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PubMed1998

[Use of PGF2alpha and GnRH for estrus synchronization in cattle].

Estrus detection has a tremendous impact on the reproductive efficiency in dairy farms. Recently the systematic use of hormones for synchronization of estrus and ovulation has been propagated. These programs are designed to facilitate estrus detection and/or increase its efficiency. Prostaglandin programs are used to improve estrus detection and reproductive management in dairy operations. All cows are treated up to three times in weekly or biweekly intervals at the end of the voluntary waiting period. This should lead to groups of cows in estrus within two to four days after PG treatment. Since PG programs cannot completely eliminate the need for estrus detection procedures for fixed time artificial insemination (AI) were developed. Fixed time AI not only requires control of the luteal phase of the cow but also synchronization of the follicular development. Treatment with GnRH will induce a new follicular wave and provide a dominant follicle in a defined growth phase at the time of PG administration seven days later. A second injection of GnRH given 48 hours after PG results in ovulation approximately 24 to 32 hours after GnRH (OvSynch-procedure). The pros and cons of hormone programs in dairy farming are discussed in the light of field trials and experiments performed in our department.

Animals↗
PubMed1978

[Measurement of LH in urine by HI-gonavis test for the predetermination of ovulation (author's transl)].

The immunological LH/HCG test HI-Gonavis was used to measure the LH-excretion in urine of 30 patients during 1 to 3 cycles. The level of LH in plasma was determined simultaneously by radioimmunoassay. 12,5IU LH/L urine, the limit of sensitivity of HI-Gonavis, coincide with 7,2 mIU/ml plasma. 50 or 100 IU LH/L urine were found in patients showing a LH plasma level which was higher than 12,5 mIU/ml. In the ovulatory cycle this value is reached 1 day before the LH-peak. From the correlation of the preovulatory increase of LH in the plasma and the LH-excretion in the urine it can be concluded, that the detection of 50 IU LH/L urine indicates the ovulation within the next 12--30 hours. The practicability of this test for the predetermination of ovulation is demonstrated by examples.

Female↗
PubMed2005

Regression and resurgence of the CL following PGF2alpha treatment 3 days after ovulation in mares.

The present study was designed to characterize and compare the physiology and ultrasonographic morphology of the corpus luteum (CL) during regression and resurgence following a single dose of native prostaglandin F2alpha (PGF) given 3 days after ovulation, with a more conventional treatment given 10 days after ovulation. On the day of pre-treatment ovulation (Day 0), horse mares were randomly assigned to receive PGF (Lutalyse; 10 mg/mare, i.m.) on Day 3 (17 mares) or Day 10 (17 mares). Beginning on either Days 3 or 10, follicle and CL data and blood samples were collected daily until post-treatment ovulation. Functional and structural regression of the CL in response to PGF treatment were similar in both the Day 3 and 10 groups, as indicated by an abrupt decrease in circulating concentrations of progesterone, decrease in luteal gland diameter and increase in luteal tissue echogenicity. As a result, the mean +/- S.E.M. interovulatory interval was shorter (P < 0.0001) in the Day 3 group (13.2 +/- 0.9 days) than in the Day 10 group (19.2 +/- 0.7 days). Within the Day 3 group, functional resurgence of the CL was detected in 75% of the mares (12 of 16) beginning 3 days after PGF treatment, as indicated by transient major (6 mares) and minor (6 mares) increases (P < 0.05 and < 0.1, respectively) in progesterone. Correspondingly, mean length of the interovulatory interval was longer (P < 0.03) in mares with major resurgence (15.8 +/- 1.6 days) than in mares with minor (11.2 +/- 1.2 days) and no resurgences (13.5 +/- 0.3 days) in progesterone. Structural resurgence of the CL in the Day 3 group and functional and structural resurgence in the Day 10 group were not detected. In conclusion, PGF treatment 3 days after ovulation resulted in structural and functional regression of the CL and hastened the interval to the next ovulation, despite post-treatment resurgences in progesterone.

Animals↗
PubMed1991

Concentrations of arachidonate metabolites, steroids and histamine in preovulatory horse follicles after administration of human chorionic gonadotrophin and the effect of intrafollicular injection of indomethacin.

This study investigated the sequence of hormonal changes within the preovulatory follicles of mares. Mares were injected i.v. with 2500 IU human chorionic gonadotrophin (hCG) when a preovulatory follicle of 35 mm in diameter was detected. Fluid was aspirated from preovulatory follicles before (0 h), and 12, 24 and 36 h after administration of hCG. Concentrations of progesterone, prostaglandin (PG) E2, PGF, 6-keto-PGF1 alpha and thromboxane B2 in follicular fluid increased significantly (P less than 0.01) between 0 and 36 h. At 36 h, PGE2 was present in highest concentrations, followed by PGF and 6-keto-PGF1 alpha; thromboxane B2 was present at lower concentrations than other prostanoids. Concentrations of 13,14-dihydro-15-keto-PGF2 alpha increased significantly (P less than 0.05) between 24 and 36 h. Leukotriene B4, leukotriene C4 and histamine were present in follicular fluid at all sampling periods and did not change significantly over time. In another experiment, buffered saline or indomethacin (either 100 or 500 micrograms) was injected into preovulatory follicles on the day that they reached 35 mm in diameter to determine whether blocking intrafollicular PG synthesis would affect ovulation. The interval between intrafollicular injection and ultrasonographic detection of luteinization was significantly longer (P less than 0.05) in mares treated with 500 micrograms indomethacin. Plasma progesterone concentrations were significantly (P less than 0.05) lower in indomethacin-treated mares than in control mares on the first 5 days after injection. These results indicate that intrafollicular concentrations of PGs increase significantly before ovulation in mares and may be involved in the ovulatory process.

6-Ketoprostaglandin F1 alpha↗
PubMed1993

Antiovulatory doses of antagonists of LH-RH inhibit LH and progesterone but not FSH and estradiol release.

The differential regulation of immunoactive FSH and LH secretion by endogenous LH-RH was studied using LH-RH antagonists (Ac-D-Trp1,2, D-Cpa2, D-Lys6, D-Ala10LH-RH (MI-1544) and (Ac-D-Nal1, D-Phe(pCl2), D- Trp3, D-Cit6, D-Ala10LH-RH (SB-030) in ovariectomized (OVX) and regularly cycling rats. Single injections of 10 micrograms and 100 micrograms doses and long-term treatment with 10 micrograms doses of MI-1544 were used in OVX animals. Serum and pituitary LH and FSH, as well as serum estradiol and progesterone was determined by RIA during and/or after the treatment. Single injections of MI-1544 in OVX animals caused prompt (in 2 h) and long-lasting (for more than 24 h) suppression of the serum LH, while no or late decrease (after more than 6 h) of the serum FSH. Long-term treatment with the same analog decreased the serum LH (by 50%) and moderately increased the pituitary LH (by 21%) but did not change the serum and the pituitary FSH concentrations. In normal rats, long-term treatment with both of our analogs also resulted in divergent alterations in the LH and FSH concentrations. Serum LH dropped to undetectable levels,while serum FSH did not change significantly. Pituitary LH increased (by 31 to 41%), while FSH decreased (by 27 to 38%). Marked depression was found in the serum progesterone (by 64%) but no significant change in the serum estradiol levels, after the long-term treatment for 21 days. The ovarian cycles were interrupted, and no ovulation appeared during the treatment. Significant decrease was detectable in the weight of the ovaries (by 46%), whereas the weight of the uteri did not change or slightly elevated (by 22%), after the treatment with SB-030 or MI-1544, respectively.

Amino Acid Sequence↗
PubMed1993

Premature luteinization is not eliminated by pituitary desensitization with leuprolide acetate in women undergoing gonadotrophin stimulation who demonstrated premature luteinization in a prior gonadotrophin-only cycle.

A total of 40 women who demonstrated premature luteinization (serum progesterone > or = 3.5 nmol/l (1.1 ng/ml) on or before the day of human chorionic gonadotrophin (HCG) administration) during ovarian stimulation with human menopausal gonadotrophins (HMG) were restimulated in 46 subsequent cycles after pituitary desensitization with the gonadotrophin-releasing hormone agonist (GnRHa, 1 mg), leuprolide acetate. Five women were treated with a double dose of agonist (2 mg) when premature luteinization was determined on the single dose protocol. In HMG-only cycles, a frank luteinizing hormone (LH) surge was detected in 30 cycles; 15 cycles were cancelled because of premature ovulation. In agonist cycles there were no cancellations, although 25 cycles demonstrated premature luteinization and in six cycles a frank LH surge was detected. Doubling the dose of the agonist did not prevent premature luteinization. Agonist cycles with and without premature luteinization did not differ in any in-vitro fertilization (IVF) outcome parameters (ampoules of gonadotrophins, day of HCG administration, peak oestradiol concentration, number of oocytes retrieved, fertilized, transferred or cryopreserved). We conclude that in patients who demonstrate premature luteinization in a gonadotrophin-only cycle, pituitary desensitization may not completely eliminate subtle luteinization or a frank LH surge.

Chorionic Gonadotropin↗
PubMed2000

A tumor necrosis factor decoy receptor homologue is up-regulated in the brook trout (Salvelinus fontinalis) ovary at the completion of ovulation.

An up-regulated cDNA fragment was obtained from differential-display polymerase chain reaction of brook trout ovarian tissue stimulated by phorbol-12-myristate-13-acetate (PMA) and calcium ionophore A23187. Using this cDNA as a probe, a full-length cDNA of 2267 base pairs was obtained by screening a library of PMA/A23187-stimulated ovarian cDNA. The mRNA obtained presumably encodes for a 302-amino acid protein showing similarities with several members of the tumor necrosis factor (TNF) receptor superfamily. The protein contains several cysteine-rich domains characteristic of mammalian TNF receptor members and is most similar to human decoy receptor 3 and osteoprotegerin, two soluble decoy TNF receptors. Consequently, this TNF receptor homologue was tentatively named a trout decoy receptor (TDcR). On Northern blots of ovarian tissue, TDcR hybridized with a 2.2-kilobase transcript that was strongly up-regulated under phorbol ester stimulation. TDcR mRNA was localized in granulosa cells and was detected in the ovary during and after natural ovulation. Its expression was up-regulated at the end of ovulation and progressively down-regulated after 48 h postovulation. Among other trout tissues tested, the transcript was present only in the testis. To our knowledge this is the first description of a member of the TNF receptor family from a lower vertebrate and the first report of a decoy-like TNF receptor in the vertebrate ovary.

Amino Acid Sequence↗
PubMed2002

Molecular cloning and partial characterization of medaka fish stromelysin-3 and its restricted expression in the oocytes of small growing follicles of the ovary.

A cDNA clone (2755-bp) for stromelysin-3 was isolated by screening the cDNA library and by 3'- and 5'-rapid amplification of cDNA ends using ovary RNA of the medaka fish Oryzias latipes. The clone encodes a protein of 492 amino acids. Stromelysin-3 mRNA was detected only in the ovary. In situ hybridization analysis revealed that stromelysin-3 mRNA was localized in the oocyte cytoplasm of small growing follicles. RT-PCR analysis of total RNAs isolated from various-sized follicles and ovulated oocytes was conducted in order to determine the mRNA levels during oocyte growth. The stromelysin-3 mRNA level was the highest in the small follicles, and the mRNA levels decreased as the follicles grew. No significant stromelysin-3 mRNA was detected in the ovulated oocytes or immature ovaries. The fish stromelysin-3 cDNA was expressed in COS-1 cells in order to characterize the intracellular localization of the protein. A 56 kDa protein was synthesized and secreted into the culture medium. The secreted stromelysin-3 exhibited gelatin-degrading activity.

Amino Acid Sequence↗
PubMed2006

Do all regularly menstruating women ovulate in each cycle?

Women may experience anovular menstruation due to some pathophysiological causes which can be detected either by invasive histological examination as well as noninvasive serial ultrasound test. The women who are regularly menstruating without ovulation in each cycle were identified in this study. In a tertiary level infertility care centre of Bangladesh in Dhaka infertile population was the subject of the study. The serial ultrasound noninvasive procedure is used for diagnosis of anovular menstruation and found very much helpful.

Adult↗
PubMed2003

Expression of messenger RNA for prostaglandin E receptor subtypes EP4/EP2 and cyclooxygenase isozymes in mouse periovulatory follicles and oviducts during superovulation.

Prostaglandin (PG) E(2) is synthesized from arachidonic acid by cyclooxygenase (COX) and acts as a regulator in ovulation and fertilization reactions. We present the temporal and regional expression patterns of mRNAs for the two Gs-coupled PGE receptors, EP2 and EP4, and for COX-1 and COX-2 in mouse periovulatory follicles and oviducts during superovulation. Analysis using reverse transcription polymerase chain reaction revealed that the mouse ovaries express a significant amount of EP4 mRNA in addition to EP2 mRNA during superovulation. In situ hybridization results revealed that the signals for EP4 mRNA were localized mostly to oocytes in the preantral follicles. Three hours after hCG injection, the signals for EP4 and EP2 mRNA were present in both granulosa and cumulus cells. However, 9 h after hCG injection, just before ovulation, the signals for EP4 mRNA were still detectable in both cell types, whereas those for EP2 mRNA were found only in cumulus cells. COX-2 mRNA expression was present in both granulosa and cumulus cells at 3 h but was present only in cumulus cells at 9 h. COX-1 mRNA expression was not found in granulosa cells at 3 h but was found in these cells at 9 h. In the oviduct, the expression of EP4 and COX-1 mRNA was localized to epithelial cells, whereas expression of EP2 mRNA was localized to the smooth muscle layer. The tightly regulated expression of both EP2 and EP4 in the preovulatory follicles may reflect the essential role of PGE(2) in the ovulation process.

Animals↗
PubMed2004

Effect of bST and reproductive management on reproductive performance of Holstein dairy cows.

The objective was to determine the effects of bovine somatotropin (bST) and two artificial insemination (AI) protocols on reproductive performance of Holstein cows. Lactating cows (n = 840) were assigned at 37 d in milk (DIM) to one of four treatments in a 2 x 2 factorial arrangement. Treatments consisted of either bST (500 mg/14 d) starting at 63 +/- 3 DIM or no bST (control), with cows either submitted for timed AI following a synchronized ovulation (Ovsynch) protocol or assigned to receive AI based on estrus detection (ED). Two injections of PGF2, at 37 +/- 3 and 51 +/- 3 DIM were used to presynchronize estrous cycles. Cows then received an injection of GnRH at 63 +/- 3 DIM, followed 7.5 d later by PGF2. Cows assigned to ED treatments were inseminated after observed estrus during a 7-d period. Cows in Ovsynch treatments received a second GnRH injection 48 h after the last PGF2alpha and received timed AI 16 to 18 h later. Pregnancy was diagnosed by ultrasound at 31 d after AI and confirmed 14 d later. Frequency of anovulation (18.5%) at 63 DIM was similar across treatments, but proportions of anovulatory cows decreased quadratically as body condition at 70 DIM increased from 2.25 to 3.75. Estrus detection rate after PGF2alpha tended to be lower in multiparous cows receiving bST, and bST reduced returns to estrus in nonpregnant cows. Conception rates were higher in cows receiving AI after ED and bST improved conception rates to first AI in cyclic cows by reducing embryonic mortality. Pregnancy loss was similar for cows inseminated following ED or the Ovsynch protocol. There was a positive impact of bST on fertility of cyclic cows inseminated at fixed time or at detected estrus, but effective resynchronization protocols are needed to optimize reinsemination of non-pregnant bST-treated cows.

Abortion, Spontaneous↗
PubMed1994

The estrus detection problem: new concepts, technologies, and possibilities.

The single most important problem limiting high reproductive efficiency in the national dairy herd is poor detection of estrus. Failure to detect estrus or erroneous diagnosis of estrus results in an estimated annual loss of over $300 million to the dairy industry in the US. New technologies for the solution of this problem must be more effective than visual observation and aids currently used to detect estrus. Ideally, technologies that provide the solution for detection problems should provide the following: continuous (24 h/d) surveillance of the cow, accurate and automatic identification of cows in estrus, operation for the productive lifetime of the cow, minimized labor requirements, and high accuracy in identifying the appropriate physiologic or behavioral events that correlate highly with ovulation. New approaches are aimed at providing automation of detection of estrus using electronic technology. Pedometry, implantable impedance sensors, and surface-applied and implantable pressure sensors are in various stages of development and use.

Animals↗
PubMed2001

Effect of deslorelin acetate on gonadotropin secretion and ovarian follicle development in cycling mares.

OBJECTIVE: To evaluate gonadotropin secretion and ovarian function after administration of deslorelin acetate to induce ovulation in mares. DESIGN: Randomized controlled trial. ANIMALS: 16 healthy mares with normal estrous cycles. PROCEDURE: 8 control mares were allowed to ovulate spontaneously, whereas 8 study mares received deslorelin to induce ovulation when an ovarian follicle > 35 mm in diameter was detected. Follicle development and serum concentrations of gonadotropins were monitored daily during 1 estrous cycle. Pituitary responsiveness to administration of gonadotropin-releasing hormone (GnRH) was evaluated 10 days after initial ovulation. RESULTS: Interovulatory intervals of mares treated with deslorelin (mean +/- SD, 25.6 +/- 2.6 days) were longer than those of control mares (22.9 +/- 1.8 days). Diameter of the largest follicle was significantly smaller during 2 days of the diestrous period after ovulation in deslorelin-treated mares than in control mares. Concentrations of follicle-stimulating hormone (FSH) were lower in deslorelin-treated mares on days 5 through 14 than in control mares. Concentrations of luteinizing hormone were not different between groups during most of the cycle. Gonadotropin release in response to administration of GnRH was lower in mares treated with deslorelin acetate than in control mares. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of deslorelin was associated with reduction in circulating concentrations of FSH and gonadotropin response to administration of GnRH during the estrous cycle. Low concentration of FSH in treated mares may lead to delayed follicular development and an increased interovulatory interval.

Animals↗
PubMed2006

Gonadotropin-induced superovulation drives ovarian surface epithelia proliferation in CD1 mice.

The ovarian surface epithelium (OSE) is a monolayer of cells that surround the ovary and accommodate repeated tear and repair in response to ovulation. OSE cells are thought to be the progenitors of 90% of ovarian cancers. Currently, the total amount of proliferation of the OSE has not been reported in response to one ovulatory event. In this study, proliferation of the OSE was quantified in response to superovulation induced by ip injection of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) in immature 27-d-old CD1 mice using bromodeoxyuridine (BrdU). BrdU incorporation into the OSE cells was measured from the time of hCG injection for a total cumulative label of 12 h. BrdU incorporation was also measured from the time of PMSG injection for a total label of 60 h to correlate proliferation with specific gonadotropin stimulation. The OSE proliferation was significantly higher in superovulated animals compared with control mice at all time points. Proliferation was also analyzed in discrete anatomical sections and indicated that OSE covering antral follicles and corpora lutea proliferated more rapidly than OSE distal to follicular growth. Finally, apoptosis was assessed in response to ovulation, and virtually no cell death within the OSE was detected. These data demonstrate that the OSE, especially near antral follicles and corpora lutea, proliferates significantly in response to the gonadotropins PMSG and hCG. Therefore, ovarian surface cell division in response to ovulation could contribute to ovarian cancer by proliferation-induced DNA mutations and transformed cell progression.

Animals↗
PubMed2002

Efficacy of PGF(2alpha) to synchronize estrus in water buffalo cows (Bubalus bubalis) is dependent upon plasma progesterone concentration, corpus luteum size and ovarian follicular status before treatment.

This study was conducted to identify factors affecting PGF(2alpha) efficacy to synchronize estrus in water buffalo cows. After detection of a corpus luteum (CL) by rectal palpation, cows were treated (im) with dinoprost (12.5, 25 or 50mg) or D(+) cloprostenol (75, 150 or 300 microg) in a total of 66 treatments. Blood samples were collected 0, 24 and 48 h after treatment and ultrasound examinations and observations for estrus were performed daily to the day of ovulation or to 6 days after treatment. No PGF(2alpha) dose-response pattern was observed and overall rates of luteal regression (progesterone <1.0 ng/ml at 48 h), estrus, no detected behavioral estrus with ovulation occurring, and ovulation were 71.2, 36.4, 19.7 and 54.5%, respectively. To analyze plasma progesterone concentrations and ovarian dynamics, cows were divided in three groups according to their response to treatment. Cows that failed to have ovulations from a follicle after treatment (Group A, n = 30) had (P < 0.05) a lower plasma progesterone concentration (2.98 ng/ml) and smaller CL area (CLA; 187.3 mm(2)) before treatment as compared with cows that had an ovulation from a follicle (4.43 ng/ml and 223.7 mm(2), respectively; Groups B and C, n = 36). In cows that failed to ovulate, plasma progesterone concentration decreased in the first 24 h, but did not decline further and was >1.0 ng/ml 48 h after treatment. Moreover, no significant change in CLA after treatment was detected, indicating that treatment induced only partial luteolysis. In cows that ovulated, plasma progesterone concentration and CLA decreased continuously from treatment to ovulation (consistent with complete luteolysis). Threshold values of 2.8 ng/ml for plasma progesterone concentration and 189 mm(2) for CLA were identified as the best predictors of ovulation before treatment (83.3 and 80.6% sensitivity and 58.6 and 65.5% specificity, respectively, with positive and negative predictive values around 71%). When the origin of the ovulatory follicle was investigated, the interval from treatment to ovulation was shorter (91.9 versus 113.3 h; P < 0.05), and the ovulatory follicle had a slower growth rate (1.02 versus 1.55 mm per day; P < 0.005), a lesser increase in diameter from treatment to ovulation (4.7 versus 8.0 mm; P < 0.001), and a greater maximum diameter (13.2 versus 12.1 mm; P < 0.05) in cows that ovulated from the largest follicle present in the ovary before treatment (Group B, n = 27) compared with cows that ovulated from the second largest follicle present in the ovary before treatment (Group C, n = 9). In summary, the efficacy of PGF(2alpha) for causing luteolysis and synchronizing estrus and ovulation in buffalo cows was dependent upon plasma progesterone concentration, CL size and ovarian follicular status before treatment.

Animals↗
PubMed1983

Use of a heat detection paste on dairy cattle in France.

The aim of the present study was to evaluate the merits of a coloured paste applied to cows as an aid to heat detection in a dairy herd. It was performed on 110 French Friesian cows under a loose housing system over one year. For comparison, the results of the previous year, with no paste application, were also computed. Results of heat detection by the herdsman and by paste removal were compared to expected ovulations assessed by regular rectal palpation and, or, plasma or milk progesterone patterns. The paste system improved the percentages of oestrus detection of post partum and post inseminated cyclic cows by 26 and 22 per cent respectively, compared to the previous year. Overall missed heat incidence was 15 per cent and over estimation was negligible (less than 5 per cent). The mean durability period of the paste in the absence of mounting was 13 days. This suggests that to achieve the above mentioned results, application of paste should be performed at least every two weeks when no previous heat has been recorded, or only once, two weeks after service to check for non-pregnancy.

Animals↗
PubMed1988

Exit of inhibin-like bioactivity from gonadotropin-stimulated prepubertal pig ovaries.

Inhibin-like bioactivity (IBA) was assessed by bioassay in the follicular fluid, ovarian venous plasma, and peripheral plasma of immature gilts in which follicular development had been synchronized by administration of pregnant mare serum gonadotropin (PMSG) and hCG. IBA was detectable in the pooled follicular fluid of control animals, but the concentration as well as the total content increased markedly with the growth of the follicle induced by PMSG. About 36-72 h after PMSG treatment, IBA was found consistently in the venous plasma of both ovaries, although in controls as well as after ovulation (i.e. +48 h after hCG) IBA was not detected. The amount of IBA exiting the ovary by way of venous circulation was only a small fraction (less than 1%) of the total activity calculated to be in each ovary at a given time. IBA was undetectable in the peripheral plasma at any sampling time. On the basis of these results we could speculate that other routes of entry of inhibin into peripheral circulation may exist in the immature pig and/or that the predominant action of IBA might be within the follicle itself.

Animals↗
PubMed1998

Ultrasonic evaluation for the time of ovulation in ewes treated with norgestomet and norgestomet followed by pregnant mare's serum gonadotropin.

Progestogens and follicular stimulants have proved reasonably successful for estrus synchronization, but time of ovulation relative to removal of the progestogen is not clearly established. We monitored time of ovulation in ewes following synchronized estrus. Ovaries of 40 Dorset and Rambouillet x Dorset ewes were evaluated during the spring and fall (20/replicate). Ewes were randomly assigned to one of two treatment groups (n = 20/group): implant-only (I) ewes received a norgestomet implant for 10 d; and implant + PMSG (PI) ewes received a norgestomet implant for 10 d with an i.m. injection of 500 IU of PMSG at implant removal. Time of estrus onset was detected with the HeatWatch Estrus Detection System. Following the initiation of estrus, ovaries were monitored via rectal ultrasonography every 6 h to determine the interval from implant removal to ovulation (OVUL), and onset of estrus to ovulation (INT). Four I and PI ewes that lost implants before scheduled removal on d 10 were removed from the study. Estrus was detected in 13 of 16 (81%) I and 14 of 16 (88%) PI ewes within 108 h after implant removal. The interval from implant removal to estrus (EST), INT, and OVUL were not affected by replicate. The INT was not different in I (33.8 h) and PI (35.0 h) ewes. Mean OVUL was greater (P < .01) in I (79.8 h) than in PI ewes (68.6 h), and mean EST was also greater (P < .01) for I (46.0 h) than for PI ewes (32.6 h). The present data indicate that ovulation occurs on average 70 to 80 h after implant removal in ewes treated with norgestomet, and PMSG reduces the interval from implant removal to ovulation.

Animals↗