Dose Of Cloprostenol Research Articles

Luteal function and estrous cycle characteristics in mares treated with subtherapeutic doses of prostaglandin F2α

Although the ovulatory effects of prostaglandins are well documented in several domestic species including horses, there has been little attention paid to the use of this ovulatory effect for clinical purposes. Mares often grow large follicles during the luteal phase that may or may not ovulate before progesterone levels decline. Clinical observations of administering prostaglandins in diestrous mares with large follicles suggest that there may be a negative correlation between follicular diameter and interval from treatment to ovulation. The objectives of this study were twofold: to investigate the cloprostenol dose rate effect on interval to ovulation and to confirm the negative correlation between follicular diameter and interval to ovulation. The hypothesis tested was that high doses of cloprostenol given in diestrus to mares with larger follicles would induce ovulation more rapidly than in mares given lower doses or with smaller follicles. To test the hypothesis, a total of 1,234 estrous cycles were induced with different doses of cloprostenol (ranging from 8.75 to 625 μg). All mares had at least one follicle of 28 mm or larger. Dominant follicles were followed by transrectal ultrasound examinations every other day until ovulation was detected. There was a significant effect of dose (P < .000) and follicular diameter (P < .000) on the interval from treatment to ovulation. The shortest mean interval (2.4 days) was observed after administration of 625 μg in mares with follicles 36 mm or larger, whereas the longest (4.9 days) occurred after 8.75 μg in follicles of 28 to 31 mm.

Origin of the preovulatory follicle in Mouflon sheep ( Ovis gmelini musimon) and effect on growth of remaining follicles during the follicular phase of oestrous cycle

Daily transrectal ultrasonographies were conducted to study development of all follicles with antral diameters ≥2 mm during the follicular phase of oestrous cycle in Mouflon, a strictly monovular wild-sheep. A total of 14 follicular phases was studied after oestrus synchronization with two cloprostenol doses, 9 days apart, in five cyclic Mouflon ewes. In 13 cycles (92.8%), the ovulatory follicle arose from those antral follicles present in both ovaries when luteolysis was induced, being the largest one with a mean size of 4.4±0.3 mm at that moment in 10 cycles (76.9%). The remaining cycles had a larger follicle, but it was decreasing in size. Appearance of new follicles ≥2 mm in size remained unaffected during the follicular phase (3.7±0.2), but there was found a linear decrease in the number of those growing to ≥3 mm (2.5±0.4 to 1.1±0.2, P<0.05) and ≥4 mm (0.6±0.2 to 0.1±0.1, P<0.005), detection of new follicles growing to ≥5 mm was negligible. Then, number of medium (4–5 mm) growing follicles present in both ovaries decreased from 1.5±0.3 at 0 h to 0.3±0.1 at 72 h ( P<0.005). In conclusion, the single ovulatory follicle is the largest growing follicle present in both ovaries at the moment of luteolysis. This follicle is selected to grow and ovulate while development of other follicles is inhibited.

Short synchronization system for estrus cycles in dairy heifers: a preliminary report

In previous studies we demonstrated that the administration of a luteolytic dose of cloprostenol to dairy cows in luteal phase, followed by hCG plus estradiol benzoate (EB) 12 h later, led to successful timed AI 48 h after the initiation of treatment. This article reports two consecutive studies. In Study 1 we determined the pregnancy rate of dairy heifers in luteal phase (established by palpation per rectum) treated with cloprostenol followed by 250 IU of hCG plus 1 mg of EB 12 h later, and inseminated 48 h after cloprostenol injection. Study 2 was designed to evaluate the efficiency this synchronization protocol, irrespective of the estrus stage of the animals. In Study 1, 1272 Friesian heifers aged 14 to 16 months with a palpable corpus luteum received 500 mcg cloprostenol. Heifers were then synchronized either according to the hCG plus EB protocol (hCG-EB, n=637), or by a second dose of cloprostenol 11 d later (PG, n=636). Animals in this last group served as controls and were inseminated 72 and 96 h after the second cloprostenol injection. The pregnancy rate was significantly higher (P<0.0001) in the hCG-EB group (59.5%, 379 637 ) than in PG (44.8%, 285 636 ). In Study 2, 135 contemporary heifers (with no corresponding information on estrus stage) were subjected to the same protocol as those in the hCG-EB group of Study 1. These animals were classified in retrospect according to estrus stage established by plasma progesterone concentration. Pregnancy rates were 66.7% ( 24 36 ), 51% ( 25 49 ) and 58% ( 29 50 ) for animals in the follicular, early/late luteal, and mid-luteal phase, respectively. The total pregnancy rate was 57.8% ( 78 135 ). These findings indicate an improved pregnancy rate for heifers subjected to single insemination after cloprostenol/hCG/EB synchronization, compared to double insemination after synchronization by 2 cloprostenol injections 11 d apart. The cloprostenol/hCG/EB protocol did result in acceptable pregnancy rates after timed AI of dairy heifers regardless of their estrus cycle phase.

Reproductive performance of lactating dairy cows treated with cloprostenol, hCG and estradiol benzoate for synchronization of estrus followed by timed AI

In previous studies, we demonstrated that the administration of a luteolytic dose of cloprostenol, followed by 750 IU hCG plus 3 mg estradiol benzoate (EB) 12 h later, synchronized estrus in cows in the luteal phase. Most cows were ready for service 48 h after the beginning of treatment. The objectives of this study were to evaluate the reproductive performance of lactating dairy cows treated with this method of estrus synchronization and to determine the effect of decreasing the hCG-EB dose on synchronization and pregnancy rates after timed AI. Data were obtained from cows first inseminated within an interval of 45 to 70 d postpartum. A total of 2472 lactating dairy cows in their first to second lactation period were assigned to 4 groups. Cows estimated to be in the luteal phase by rectal palpation were treated with 500 mcg, im, of cloprostenol and assigned to 1 of 3 groups to be intramuscularly injected with hCG-EB 12 h later at the following doses: Group 1 (n=626), 250 IU of hCG and 1 mg of EB; Group 2 (n=592), 500 IU of hCG and 2 mg of EB; and Group 3 (n=664), 750 IU of hCG and 3 mg of EB. Cows displaying natural estrus were inseminated to serve as controls (n=590). The synchronized cows were inseminated 48 h after cloprostenol injection, and control animals visually determined to be in natural estrus during the morning or afternoon were inseminated the following morning. Pregnancy diagnosis was performed by rectal palpation at 34 to 40 d postinsemination. All synchronized cows showed estrous activity within 24 to 36 h after cloprostenol treatment and were considered to be ready for service 48 h after this treatment. There was a significant effect of treatment on the pregnancy rate, either to first AI or to 2 rounds of AI. The pregnancy rate in response to first or second rounds of AI was similar to control rates for cows in Groups 1 and 2, and lower than control rates in Group 3. Cows in Group 1 showed a higher pregnancy rate to first AI than those in Group 3 (P<0.0001), and a higher pregnancy rate to second AI rounds than cows in Groups 2 (P<0.02) and 3 (P<0.0001). The number of cows returning to estrus was unaffected by treatment. However, treatment significantly decreased (P<0.01) the time of return to estrus as the hCG-EB dose increased. These findings indicate that the lowest dose of hCG-EB treatment tested gave the overall best pregnancy results among the treated groups. Furthermore, the synchronization protocol used in this experiment allows effective AI management of lactating dairy cows without the need for estrus detection.

Estrus synchronization with lower dose of PGF 2α 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 Eexperiment 1, cyclic buffalo (n=10) were assigned to 2 equal groups receiving either 500 μg im cloprostenol (Estrumate, ICI) or 125 μg 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 PGF 2α 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 μg of cloprostenol groups, respectively. In Experiment 2, multiparous, lactating subestrous buffaloes (n=137) were treated either with 125 μg ivsm cloprostenol or 500 μg im 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 μg 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 μg cloprostenol, respectively. These results indicated that 125 μg ivsm and 500 μg im 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.

The effect of continuous presence of bucks on hastening the onset of estrus in synchronized does during the breeding season

Nubian goats were synchronized for estrus by using two doses of cloprostenol at 12-day intervals (CLO; n=14) or by using progestagen intravaginal pessaries impregnated either with fluorgestone acetate (FGA; n=14) or medroxyprogesterone acetate (MAP; n=10) over a 12-day period. Each group of synchronized females was equally divided into an experimental and a control group. Does in the experimental group were continuously exposed to an aproned teaser for 36 h, after the synchronization treatment had terminated, whereas those in the control group were not. In both groups, estrus was detected using another vasectomized buck twice a day (0700 and 1900 h) during 5 days after pessary removal or after the second cloprostenol injection. Estrus initiation for the experimental and control groups was at (mean±SD) 37.6±16.6 and 48.3±17.1 h, respectively ( P<0.03). Estrus onset for CLO, MAP and FGA groups was at 48.0±9.1, 50.4±17.9 and 32.6±19.5 h, respectively ( P<0.01). The effect of the FGA treatment was different from that of MAP and CLO ( P<0.01), but the difference between MAP and CLO treatments was not significant ( P>0.05). It is concluded that the continuous presence of a male hastens estrus onset in does synchronized for estrus using either a progestagen pessary or cloprostenol injection.

Luteolysis induced by a prostaglandin F2alpha analogue occurs independently of prolactin in the rat.

The hypothesis that prolactin exerts a stimulatory dominance over the luteolytic effect of prostaglandin (PG) F2alpha on corpus luteum maintenance and progesterone production was experimentally tested. A dose-dependent effect of the stable PGF2alpha analogue cloprostenol (dose range 200 ng(-5) microg) was found 12 h after s.c. injection, in Day 9 adult pseudopregnant rats: 1) LH receptor mRNA levels, as measured by RNase protection assay, were dramatically decreased (by 67%) by a single s.c. dose of 200 ng cloprostenol; and 2) serum progesterone levels were significantly (p < 0.05) decreased (by 43%) whereas 20alpha-dihydroprogesterone significantly (p < 0.05) increased (by 80%) initially at a 0.5-microg dose of cloprostenol. To study the integrated response to prolactin and PGF2alpha, we investigated the effect of cloprostenol treatment in sterile-mated female rats with or without circulating prolactin. Prolactin secretion was inhibited by s.c. injection of bromocriptine (1 mg) in the morning of the ninth day of pseudopregnancy. A group of rats was left prolactin-depleted; in another group prolactin was reintroduced by adding 8 IU ovine prolactin. It was found that after injection of 0.5 microg cloprostenol the LH receptor mRNA levels and the serum progesterone/20alpha-dihydroprogesterone ratio were not significantly different whether the rats had circulating endogenous/exogenous prolactin or were prolactin-depleted. Therefore, although prolactin exerts a stimulatory influence on both progesterone production and corpus luteum LH receptor gene expression, the conclusion is reached that prolactin alone cannot antagonize the luteolytic effect of PGF2alpha.

Effect of two doses of cloprostenol in two schemes for estrous synchronization in Nubian goats

In experiment 1, 12 nulliparous does were randomly assigned to 3 groups. Animals in each group received either: (a) 125 μg cloprostenol (CLO), (b) 62.5 μg CLO or (c) 0.5 ml saline solution injected between the 8th and 15th day of estrous cycle (estrus=day 0). Interval from CLO injection to estrus was (mean±SE) 60.5±11.9 and 60.5±8.3 h for does receiving 125 and 62.5 μg CLO, respectively ( P>0.05). None of the does receiving saline solution exhibited estrus. Estrus duration was (mean±SE) 22.8±1.8 and 24.5±3.5 h for groups a and b respectively ( P>0.05). Fertility rate from natural breeding following either 125 and 62.5 μg CLO was 3 out of 4. In the second experiment, 16 multiparous does were randomly assigned to 2 groups. The first group received as a first injection 125 μg CLO and as a second injection 12 days apart 62.5 μg CLO while the second group received the inverse treatment (first injection 62.5 μg and second injection 125 μg). Estrus response, the interval from treatment to estrus, and estrus duration after the first injection in both groups and after the second injection in both groups were compared. The results were: 50 and 87.5% ( P<0.02), 72.0±4.5 and 52.3±1.9 h ( P<0.01), 40.5±2.2 and 40.3±3.5 h ( P>0.05), respectively. Fertility rates from artificial insemination for 125 and 62.5 μg CLO were 4 in 8 and 5 in 8, respectively. It is concluded that 62.5 μg CLO by the intramuscular route is luteolytic in Nubian goats, and that a scheme of two doses 12 days apart should be an effective method for estrous synchronization.

Influence of varied progestogen treatments on ovarian follicle status and subsequent ovarian superstimulatory responses in cows.

The influence of ovarian follicle status and follicle dominance on the response to superstimulatory treatment with FSH was examined in cows. In Experiment 1, oestrus was synchronised using Crestar and on Days 4-6 of the ensuing oestrous cycle cows were assigned to: Group NO (n = 9), control, endogenous CL and no treatment; Group N1 (n = 15), injected with a luteolytic dose of cloprostenol (500 micrograms) and implanted with one implant (3 mg) of the synthetic progestogen, norgestomet; Group N8 (n = 18), injected with 500 micrograms cloprostenol and implanted with eight (24 mg) implants of norgestomet. On Days 9-11, seven implants were removed from six cows in Group N8 and these cows, plus eight Group N1 and all Group N0 cows, were superstimulated with porcine FSH (Folltropin-V) over 4 days (360 mg total dose). The remaining implants were removed from cows in Groups N1 and N8 on Days 11-13, and all cows received 500 micrograms cloprostenol. Numbers and sizes of ovarian follicles, and CL, were recorded by trans-rectal ultrasonography; the largest follicle > 10 mm in diameter was considered morphologically dominant (DF). On Days 9-11, the proportions of cows with a DF were: Group N0, 3/9; Group N1, 14/15; Group N8, 0/18. Total follicles on the 4th day of FSH treatment were greater (P < 0.05) for cows in Group N1 (21.6 +/- 4.2) compared with Group N0 (10.9 +/- 2.4), with cows in Group N8 (13.2 +/- 0.9) not different from the other two groups. Subsequent numbers of CL were lower (P < 0.05) for cows in Group N1 (5.0 +/- 1.3) compared with Group N0 (9.4 +/- 2.0), with cows in Group N8 (8.5 +/- 1.0) not different from the other two groups. In Experiment 2, oestrus was synchronised in cows and on Days 4-6, cows were assigned to: Group C0 (n = 7), control, endogenous CL and no treatment; Group C3 (n = 6), received three CIDR-B intra-vaginal devices that delivered progesterone. On Days 9-11, two CIDR-B were removed from cows in Group C3 and all cows treated with FSH as in Experiment 1. The remaining CIDR-B was removed from cows in Group C3 on Days 11-13 and all cows injected with 500 micrograms cloprostenol. Proportions of cows with a DF on Days 9-11 and diameter of largest follicle were: Group C0, 6/7 and 12.6 +/- 0.9 mm; Group C3, 2/6 and 9.6 +/- 0.8 mm. Numbers of CL on Day 8 after oestrus were: Group C0, 20.0 +/- 7.1; Group C3, 14.8 +/- 4.8 (P > 0.05). Exposure to low dose norgestomet allowed development of a persistent dominant follicle, resulting in a reduced response to superstimulation with FSH. High dose progestogen restricted follicle growth without apparent effects on responses to superstimulation.

Natural and induced ovarian synchrony in golden lion tamarins (Leontopithecus rosalia).

Ovarian cycle synchrony was assessed in spontaneously cycling female golden lion tamarins by monitoring longitudinal (16 mo) urinary steroid metabolite (estrone conjugates; pregnanediol-3 alpha-glucuronide, PdG) excretion in four pairs (n = 8) of females isolated from males. The overall mean ovarian cycle duration was 18.5 +/- 0.3 days (n = 136 cycles; mean range, 15.7-21.0 days), and there was no evidence of reproductive seasonality. Laparoscopic ovarian examinations confirmed that cyclic fluctuations in urinary steroid metabolite excretion were temporally associated with the formation and demise of corpora lutea. Evaluation of ovarian synchronization tested the null hypothesis that urinary hormone cycles were expressed randomly relative to those of cagemates or other females housed in separate cages but within close proximity. Natural ovarian synchrony (expressed as the mean difference in ovarian cycle onset) between cagemates (4.1 +/- 0.4 days) and among noncagemates (4.2 +/- 0.2 days) did not differ (p > 0.05) from a random ovarian cycle distribution. Two trials also were conducted to evaluate the efficacy of the prostaglandin (PG) F2 alpha analogue, cloprostenol, for artificially synchronizing ovarian cycles. Induced ovarian synchrony was not achieved with a single 0.8-microgram i.m. injection of cloprostenol. However, doubling the cloprostenol dose (1.6 micrograms) caused a rapid decrease in mean urinary PdG (p < 0.05) within 2 days, and synchronous ovulation was demonstrated by an increase (p < 0.01) in mean urinary PdG 10 days after cloprostenol administration. In summary, females housed in pairs, in the absence of males, exhibit spontaneous, year-round ovarian cycles with no evidence of among-female ovarian synchrony. Results also suggest that this New World primate has a reduced sensitivity to cloprostenol (compared to common marmosets) but that a single, midcycle cloprostenol injection of 1.6 micrograms effectively induces luteolysis and synchronous ovulation.

Failure of the LH-releasing hormone agonist, deslorelin, to prevent development of a persistent follicle in heifers synchronized with norgestomet

The use of exogenous progestagens for estrus synchronization in cattle can result in a persistent dominant follicle which is associated with reduced fertility. We examined whether the LHRH agonist, deslorelin, would prevent the formation of a persistent follicle in heifers synchronized with norgestomet. The estrous cycles of heifers were synchronized with cloprostenol, and on Day 7 of the ensuing cycle the heifers received one of the following treatments for 10 d: Group C (n = 5), untreated control; Group N (n = 6), injection of a luteolytic dose of cloprostenol on Days 7 and 8 and implant of norgestomet from Day 7 to Day 17 (i.e. typical 10-day norgestomet implant period); Group D (n = 6), injection of cloprostenol on Days 7 and 8 and implants of deslorelin from Day 7 to Day 17; Group ND (n = 6), injections of cloprostenol and both norgestomet and deslorelin implants as above. Follicle growth was monitored using ultrasonography. Group-N heifers showed continued follicle growth and had larger follicles on Day 17 of the cycle than Group-C heifers (16.8 ± 1.6 and 10.4 ± 1.6 mm). Follicle growth for Group-D and ND heifers was similar and variable, and seemed to depend on follicle status at the initiation of treatment. Heifers with follicles of 5 to 10 mm (n = 9) in diameter either showed no follicle growth ( 2 9 ) or developed large follicles ( 7 9 ), while heifers with follicles approximately 12 mm (n = 3) in diameter showed follicle atresia with no further significant growth. On Day 17, size of the largest follicle was similar for Group-ND (14.3 ± 2.9) and Group-D (16.8 ± 1.6) heifers. Heifers in Group N showed estrous behavior 1.8 ± 0.2 d after treatment, whereas heifers in Groups D and ND did not show estrus for 2 to 4 wk. The results show that combined treatment with progestagen and an LHRH agonist does not consistently prevent the development of a persistent dominant follicle and that return to estrus can be delayed after treatment with an LHRH agonist.

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 2α 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 2α 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 2α administration and, in part, to incomplete luteolysis following a single dose of PGF 2α. 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 2α 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 2α induced luteolysis, especially when 2 doses of PGF 2α were administered 12 h apart.

Evidence that most of the radioimmunoassayable inhibin secreted by the corpus luteum of the common marmoset monkey is of a non-dimeric form.

Although recent data for several species of primate, including human and marmoset, indicate that the corpus luteum secretes high levels of radioimmunoassayable inhibin, the nature of the immunoreactive (ir) inhibin detected has not been established. In this study, plasma ir-inhibin levels during the ovarian cycle of the marmoset (n = 12 animals) were measured by alpha-subunit-directed inhibin RIA, and values were compared with those estimated by a recently developed two-site immunoradiometric assay (IRMA) specific for inhibin alpha-beta dimer. Consistent with earlier data, plasma levels of ir-inhibin measured by RIA (overall mean value 133 +/- 7 ng/ml; n = 171) reached values 4-fold higher (p less than 0.001) during the luteal phase (222 +/- 20 ng/ml) than during the follicular phase (58 +/- 8 ng/ml), being directly correlated with plasma progesterone levels (r = 0.65; p less than 0.001). In contrast, plasma ir-inhibin levels estimated by IRMA were substantially lower than those measured by RIA (overall mean value 9.62 +/- 1.08 ng/ml; n = 171) and did not vary significantly during the cycle. Administration of a luteolytic dose of cloprostenol during the late luteal phase/early pregnancy led to an abrupt fall in plasma concentrations of progesterone (95%) and alpha-inhibin measured by RIA (82%), whereas dimeric inhibin levels remained unchanged. Analysis of marmoset luteal extracts (n = 5) by RIA, IRMA, and inhibin bioassay yielded inhibin estimates of 102.6 +/- 21.0, 0.632 +/- 0.103, and less than 2.0 ng/mg, respectively, thus confirming that only a very small proportion of the inhibin produced was dimeric (i.e., bioactive) in nature.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of a prostaglandin F 2α analogue on the ovulatory response of superovulated heifers

Thirty-one cycling heifers were superovulated and subsequently ovanectomized to determine if preovulatory follicles could be induced to ovulate by the administration of cloprostenol, a potent agonist of prostaglandin F 2α. Superovulation was induced, during the mid-luteal phase, with a total dose of 20 mg porcine pituitary extract of follicle stimulating hormone (FSH) given twice daily over 4 days in decreasing doses; a luteolytic dose of cloprostenol was administered on the third day. Two experiments were carried out in which ovariectomies (OVX) were performed at 64 h following cloprostenol injection. Owing to the variable interval between the preovulatory peak of luteinizing hormone (LH) and OVX observed in Experiment I, the preovulatory LH surge was induced in Experiment II by 100 μg of a synthetic analogue of gonadotropin releasing hormone (GnRH) given 36 h after the luteolysin. To test the hypothesis that cloprostenol is able to induce, enhance or synchronize ovulation, two different doses of this hormone, 1.25 or 2.5 mg, were injected at 4 and 2 h or at 2 and 1 h prior to OVX. Plasma progesterone (P 4) and LH concentrations and follicular fluid P 4: estradiol-17β (E 2) ratios in the non-ovulated follicles were utilized to identify animals that had a typical response to the superovulatory treatment and, at OVX, total number of follicles 8 mm or more in diameter, and number of ovulations were recorded. When data from both experiments were considered, it was observed that: (1) GnRH injection did not affect ovulation rate; (2) cloprostenol injections induced more follicles ( P < 0.01) to ovulate, 59.3% vs. 20.1%, SE = 9.8, in cloprostenol-treated vs. controls, respectively, at the time tested; (3) cloprostenol dose had a positive linear effect ( P < 0.01) on ovulation rate. In conclusion, the data suggest that prostaglandin F 2α or its analogues could be used to induce a more synchronous ovulation of follicles in superovulated heifers.

The use of lower doses of the prostaglandin analogue, cloprostenol, for oestrus synchronization in heifers

In an attempt to reduce costs for cattle oestrus synchronization, the use of lower doses (50 and 25% of the conventional dose) of the prostaglandin F 2α analogue, cloprostenol, given by either intramuscular (IM) or intravulvo-submucosal (IVSM) injection, was investigated. There were no differences in the luteolytic response, as measured by either the fall in plasma progesterone or onset of oestrus, between lower cloprostenol doses administered by either method and 500 μg given by IM injection.

The effect of dose of cloprostenol on return to estrus of superovulated donor cows

A study was designed to evaluate the superovulatory response in the cow when either estradiol 17β or gonadotrophin releasing hormone (GnRH) was used in a superovulatory regimen with follicle stimulating hormone (FSH-P). Fifty-four cyclic crossbred females were superovulated in replicates between Days 8 and 12 of their cycle. All animals were treated with 28 mg of FSH-P in twice-daily decreasing doses, each receiving 500 μg cloprostenol (PGF) 48 h after initiation of treatment. Group 1 served as FSH-P controls, Group 2 received FSH-P and 400 μg of estradiol 17β 36 h after PGF, and Group 3 received FSH-P and 250 μg GnRH 48 h after PGF. Inseminations with one vial of frozen semen were done at 12, 24 and 36 h after the onset of estrus. Ova/embryos were collected nonsurgically at Day 7 postestrus. Numbers of corpora lutea (CL) were recorded after palpation per rectum and the recovered ova and embryos were evaluated. All females were bled for endocrine examination. There were no differences in ovarian response among these treatments. Mean total ova/embryos collected in Group 3 was significantly higher than in Groups 1 or 2 (P < 0.05); however, no significant difference existed between groups in the mean numbers of fertilized or transferable embryos. Similarly, no significant differences existed between groups for recovery rate, fertilization rate, or percentage of transferable embryos. Serum estradiol levels were significantly higher at the expected end of ovulation in Group 2, and this tended to be associated with higher fertilization and transferable embryo rates. Furthermore, a significant positive correlation was found to exist between CL numbers and each of the ova/embryo parameters and the estradiol levels at estrus.

Pulsatile secretion of inhibin, oestradiol and androstenedione by the ovary of the sheep during the oestrous cycle

The pattern of pulsatile secretion of inhibin, oestradiol and androstenedione by the ovary at different stages of the oestrous cycle in sheep was studied in five Finn-Merino ewes in which the left ovary had been auto-transplanted to the neck. The ewes had jugular venous blood samples collected at 4-hourly intervals from 42 h before the induction of luteolysis by i.m. injection of cloprostenol (100 micrograms) on day 10 of the oestrous cycle, until day 3 of the following cycle. There were five periods of intensive blood sampling, when both ovarian and jugular venous blood samples were collected, as follows: (a) mid-luteal phase, before the second injection of cloprostenol on day 10 (15-min intervals for 6 h); (b) early follicular phase, 24 h after the second injection of cloprostenol (10-min intervals for 4 h); (c) late follicular phase, 48 h after the second injection of cloprostenol (10-min intervals for 4 h); (d) after the LH surge on day 1 of the cycle, 76 h after the second injection of cloprostenol (10-min intervals for 4 h); (e) early luteal phase on day 3 of the cycle, 120 h after the second injection of cloprostenol (10-min intervals for 3 h). Plasma was collected and the samples assayed for LH, FSH, progesterone, oestradiol, androstenedione and inhibin. The ovarian secretion rates for oestradiol, androstenedione and inhibin were calculated. All ewes responded normally to the luteolytic dose of cloprostenol with the preovulatory surge of LH occurring within 56.4 +/- 1.6 h (mean +/- S.E.M.) followed by the establishment of a normal luteal phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Pregnancy Rate of Dairy Cows Following Synchronization of Estrus with Cloprostenol, hCG and Estradiol Benzoate

After assessment of luteal function by the milk progesterone test, oestrus was synchronized in 78 lactating Friesian cows with a luteolytic dose of cloprostenol which was followed by injection of hCG and estradiol benzoate 12 hours later. The cows were inseminated 48 hours after the injection of cloprostenol. Thirty-eight of the 78 cows became pregnant (48.7 per cent), compared with 59 of the 115 cows (51.3 percent) which were inseminated at natural oestrus. These results suggest that in dairy cows synchronized with cloprostenol, hCG and estradiol benzoate fertility is not altered.

Effect of continuous infusion of oxytocin on prostaglandin F2 alpha secretion and luteolysis in the cyclic ewe

Circulating concentrations of 13,14-dihydro-15-keto PGF2 alpha (DHKF2 alpha), luteinizing hormone (LH) and prolactin (PRL) have been measured in cyclic ewes treated with continuous infusions of oxytocin, in order to investigate the mechanism by which the treatment delays luteal regression. Continuous infusion of oxytocin reduced prostaglandin F2 alpha (PGF2 alpha) secretion but had no detectable direct effect on LH or PRL. Oxytocin (3 nmol h-1 i.v.) given from Day 12 or 13 until Day 18 after oestrus delayed luteolysis, eight out of nine treated ewes not returning to behavioural oestrus until Day 29.1 +/- 3.2 (mean +/- s.e.m.; cycle length of control ewes 16.7 +/- 0.3 days). In the ewe in which oxytocin failed to prevent luteolysis, luteal regression had commenced before oxytocin treatment was started. In three ewes undergoing delayed luteolysis (cycle lengths, 21, 24 and 25 days) basal concentrations of PGF2 alpha (measured as DHKF2 alpha) were unchanged, but there was only one episode of PGF2 alpha secretion compared with 20 episodes in three control ewes. Prolactin secretion was pulsatile during oxytocin infusion, and levels were low following infusion in ewes with cycle length greater than 25 days while the corpora lutea were maintained. Circulating PRL concentrations were high in ewes undergoing delayed luteolysis but there was not discrete episode of PRL secretion associated with the pre-ovulatory LH surge in these animals. To investigate the possibility that the pattern of PGF2 alpha secretion was affected by depletion of oxytocin from corpora lutea, ewes previously treated with oxytocin to delay luteolysis were given a luteolytic dose of cloprostenol on Day 21 after oestrus. The amount of oxytocin secreted in response to cloprostenol was less than 10% of that seen in ewes similarly treated on Days 11-13 after oestrus. Low levels of luteal oxytocin may therefore reduce PGF2 alpha secretion in ewes undergoing delayed luteolysis.

Luteolytic effect of a low dose of cloprostenol monitored by changes in vaginal resistance in suboestrous buffaloes

Buffalo cows were treated by manual enucleation of the corpora lutea, intramuscular injection of 500 μg cloprostenol, or intravulvosubmucosal injection of 100 μg cloprostenol. Oestrus was detected by an electronic probe which measured changes in the intravaginal electrical resistance. There were no significant differences in oestrous response (87–100%) or subsequent conception (44.4–46.7%) between treatment groups.