OBJECTIVE

To compare the reproductive performance and pattern of onset of oestrus in dairy heifers in which oestrous cycles were synchronised with two doses of prostaglandin (PG) F2alpha and oestrus was synchronised with oestradiol benzoate (ODB).

METHODS

Dairy heifers in two herds (herd A, n = 192; herd B, n = 267) were treated with two doses of an analogue of PGF2alpha (cloprostenol, 375 microg, IM) 12 days apart. Heifers not detected in oestrus 48 h after the last dose of PGF2alpha were either left untreated (No ODB, n = 147) or treated with ODB (0.75 mg IM, n = 126). Onset of oestrus was monitored at 0, 24, 48, 80, 96 and 120 h after the last dose of PGF2alpha Heifers were inseminated on detection of oestrus.

RESULTS

After the last dose of PGF2alpha, oestrous detection rates at 80 h (43.5 vs 72.6%, P < 0.001), 96 h (74.1 vs 84.9%, P =0.025) and 120 h (78.2 vs 86.3%, P = 0.082) were less in the No ODB compared to the ODB heifers, respectively. Conception rates (percentage pregnant that were inseminated) were greater in the No ODB compared to the ODB heifers (64.3% vs 47.6%, respectively; P = 0.006), while pregnancy rates (percentage pregnant that were treated) were also greater in the No ODB compared to the ODB heifers, but differences were not significant (50.3% vs 41.1%, respectively; P = 0.068).

CONCLUSIONS

Administration of ODB to heifers not in oestrus 48 h after a two-dose PGF2alpha treatment increases the percentage of heifers detected in oestrus by 80 h, 96 h and 120 h after treatment, by an estimated 29%, 11% and 8%, respectively. However, administration of ODB decreases conception rates by an estimated 17%, and may decrease pregnancy rates (estimated 9% difference). Results are consistent with the hypothesis that ODB can increase submission rates but reduce conception rates following a two dose treatment with PGF2alpha.

The study of bovine germ cells of known developmental stage calls for alternatives to the recovery of fetuses by surgery or slaughter. Fetuses were therefore obtained during the second month of pregnancy by aborting 49 animals using a progressively modified treatment regimen of cloprostenol, prostaglandin E2 (PGE2) and oxytocin. The viability of fetuses was monitored by ultrasonography throughout treatment. Intracervical treatment with PGE2 led to cervical dilation in all treated animals. However, retrieval of the fetuses by subsequent flushing of the uterus was successful in only two of six animals. When i.m. injections of cloprostenol were given 20-40 h before PGE2 treatment, fetuses < or = 40 days of gestation were expelled spontaneously, while the majority of fetuses>> or = 50 days of gestation were retained. When i.m. injections of oxytocin were given in relation to clinical signs of impending fetal expulsion after cloprostenol and PGE2 treatment, 20 of 22 fetuses were expelled 42-53 h after the cloprostenol injection. Of these 20 fetuses, 19 were expelled 0-7 h after the cessation of fetal heartbeat. The subsequent fertility of animals was not affected. Thus, the final protocol allowed bovine fetuses to be retrieved at predictable times, within a few hours of death, with little maternal trauma and without affecting subsequent fertility.

Luteolysis was induced by an injection of 500 micrograms cloprostenol (a prostaglandin (PG) analogue) in pregnant (P) Holstein heifers on Days 17 or 24 of gestation and in non-pregnant (NP) Holstein heifers on Day 17 of the oestrous cycle (oestrus = Day 0). Heifers in Groups P-17 (N = 8) and P-24 (N = 8) were inseminated twice whereas those in Group NP-17 (N = 8) were not inseminated. Immediately after PG injection, embryos were recovered by uterine flushing (400 ml) to confirm pregnancy in Groups P-17 and P-24. Uterine flushing with an equivalent volume of physiological saline was also done in Group NP-17. The interval from PG injection to oestrus and to the peak of luteinizing hormone (LH) as well as profile of increase in plasma oestradiol concentrations during that period did not differ (P greater than 0.1) among the groups. However, the proportion of heifers exhibiting abnormal luteal phases (primarily of short duration) during the oestrous cycle after PG injection was greater (P less than 0.01) in Group P-24 than in Groups NP-17 + P-17 pooled (6/8 vs 3/16). These results suggest that the previous presence of a conceptus did not have any effect on the onset of oestrus, or on plasma concentrations of oestradiol and LH after PG-induced luteolysis on Days 17 or 24 of gestation. However, luteal function during the subsequent oestrous cycle was impaired if heifers were 24 days pregnant when luteolysis was induced.

Three hundred and one Holstein cows (n=301), calving at a commercial free-stall dairy farm, were randomly assigned to 1 of 3 prostaglandin treatment groups or a placebo group. The placebos were packaged 3 ways to mimic the 3 commercial prostaglandin preparations. Group 1 received 1 mg fenprostalene and 1.6 mg oxytetracycline; Group 2 received the fenprostalene placebo (2 ml polyethylene glycol and 1.6 mg oxytetracycline); while Group 3 was given 25 mg dinoprost. Group 4, the dinoprost placebo received 5 ml saline; Group 5 received 500 microg cloprostenol; and Group 6 the cloprostenol placebo received 2 ml saline. The treatments were administered between Days 24 and 31 post partum. Double blind techniques were used in administering treatments and in assessing the response to treatment. There were no significant differences among treatment groups with respect to incidence of retained fetal membranes, endometritis, pyometra, anestrus, number of services per pregnancy, calving-to-first estrus interval, services per conception, number of prostaglandin treatments other than those administered between Days 24 and 31 post partum, the percentage culled for reproductive reasons and all factors combined. Cows receiving fenprostalene, dinoprost or cloprostenol had a decreased calving-to-conception interval compared with that of the controls (P = 0.05). It is concluded that, in the herd studied, treatment with any of the 3 commercially available prostaglandin products between Days 24 and 31 post partum was beneficial for reproductive performance.

Studied was the synchronizing effect of the prostaglandin F2a analague - estrumate (ICI, England). with the Tsigai sheep. The investigations included observations on the clinical characteristics of the estrus, determination of the hormonal profile in naturally manifested estrus and in estrus induced with prostaglandin, and the conception rate with the first two successive estrus cycles along with the total conception. Estrumate was used twice ar a 9-day interval in a single dose of 125 mg, with a following programmed artificial insemination at the 48 h and the 72d hour after the second treatment. The conception rate with the first estrus of the ewes of the control and the test group was comparatively low - 41.3 and 30.4 per cent, and with the two successive cycles - 68.5 and 76.8 per cent, respectively. The total conception of the test group was 96.4 per cent as against 87.5 per cent of the control group. The studies on the content and dynamics of the basic hormones taking part in the endocrine regulation of the cycle functions in sheep with naturally manifested estrus and those with prostaglandine-unduced estrus did not show reliable differences in the hormonal profile. It was found that estrumate could successfully be used to synchronized the estrus cycle with the Tsigai sheep - a breed with pronounced conservatism' in the manifestation of cyclic functions.

Prostaglandins were highlighted in the seminal plasma and then in the rest of the male and female genital tract. Prostaglandin analogs, firstly used in obstetrics and gynecology, are now widespread in both sexes, especially in the treatment of gastric and duodenal ulcers, glaucoma, etc. Therefore, we tried to highlight the effects of repeated administration of Cloprostenol and CIPG isopropyl ester (both prostaglandin F2α analogs) for the male gonad. In our experiment, we used Cloprostenol and CIPG isopropyl ester. We used three groups of white, male mice, aged 50-80 days, kept in standard laboratory conditions, which received the same feed. Each group included 12 mice. The first batch was the control group and received no substance at all. The second batch received 25 μg/kg of Cloprostenol dose per body per day, intraperitoneal administration (a single dose per day) on a daily basis for a four weeks period of time. The third batch received a 25 μg/kg CIPG isopropyl ester dose per body/day intraperitoneal administration (a single dose per day) on a daily basis for a four weeks period of time. After 7, 14 and 28 days of treatment, we sacrificed four animals in each of the batches by cutting their carotid arteries. The prostanoid analogs we used, Cloprostenol and CIPG isopropyl ester, have similar actions on male gonad in mice. These analogs induced significant changes in the evolution of the spermatogenesis and spermiogenesis. In relation to the treatment duration there were cellular changes suggesting apoptosis in different stages. With regard to spermiogenesis, the ultrastructural aspects indicate a decrease of the sperm structuring processes, especially in the acrosomal apparatus and chromatin.

The objective of this study was to use estrous behavior alone to determine the appropriate time for beginning an oxytocin treatment protocol for estrus suppression. We hypothesized that administration of oxytocin beginning 8 days after the onset of estrus will prolong the luteal phase in mares. Twenty-three light breed mares (aged 4-20 years) were exposed to a stallion and observed for signs of sexual receptivity. Mares not displaying signs received 250 μg of cloprostenol intramuscularly (IM) and were teased again 3-4 days later. On the day that estrous behavior was observed (Day 0), mares were randomly divided into two groups: oxytocin (n = 11): oxytocin (60 IU, IM) was administered once daily from Day 8-17; control (n = 12): did not receive treatment. Blood was collected from all mares every 4 days throughout Day 17, and every 7 days thereafter until Day 45. Serum progesterone concentrations >1.0 ng/mL were indicative of a functioning corpus luteum. Interestrus interval was defined as the period between Day 0 and the day when progesterone next reached <1.0 ng/mL. The average interestrus interval was higher for treated mares compared with control mares (32.4 ± 4.2 vs. 21.8 ± 1.5 days, respectively, P = .01). In the oxytocin group, the interestrus interval was longer than 31 days in 6 of 11 (54.5%) mares and up to 45 days in 5 of 11 mares (45.5%). We conclude that luteal maintenance beyond 30 days was attained by once-daily oxytocin administration beginning 8 days following behavioral estrus in a majority of mares.

A study was conducted to determine the timing of ovulation relative to the onset of oestrus and the preovulatory LH surge in fallow deer. Mature fallow does were randomly allocated to two treatments (N = 10 per treatment) designed to synchronize oestrus on or about 17 May. Does assigned to Group 1 (prostaglandin-induced oestrus) each initially received single intravaginal CIDR [Controlled Internal Drug Release] devices for 13 days followed by an i.m. injection of 750 mg cloprostenol on Day 12 (15 May) of the subsequent luteal cycle. Does assigned to Group 2 (progesterone-induced oestrus) each received CIDR devices for 13 days, with withdrawal occurring on 15 May. All does were run with crayon-harnessed bucks (10:1 ratio) from the start of synchronization (18:00 h 15 May). Ten does (5 per group) were blood sampled via indwelling jugular cannulae every 2 h for 72 h from cloprostenol injection or CIDR device withdrawal and the plasma was analysed for concentrations of progesterone and LH by radioimmunoassay. Does within each treatment were randomly allocated to an ovarian examination time of 12, 16, 20 or 24 h after the onset of oestrus. Laparoscopy was repeated at 12-h intervals until ovulation was recorded. The ovaries of does failing to exhibit oestrus were examined 72 and 86 h after cloprostenol injection or CIDR device withdrawal. A total of 17 does were observed to exhibit oestrus at a mean (+/- s.e.m.) interval from treatment of 44.6 +/- 3.6 h for Group 1 (N = 9) and 34.1 +/- 2.5 h for Group 2 (N = 8).(ABSTRACT TRUNCATED AT 250 WORDS)

OBJECTIVE

The objective of this study was to compare reproductive performance parameters for two protocols for estrus synchronization in dairy heifers in Germany.

METHODS

In the CIDR group (n=93) all heifers received a controlled intravaginal progesterone releasing insert (Eazi-Breed™ CIDR®; Pfizer Pharma GmbH; containing 1,38g of progesterone) on day 0. On day 7 these cows were given prostaglandin F2α (PGF2α) analogue cloprostenol (Estrumate®, Intervet Deutschland GmbH, 0.5mg per animal i.m.), and the CIDR® insert was removed. Any mucus attached to the insert was scored on a 4-point scale: 0=no mucus; 1=clear; 2=bloody; 3=yellow/cloudy mucus. In the PG group (n=98) all heifers were given PGF2α analogue cloprostenol on day 7. Between day 8 and 11 heat detection was conducted twice daily for 30 minutes. All heifers in estrus were bred by artificial insemination (AI) and pregnancy was diagnosed 40 days after AI by transrectal palpation.

RESULTS

In the CIDR group the 4-day-service rate was 91.4%, in the PG group 70.4% (p<0.05). More heifers in the CIDR group were pregnant than in the PGF2α protocol (76.3 vs. 56.1%,p<0.05). Mucus scores of 2 and 3 indicative of vaginal irritation were observed in 91.9% of the CIDR group but did not affect the pregnancy outcome (OR = 0.652, CI95 =0.235-1.810; p=0.411).

CONCLUSIONS

In conclusion, the CIDR protocol improved reproductive parameters of dairy heifers compared with a PGF2α protocol. Mucus after removal of the CIDR® insert did not affect pregnancy rates.

Fifty Holstein heifers were each superovulated three times with FSH-P. At 60 h after the first injection of FSH-P, the animals received either prostaglandin F(2alpha), cloprostenol or fenprostalene in random order. A significant decrease in serum progesterone and a significant increase in serum estradiol-17beta were observed within 24 h of prostaglandin injection, but there were no significant differences among the three treatments. Neither were there any significant differences among the treatments with respect to the frequency of nonresponse to FSH-P treatment, nor the total number of ova/embryos collected between Days 6 and 8 of gestation.

The study evaluates the effect of three hormonal protocols on ovarian dynamics and progesterone (P4) secretion of buffalo (Bubalus bubalis). Twenty-nine pluriparous Murrah buffaloes were used. The protocols were as follows: OVSYNCH (n = 10): 100 μg of gonadorelin (day 0), 500 μg of cloprostenol (day 7), and 100 μg of gonadorelin (day 9). CIDR+EB (intravaginal device (CIDR®) + estradiol benzoate; n = 10): CIDR plus 2 mg of EB (day 0), withdrew of CIDR, 500 μg of cloprostenol (day 7) and 1 mg of EB (day 8). CIDR+eCG (n = 9): CIDR plus 2 mg of EB (day 0), withdrew of CIDR, 500 μg of cloprostenol and 400 IU of eCG (day 7). Follicles were counted with an ultrasound and measured at 0, 24, and 54 h. The maximum follicle diameter and ovulation were evaluated at 70, 80, and 94 h after CIDR withdrew. Estrous was detected per 1 h three times daily. Blood samples were collected on days 0, 7, 10, 15, and 22 to determine P4 concentration. In CIDR+EB protocol, 50% of buffaloes presented estrous, at 69.6 h. All buffaloes ovulated. CIDR+eCG group had the shortest (69 h) ovulation time. No treatment differences for follicular population, maximum follicle diameter, and P4 concentration on days 7 and 10 (P > 0.05) were found. The P4 concentration in OVSYNCH and CIDR+eCG protocols were > 1 ng/ml, on days 15 and 22 (P < 0.05). There was no difference in ovarian activity; however, the P4 secretion was normal in the OVSYNCH and CIDR+eCG protocols compared to the CIDR+EB protocol.

Keywords: Estrous; Follicular population; Maximum follicle diameter; Ovulation; Progesterone.

In 1990 three experiments were performed in heifers 184 to 505 day-old with the weight 190 to 390 kg to test some biotechnical methods while studying the level of reproduction functions. Heifers were examined in 4 to 24-hour intervals by direct observations of animal behaviour, by clinical and gynaecological examinations of larger animals. The progesterone concentration in the peripheral blood was determined by the RIA method and simultaneously with the blood samplings, the values of impedance of vaginal mucosa were measured by means of several types of the Estral device (CSFR) for cattle. To detect the functional responses to prostaglandins administered, the following forms of substances were used: racemic mixture of optically active forms D (+) and L (-) in the Czechoslovak preparation Oestrophan inj. Spofa (0.25 mg of cloprostenol in 1 ml of solution) and the dextrorotatory D isomer--cloprostenol (0.075 mg in 1 ml of solution) in the Czechoslovak preparation Remophan inj. Spofa. Evaluating the results of the group 1 based on clinical and ethological examinations, the values of impedance of vaginal mucosa and progesterone levels (Tab. I), the functional maturity of sexual organs in heifers were determined. No significant differences were found while compared the luteolytic effects between D-cloprostenol in the Remophan preparation and the conventional mixture of optically active forms of Oestrophan. All methods used confirm the functional maturity of sexual organs (including a response to prostaglandin analogues administered) in heifers 11-12 month old. The values of impedance of vaginal mucosa varied during oestrus in some heifers and this fact is to be taken into account in practice.(ABSTRACT TRUNCATED AT 250 WORDS)

Groups of five pregnant bitches were treated to terminate the pregnancy with four combinations of drugs, starting 28 days after the estimated surge of luteinising hormone (LH), 22 to 28 days after the first mating. The treatments were: cabergoline administered orally for 10 days at a dose of 5 micrograms/kg and a single subcutaneous injection of 2.5 micrograms/kg cloprostenol at the start of the treatment; the same dose of cabergoline plus two doses of 1 microgram/kg cloprostenol administered on days 28 and 32 after the LH surge; bromocryptine administered orally at a dose of 30 micrograms/kg three times a day for 10 days plus a single dose of 2.5 micrograms/kg cloprostenol; the same dose of bromocryptine plus two doses of 1 microgram/kg cloprostenol; and a group of five pregnant bitches was left untreated. The pregnancies were terminated in all but one of the treated bitches, in each case by resorption of the fetuses. There were few side effects in the bitches treated with two doses of 1 microgram/kg cloprostenol, and were present but acceptable in those treated with one dose of 2.5 micrograms/kg. Plasma progesterone concentrations decreased to less than 1 ng/ml within 72 hours of the start of treatment and remained low except in the bitch in which pregnancy was not terminated. In the five untreated bitches, plasma progesterone remained high and they whelped normally. In the treated groups, the intervals between successive displays of oestrus were reduced by approximately 70 days in comparison with previous cycles or with the control group, but the fertility of the dogs was not affected adversely.

The study comprise seven cows which were injected i.m. with 500 microgram of a synthetic prostaglandin analogue (cloprostenol) at different stages of their estrous cycles. Peripheral blood plasma levels of progesterone and the main blood plasma metabolite of prostaglandin F2 alpha, 15-keto-13,14-dihydroprostaglandin F2 alpha were determined. The injection of cloprostenol initiated luteolysis in all cases as evidenced by decreasing progesterone levels and occurrence of heat. In two animals injected on days 6 and 12, respectively, of the estrous cycle no release of endogenous prostaglandin F2 alpha was found. In animals injected on day 13 and 15 of their estrous cycles, respectively, a minor but sustained release of prostaglandin F2 alpha was found. In three animals injected on days 17, 17 and 19 of their estrous cycles, respectively, the endogenous release of prostaglandin F2 alpha had already started and no specific effect attributed to the injection of cloprostenol could be observed. It is concluded that the injection of cloprostenol initiates luteolysis with subsequent heat and ovulation. The release of endogenous prostaglandin F2 alpha occasionally seen in conjunction with the induced luteolysis is different and less pronounced as compared to the release seen during normal luteolysis in the cow.

The effect of a prostaglandin analogue (cloprostenol) for initiation of parturition in sows with prolonged gestation (greater than or equal to 117 days) has been studied. The length of the period from injection to farrowing varied from 15 to 48 hours in sows with plasma progesterone level higher than 10.0 nmol/l at treatment, being on average 25.7 hours. Litter size at birth and at time of weaning are presented.

In the horse, it is still unclear if and to what extent low progestin concentration contributes to early conceptus loss. In the present study, we have investigated if reduced or elevated progestin concentration in the early luteal phase influences endometrial function and conceptus development. We hypothesized that reduced progestin concentration via delayed downregulation of endometrial progesterone receptors (PR) influences endometrial function in healthy fertile mares while progestin substitution does not. Genitally healthy estrous mares (n = 8; age 4-14 years) were inseminated and treated with either altrenogest (0.044 mg/kg once daily orally) on days 5-10 after ovulation (ALT), cloprostenol (125 μg once daily intramuscularly) on days 0-3 after ovulation (CLO) or left untreated (CON). ALT and CLO treatment were chosen to increase and decrease total peripheral progestin concentration, respectively. Each treatment was given to every mare in consecutive cycles. On day 14 after ovulation, endometrial fluid was collected with a cotton roll inserted into the uterus and an endometrial biopsy for immunohistological demonstration of progesterone (PR) receptor distribution was collected. In endometrial fluid, free amino acid concentrations were analyzed by ion exchange liquid chromatography with an amino acid analyzer. Cell nuclei staining positive for the PR were determined in the luminal and glandular epithelium as well as in the stroma. Pregnancy rate tended to differ among treatments. The percentage of luminal epithelial cells staining positive for PR differed among treatments (p < 0.05) and was higher in CLO (84.1 ± 1.9%) than in ALT (70.7 ± 4.7%) and CON cycles (72.8 ± 4.1%). Concentrations of the amino acids isoleucine (CON 0.17 ± 0.03, CLO 0.14 ± 0.02, ALT 0.23 ± 0.04 μmol) and lysine (CON 0.27 ± 0.08, CLO 0.18 ± 0.05, ALT 0.44 ± 0.13 μmol) were influenced by treatment (p < 0.05) and lower in CLO than in ALT and CON cycles. In conclusion, impaired luteal function due to CLO treatment during the early luteal phase of pregnant mares delayed downregulation of progesterone receptors in the endometrial epithelium on day 14. This influenced endometrial function as reflected in lower concentrations of the amino acids lysine and isoleucine in endometrial secretions. Enhanced progestin concentration had less clear effects in healthy fertile mares.

During the previous decade several studies focused on postpartum treatment with prostaglandin for improvement of reproductive performance in sows. The aim of the study was to investigate the effect of administration of a prostaglandin F(2 alpha) (PGF(2 alpha)) analogue in sows within 24-48 h after farrowing on sow and litter performance. In five commercial farms, the sows were randomly assigned to either treatment A (2 ml cloprostenol, Planate) or treatment B (2 ml physiological saline solution, i.m.). Fifteen per cent of all sows were at random selected for progesterone analysis. Litter performance was assessed by measuring pre-weaning mortality and average daily weight gain (ADG). Sow performance was assessed by measuring weaning-to-oestrus interval (WOI), the percentage of sows returning to oestrus and litter size during subsequent farrowing. Administration of a PGF(2 alpha) analogue within 24-48 h postpartum had no effect on the rate of progesterone decline measured over 24 h compared with that of the controls. Litter performance and WOI were not affected by treatment. The subsequent litter size in sows of parity seven and more showed a significant difference of 1.98 piglets (p < 0.01) between both groups, to the benefit of the cloprostenol group. In conclusion, administration of a synthetic PGF(2 alpha) analogue, cloprostenol, within 24-48 h after farrowing improved litter size at next farrowing in older >>or=7 parity) sows.

Sixty-seven pregnant bitches were given atropine sulphate (0.025 mg kg-1), prifinium bromide (0.1 ml kg-1) and metopimazine (0.5 mg kg-1) and 15 min later 2.5 micrograms cloprostenol kg-1 s.c., three times at 48 h intervals (day 1, day 3, day 5). After one treatment, 53 of the 67 bitches had aborted, and after a second treatment, 62 of the 67 bitches had aborted. In 18 bitches, progesteronemia kinetics were followed-up: the first injection of cloprostenol resulted in a significant (P < 0.01) fall in progesteronemia. In 12 of the 18 bitches that had aborted following the first protocol, this rapid fall in progesterone was noteworthy as it decreased progesterone concentration on average from 17.07 +/- 8.20 ng ml-1 on day 1 to 1.31 +/- 0.34 ng ml-1 on day 3. The premedication administered 15 min before the injection of prostaglandins, prevented the appearance of side effects in 39 of the 67 bitches (58.2%).

Regular measurements of progesterone in milk were made to monitor ovarian activity in over 300 commercial dairy cows from partiurition until pregnancy established. Six animals (approximately 1-5 per cent) which had not previously been inseminated showed prolonged luteal activity lasting for over 30 days. No apparent uterine abnormalities or infections were found in these cases. Prostaglandin analogue cloprostenol (Estrumate ICI) given intramuscularly induced complete luteolysis in treated animals. The subsequent fertility varied, but at least three of the six cows conceived again.

This study characterizes the physiological and morphological changes related to partial luteolysis in bovine corpus luteum (CL) after challenges with sub-doses of cloprostenol sodium on Day 6 (D6) of the estrous cycle. Cows (n = 12/treatment) were treated as follows: Control (2 mL, saline, i.m.); 2XPGF (two treatments i.m. 500 μg of cloprostenol sodium 2 h apart) and 1/6PGF (83.3 μg of cloprostenol sodium, i.m., once). Plasma progesterone (P4) concentration, CL volume and blood flow were measured immediately before the treatments, then every 8 h (h) for 48 h. In the Control, P4 concentrations were higher at 48 h than at 0 h. P4 decreased 8h after 2XPGF treatment (P < 0.05), and remained low until the end of the trial. P4 decreased in 1/6PGF between 8 and 16 h (P < 0.05), then began to rebound at 24 h. Luteal volume was higher in Controls at 48 h than at 0 h. Under 1/6PGF, luteal volume decreased at 24 h (P < 0.05) and began to rebound at 32 h. Luteal volume and blood flow were reduced starting at 24 and 32 h, respectively, after 2XPGF treatment (P < 0.05). In this study, we were able to describe the partial luteolysis phenomenon, induced by a treatment of a D6CL with cloprostenol sub-dose.

To advance the understanding of early pregnancy and pregnancy failure in horses, this study determined how luteolysis induced by cloprostenol (an analogue of prostaglandin F2α) affects conceptus development. Mares were injected on Days 12, 14, 16 or 18 of pregnancy with either cloprostenol (treatment groups, total n=83 pregnancies) or saline (controls, n=81), and growth of the conceptuses was monitored and compared by daily ultrasonography until they were collected transcervically on Days 15-22, 1-4 days after the injections. The comparisons were extended in the recovered conceptuses by counting somites, measuring the volume and osmolality of yolk-sac fluid and its concentrations of proteins, estrone sulfate and progesterone, and by assessing the morphology of the capsule and vascular system. When luteolysis was initiated on or before Day 16, most pregnancies survived until the time of collection and the conceptuses in respective treated and control groups on Days 15-20 were very similar except for some effects of treatment on the capsule and vascular development. In contrast, after luteolysis was initiated on Day 18, abortion often ensued within 3 days and most conceptuses collected had degenerated, therein constituting a predictable system in which to study the pathogenesis of a particular cause of pregnancy failure.

The aims of this study were to study the effects of fasting on progesterone (P4) production in the pig and to verify whether fasting influences luteal expression of PGF(2alpha) receptor (FPr) and prostaglandin secretion. Superovulated prepubertal gilts were used; half of them were fasted for 72h starting on day 2 (F2) or 9 (F9) of the induced estrous cycle, respectively, while two groups (C2 and C9) served as respective controls. Plasma P4 and PGFM concentrations were determined by RIA while FPr mRNA expression in CLs collected at the end of fasting period was measured by real-time PCR. In experiment 1, plasma P4 concentrations in fasted gilts were significantly (P<0.01) higher than in controls starting from day 3 (F2; n=6) and 10 (F9; n=6). FPr mRNA expression was similar in F2 and C2 (n=6) CLs while it was significantly (P<0.05) higher in F9 than in C9 (n=6) CLs. In experiment 2, cloprostenol administered on day 12 significantly (P<0.05) increased FPr mRNA expression in CLs from both F9 (n=6) and C9 (n=6) gilts. At the time of cloprostenol injection PGFM levels were significantly higher (P<0.05) in the fasted group and cloprostenol-induced luteolysis in fasted but not in normally fed gilts. Results from this study indicate that fasting in prepubertal gilts induced to ovulate stimulates luteal P4 and PGFM production as well as FPr mRNA expression, thus increasing luteolytic susceptibility.

Cloprostenol was previously believed to be unable to release endogenous prostaglandin F2alpha (PGF2alpha) when administered during early bovine diestrus. A prostaglandin release is, however, seen in late diestrus. The aim of this study is to find out whether dexcloprostoenol (containing the only biologically active isomer, d-isomer, of cloprostenol) induces endogenous PGF2alpha release during early and late diestrus. Twelve heifers of the Finnish Ayrshire breed were allocated into two equal groups. Their estrous cycles were synchronized with dexcloprostenol. A further luteolysis was induced with 0.15 mg of dexcloprostenol either on Day 7 (group D7 or early diestrus) or on Day 14 (group D14 or late diestrus) after ovulation. Blood for progesterone and the PGF2alpha metabolite 15-ketodihydro-PGF2alpha determinations was collected immediately before dexcloprostenol treatment and thereafter every second hour for 48 h. Five of the six heifers in both groups showed significantly increased blood levels of 15-ketodihydro-PGF2alpha at some time during the 48-h experimental period. The intervals from treatment to the first significant increases of the PGF2alpha metabolite were 32.8+/-2.3 h (min. 30 h, max. 36 h) and 20.0+/-4.2 h (min. 14 h, max. 24 h) in groups D7 and D14, respectively (P < 0.01). We have concluded that dexcloprostenol induced endogenous PGF2alpha release in most cases, regardless the time of its administration (early or late diestrus). This release, however, differs from that observed during spontaneous luteolysis.

In this study, the effects of oxytocin and an analog of prostaglandin (cloprostenol) on the uterine involution and pregnancy rates were investigated. Mares received 3 ml of 0.9% NaCl in Group C (n=10), 30 IU/mare of oxytocin in Group O (n=10) and 250 microg/mare of cloprostenol in Group P (n=10) within 12h after parturition. The gravid uterine horn's cross-sectional diameter was measured by ultrasonography. The mean uterine diameters did not differ significantly between the treatment (O and P) and the control (C) groups (p>0.05). The difference between the postpartum ovulation periods (Group C: 12.6+/-0.72 days, Group O: 15+/-1.33 days, Group P: 14.6+/-1.11 days), the pregnancy rates at foal heat (Group C: 60%, Group O: 60%, Group P: 80%) and the embryonic death rates at foal heat (Group C: 33.3%, Group O: 16%, Group P: 25%) were not found to be statistically significant between the treatment and the control groups. The mean progesterone concentrations were similar in all groups and decreased continuously from parturition to until foal heat (Group C: from 2.43+/-0.24 to 0.66 ng/ml, Group O: from 3.07+/-0.6 to 0.27+/-0.27 ng/ml and Group P: from 2.8+/-0.44 to 0 ng/ml) (p>0.05). In conclusion, it was decided that the oxytocin and PGF2alpha treatments performed on the mares with the purpose of stimulating involution had no effect on the duration of parturition-first ovulation, the shrinkage of the uterus diameter, the pregnancy and embryonic death rates.