals from luteolysis to ovulation (98.3+/-6.9 vs 77.7+/-3.4h; P<0.05) and ovulation to progesterone rise (82.3+/-4.2 vs. 60.6+/-5.5h; P<0.01) were longer in late rise cows. There was no difference between groups in the interval from oestrus or LH surge to ovulation. In conclusion the results of this study further highlight the high variability that exists in the timing and interrelationships of follicular phase events in the modern dairy cow, reemphasising the challenges that exist in optimising mating strategies. However, the data do suggest that in cows with poor post ovulatory progesterone secretion, the key problem appears to be poor post ovulatory development rather than a delay in ovulation.     

Changes in Plasma Concentrations of LH, FSH, Estradiol 17-β and Progesterone During Oestrus in Mithun (Bos frontalis)

The objective of the present study was to establish the changes in plasma concentrations of LH, FSH, estradiol 17-beta (E2) and progesterone (P4), as well as to understand their temporal relationships during oestrus in mithun (Bos frontalis). The experiment was conducted on 11 mithuns during third or fourth postpartum oestrous cycle. Since oestrus onset the jugular vein blood samples were collected every 2 h for 72 and 96 h, respectively from the animals without and with standing heat. The LH, FSH, E2 and P4 concentrations were estimated in plasma. The P4 concentration was fluctuated throughout the oestrus period and the average P4 concentration was found significantly (p<0.05) lower on the day of oestrus onset. The multiple rises in LH and FSH concentrations above the basal level in spike like fashion were observed throughout the oestrus period irrespective of the occurrence of standing heat. A significant (p<0.01) gradual increase in the average daily E2 concentration was observed till day 2 following oestrus onset irrespective of the occurrence of standing heat. A significant (p<0.05) simultaneous increase in LH, FSH and E2 concentrations and a transient increase in P4 concentration at approximately the time of standing heat onset were observed. During investigation a definite temporal coupling between LH and FSH rises was absent throughout the oestrus period. The results suggest that (1) the multiple short-duration low-amplitude LH and FSH surges during oestrus may be crucial for the final maturation of ovulatory follicle and subsequent ovulation in mithun; (2) a differential mechanism for controlling LH and FSH secretions probably exists in mithun.     

Effects of charcoal-extracted, bovine follicular fluid on gonadotropin concentrations, the onset of estrus and luteal function in heifers

A study was conducted to determine the effect of charcoal-extracted, bovine follicular fluid (CFF) on plasma follicle stimulating hormone (FSH) and luteinizing hormone (LH) concentrations, the interval from luteolysis to estrus, and subsequent luteal function in heifers. Fifteen Angus, Simmental and Hereford heifers were allotted by age, weight and breed to a control (C, n = 8) or a CFF (n = 7) group. Heifers received injections of saline or CFF (iv, 8 ml/injection) every 12 h from d 1 (d 0 estrus) through d 5 of the estrous cycle. On d 6, each heifer was injected (im) with 25 mg of prostaglandin F2 alpha (PGF2 alpha). Blood samples were collected every 12 h by venipuncture starting just before the first saline or CFF injection and continuing until estrus. Thereafter, blood samples were collected every other day during the subsequent estrous cycle and assayed for FSH, LH, estradiol-17 beta and progesterone by radioimmunoassay. Injections of CFF had no effect (P greater than .05) on circulating FSH or LH concentrations from d 1 to 5 relative to the C group; however, there was a transient rise (P less than .05) in FSH concentrations 24 h following cessation of CFF injections. This transient rise in FSH was not immediately followed by an increase in plasma estradiol-17 beta concentrations. Although CFF injections did not interfere with PGF2 alpha-induced luteolysis, the interval from PGF2 alpha injection to estrus was delayed (P less than .05) by 5 d in the CFF group compared with the C group.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparative study of induction of estrus and ovulation by three different intravaginal devices in ewes during the non-breeding season

The aim of the present study was to compare three methods of estrus synchronization in ewes during the non-breeding season. Forty-two ewes were randomly grouped for three treatments with different intravaginal devices for 12 days: Group A) CIDR, Group B) Self-made P sponge, Group C) MAP (medroxyprogesterone acetate) cream sponge. Furthermore, all groups were divided into two treatments with (R) or without ram presence to examine the "ram effect". Blood was collected from all treated ewes, and progesterone (P(4)), estradiol 17-beta (E(2)) and luteinizing hormone (LH) concentrations were measured by enzyme-immunoassay. All ewes showed estrus behavior between Day 0 to 3 after device removal, and the mean onset times of their estrus were 23.0, 33.0 and 21.0 h for Groups AR, BR and CR, respectively. On Day 5 as examined by laparoscopy, the ovulation rates (and number of ovulated ewes) were 1.45 (11/11), 1.25 (12/14) and 1.21 (14/14) for Groups A, B and C, respectively. In Group C, the time to LH surge was significantly (P<0.05) later (32.4 h) than those in Groups A (27.0 h) and B (25.5 h). Ram presence did not affect the number of ovulated ewes, ovulation rate or time to LH surge. The ram introduction group had significantly (P<0.05) lower E(2) concentrations during the period from 0 h to 36 h than the groups without ram presence. These results suggest that the self-made P sponge or MAP cream sponge was effective as well as CIDR, and ram introduction was not necessary, for induction of estrus and ovulation during the non-breeding season.     

Preventive effects of CIDR-based protocols on premature ovulation before timed-AI in Ovsynch in cycling beef cows

Ovsynch is a program developed to synchronize ovulation for timed breeding. In this paper, the authors investigate whether controlled internal drug release (CIDR)-based protocols prevent premature ovulation before timed-artificial insemination (AI) when Ovsynch is started a few days before luteolysis in cycling beef cows. Nine beef cows at 16 days after oestrus were treated with (1) Ovsynch, i.e. gonadotropin releasing hormone (GnRH) analogue on day 0, prostaglandin (PG) F(2alpha) analogue on day 7 and GnRH analogue on day 9 with timed-AI on day 10, (n=3); (2) Ovsynch+CIDR (Ovsynch protocol plus a CIDR for 7 days from day 0, n=3), or (3) oestradiol benzoate (OB)+CIDR+GnRH (OB on day 0 in lieu of the first GnRH treatment, followed by the Ovsynch+CIDR protocol, n=3). In the Ovsynch group (1) plasma progesterone concentrations fell below 0.5 ng/mL earlier (day 5) than in both CIDR-treated groups (2) and (3), where this occurred on day 8. Plasma oestradiol-17beta concentrations peaked on day 8 in the Ovsynch group and on day 9 in both CIDR-treated groups. The dominant follicle ovulated on day 10 in the Ovsynch group and on day 11 in both CIDR-treated groups. Thus, both CIDR-based protocols prevented premature ovulation before timed-AI in Ovsynch when the protocol was started a few days before luteolysis. This reflects the fact that progesterone levels remained high until the beef cattle were treated with PGF(2alpha).