Effects of intravulvo-submucosal cloprostenol injections on hormonal profiles and fertility in subestrous cattle

Eighty-two subestrous cattle were treated with different doses of cloprostenol through intramuscular (i.m.) and intravulvo-submucosal (i.v.s.m.) injections to study hormonal profile and fertility. The study was divided into two experiments. In Experiment I, 13 cows were treated with one of three doses of cloprostenol (500 mug i.m., 125 and 62.5 mug i.v.s.m.) to measure response of progesterone (P(4)) and estradiol (E(2)). P(4) decreased abruptly and E(2) levels increased from basal levels following injections of the two larger doses of cloprostenol. P(4) decreased to<5 nmol/l approximately 72 h after treatment. E(2) levels increased to >300 pmol/l 24 h after cloprostenol injections except in cows treated with 62.5 mug dose. Close agreement was observed between P(4) profiles and clinical findings following 500 and 125 mug of cloprostenol treatment. In Experiment II, 69 subestrous cows were treated with either 500 mug i.m. or 250, 125 or 62.5 mug i.v.s.m. doses of cloprostenol. The percent of cows in estrus 96 h following treatment were 60, 80, 67.8 and 18%, respectively. A total of 29 cows were artificially inseminated and 41.3% conceived. We concluded that i.v.s.m. injections of cloprostenol at the dosage of 125 mug and above causes luteolysis, induces estrus and establishes fertility in subestrous cattle. The method is economical but time consuming when compared to the intramuscular route.     

Synchronization of ovulation in cyclic gilts with porcine luteinizing hormone (pLH) and its effects on reproductive function

The overall objective was to evaluate the use of porcine luteinizing hormone (pLH) for synchronization of ovulation in cyclic gilts and its effect on reproductive function. In an initial study, four littermate pairs of cyclic gilts were given altrenogest (15 mg/d for 14 d). Gilts received 500 microg cloprostenol (Day 15), 600 IU equine chorionic gonadotropin (eCG) (Day 16) and either 5mg pLH or saline (Control) 80 h after eCG. Blood samples were collected every 4h, from 8h before pLH/saline treatment to the end of estrus. Following estrus detection, transcutaneous real-time ultrasonography and AI, all gilts were slaughtered 6d after the estimated time of ovulation. Peak plasma pLH concentrations (during the LH surge), as well as the amplitude of the LH surge, were greater in pLH-treated gilts than in the control (P=0.01). However, there were no significant differences between treatments in the timing and duration of estrus, or the timing of ovulation within the estrous period. In a second study, 45 cyclic gilts received altrenogest for 14-18d, 600 IU eCG (24h after last altrenogest), and 5mg pLH, 750 IU human chorionic gonadotropin (hCG), or saline, 80 h after eCG. For gilts given pLH or hCG, the diameter of the largest follicle before the onset of ovulation (mean+/-S.E.M.; 8.1+/-0.2 and 8.1+/-0.2mm, respectively) was smaller than in control gilts (8.6+/-0.2mm, P=0.05). The pLH and hCG groups ovulated sooner after treatment compared to the saline-treated group (43.2+/-2.5, 47.6+/-2.5 and 59.5+/-2.5h, respectively; P<0.01), with the most synchronous ovulation (P<0.01) in pLH-treated gilts. Embryo quality (total cell counts and embryo diameter) was not significantly different among groups. In conclusion, pLH reliably synchronized ovulation in cyclic gilts without significantly affecting embryo quality.     

The use of estradiol and/or GnRH in a two-dose PGF protocol for breeding management of beef heifers

The objective was to determine reproductive performance following AI in beef heifers given estradiol to synchronize ovarian follicular wave emergence and estradiol or GnRH to synchronize ovulation in a two-dose PGF-based protocol. In Experiment 1, 561 cycling (confirmed by ultrasonography), Angus heifers received 500 microg cloprostenol, i.m. (PGF) twice, 14 days apart (days 0 and 14) and were equally allocated to four groups in a 2 x 2 factorial design. On Day 7, heifers received either 2 mg estradiol benzoate (EB) and 50 mg progesterone (P), i.m. in oil (EBP group) or no treatment (NT group). Half the heifers in each group received 1mg EB, i.m. in oil on Day 15 (24h after the second PGF treatment) with TAI 28 h later (52 h after PGF), and the other half received 100 microg GnRH, i.m. on Day 17 (72 h after PGF) concurrent with TAI. All heifers were observed for estrus twice daily from days 13 to 17; those detected in estrus more than 16 h before scheduled TAI were inseminated 4-16 h later and considered nonpregnant to TAI. Overall pregnancy rate (approximately 35 days after AI) was higher in heifers that received EBP than those that did not (61.6% versus 48.2%, respectively; P < 0.002); but was lower in heifers that received EB after PGF than those that received GnRH (50.0% versus 59.8%; P < 0.02). Although estrus was detected prior to TAI in 77 of 279 heifers (27.6%) treated with EBP (presumably due to induced luteolysis), they were inseminated and 53.2% became pregnant. Overall pregnancy rates were 51.4, 68.3, 45.0, and 55.0% in the NT/GnRH, EBP/GnRH, NT/EB, and EBP/EB groups, respectively (P < 0.05). In Experiment 2, 401 cycling, Angus heifers were used. The design was identical to Experiment 1, except that 1.5mg estradiol-17beta (E-17beta) plus 50mg progesterone (E-17betaP) and 1mg E-17beta were used in lieu of EBP and EB, respectively. All heifers receiving E-17beta 24h after the second injection of PGF (NT/E-17beta and E-17betaP/E-17beta) were TAI 28 h later without estrus detection, i.e. 52 h after PGF. Heifers in the other two groups received 100 microg GnRH, i.m. 72 h after PGF and were concurrently TAI; heifers in these two groups that were detected in estrus prior to this time were inseminated 4-12h later and considered nonpregnant to TAI. Estrus rate during the first 72 h after the second PGF treatment was higher (P < 0.05) in the E-17betaP/GnRH group (45.0%; n = 100) than in the NT/GnRH group (16.0%; n = 100), but conception rate following estrus detection and AI was not different (mean, 57.4%; P = 0.50). Overall pregnancy rate was not significantly different among groups (mean, 46.9%; P = 0.32). In summary, the use of EB or E-17beta to synchronize follicular wave emergence and estradiol or GnRH to synchronize ovulation in a two-dose, PGF-based protocol resulted in acceptable fertility to TAI. However, when 2mg EB was used to synchronize follicular wave emergence, early estrus occurred in approximately 28% of heifers, necessitating additional estrus detection. A combination of estrus detection and timed-AI in a two-dose PGF protocol resulted in highly acceptable pregnancy rates.     

Estrus synchronization with lower dose of PGF2 alpha and subsequent fertility in subestrous buffalo

Two experiments were conducted to determine luteal regression, estrous response and fertility in buffalo receiving cloprostenol via 2 routes of administration. In Experiment 1, cyclic buffalo (n = 10) were assigned to 2 equal groups receiving either 500 micrograms i.m. cloprostenol (Estrumate, ICI) or 125 micrograms cloprostenol injected intravulvosubmucosal (ivsm) ipsilateral to the side of the corpus luteum (CL) on Day 11 of an induced estrous cycle. Serum progesterone (P4) concentrations were evaluated immediately before treatment and at 24, 48, 72, 96 and 120 h after PGF2 alpha administration. The decline in serum P4 concentrations was significantly different (P < 0.05) between groups up to 48 hrs after treatment. However, no significant difference (P > 0.05) was observed for the interval from treatment to the onset of estrus (94.9 +/- 10.7 vs 96.0 +/- 15.9 h) for 500 or 125 micrograms of cloprostenol groups, respectively. In Experiment 2, multiparous, lactating subestrous buffaloes (n = 137) were treated either with 125 micrograms ivsm cloprostenol or 500 micrograms i.m. cloprostenol (n = 28 vs 33, respectively) during peak breeding (September-February) or low breeding (March-August) season (n = 37 vs 39, respectively). Buffalo observed in estrus were inseminated twice with frozen-thawed semen at 12 and 22 h after the onset of estrus. Buffalo that failed to exhibit estrus were given a second equal dose of cloprostenol at an 11-d interval and underwent fixed-time insemination at 72 and 96 h. The interval to the onset of estrus was 85.0 +/- 4.4 vs 73.2 +/- 2.6 h during peak breeding and 96.1 +/- 2.6 vs 92.1 +/- 3.8 h during the low breeding season for buffalo treated with 125 and 500 micrograms cloprostenol, respectively. These intervals were different (P < 0.05) between seasons but not between treatments in the same season. Conception rates of 47.8 vs 53.1% during peak breeding and 23.5 vs 25.6% during low breeding season were also different (P < 0.05) between seasons but not between the treatments in the same season for buffalo treated with 125 and 500 micrograms cloprostenol, respectively. These results indicated that 125 micrograms ivsm and 500 micrograms i.m. cloprostenol were equally effective for synchronizing estrus in subestrous buffalo. No negative effect of a lower dose of cloprostenol was observed on estrus synchrony and subsequent fertility; however, season of treatment had a significant effect on conception rates.     

Progesterone (CIDR)-based timed AI protocols using GnRH, porcine LH or estradiol cypionate for dairy heifers: ovarian and endocrine responses and pregnancy rates

The overall objective was to compare the efficacy of GnRH, porcine LH (pLH) and estradiol cypionate (ECP), in a modified Ovsynch/fixed-time AI (FTAI) protocol that included a controlled internal drug [progesterone] release (CIDR) device. In Experiment 1, heifers received a CIDR on Day -10, and PGF (25mg) on Day -3. At CIDR insertion, heifers received 100 microg of GnRH (n=6), 0.5mg of ECP (n=6), 5.0mg of pLH (n=6) or 2 mL of saline (n=7); these treatments were repeated on Day -1, except for ECP, that was repeated on Day -2, concurrent with CIDR-removal. The 5.0 mg pLH was the least effective with a longer interval to ovulation than the other groups combined (102 versus 64 h; P<0.05). Overall mean LH concentrations (1.6 ng/mL) and area under the curve (AUC) did not differ among treatments, but mean peak LH concentration was lower in heifers given 5 mg of pLH compared to all other groups (4.5 versus 10.3 ng/mL; P<0.05). In Experiment 2, heifers on CIDR-based Ovsynch protocols were given 12.5mg pLH (n=6; pLH-low), 25.0 mg pLH (n=6, pLH-high), or 100 microg GnRH (n=5; control). Heifers in the pLH-high group had greater (P<0.01) plasma LH concentrations (between 12 and 20 h) than GnRH-treated heifers, but the pLH treatments did not differ (P>0.10). Area under the curve for LH (ng/32 h) was at least 50% greater (P<0.01) in pLH-treated heifers compared to GnRH-treated heifers (mean, 41.3, 56.3 and 20.3 for pLH-low, pLH-high and GnRH, respectively). Ovulation occurred in 15 of 17 heifers. Progesterone concentrations were higher on Days 9 and 14 in heifers given 25mg of pLH, suggesting enhanced CL function. In Experiment 3, 240 heifers were assigned to CIDR-based Ovsynch/FTAI protocols. The first and second hormonal treatments (with an intervening PGF treatment on Day -3) were GnRH/GnRH (100 microg), ECP/ECP (0.5 mg), pLH/pLH (12.5 mg) or GnRH/ECP, respectively; pregnancy rates were 58.7, 66.1, 45.9 and 48.3%, respectively (ECP/ECP>both pLH/pLH and GnRH/ECP; P相似文献   

Influence of GnRH administration on timing of the LH surge and ovulation in dwarf goats

This study was conducted to determine whether or not exogenous gonadotropin releasing hormone (GnRH) alters the timing or improves the synchrony of estrus, the LH surge, and ovulation following estrous synchronization in dwarf goats, and to assess the effects of season on these parameters. In January and June, estrus was synchronized in 12 Pygmy and Nigerian Dwarf goats with a 10-day progestagen sponge, 125 microg cloprostenol i.m. 48 h before sponge removal, and 300 IU equine chorionic gonadotrophin (eCG) i.m. at sponge removal. Six of the 12 goats were given 50 microg GnRH i.m. 24h after sponge removal. Onset of estrus was monitored using two males. Samples for plasma LH were collected at 2 h intervals beginning 22 h after sponge removal and ending at 48 h in January and at 58 h in June. Time of ovulation time was confirmed by laparoscopy at 36, 50, 60, and 74 h in January and at 50, 60, and 74 h in June. Administration of GnRH had no significant effect on the onset of estrus; however, it reduced the interval from sponge removal to the LH surge and improved the synchrony of the LH surge (P<0.05). Treatment with GnRH also reduced the interval from sponge removal to ovulation and improved the synchrony of ovulation (P<0.05). Season had a significant effect on the timing and the synchrony of estrus with and without GnRH treatment (P<0.05). A seasonal shift was also observed in the timing of the LH surge in the absence of GnRH treatment (P<0.05). Further research is required to determine the optimum time for GnRH administration and the minimum effective dose in dwarf goats.     

The use of GnRH or estradiol to facilitate fixed-time insemination in an MGA-based synchronization regimen in beef cattle

Two experiments were conducted to compare pregnancy rates when GnRH or estradiol were given to synchronize ovarian follicular wave emergence and ovulation in an MGA-based estrus synchronization program. Crossbred beef cattle were fed melengestrol acetate (MGA, 0.5 mg per day) for 7 days (designated days 0-6, without regard to stage of the estrous cycle) and given cloprostenol (PGF; 500 microg intramuscular (im)) on day 7. In Experiment 1, lactating beef cows (n=140) and pubertal heifers (n=40) were randomly allocated to three groups to receive 100 microg gonadorelin (GnRH), 5 mg estradiol-17beta and 100 mg progesterone (E+P) in canola oil or no treatment (control) on day 0. All cattle were observed for estrus every 12 h from 36 to 96 h after PGF. Cattle in the GnRH group that were detected in estrus 36 or 48 h after PGF were inseminated 12 h later; the remainder were given 100 microg GnRH im 72 h after PGF and concurrently inseminated. Cattle in the E+P group were randomly assigned to receive either 0.5 or 1.0 mg estradiol benzoate (EB) in 2 ml canola oil im 24 h after PGF and were inseminated 30 h later. Cattle in the control group were inseminated 12 h after the first detection of estrus; if not in estrus by 72 h after PGF, they were given 100 microg GnRH im and concurrently inseminated. In the absence of significant differences, all data for heifers and for cows were combined and the 0.5 and 1.0 mg EB groups were combined into a single estradiol group. Estrus rates were 57.6, 57.4 and 60.0% for the GnRH, E+P and control groups, respectively (P=0.95). The mean (+/-S.D.) interval from PGF treatment to estrus was shorter (P<0.001) and less variable (P<0.001) in the E+P group (49.0+/-6.1 h) than in either the GnRH (64.2+/-15.9 h) or control (66.3+/-13.3 h) groups. Overall pregnancy rates were higher (P<0.005) in the GnRH (57.6%) and E+P (55.7%) groups than in the control group (30.0%) as were pregnancy rates to fixed-time AI (47.5, 55.7 and 28.3%, respectively). In Experiment 2, 122 crossbred beef heifers were given either 100 microg GnRH or 2 mg EB and 50 mg progesterone in oil on day 0 and subsequently received either 100 microg GnRH 36 h after PGF and inseminated 14 h later or 1 mg EB im 24 h after PGF and inseminated 28 h later in a 2 x 2 factorial design. Pregnancy rates were not significantly different among groups (41.9, 32.2, 33.3 and 36.7% in GnRH/GnRH, GnRH/EB, EB/GnRH and EB/EB groups, respectively). In conclusion, GnRH or estradiol given to synchronize ovarian follicular wave emergence and ovulation in an MGA-based synchronization regimen resulted in acceptable pregnancy rates to fixed-time insemination.     

The use of progestins in regimens for fixed-time artificial insemination in beef cattle

Four experiments were conducted to investigate modifications to gonadotropin releasing hormone (GnRH)-based fixed-time Al protocols in beef cattle. In Experiment 1, the effect of reducing the interval from GnRH treatment to prostaglandin (PGF) was examined. Lactating beef cows (n = 111) were given 100 mg gonadorelin (GnRH) on Day 0 (start of treatment) and either 500 microg cloprostenol (PGF) on Day 6 with Al and 100 microg GnRH 60 h later, or PGF on Day 7 with Al and GnRH 48 h later (6- or 7-day Co-Synch regimens). Pregnancy rates were 32/61 (53.3%) versus 26/50 (52.0%), respectively (P = 0.96). In Experiment 2. cattle (n = 196) were synchronized with a 7-day Co-Synch regimen and received either no further treatment or a CIDR-B device (Days 0-7). Pregnancy rates were 32/71 (45.1%) versus 33/77 (42.9%) in cows (P < 0.8), and 9/23 (39.1 %) versus 17/25 (68.0%) in heifers (P < 0.05). In Experiment 3, 49 beef heifers were randomly assigned to receive 12.5 mg pLH on Day 0, PGF on Day 7 and 12.5 mg of pLH on Day 9 with Al 12 h later (pLH Ovsynch), or similar treatment plus a CIDR-B device from Days 0 to 7 (pLH Ovsynch + CIDR-B), or 1 mg estradiol benzoate (EB) and 100 mg progesterone on Day 0, a CIDR-B device from Days 0 to 7 (EB/ P4 + CIDR-B), PGF on Day 7 (at the time of CIDR-B removal) and 1 mg i.m. EB on Day 8 with AI on Day 9 (52 h after PGF). Pregnancy rate in the EB/P4 + CIDR-B group (75.0%) was higher (P < 0.04) than in the pLH Ovsynch group (37.5%): the pLH Ovsynch + CIDR-B group was intermediate (64.7%). In Experiment 4, 266 non-lactating cows were allocated to a 7-day Co-Synch protocol (Co-Synch), a 7-day Co-Synch plus 0.6 mg per head per day melengestrol acetate (MGA) from Days 0 to 6 inclusive (Co-Synch + MGA) or MGA (Days 0-6) plus 2 mg EB and 50 mg progesterone on Day 0. 500 microg PGF on Day 7, 1 mg EB on Day 8 and fixed-time Al 28 h later (EB/ P4 + MGA). Pregnancy rates (P < 0.25) were 44.8% (39/87: Co-Synch), 47.8% (43/90; Co-Synch + MGA), and 60.7% (54/89: EB/P4 + MGA). In conclusion, a 6- or 7-day interval from GnRH to PGF in a Co-Synch regimen resulted in similar pregnancy rates in cows. The addition of a progestin to a Co-Synch or Ovsynch regimen significantly improved pregnancy rates in heifers but not in cows. Progestin-based regimens that included EB consistently resulted in high pregnancy rates to fixed-time Al.     

Possibility of reducing the luteolytic dose of cloprostenol in cyclic dairy cows

The administration of cloprostenol by intravulvosubmucous (i.v.s.m.) injection at 1 2 and 1 4 of the dose usually given by intramuscular (i.m.) injection, was tested in dairy cows for luteolysis and estrus synchronization. The i.m. injection was used in ten adult cows at the usual dose of 500 mug/animal. Eleven adult cows and 11 heifers were treated i.v.s.m. with a dose equivalent to 250 mug/animal and 125 mug/animal, respectively. Two injections of cloprostenol were administered 11 days apart to the cows not detected in oestrus after a single injection. Forty-three out of the total 46 animals were detected to be in dioestrus at the time of at least one of the injections, as reflected by the plasma progesterone concentrations at the time of treatments. Three out of the 43 animals injected during dioestrus were refractory to the luteolytic effect of cloprostenol; this appeared to be independent of the dosage and the route of administration (refractory cows were: one adult cow treated i.m. and two treated i.v.s.m. with 125 mug of cloprostenol). The mean time interval from injection to the onset of heat was 82.8 hours with a confidence limit for 95% of probability between 67.9 hours and 92.7 hours. The difference between treatments is not significant. The results suggest that in heifers and adult cows cloprostenol can be given i.v.s.m. route at a reduced dose of 1 4 of the usual 500 mug i.m. dosage without affecting the luteolytic effect of the drug or fertility.     

Factors affecting superovulation in heifers treated with PMSG

In this study we determined 1) if the immunoneutralization of PMSG affected the ovulatory response, the number of large follicles and embryo yield compared with that of PMSG alone or pFSH, and 2) whether the stage of the estrous cycle at which PMSG was injected affected the ovulatory response and yield of embryos in superovulated heifers. Estrus was synchronized in 99 (Experiment 1) and 71 (Experiment 2) heifers using prostaglandin F2alpha (PG) analogue, cloprostenol, given 11 d apart in replicate experiments over 2 yr. In Experiments 1 and 2, heifers were randomly allocated to 1 of 3 treatments (initiated at mid-cycle): Treatment 1--24 mg of pFSH (Folltropin) given twice daily for 4 d; Treatment 2--a single injection of 2000 IU PMSG; Treatment 3--2000 IU PMSG followed by 2000 IU of Neutra-PMSG at the time of first insemination. In Experiment 3, 116 heifers were given 2000 IU PMSG on Day 2 (n = 28), Day 3 (n = 27), Day 10 (n = 41) or Day 16 (n = 20) of the estrous cycle. The PG was given at 48 h (500 microg cloprostenol) and 60 h (250 microg cloprostenol) after the first gonadotropin treatment. Heifers were inseminated twice during estrus, and embryos were recovered on Day 7, following slaughter and graded for quality. The numbers of ovulations and large follicles (> or =10 mm) were also counted. There was no effect of treatment on ovulation rate in Experiment 1, but in Experiment 2 it was greater (P < 0.002) in heifers given PMSG (14.7 +/- 1.5) than pFSH (7.5 +/- 1.4) or PMSG-neutra-PMSG (8.7 +/- 1.5). The number of large follicles was higher following PMSG than pFSH treatment in Experiment 1, and it was higher (P < 0.004) in heifers given PMSG (5.5 +/- 0.8) than pFSH (1.12 +/- 0.7) or PMSG-neutra-PMSG (2.7 +/- 0.8) in Experiment 2. The use of Neutra-PMSG did not affect the numbers of embryos recovered or numbers of Grade 1 or 2 embryos, but it did decrease the number of Grade 3 embryos in both experiments. In Experiment 3, the ovulation rate decreased (P < 0.004) when PMSG was given on Day 3 (5.7 +/- 1.46) of the cycle rather than on Day 2 (12.3 +/- 1.64), Day 10 (13.4 +/- 1.45) or Day 16 (12.5 +/- 1.87). There was no effect of day of treatment on the numbers of large follicles. The mean numbers of embryos recovered were lower (P < 0.01) in heifers treated on Day 3 (2.1 +/- 0.67) than on Day 2 (6.8 +/- 1.0), Day 10 (6.4 +/- 0.86) or Day 16 (7.8 +/- 1.87). It is concluded that Neutra-PMSG given to heifers treated with PMSG did not improve embryo yield or quality and that treatment with PMSG early in the cycle can result in acceptable embryo yields provided sufficient time elapses between treatment and luteolysis.     

Timing of the onset and duration of ovulation in superovulated beef heifers

Thirty-two beef heifers were induced to superovulate by the administration of follicle stimulating hormone-porcine (FSH-P). All heifers received 32 mg FSH-P (total dose) which was injected twice daily in decreasing amounts for 4 d commencing on Days 8 to 10 of the estrous cycle. Cloprostenol was administered at 60 and 72 h after the first injection of FSH-P. Heifers were observed for estrus every 6 h and were slaughtered at known times between 48 to 100 h after the first cloprostenol treatment. The populations of ovulated and nonovulated follicles in the ovaries were quantified immediately after slaughter. Blood samples were taken at 2-h intervals from six heifers from 24 h after cloprostenol treatment until slaughter and the plasma was assayed for luteinizing hormone (LH) concentrations. The interval from cloprostenol injection to the onset of estrus was 41.3 +/- 1.25 h (n = 20). The interval from cloprostenol injection to the preovulatory peak of LH was 43.3 +/- 1.69 h (n = 6). No ovulations were observed in animals slaughtered prior to 64.5 h after cloprostenol (n = 12). After 64.5 h, ovulation had commenced in all animals except in one animal slaughtered at 65.5 h. The ovulation rate varied from 4 to 50 ovulations. Approximately 80% of large follicles (> 10 mm diameter) had ovulated within 12 h of the onset of ovulation. Onset of ovulation was followed by a dramatic decrease in the number of large follicles (> 10 mm) and an increase in the number of small follicles (相似文献   

Effects of cloprostenol, human chorionic gonadotropin and estradiol benzoate treatment on estrus synchronization in dairy cows

Two consecutive experiments were conducted. In Experiment 1, 24 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received intramuscularly (i.m.) 500 mcg of cloprostenol, 1250 IU of human chorionic gonadotropin (hCG) and 5 mg of estradiol benzoate 12 h after cloprostenol treatment. Cows in Group II received 750 IU i.m. of hCG and 3 mg of estradiol benzoate 12 h after cloprostenol treatment. Treatment was given on Day 16 after estrus in both groups. All animals showed estrus within 24 to 48 h after cloprostenol treatment. The average interval from cloprostenol injection to the onset of estrus was not influenced by treatments. Four cows in Group I failed to ovulate and became cystic. In Experiment 2, 71 Friesian lactating cows were randomly assigned to two groups. Cows in Group I received 500 mcg i.m. of cloprostenol after corpus luteum detection by palpation per rectum. Cows in Group II received 500 mcg of cloprostenol plus 750 IU of hCG and 3 mg of estradiol benzoate 12 h after. When estrus ready for service was confirmed by rectal examination, cows were inseminated. The percentage of cows ready for service tended to be lower (P < 0.06) between cows in Group I (88%) and those in Group II (100%). The average interval from cloprostenol treatment to service was longest (P < 0.001) in Group I (78.7 h +/- 14.9, X +/- SD) vs Group II (48 h +/- 2.9). The degree of readiness for service synchrony was lowest (P < 0.001) in Group I (59.3%) vs Group II (94.2%). The pregnancy rates of cows synchronized or treated were not altered by hCG-estradiol benzoate treatment (P > 0.25). These results suggest that in dairy cows treated with cloprostenol following palpation per rectum of a corpus luteum and then with 750 IU of hCG and 3 mg of estradiol benzoate 12 h later, a single fixed-time insemination at 48 h after cloprostenol treatment should be performed.     

Seasonal variation in preovulatory events associated with synchronization of estrus in dwarf goats

This experiment was conducted to define the temporal relationships among estrus, the LH surge and ovulation after estrus synchronization in dwarf goats and to assess the effect of season on these parameters. In November (breeding season), March (transition period) and July (non-breeding season), estrus was synchronized in 12 dwarf goats by means of intravaginal sponges containing 60 mg medroxyprogesterone acetate (MAP) for 10 d, coupled with 125 microg cloprostenol i.m. 48 h before sponge removal and 300 IU eCG i.m. at sponge removal. A different group of animals was used during each time period. Onset of estrus was monitored using two males, and blood samples for the measurement of plasma LH were collected at 2-h intervals from 24 to 60 h after sponge removal. Ovulation was confirmed by laparoscopy at 54 and 72 h after sponge removal. A seasonal shift was detected in the intervals to onset of estrus, LH surge, and ovulation after sponge removal (P<0.05), with sponge removal to onset of estrus being shorter (P<0.05) in November (25.0 +/- 1.56 h) and July (28.9 +/- 2.43 h) than in March (40.9 +/- 3.27 h). The intervals between onset of estrus and the LH surge and between the LH surge and ovulation were found to be constant throughout the different seasons. An optimal time for breeding, artificial insemination, oocyte and embryo recovery, and embryo transfer may be predicted using information gained from these studies.     

Effects of oxytocin on cloprostenol-induced luteolysis, follicular growth, ovulation and corpus luteum function in heifers

Twenty-five normally cyclic Holstein heifers were used to examine the effects of oxytocin on cloprostenol-induced luteolysis, subsequent ovulation, and early luteal and follicular development. The heifers were randomly assigned to 1 of 4 treatments: Group SC-SC (n=6), Group SC-OT (n=6), Group OT-SC (n=6) and Group OT-OT (n=7). The SC-SC and SC-OT groups received continuous saline infusion, while Groups OT-SC and OT-OT received continuous oxytocin infusion (1:9 mg/d) on Days 14 to 26 after estrus. All animals received 500 microg, i.m. cloprostenol 2 d after initiation of infusion (Day 16) to induce luteolysis. Groups SC-OT and OT-OT received oxytocin twice daily (12 h apart) (0.33 USP units/kg body weight, s.c.) on Days 3 to 6 of the estrous cycle following cloprostenol-induced luteolysis, while Groups SC-SC and OT-SC received an equivalent volume of saline. Daily plasma progesterone (P4) concentrations prior to cloprostenol-induced luteolysis and rates of decline in P4 following the induced luteolysis did not differ between oxytocin-infused (OT-OT and OT-SC) and saline-infused (SC-SC and SC-OT) groups (P >0.1). Duration of the estrous cycle was shortened in saline-infused heifers receiving oxytocin daily during the first week of the estrous cycle. In contrast, oxytocin injections did not result in premature inhibition of luteal function and return to estrus in heifers that received oxytocin infusion (OT-OT). Day of ovulation, size of ovulating follicle and time of peak LH after cloprostenol administration for oxytocin and saline-treated control heifers did not differ (P >0.1). During the first 3 d of the estrous cycle following luteal regression, fewer (P <0.01) follicles of all classes were observed in the oxytocin-infused animals. Day of emergence of the first follicular wave in heifers treated with oxytocin was delayed (P <0.05). The results show that continuous infusion of oxytocin during the mid-luteal stage of the estrous cycle has no effect on cloprostenol-induced luteal regression, timing of preovulatory LH peak or ovulation. Further, the finding support that an episodic rather than continuous administration of oxytocin during the first week of the estrous cycle results in premature loss of luteal function. The data suggest minor inhibitory effects of oxytocin on follicular growth during the first 3 d of the estrous cycle following cloprostenol-induced luteolysis.     

The effects of buck teasing on synchronization of estrus in goats after intravulvo-submucosal administration of cloprostenol

A study was conducted on 35 East African shorthorned female goats to determine if a combination of buck teasing and low doses of a prostaglandin (PGF(2) alpha) analogue, cloprostenol, given intravulvo-submucosally (i.v.s.m.) would be suitable for synchronization of estrus. Goats were allotted, with the onset of estrus, to seven groups (n = 5 goats per group). Five of the seven groups received varying doses of cloprostenol: Group 1 (125 mug cloprostenol i.m. per goat); Group 2 (62.5 mug cloprostenol i.v.s.m. per goat); Group 3 (62.5 mug cloprostenol i.v.s.m. per goat plus buck teasing); Group 4 (31.25 mug cloprostenol i.v.s.m. per goat); Group 5 (31.25 mug cloprostenol i.v.s.m. per goat plus buck teasing); Group 6 (buck teasing); Group 7, (2 ml physiological saline i.v.s.m. per goat, control group). Plasma progesterone concentration was measured on day of treatment and for 6 d thereafter. All goats in groups 1, 2, 3 and 5 exhibited estrus within 68 h. Thus, the number of goats receiving low doses of PG-cloprostenol intravulvo-submucosally observed in estrus increased (P < 0.05) with exposure to bucks. Exhibition of behavioral signs of estrus was maximal between 2 and 20 h after onset of signs of estrus. The exposure of females to males prior to intrauterine penetration was an advantage because copious mucus eased penetration.     

Ovarian synchronization following ultrasound-guided transvaginal follicle ablation in heifers

In Experiments 1 and 2, ultrasound-guided transvaginal follicle aspiration was used as a method of follicle ablation to induce and synchronize subsequent follicular wave emergence and enhance ovulation synchrony following PGF(2alpha) administration. Heifers were at unknown stages of the estrous cycle at the start of both experiments in which all follicles >/=5 mm in diameter were ablated; luteolysis was induced 4 d later with cloprostenol (500 ug/dose, im). In Experiment 1, heifers were randomly assigned to either an ablation (n=17) or a procedural control (no follicle ablation, n=17) group. Ablation-induced wave emergence was indicated by a significant increase in the total number of follicles >/=5 mm within 2 d of ablation (mean, 1.5 d), which was preceded by a significant surge in circulating FSH. Although the mean (+/-SEM) interval from PGF(2alpha) administration to ovulation did not differ between follicle-ablated heifers (5.1+/-0.5 d range, 3 to 9 d) and control heifers (5.1+/-1.0 d; range, 1 to 5 d), the variability of the interval was different (P<0.05). Inequality of variance between the 2 groups was attributed to a greater (P<0.08) degree of ovulation synchrony in the ablation group than in the control group; 13 16 (81%) versus 9 17 (53%), respectively, ovulated within 5 d of cloprostenol administration. Relative asynchrony of ovulations in control heifers was associated with the status of the follicular wave at the time of PGF(2alpha) administration and, in part, to incomplete luteolysis following a single dose of PGF(2alpha). Experiment 2 was designed to examine the efficacy of 2 doses of cloprostenol 12 h apart (n=7) versus a single dose (n=8) to induce complete luteolysis subsequent to follicle ablation-induced wave emergence. Two doses of cloprostenol potentiated ovulation synchrony; more (P<0.05) 2-dose heifers (7 7 , 100%) than single-dose heifers (4 8 , 50%) ovulated within 5 d after PGF(2alpha) administration. In summary, ultrasound-guided transvaginal follicle ablation, done at random during the estrous cycle, induced and synchronized subsequent follicular wave emergence, and resulted in a high degree of ovulation synchrony among heifers after PGF(2alpha) induced luteolysis, especially when 2 doses of PGF(2alpha) were administered 12 h apart.     

Effects of GnRH on superovulated cattle

Gonadotropin releasing hormone (GnRH) was given to 109 cows and heifers during the course of 224 superovulations. Follicle stimulating hormone (FSH) was administered twice daily (5 or 6 mg) for 3.5 to 4 days beginning on any of Days 9 to 14 of the estrous cycle; prostaglandin (45 mg PGF(2)alpha or 750 ug cloprostenol) was given in a split dose on the fourth day. Donor cows and heifers were placed into four groups according to previous superovulation treatments, which consisted of one to three treatments or of no previous treatment. Every other cow or heifer within each of the four subgroups was treated with GnRH (200 mug i.m.) at standing estrus. Only donors that exhibited estrus within 32 to 72 h after the first prostaglandin treatment were used in the study. Animals were inseminated artificially 12 and 24 h after standing estrus was first observed. No differences were noted in the number of ovulations, total ova or transferable embryos recovered from the GnRH or control groups; however, two interactions were detected. Cows given GnRH had fewer palpable corpora lutea than control cows (P < 0.05), but this difference was not seen in heifers. The second interaction was that GnRH seemed to depress ovulation rate in donors not previously superovulated, but this effect was not observed with subsequent superovulations. Cows yielded more total ova than heifers (P < 0.01). There was no difference in return to estrus between GnRH and control groups after a second prostaglandin treatment at the time of embryo recovery. Most donors within each group resumed cycling between 5 and 12 d after embryo recovery.     

Induction of parturition, progesterone secretion, and delivery of placenta in beef heifers given relaxin with cloprostenol or dexamethasone

Sixty primiparous beef heifers from a crossbreeding study were used to examine the effects of inducing parturition with relaxin (3,000 U/mg) combined with cloprostenol (500 micrograms, i.m., n = 30) or dexamethasone (20 mg, i.m., n = 30) at Day 273, 10 +/- 1 days before expected parturition (Day 283). Heifers were assigned at random within cloprostenol and dexamethasone groups to receive relaxin (1 mg, n = 5/treatment), i.m. or in the cervical os (OS), at 0 h (the same time as cloprostenol and dexamethasone) or 24 h later. Eleven and six first-calving heifers and sixteen and nine second-calving cows also received cloprostenol + relaxin and cloprostenol + phosphate-buffered saline, respectively. Radioimmunoassay of daily plasma samples indicated an abrupt decrease in progesterone with time (p less than 0.001), from 7.5 +/- 0.50 to 1.0 +/- 0.30 ng/ml (mean +/- SE) within 48 h for all groups. The mean rate of progesterone decrease (ng/ml in 24 h) was accelerated (p less than 0.01) in relaxin-treated heifers (5.3 +/- 0.36), in contrast to dexamethasone- and cloprostenol-treated control heifers (2.8 +/- 0.40). Relaxin combined with cloprostenol or dexamethasone shortened the calving period in these heifers by reducing the interval between treatment and calving (33 vs. 56 h; p less than 0.01). The incidence and duration of retained placenta were reduced by 22 vs. 75% and 14 vs. 34 h for relaxin combined with cloprostenol or dexamethasone as compared with cloprostenol- or dexamethasone-treated controls, respectively (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of estradiol cypionate (ECP) on ovarian follicular dynamics,synchrony of ovulation,and fertility in CIDR-based,fixed-time AI programs in beef heifers

Estradiol cypionate (ECP) was used in beef heifers receiving a controlled internal drug release (CIDR; insertion = Day 0) device for fixed-time AI (FTAI) in four experiments. In Experiment 1, heifers (n = 24) received 1mg ECP or 1mg ECP plus 50mg commercial progesterone (CP) preparation i.m. on Day 0. Eight or 9 days later, CIDR were removed, PGF was administered and heifers were allocated to receive 0.5mg ECP i.m. concurrently (ECP0) or 24h later (ECP24). There was no effect of treatment (P = 0.6) on mean (+/-S.E.M.) day of follicular wave emergence (3.9+/-0.4 days). Interval from CIDR removal to ovulation was affected (P<0.05) only by duration of CIDR treatment (88.3+/-3.8h versus 76.4+/-4.1h; 8 days versus 9 days, respectively). In Experiment 2, 58 heifers received 100mg progesterone and either 5mg estradiol-17beta or 1mg ECP i.m. (E-17beta and ECP groups, respectively) on Day 0. Seven (E-17beta group) or 9 days (ECP group) later, CIDR were removed, PGF was administered and heifers received ECP (as in Experiment 1) or 1mg EB 24h after CIDR removal, with FTAI 58-60h after CIDR removal. Follicular wave emergence was later (P<0.02) and more variable (P<0.002) in heifers given ECP than in those given E-17beta (4.1+/-0.4 days versus 3.3+/-0.1 days), but pregnancy rate was unaffected (overall, 69%; P = 0.2). In Experiment 3, 30 heifers received a CIDR device and 5mg E-17beta, with or without 100mg progesterone (P) i.m. on Day 0. On Day 7, CIDR were removed and heifers received ECP as described in Experiment 1 or no estradiol (Control). Intervals from CIDR removal to ovulation were shorter (P<0.05) in ECP0 (81.6+/-5.0h) and ECP24 (86.4+/-3.5h) groups than in the Control group (98.4+/-5.6h). In Experiment 4, heifers (n = 300) received a CIDR device, E-17beta, P, and PGF (as in Experiment 3) and after CIDR removal were allocated to three groups (as in Experiment 2), with FTAI 54-56h (ECP0) or 56-58h (ECP24 and EB24) after CIDR removal. Pregnancy rate did not differ among groups (overall, 63.6%, P = 0.96). In summary, although 1mg ECP (with or without progesterone) was less efficacious than 5mg E-17beta plus 100mg progesterone for synchronizing follicular wave emergence, 0.5mg ECP (at CIDR removal or 24h later) induced a synchronous ovulation with an acceptable pregnancy rate to fixed-time AI.     

Neither duration of progesterone insert nor initial GnRH treatment affected pregnancy per timed-insemination in dairy heifers subjected to a Co-synch protocol

Our objectives were to: 1) compare response to cloprostenol, synchrony of ovulation, and pregnancy per timed-AI (P/TAI) in a 5 d versus a 7 d Co-synch + PRID protocol (Experiment 1); and 2) investigate whether the initial GnRH is necessary to achieve acceptable P/TAI in a 5 d Co-synch + PRID protocol (Experiment 2) in dairy heifers. In Experiment 1, 64 Holstein heifers, 15 to 17 mo, were assigned by age to receive 100 μg of GnRH and a PRID for 5 or 7 d (PRID5 and PRID7, respectively). At PRID removal 500 μg of cloprostenol (PGF) was given i.m. Heifers received the second GnRH treatment concurrently with TAI at 72 (PRID5) or 56 (PRID7) h after PRID removal. Transrectal ultrasonography monitored ovarian dynamics, ovulation synchrony, and pregnancy status (28 and 45 d after TAI). Plasma progesterone concentrations were determined at PRID removal and TAI. Five of seven heifers that ovulated before TAI became pregnant, and only two heifers did not respond to PGF treatment in the PRID5 group. Five PRID5 and 2 PRID7 heifers failed to ovulate after the second GnRH. However, P/TAI did not differ between PRID5 (59.4%) and PRID7 (58.1%). Overall ovulation response to first GnRH treatment was only 31.7%, and a larger proportion of heifers that did not ovulate became pregnant (65.1 versus 45.0%). In Experiment 2, 56 Holstein heifers, assigned as in Experiment 1, were subjected to a PRID5 protocol with (PRID5G) or without (PRID5NoG) GnRH at PRID insertion; all heifers were TAI 72 h after PRID removal. Transrectal ultrasonography and progesterone determinations were performed as in Experiment 1. Pregnancy per TAI did not differ whether or not heifers received GnRH at PRID insertion (67.9 versus 71.4%). Consistent with our previous findings, seven of nine heifers that ovulated before TAI became pregnant, and only two heifers did not respond to PGF treatment. Combining both experiments, length of proestrus but not ovulatory follicle diameter was identified as a significant predictor of probability of pregnancy 28 d after TAI, with a maximum predicted probability of 80.1% when the length of proestrus was 3 d. In summary, a PRID5 protocol resulted in comparable P/TAI to a PRID7 protocol. Most of the heifers that ovulated before TAI in the PRID5, PRID5G, and PRID5NoG protocols became pregnant. More than one PGF or a GnRH treatment at PRID insertion in a 5 d Co-synch + PRID protocol was not required to achieve acceptable P/TAI in dairy heifers.