Ultrasonography and hormone profiles of persistent ovarian follicles (cysts) induced with low doses of progesterone in cattle

Reproduction ◽  
2000 ◽  
pp. 361-366 ◽  
Author(s):  
KM Noble ◽  
JE Tebble ◽  
D Harvey ◽  
H Dobson
Keyword(s):  
Ovarian Follicles ◽  
Oestrous Cycle ◽  
Blood Collection ◽  
Progesterone Concentration ◽  
Plasma Progesterone ◽  
Follicular Wave ◽  
Low Concentrations ◽  
Group 2 ◽  
Intravaginal Device ◽  
Group 1

The aims of this study were to expose dominant ovarian follicles at the end of the oestrous cycle to low progesterone concentrations similar to those that occur during stress, and to examine the effect of a subsequent small increase in progesterone 10 days later. Half a progesterone releasing intravaginal device (0.5 PRID) was administered to 13 heifers from day 15 of the oestrous cycle. In group 1 (n = 7), one 0.5 PRID remained in place until day 40 or until each heifer ovulated. In group 2 (n = 6), the first 0.5 PRID was removed on day 28, and replaced immediately with a second 0.5 PRID. Ultra-sonography and blood collection (10 ml) were conducted each day for 26 days from day 14 and then on alternate days. The largest follicle that emerged during the first 5 days after insertion of the initial 0.5 PRID remained > 10 mm in diameter for 15.3 +/- 1.7 and 11.6 +/- 0.4 days in groups 1 and 2, respectively. This period of dominance, during which no other follicles emerged, was closely correlated with the duration of plasma oestradiol concentrations exceeding 10 pg ml(-1). In four heifers from group 1, the persistent follicle ovulated between days 30 and 37 (sub-group 1a; 0.5 PRID expelled). In three heifers from sub-group 1b (0.5 PRID retained), the dominant follicle secreted oestradiol for 17 +/- 5 days but remained detectable by ultrasonography for a total of 33 +/- 8 days (range 26-52 days). Monitoring continued beyond day 40 in these animals. In group 2, the new 0.5 PRID inserted on day 28 resulted in an increase in plasma progesterone concentration of 0.9 +/- 0.3 ng ml(-1). Simultaneously, oestradiol decreased by 10.1 +/- 3.3 pg ml(-1), and a new follicular wave emerged 5-7 days later. In conclusion, exposure to very low concentrations of progesterone produced persistent follicles that secreted oestradiol for 17 days. This oestradiol production could be disrupted by a second increase of 0.9 ng ml(-1) in peripheral progesterone concentration. In the absence of the second progesterone treatment, some of the persistent follicles remained detectable by ultrasonography for up to 52 days, despite cessation of oestradiol secretion.

scholarly journals Effect of deslorelin on the induction of estrus in anestrous bitches

2010 ◽  
Vol 62 (3) ◽  
pp. 615-621 ◽  
Author(s):  
L.L. Lanna ◽  
A.P. Marques Jr. ◽  
R.H. Douglas
Keyword(s):  
Clinical Signs ◽  
Control Group ◽  
Progesterone Concentration ◽  
Plasma Progesterone ◽  
Clinical Evaluations ◽  
Injectable Formulation ◽  
Vaginal Cytology ◽  
Group 2 ◽  
And Control ◽  
Group 1

The efficacy of one or multiple doses of an injectable formulation of deslorelin (a GnRH agonist) was evaluated to induce estrus in anestrous bitches. Thirteen animals composed three groups: group 1 (n=5, single IM injection of 2mg deslorelin), group 2 (n=5, four IM injections of 2mg deslorelin in alternate days), and control group (n=3, four IM saline injections in alternate days). Daily clinical evaluations, sexual behavior, vaginal cytology, plasma progesterone concentration, ovaryhysterectomy and macroscopic evaluation of the uterus and ovaries were done. In group 1, none of the bitches showed signs of estrus, while two developed clinical signs and vaginal cytology of proestrus. In group 2, all animals presented proestrus, four presented estrus, and three ovulated; resulting in a functional corpus luteum and high progesterone concentration until day 25 of diestrus, when ovaryhysterectomy was performed. The duration of the stages of deslorelin induced cycles and the progesterone profile were similar to those described in the literature, and no side effects were observed. In conclusion, injectable formulation of deslorelin in multiple injections was effective to induce fertile estrus in anestrous bitches.

Effect of an inhibitor of 3β-hydroxysteroid dehydrogenase on progesterone concentrations and embryo survival in sheep

1987 ◽  
Vol 112 (2) ◽  
pp. 205-213 ◽  
Author(s):  
C. J. Ashworth ◽  
I. Wilmut ◽  
A. J. Springbett ◽  
R. Webb
Keyword(s):  
Luteal Phase ◽  
Hydroxysteroid Dehydrogenase ◽  
Oestrous Cycle ◽  
Silicone Elastomer ◽  
Progesterone Concentration ◽  
Embryo Survival ◽  
Progesterone Production ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

ABSTRACT The effect of an inhibitor of 3β-hydroxysteroid dehydrogenase on peripheral progesterone concentration during the luteal phase of the oestrous cycle and on embryo survival was determined in sheep. Following administration of 10, 50, 100 or 250 mg epostane (4,5-epoxy-17-hydroxy-4,17,dimethyl-3-oxo-androstane-2-carbonitrile) progesterone concentrations were significantly lower than control levels 4 h after injection, from 2·5 to 22 h, 1·5 to 24 h and 1 to 24 h after injection respectively. There appeared to be no effect on peripheral oestradiol concentrations. Adrenal progesterone production was small and not influenced by epostane treatment. Epostane was administered on day 9 of the oestrous cycle to cause a reduction in progesterone concentrations for approximately 12-18 h on day 9 only (group 1, 250 mg epostane on day 9), or a series of such reductions on 3 consecutive days (group 2, 50 mg epostane on days 9, 10 and 11) or a continuous reduction for 3 days (group 3, 250 mg epostane on days 9, 10 and 11). The proportion of ewes that were pregnant was significantly (P<0·05) lower in ewes treated to give a continuously low progesterone concentration for 3 days than in either controls or ewes in which progesterone concentration was reduced for less than 24 h (in controls and groups 1, 2 and 3 the proportion was 85, 92, 54 and 18% of ewes treated respectively). Embryo survival was not affected by administration of 250 mg epostane on days 9, 10 and 11 if luteal phase levels of progesterone were maintained by insertion of a silicone elastomer implant of the steroid. The proportion of embryos surviving was 72% in controls compared with 78% in the treated animals. J. Endocr. (1987) 112, 205–213

scholarly journals The ovulation rate, plasma progesterone and estradiol concentration, and litter size of a local ewe breed kept in a barn vs. those kept under an overhead shelter

2016 ◽  
Vol 59 (1) ◽  
pp. 145-150 ◽  
Author(s):  
Ewa Kuźnicka ◽  
Witold Rant ◽  
Aurelia Radzik-Rant ◽  
Małgorzata Kunowska-Slósarz ◽  
Marek Balcerak
Keyword(s):  
Litter Size ◽  
Negative Correlation ◽  
Reproductive Performance ◽  
Environmental Conditions ◽  
Corpora Lutea ◽  
Progesterone Concentration ◽  
Plasma Progesterone ◽  
Group 2 ◽  
Estradiol Concentration ◽  
Group 1

Abstract. A herd of sheep (40 heads) was divided into two equal groups: group 1 was kept under an overhead shelter and group 2 in a warm barn. The effect of maintenance on ewe's reproductive performance, corpora lutea and corpora lutea of pregnancy rate, as well as the concentration of plasma progesterone and estradiol in peripheral blood was investigated. At the first laparoscopy fewer corpora lutea than during the following one were observed (P ≤ 0.01). In sheep kept under the overhead shelter, a greater number of corpora lutea were noted. More corpora lutea of pregnancy were observed in group 1 than in the group from the barn. On the first day after mating the average level of progesterone was 190 pg mL−1, and after 2 weeks it increased to more than 300 pg mL−1 (P ≤ 0.01). The positive correlation between the number of corpora lutea of pregnancy and progesterone concentration (P ≤ 0.01) and the negative correlation (P ≤ 0.01) with number of corpora lutea of pregnancy, as well as between the litter size and estradiol concentration, were observed. Harsh environmental conditions did not cause a significant decrease of the reproduction performance of ewes kept under the overhead shed.

scholarly journals Expression Profiles of the Progesterone Receptor, Cyclooxygenase-2, Growth Differentiation Factor 9, and Bone Morphogenetic Protein 15 Transcripts in the Canine Oviducts during the Oestrous Cycle

Animals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 454
Author(s):  
Jaime Palomino ◽  
Javiera Flores ◽  
Georges Ramirez ◽  
Victor H. Parraguez ◽  
Monica De los Reyes
Keyword(s):  
Gene Expression ◽  
Bone Morphogenetic Protein ◽  
Cyclooxygenase 2 ◽  
Oestrous Cycle ◽  
Progesterone Concentration ◽  
Plasma Progesterone ◽  
Morphogenetic Protein ◽  
Growth Differentiation Factor 9 ◽  
Bone Morphogenetic Protein 15 ◽  
Cox 2

The gene expression in the canine oviduct, where oocyte maturation, fertilization, and early embryonic development occur, is still elusive. This study determined the oviductal expression of (PR), cyclooxygenase-2 (COX-2), growth differentiation factor 9 (GDF-9), and bone morphogenetic protein 15 (BMP-15) during the canine oestrous cycle. Samples were collected from bitches at anoestrus (9), proestrus (7), oestrus (8), and dioestrus (11), after routine ovariohysterectomy and the ovarian surface structures and plasma progesterone concentration evaluated the physiological status of each donor. The oviductal cells were isolated and pooled. Total RNA was isolated, and gene expression was assessed by qPCR followed by analysis using the t-test and ANOVA. The PR mRNA increased (P < 0.05) from the anoestrus to dioestrus with the plasma progesterone concentration (r = 0.8). COX-2 mRNA expression was low in the anoestrus and proestrus, and negligible in the oestrus, while it was around 10-fold higher (P < 0.05) in the dioestrus. The GDF-9 mRNA was expressed during all phases of the oestrous cycle and was most abundant (P < 0.05) during oestrus phase. The BMP-15 mRNA decreased (P < 0.05) in the anoestrus and proestrus phases. Thus, the transcripts were differentially expressed in a stage-dependent manner, suggesting the importance of oestrous cycle regulation for successful reproduction in dogs.

scholarly journals Pengaruh Monoklonal Antibodi Bovine Zona Pelusida 3 (bZP3) terhadap Diameter dan Atresia Folikel Ovarium Mencit (Mus musculus)

2018 ◽  
Vol 24 (1) ◽  
pp. 37
Author(s):  
Annisa Trissatharra ◽  
Sri Ratna Dwiningsih ◽  
Ratna Sofaria Munir
Keyword(s):  
Mus Musculus ◽  
Ovarian Follicles ◽  
Observation Time ◽  
Control Group ◽  
Control Group Design ◽  
Treatment Groups ◽  
Group 4 ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Objectives: To identify the effect of monoclonal antibody bZP3 at ovarian follicles that undergo atresia and diameter of various ovarian follicles.Materials and Methods: This is a true experimental research with post only control group design. Samples were 36 female mices (Mus musculus) which is divided into 6 groups, there are 3 control groups (group 1, 2, and 3) injected by Phospatase Buffer Saline (PBS) 50µl and 3 treatment groups (group 4, 5, and 6) injected by Mab bZP3 50µl. Group 1 and 4 terminated at 5th day, group 2 and 5 terminated at 10th day, and group 3 and 6 terminated at 20th day. Evaluation of atretic ovarian follicles and diameter of ovarian follicles performed by hematoxylin eosin (HE) and the data processed by parametric statistic.Results: There are no significant in different among groups in the aspect of atretic follicles and diameter of folicles (p>0.05), but descriptively, number of follicles undergo atresia of the follicle primary, secondary, and tertiary treatment group was higher than the control group, except on the 20th day of observation time.Conclusion: administration of Mab bZP3 had no effect to amount of atretic follicles and diameter of folicles during observation time.

Relationships between follicle-stimulating hormone, follicle growth and ovulation rate in sheep

1996 ◽  
Vol 8 (2) ◽  
pp. 279 ◽  
Author(s):  
RC Fry ◽  
MA Driancourt
Keyword(s):  
Follicle Stimulating Hormone ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Ovulation Rate ◽  
Follicle Growth ◽  
Group I ◽  
Group 3 ◽  
Group 2 ◽  
Group 1 ◽  
Stimulating Hormone

The changes in follicle-stimulating hormone (FSH) concentration required to affect follicle growth and ovulation rate within individual ewes were examined. Relationships between peripheral FSH concentrations during the late-luteal and follicular phase and subsequent ovulation rates were investigated in 22 ewes from 4 breeds over 3 successive cycles (Experiment 1). Ewes were grouped as follows: Group 1 (n = 6), ewes exhibiting the same ovulation rate at each oestrous cycle: Group 2 (n = 5), ewes with three different ovulation rates at each oestrous cycle; and Group 3 (n = 11), ewes with the same ovulation rate at two oestrous cycles and a different ovulation rate on one occasion. Data from ewes in Group 1 and 3 provided estimates on the variation in FSH concentrations between cycles which were not large enough to alter ovulation rate (range, 0-67% variation in FSH concentration). In Group-2 ewes, there was no consistent association between increases in ovulation rate and the proportional increases in FSH concentrations. Differences in FSH concentrations were often less than those that did not alter ovulation rate in Group-I ewes. Furthermore, only 3 of 11 Group-3 ewes demonstrated high FSH concentrations associated with high ovulation rate (or low FSH concentrations and low ovulation rate) when compared with the concentrations found at the two cycles in which ovulation rate was similar. Hence, there was little evidence that FSH concentrations during the late-luteal and follicular phase are associated with changes in ovulation rate within individual ewes. In Experiment 2, follicles of similar size obtained from the same ewe (FecBFec+ and Romanov) showed markedly different responses in vitro to graded doses of FSH as measured by aromatase activity. It is concluded that, within a ewe, the large variability between gonadotrophin-dependent follicles in their requirement for FSH prevented the expression of any thresholds of ovarian response to FSH.

404 SUPEROVULATORY RESPONSE IN BEEF DONORS TREATED DURING THE FIRST FOLLICULAR WAVE OR FOUR DAYS AFTER PROGESTERONE AND ESTRADIOL ADMINISTRATION

2010 ◽  
Vol 22 (1) ◽  
pp. 358 ◽  
Author(s):  
D. Carballo Guerrero ◽  
A. Tríbulo ◽  
R. Tríbulo ◽  
H. Tríbulo ◽  
G. A. Bó
Keyword(s):  
Estrous Cycle ◽  
Animal Health ◽  
Estradiol Benzoate ◽  
Control Group ◽  
Wave Groups ◽  
Follicular Wave ◽  
Estrus Detection ◽  
Group 3 ◽  
Group 2 ◽  
Group 1

Although we have previously shown that ovarian superstimulation during the first follicular wave resulted in a successful response (Carballo Guerrero D et al. 2009 Reprod. Fertil. 21, 242), the current protocol needs to be optimized in order to be used in the field. Therefore, an experiment was designed to simplify this treatment and to compare it with the traditional superstimulation protocol using progesterone and estradiol. Simmental cows (n = 14) were subjected to 3 superstimulation treatments (2 first wave groups and 1 control group) in a crossover design (i.e. all cows received the 3 treatments and all treatments were represented on each collection day). Cows in Group 1 received a progesterone-releasing device (Cue-Mate®, Bioniche Animal Health, Belleville, Ontario, Canada) along with 0.150 mg of D + cloprostenol (PGF; Bioprost-D®, Biotay, Buenos Aires, Argentina) at random stages of the estrous cycle. A second PGF was injected 5 days after Cue-Mate® insertion, followed by GnRH (0.050 mg of lecirelin; Biosin-OV®, Biotay) 36 h later (i.e. 7 days after Cue-Mate® insertion). Based on previous studies, ovulation was expected to occur 30 to 36 h later. Therefore, superstimulation treatments were initiated 36 h after GnRH (Day 0), with a total dose of 400 mg NIH-FSH-P1 of Folltropin®-V (Bioniche Animal Health) in twice-daily decreasing doses over 4 days. Prostaglandin was administered with the last 2 Folltropin®-V injections and Cue-Mate® devices were removed with the last Folltropin®-V injection. Cows received 12.5 mg of porcine LH (Lutropin®-V, Bioniche Animal Health) 24 h after Cue-Mate® removal and were AI 12 and 24 h later. Ova/embryos were collected 7 days after porcine LH and evaluated following IETS recommendations. Cows in Group 2 were treated similarly to those in the Group 1, except they did not receive the second PGF injection 5 days after Cue-Mate® insertion (thus eliminating the need to handle animals on that day). Finally, cows in Group 3 [estradiol benzoate (EB)+P4 control group] received a Cue-Mate® plus 2.5 mg of EB (Bioestradiol®, Biotay) and 50 mg of progesterone (P4; Lab., Rio de Janeiro, Argentina) at random stages of their estrous cycle. Superstimulation treatments were initiated 4 days later (Day 0) following the same protocol used in Group 1. Data were transformed to square root and analyzed by ANOVA. Mean (± SEM) numbers of ova/embryos collected, fertilized ova, and transferable embryos did not differ among groups (12.9 ± 2.0, 9.8 ± 1.7, and 6.6 ± 1.2; 11.5 ± 1.7, 9.3 ± 1.5, and 7.7 ± 1.6; and 14.5 ± 2.8, 9.4 ± 2.3, and 6.8 ± 1.7 for Groups 1, 2, and 3, respectively). In conclusion, data demonstrated that superstimulation during the first follicular wave can be successfully used in groups of randomly cycling donors without the need for estrus detection or estradiol to synchronize follicular wave emergence. The protocol is easy to follow and embryo production is comparable to that of the estradiol and progesterone protocol.

351 A COMPARISON OF 2 APPROACHES FOR THE USE OF GnRH TO SYNCHRONIZE FOLLICLE WAVE EMERGENCE FOR SUPEROVULATION

2015 ◽  
Vol 27 (1) ◽  
pp. 263 ◽  
Author(s):  
R. H. Hinshaw ◽  
M. L. Switzer ◽  
R. J. Mapletoft ◽  
G. A. Bó
Keyword(s):  
Mixed Models ◽  
Animal Health ◽  
Treatment Protocol ◽  
Prostaglandin F2α ◽  
Random Variable ◽  
Crossover Design ◽  
Dominant Follicle ◽  
Follicular Wave ◽  
Group 2 ◽  
Group 1

Although oestradiol has been used successfully to synchronize follicle wave emergence for superovulation, it cannot be used in many countries. Attention has turned to alternatives, including the use of GnRH to induce ovulation of a dominant follicle, which will be followed by emergence of a new follicular wave in 1 to 2 days. However, GnRH synchronizes follicular wave emergence only when it induces ovulation and administration of GnRH at random stages of the oestrous cycle results in ovulation in less than 60% of animals. The objective of the study was to compare superovulatory response and ova/embryo production following synchronization of follicle wave emergence for superovulation with GnRH administered 2 days after insertion of a progestin device, with a protocol in which GnRH is administered 7 days after administration of prostaglandin F2α and a progestin device. Beef donors of various breeds were placed at random into 1 of 2 groups and superstimulated by replicate so that one cow in each group had ova/embryos collected on the same day. Sixty-six superstimulations were performed in this study; 26 were performed in 13 donors that were superstimulated twice in a crossover design, and 40 donors were superstimulated once (i.e. 20 donors in each treatment group). Cows in group 1 received CIDR devices (Zoetis Animal Health, USA) on Day –2 and 100 μg of GnRH (Cystorelin, Merial USA) on Day 0; FSH treatments were initiated on Day 2 with 288 mg of Folltropin-V (Vetoquinol, Canada) given in twice-daily decreasing doses for 4 days. Prostaglandin F2α (PGF; 35 mg dinoprost, Lutalyse, Zoetis) was given with the last 2 injections of Folltropin-V and CIDR were removed with the last Folltropin-V administration (i.e. Day 6). Donors received a second GnRH at the onset of oestrus and were AI 8 and 20 h later. Donors that were still in standing oestrus at the second AI were AI again at 30 h. Ova/embryo collections were done on Day 14 and embryos were classified according to the IETS manual. Cows in group 2 received an injection of PGF and a CIDR on Day –7 and 100 μg of GnRH on Day 0; FSH treatments were initiated on Day 2 and the remainder of the treatment protocol was as in group 1. Data (total ova/embryos collected and transferable embryos) were analysed by ANOVA for mixed models, using treatment as a fixed variable and cow (i.d.) as a random variable. The group 1 cows produced a mean (± s.e.m.) of 18.6 ± 1.9 total ova/embryos of which 12.7 ± 1.5 were of transferable quality (7.2 ± 1.3 grade 1). Cows in group 2 produced a mean (± s.e.m.) of 19.5 ± 1.7 total ova/embryos, of which 14.8 ± 1.5 were of transferable quality (8.9 ± 1.2 grade 1). Although 2 more transferable embryos were obtained in group 2, differences were not significant (P > 0.3). At the same time as this experiment was done, 214 other cows were superstimulated in this practice, yielding an average of 7.9 transferable embryos per donor. Results suggest that both approaches are efficacious for the superstimulation of beef cows.Special thanks to Vetoquinol/Bioniche Animal Health, USA for support.

72 EFFECT OF PROGESTERONE SUPPLEMENTATION ON DAY 4 AFTER TIMED ARTIFICIAL INSEMINATION ON PREGNANCY RATE OF LACTATING DAIRY COWS

2017 ◽  
Vol 29 (1) ◽  
pp. 143
Author(s):  
G. Tortorelli ◽  
A. J. Azrak ◽  
V. da Costa Andrade ◽  
R. dos Santos Ramos ◽  
A. S. Moraes ◽  
...  
Keyword(s):  
Dairy Cows ◽  
Pregnancy Rate ◽  
Fixed Time ◽  
Lactating Dairy Cows ◽  
Embryonic Loss ◽  
Progesterone Supplementation ◽  
Group 2 ◽  
Intravaginal Device ◽  
One Way Anova ◽  
Group 1

Progesterone plays an important role in the maintenance of pregnancy. It is hypothesised that insufficient progesterone early in pregnancy may result in embryonic loss, and that supplemental progesterone would decrease pregnancy loss in dairy cows. The aim of this study was to compare the effect of progesterone supplementation after timed AI on pregnancy rate of dairy cows. The experiment was conducted in a single commercial herd, in Sao Paulo State (Brazil), during a period of 1 year (January–December 2016). The cows were assigned at a nonpregnancy diagnosis 32 ± 3 days after AI to 1 to 6 resynchronization treatments. They were submitted to the same fixed time AI protocol: Day 0, 0.1 mg of gonadorelin, 2 mg of oestradiol benzoate, and an intravaginal device of 1.9 g of progesterone; Day 7, 25 mg of dinoprost tromethamine; Day 8, 25 mg of dinoprost tromethamine, 1 mg of oestradiol cipionate, and device withdrawal; Day 10, AI. At Day 14, the cows were alternately arranged in 2 groups. Group 1 received a 900-mg progesterone supplementation IM injection, and Group 2 did not receive progesterone supplementation. Then, 32 ± 3 days after insemination, pregnancy diagnosis was performed by transrectal ultrasonography, and the data were tabulated. Full statistical analysis will be done at the end of the study, when more than 500 cows will be allocated to the 2 groups. From January until April 2016, 230 lactating dairy cows were submitted to the experiment. Both groups had similar average days in lactation (166), average number of lactations (1.95), and average number of inseminations (4.3). Group 1 had a pregnancy rate of 25% (29/116), and group 2 had a pregnancy rate of 15.8% (18/114) (P = 0.01, one-way ANOVA). Based on these preliminary data, pregnancy rates of lactating dairy cows may be improved with progesterone supplementation on Day 4 after insemination. These results need to be confirmed on larger numbers of cows.

Induction of ovulation with GnRH or oestradiol benzoate lowers plasma progesterone concentration within the first week of ovulation in non-lactating Holstein cows

2003 ◽  
Vol 2003 ◽  
pp. 1-1
Author(s):  
B.V.E. Segwagwe ◽  
K.L. Macmillan ◽  
P.D. Mansell
Keyword(s):  
Comparative Study ◽  
Corpus Luteum ◽  
Holstein Cows ◽  
New Wave ◽  
Progesterone Concentration ◽  
Plasma Progesterone ◽  
Induction Of Ovulation ◽  
Follicular Wave ◽  
Oestradiol Benzoate

Oestrous synchronisation involves synchronisation of ovarian follicular turnover, new wave emergence, and finally induction of ovulation which can be achieved with an injection of either GnRH (Pursley et al. 1997)or oestradiol benzoate (ODB) (Day et al. 2000). A comparative study investigating corpus luteum (CL) and follicular emergence after the administration of either GnRH or ODB at pro-oestrus has not been reported. It was hypothesised that the injection of ODB at pro-oestrus would delay emergence of the first post-ovulatory follicular wave, but that CL development and plasma progesterone concentrations would be similar in cows induced to ovulate with either GnRH or ODB.

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