Synchronization of follicular wave emergence in the seasonally anestrous ewe: the effects of estradiol with or without medroxyprogesterone acetate

Fertility is often lower in anestrous compared to cyclic ewes, after conventional estrus synchronization. We hypothesized that synchronization of ovarian follicular waves and ovulation could improve fertility at controlled breeding in anestrous ewes. Estradiol-17beta synchronizes follicular waves in cattle. The objectives of the present experiments were to study the effect of an estradiol injection, with or without a 12-d medroxyprogesterone acetate (MAP) sponge treatment, on synchronization of follicular waves and ovulation in anestrous ewes. Twenty ewes received sesame oil (n=8) or estradiol-17beta (350 microg; n=12). Eleven ewes received MAP sponges for 12d and were treated with oil (n=5) or estradiol-17beta (n=6) 6d before sponge removal. Saline (n=6) or eCG (n=6) was subsequently given to separate groups of ewes at sponge removal in the MAP/estradiol-17beta protocol. Estradiol treatment alone produced a peak in serum FSH concentrations (4.73+/-0.53 vs. 2.36+/-0.39 ng/mL for treatment vs. control; mean+/-S.E.M.) after a short-lived (6 h) suppression. Six of twelve ewes given estradiol missed a follicular wave around the time of estradiol injection. Medroxyprogesterone acetate-treated ewes given estradiol had more prolonged suppression of serum FSH concentrations (6-18 h) and a delay in the induced FSH peak (32.3+/-3.3 vs. 17.5+/-0.5 h). Wave emergence was delayed (5.7+/-0.3 vs. 1.4+/-0.7d from the time of estradiol injection), synchronized, and occurred at a predictable time (5-7 vs. 0-4d) compared to ewes given MAP alone. All ewes given eCG ovulated 3-4d after injection; this predictable time of ovulation may be efficacious for AI and embryo transfer.     

Effect of eCG on the pregnancy rate of ewes transcervically inseminated with frozen-thawed semen outside the breeding season

An experiment was conducted to determine whether factors affecting pregnancy rate out-of-season are associated more with transcervical artificial insemination (T-AI) procedures or with the reproductive state of the ewe. Twenty Finncross ewes were treated with progesterone sponges, and at sponge removal (0 h) 10 ewes were treated with eCG. Blood samples were collected for LH and progesterone analyses, and follicular development was monitored using ultrasonography. Ewes were inseminated from 48 to 52 h with 200 million motile frozen-thawed spermatozoa. The incidence of estrus, LH surges and ovulation was greater (P < 0.01) and intervals to these responses were shorter (P < 0.01) in the eCG-treated ewes. The number of follicles > 5 mm was higher (P < 0.05) in eCG-treated than control ewes. Progesterone concentrations increased and remained elevated through Day 19 in 7 eCG-treated and in 1 control ewe, and these ewes were pregnant based upon ultrasonographic examination. The results demonstrate that the T-AI technique using frozen-thawed semen produces a relatively high (70%) pregnancy rate out-of-season. The pregnancy rate was found to reflect primarily the reproductive condition of the ewe.     

Relationships of changes in ultrasonographic image attributes to ovulatory and steroidogenic capacity of large antral follicles in sheep

Ovarian steroidogenesis and antral follicular development in ewes, following the treatment with medroxyprogesterone acetate (MAP) and equine chorionic gonadotrophin (eCG), are affected by the reproductive season. The objective of this study was to compare the ultrasonographic attributes of large antral follicles between cyclic (December) and seasonally anovular (June–July) ewes, after a 12-day treatment with MAP-soaked intravaginal sponges, with or without the administration of 500 IU of eCG at sponge removal, and to determine whether there is a correlation between the ultrasonographic attributes of the follicular wall and serum concentrations of oestradiol. Digital images of ovulatory follicles from cyclic ewes and eCG-treated anoestrous ewes (n = 34 follicles), and of anovulatory follicles attaining ≥5 mm in control anoestrous ewes (n = 8 follicles), were analysed using the spot and line techniques designed to determine the echotextural characteristics of the follicular antrum (central and peripheral), follicular wall and perifollicular ovarian stroma. The mean diameter of ovulatory follicles was greater (P < 0.001) in cyclic than anoestrous ewes, with or without the eCG treatment. The mean pixel heterogeneity (SD of numerical pixel values) of the follicular antrum (P < 0.05), as well as mean pixel intensity and heterogeneity of the peripheral antrum, follicular wall proper and perifollicular ovarian stroma (P < 0.05), were consistently greater in anoestrous than cyclic ewes at the time of sponge removal and 24 h after the treatment with MAP sponges or MAP/eCG. Mean oestradiol concentrations were greater (P < 0.05) in cyclic compared to anoestrous ewes in both MAP- and MAP/eCG-treated animals, from 1 to 2 days after sponge withdrawal. There was a moderate negative correlation (r² = 0.12, P < 0.05; Pearson's Product Moment and r² = 0.23, P < 0.05; ANCOVA) between mean pixel heterogeneity (standard deviation of mean pixel values) of the follicular wall proper (all follicles ≥5 mm in diameter) and serum concentrations of oestradiol after sponge withdrawal. Our results indicate that large antral follicles from cyclic and seasonally anovular ewes exhibit distinctive ultrasonographic characteristics. The differences in follicular echotexture appear to be related mainly to seasonal variations in ovarian follicular morphology and oestradiol production.     

A new approach to enhance reproductive performance in sheep using royal jelly in comparison with equine chorionic gonadotropin

The objective was to compare the effects of royal jelly (RJ) and eCG treatments on reproductive performance of ewes synchronized using intravaginal progesterone-releasing devices. Forty-two cycling Awassi ewes were treated intramuscularly (i.m.) with 15 mg PGF2alpha. On the following day, all ewes were administered with CIDR-G for 12 days and were randomly allocated to three (RJ, eCG and control) groups of 14 ewes each. Ewes in the RJ-treated group received daily i.m. treatments of 400mg RJ during the period of CIDR-treatment. Each ewe in the eCG-treated group received an i.m. treatment of 500 IU eCG at the time of CIDR-G removal (day 0) and no further treatment was given to ewes in the control group. Ewes were exposed to four fertile rams for 72 h, from the time of CIDR-G removal, and checked for breeding marks at 6-h intervals. Blood samples were collected from day -13 until day 0 and thereafter until day 19 for progesterone analysis. Royal jelly treatment resulted in a greater rate of decline and lower (P<0.02) progesterone concentrations between days -10 and 0 than eCG-treated and control ewes. Expression of estrus was similar among the three groups and intervals to onset of estrus were shorter (P<0.01) in RJ-treated (31.3h) and eCG-treated (29.8h) than control (41.3h) ewes. First-cycle pregnancy and lambing rates were greater (P<0.05) in RJ-treated (71.4 and 71.4%) and eCG-treated (85.7 and 78.6%) than in control (42.9 and 35.7%) ewes, respectively. Results demonstrate that the treatments of RJ and eCG in conjunction with CIDR-G were similarly effective in induction of estrus and improvement of pregnancy and lambing rates.     

Ovarian and endocrine responses to prostaglandin F2alpha (PGF2alpha) given at the expected time of the endogenous FSH peak at mid-cycle in ewes

In the ewe, a rise in circulating concentrations of FSH preceding follicular wave emergence begins in the presence of growing follicles from a previous wave. We hypothesized that prostaglandin F(2alpha) (PGF(2alpha)) given at the time of an endogenous FSH peak in cyclic ewes would result in synchronous ovulation of follicles from two consecutive waves, increasing ovulation rate. Twelve Western White Face (WWF) ewes received a single i.m. injection of PGF(2alpha) (15 mg/ewe) at the expected time of a peak in FSH secretion, from Days 9 to 12 after ovulation. The mean ovulation rate after PGF(2alpha) treatment (2.3+/-0.3) did not differ (P>0.05) from the pre-treatment ovulation rate (1.7+/-0.1). Five ewes ovulated follicles from follicular waves emerging before and after PGF(2alpha) injection (3.0+/-0.6 ovulations/ewe) and seven ewes ovulated follicles only from a wave(s) emerging before PGF(2alpha) treatment (2.0+/-0.3 ovulations/ewe; P>0.05). The mean interval from PGF(2alpha) to emergence of the next follicular wave (1.0+/-0.4 and 4.0+/-0.0 d, respectively; P<0.001) and the interval from PGF(2alpha) treatment to the next FSH peak (0 and 3.5+/-0.4d, respectively; P<0.05) differed between the two groups. Six ewes ovulated after the onset of behavioral estrus, with a mean ovulation rate of 1.7+/-0.2, and six ewes ovulated both before and after the onset of estrus (3.0+/-0.5 ovulations/ewe; P<0.05). None of the ovulations that occurred before estrus resulted in corpora lutea (CL) with a full life span. At 24h before ovulation, follicles ovulating before or after the onset of estrus differed in size (4.1+/-0.3 or 5.5+/-0.4mm, respectively; P<0.05) and had distinctive echotextural characteristics. In conclusion, the administration of PGF(2alpha) at the expected time of an FSH peak at mid-cycle in ewes may alter the endogenous rhythm of FSH secretion and was not consistently followed by ovulation of follicles from two follicular waves. In non-prolific WWF ewes, PGF(2alpha)-induced luteolysis disrupted the normal distribution of the source of ovulatory follicles and may be associated with untimely follicular rupture and luteal inadequacy.     

The control of follicular wave development for self-appointed embryo transfer programs in cattle.

Our expanding knowledge of the control of follicular wave dynamics during the bovine estrous cycle has resulted in renewed enthusiasm for the prospects of precisely controlling the follicular and luteal dynamics and finely controlling the time of ovulation. Follicular wave development can be controlled mechanically by ultrasound-guided follicle ablation or hormonally by treatments with GnRH or estradiol and progestogen/progesterone in combination. Treatment of cattle with GnRH in combination with prostaglandin F2 alpha (PGF) 7 d later and a second GnRH 48 h after PGF (known as Ovsynch) has resulted in acceptable pregnancy rates after fixed-time AI in lactating dairy cows and in recipients in which embryos were transferred without estrus detection. Alternatively, treatments with estradiol and progestogen/progesterone-releasing devices resulted in synchronous emergence of a new follicular wave and, when a second estradiol treatment was given 24 h after device removal, synchronous ovulation and high pregnancy rates to fixed-time AI. Self-appointed embryo transfer (without estrus detection) using estradiol and progesterone treatments have resulted in pregnancy rates comparable with those obtained with recipients transferred 7 d after estrus. Furthermore, estradiol and progesterone treatments combined with PGF and eCG (given 1 d after the expected time of wave emergence) have resulted in high rates of recipients selected for transfer (84.6%) and an overall pregnancy rate of 48.7% (recipients pregnant/recipients treated). Estradiol and progestogen/progesterone treatments have also been widely used for self-appointed superstimulation protocols with equivalent embryo production to that of donor cows superstimulated using the traditional approach beginning 8 to 12 d after estrus. In summary, exogenous control of luteal and follicular development facilitates the application of assisted reproductive technologies in cattle by offering the possibility of planning the superstimulation of donors and synchronization of recipients at a self-appointed time, without the necessity of estrus detection and without sacrificing results.     

Ovarian function in ewes at the onset of the breeding season

Transrectal ultrasonography of ovaries was performed each day, during the expected transition from anoestrus to the breeding season (mid-August to early October), in six Western white-faced cross-bred ewes, to record ovarian antral follicles > or = 3 mm in size and luteal structures. Jugular blood samples were collected daily for radioimmunoassay (RIA) of follicle-stimulating hormone (FSH), oestradiol and progesterone. The first ovulation of the breeding season was followed by the full-length oestrous cycle in all ewes studied. Prior to the ovulation, all ewes exhibited a distinct increase in circulating concentrations of progesterone, yet no corpora lutea (CL) were detected and luteinized unovulated follicles were detected in only three ewes. Secretion of FSH was not affected by the cessation of anoestrus and peaks of episodic FSH fluctuations were associated with the emergence of ovarian follicular waves (follicles growing from 3 to > or = 5 mm). During the 17 days prior to the first ovulation of the breeding season, there were no apparent changes in the pattern of emergence of follicular waves. Mean daily numbers of small antral follicles (not growing beyond 3 mm in diameter) declined (P < 0.05) after the first ovulation. The ovulation rate, maximal total and mean luteal volumes and maximal serum progesterone concentrations, but not mean diameters of ovulatory follicles, were ostensibly lower during the first oestrous cycle of the breeding season compared with the mid-breeding season of Western white-faced ewes. Oestradiol secretion by ovarian follicles appeared to be fully restored, compared with anoestrous ewes, but it was not synchronized with the growth of the largest antral follicles of waves until after the beginning of the first oestrous cycle. An increase in progesterone secretion preceding the first ovulation of the breeding season does not result, as previously suggested, from the ovulation of immature ovarian follicles and short-lived CL, but progesterone may be produced by luteinized unovulated follicles and/or interstitial tissue of unknown origin. This increase in serum concentrations of progesterone does not alter the pattern of follicular wave development, hence it seems to be important mainly for inducing oestrous behaviour, synchronizing it with the preovulatory surge of luteinizing hormone (LH), and preventing premature luteolysis during the ensuing luteal phase. Progesterone may also enhance ovarian follicular responsiveness to circulating gonadotropins through a local mechanism.     

Reproductive responses in ewes treated with eCG or increasing doses of royal jelly

This experiment was conducted to evaluate the effect of administering increasing doses of royal jelly (RJ) on reproductive parameters in ewes. Additionally, this study compared using RJ vs. equine chorionic gonadotropin (eCG) in estrous cycle control. In May (transitional period between anestrous and the breeding season) 37 multiparous, winter-lambing Awassi ewes 3-6 years of age (average body weight of 53+/-1.2 kg) were fitted with intravaginal flourogestone acetate-impregnated sponges (FGA, 40 mg) for 12 days. Ewes were randomly assigned into five treatment groups to receive no RJ (CON, n=7), 250 mg RJ/d (RJ250, n=8), 500 mg RJ/d (RJ500, n=8), 750 mg RJ/d (RJ750, n=7), or 600IU eCG (eCG, n=7). Royal jelly was administrated orally on daily basis when sponges were in place while eCG was administered on the day of sponge withdrawal (d 0). Behavioral estrus was checked using fertile Awassi rams at 6h intervals for 5 days beginning on d 1. Interval from d 0 to onset of estrus was shorter (P<0.05) in eCG than in CON and RJ250 groups. No differences in the onset of estrus were detected among the RJ-treated groups. The intervals from d 0 to first progesterone rise were shorter (P<0.05) in the eCG-treated compared with RJ-treated and control ewes (100+/-15.3, 138.4+/-14, 135.7+/-15, 155.6+/-15, 154.4+/-15.1h in eCG, CON, RJ250, RJ500, and RJ750, groups, respectively). The overall pregnancy rate from mating at induced estrus was 75.7% (28/37). Of these ewes, 23/37 (64.8%) lambed within 155 days following d 0. Lambing rate was higher (P<0.05) in the RJ500 group compared with controls. Lambing rate from mating at induced estrus was 2/7 (28.5%), 4/8 (50%), 8/8 (100%), 4/7 (57%), and 5/7 (71%) in CON, RJ250, RJ500, RJ750, and eCG groups, respectively. Results of the present study demonstrate that eCG but not RJ was effective in improving estrus expression in ewes during the transition between the non-breeding and breeding seasons. Royal jelly may be effective in improving pregnancy and lambing rates but further studies are required to confirm such findings.     

Dynamics of follicular growth and progesterone concentrations in cyclic and anestrous suckling Nelore cows (Bos indicus) treated with progesterone,equine chorionic gonadotropin,or temporary calf removal

The objective of this study was to investigate the effects of eCG and temporary calf removal (TCR) associated with progesterone (P4) treatment on the dynamics of follicular growth, CL size, and P4 concentrations in cyclic (n = 36) and anestrous (n = 30) Nelore cows. Cyclic (C) and anestrous (A) cows were divided into three groups. The control group received 2 mg of estradiol benzoate via intramuscular (IM) injection and an intravaginal device containing 1.9 g of P4 on Day 0. On Day 8, the device was removed, and the animals received 12.5 mg of dinoprost tromethamine IM. After 24 hours, the animals received 1 mg of estradiol benzoate IM. In the eCG group, cows received the same treatment described for the control group but also received 400 UI of eCG at the time of device removal. In the TCR group, calves were separated from the cows for 56 hours after device removal. Ultrasound exams were performed every 24 hours after device removal until the time of ovulation and 12 days after ovulation to measure the size of the CL. On the same day as the CL measurement, blood was collected to determine the plasma P4 level. Statistical analyses were performed with a significance level of P ≤ 0.05. In cyclic cows, the presence of the CL at the beginning of protocol resulted in a smaller follicle diameter at the time of device removal (7.4 ± 0.3 mm in cows with CL vs. 8.9 ± 0.4 mm in cows without CL; P = 0.03). All cows ovulated within 72 hours after device removal. Anestrous cows treated with eCG or TCR showed follicle diameter at fixed-timed artificial insemination (A-eCG 10.2 ± 0.3 and A-TCR 10.3 ± 0.5 mm) and follicular growth rate (A-eCG 1.5 ± 0.2 and A-TCR 1.3 ± 0.1 mm/day) similar to cyclic cows (C-eCG 11.0 ± 0.6 and C-TCR 12.0 ± 0.5 mm) and (C-eCG 1.4 ± 0.2 and C-TCR 1.6 ± 0.2 mm/day, respectively; P ≤ 0.05). Despite the similarities in CL size, the average P4 concentration was higher in the A-TCR (9.6 ± 1.4 ng/mL) than in the A-control (4.0 ± 1.0 ng/mL) and C-TCR (4.4 ± 1.0 ng/mL) groups (P < 0.05). From these results, we conclude that eCG treatment and TCR improved the fertility of anestrous cows by providing follicular growth rates and size of dominant follicles similar to cyclic cows. Additionally, TCR increases the plasma concentrations of P4 in anestrous cows.     

Fixed-time AI protocols replacing eCG with a single dose of FSH were less effective in stimulating follicular growth, ovulation, and fertility in suckled-anestrus Nelore beef cows

The aim of the present study was to evaluate the effects of a single treatment with FSH on diameter of the largest follicle and on conception rates of suckled Bos indicus beef cows submitted to timed artificial insemination (TAI). Four hundred fifty-six suckled anestrous Nelore beef cows at 30-60 days postpartum were assigned to treatments. At the first day of the estrous synchronization protocol (Day 0), all cows received a progesterone-releasing intravaginal device plus 2mg of estradiol benzoate. On Day 8, cows were assigned to blocks according to the diameter of the largest follicle and then allocated to one of three treatment groups (Control, FSH, or eCG) within each block. Simultaneously to progesterone device withdrawal on Day 8, cows in the eCG treatment group (n=150) received 300 IU of eCG and cows in FSH treatment group (n=153) received 10mg of FSH, and Control cows (n=153) did not receive any additional treatment. Additional treatments with 150 μg of cloprostenol and 1mg of estradiol cypionate (EC) were also administered concurrently to progesterone device removal in all cows on Day 8. Two days later (D10), TAI and ovarian ultrasonic examinations to evaluate follicle size were performed in all cows. On Day 12, a subset of cows (n=389) were submitted a second ultrasonic exam to confirm ovulation. Final follicular growth (mm/day) was less (P=0.006) in both Control (0.95±0.11) and in FSH-treated cows (0.90±0.10) than in eCG-treated cows (1.40±0.13). Interestingly, there was a treatment-by-BCS interaction in ovulation results (P=0.03), in which, eCG treatment increased percentage of cows having ovulations with a lesser BCS. Similarly, there was a treatment-by-BCS interaction for conception (P=0.04), where the eCG treatment increased fertility in cows with a lesser BCS. In conclusion, FSH failed to stimulate final follicular growth, ovulation, and conception rate in sucked-anestrous beef cows submitted to TAI as effectively as eCG. However, physiological effects of eCG seem to be more evident in cows with a lesser BCS.     

Effects of a gonadotropin-releasing hormone agonist on rat ovarian follicle apoptosis: regulation by epidermal growth factor and the expression of Bcl-2-related genes

The purpose of the present study was to evaluate the in vivo effect of the GnRH analogue leuprolide acetate (LA) on follicular development and apoptosis-related mechanisms in preovulatory ovarian follicles (POF) obtained from prepubertal eCG-treated rats. Serum progesterone and estradiol levels were measured, and a significant decrease in circulating estradiol levels was observed in the LA group, whereas serum progesterone levels remained unchanged. Ovarian histology revealed an inhibitory effect of LA treatment on the follicular development induced by eCG. After 48 h of LA treatment, the numbers of atretic and preantral follicles were increased as compared with controls, whereas the number of antral follicles had decreased. Cells undergoing DNA fragmentation were quantified by performing in situ 3' end labeling of DNA with digoxygenin-dUTP on ovarian sections. LA treatment caused an increase in the percentage of apoptotic cells in preantral and antral follicles. DNA isolated from these POF incubated 24 h in serum-free medium exhibited the typical apoptotic DNA degradation pattern. Treatment of follicles with epidermal growth factor (EGF) suppressed the spontaneous onset of DNA fragmentation, and a similar effect was observed in LA follicles. POF obtained from LA-treated rats showed no changes in Bcl-2 or Bax protein levels. However, a reduction in the Bcl-xL:Bcl-xS ratio was observed, with a greater decrease in Bcl-xL compared with Bcl-xS during the incubation, suggesting a lower stability of the Bcl-xL isoform in the LA group. These results indicate that in vivo GnRH agonist treatment produces an increase in the apoptosis process in POF from eCG-treated rats, and this effect is reversed in vitro by EGF. This GnRH analogue also reduced the stability of the Bcl-xL protein, thus interfering with follicular development by an as yet unknown mechanism.     

Ovarian response and pregnancy rate following different doses of eCG treatment in Chall ewes

The purpose of the study was to investigate the effects of different doses of equine chorionic gonadotropin (eCG) treatment on follicular development, ovulation and pregnancy rate during the breeding season in fat-tailed Chall ewes. Seventy-two cycling (62.5 ± 2.5 kg), multiparous Iranian Chall ewes were used in the trial. The ewes were randomly allocated to 6 groups (n = 12/group). Estrus was synchronized with the aid of controlled intravaginal drug release (CIDR) devices, inserted for 14 days. At the time of CIDR removal (day 14), the ewes received i.m. either 0 (control group, G0), 450 (G450), 550 (G550), 650 (G650), 750 (G750) or 850 (G850) IU eCG. Vasectomized rams were used to detect estrus in the ewes from 24 h after CIDR removal. Ovarian follicular activity was monitored with the aid of transrectal ultrasonography on the day of CIDR insertion (day 0) and daily from the day of eCG treatment (day 14), until estrus (day 16). During these days, blood samples were collected for the determination of plasma progesterone and estradiol concentrations. Laparoscopic intrauterine inseminations were conducted 54–60 h after CIDR removal. The number of CL's and pregnancy diagnosis was recorded using ultrasonography 7 and 54 days following AI, respectively. Half of ewes in control group and most of the ewes treated with eCG showed signs of estrus within 36 h of CIDR removal. The ewes in groups G750 and G850 recorded the highest number of large follicles at estrus and CL's 7 days later. The pregnancy rate in groups G550 (75.0%) and G650 (75.0%) was higher (P < 0.05) than that in the other groups. The ovarian response and estradiol concentration, as well as pregnancy rate showed that 550 or 650 IU eCG treatment is the most effective doses in improving the pregnancy rate in Iranian Chall ewes.     

Induction of estrus and superovulation in seasonally anestrous ewes

The induction of estrus in 17 previously cycling nulliparous ewes, 9 to 10 months of age, was attempted with Medroxyprogesterone acetate (MAP) pessaries during the early anestrous period (March-April). Ewes were verified to be anestrous by the lack of estrous behavior in the presence of a vasectomized ram and by a radioimmunoassay for serum progesterone in two samples taken 7 days apart showing less than 1 ng/ml serum progesterone. Superovulation was attempted with injections of either FSH or FSH + LH. MAP vaginal pessaries remained in place for a period of 12 days and FSH was administered to all ewes (IM) at 12 hr intervals over a 3 day period; 5 mg was injected twice on day 11 after pessary insertion, followed by 4 and 3 mg injections twice daily on each succeeding day, for a total of 24 mg per ewe. Nine ewes were given 25 mg LH (IV) within 8 hrs after the onset of behavioral estrus in addition to FSH. Ewes were hand-mated to several rams at 12 hr intervals throughout the estrus period. Ovulation and fertilization rates were recorded for each ewe following midline laparotomy and embryo collection. All ewes were in estrus between 36 and 48 hrs after removal of the MAP pessaries. In ewes injected with FSH only, 8 of 8 ovulated with a mean ovulation rate of 6.0 +/- 4.4 and a fertilization rate of 70%. Nine of 9 ewes receiving both FSH + LH ovulated with a mean ovulation rate of 13.9 +/- 13.1 and a fertilization rate of 72%. Statistical analysis by Students t-test resulted in differences in number of ova recovered (P<.05) between FSH only and FSH + LH treated ewes and a trend towards increased ovulation rate in FSH + LH treated ewes. These results show that early seasonally anestrous ewes can be successfully induced and synchronized for estrus with MAP pessaries and the number of ova recovered is increased with the inclusion of LH in the superovulation regime.     

Effects of a 6-day treatment with medroxyprogesterone acetate after prostaglandin F2 alpha-induced luteolysis at midcycle on antral follicular development and ovulation rate in nonprolific Western white-faced ewes

Medroxyprogesterone acetate (MAP) from intravaginal sponges prolongs the lifespan of large ovarian follicles when administered after prostaglandin F2alpha (PGF2alpha)-induced luteolysis early in the luteal phase of ewes. The present study was designed to determine whether a PGF2alpha/MAP treatment applied at midcycle would alter the pattern of antral follicle growth and increase ovulation rate in nonprolific ewes. A single injection of PGF2alpha (15 mg, i.m.) was given, and an intravaginal MAP (60 mg) sponge was inserted for 6 days, on approximately Day 8 after ovulation, in 7 (experiment 1), 8 (experiment 2) or 11 (experiment 3) ultrasonographically monitored, cycling Western white-faced ewes; seven ewes (experiment 1) served as untreated controls. Blood samples were collected each day and also every 12 min for 6 h, halfway through the period of treatment with MAP (experiment 1), or every 4 h, from 1 day before to 1 day after sponging (experiment 2). Seventeen of 26 treated ewes (experiment 1, n = 6; experiment 2, n = 5; experiment 3, n = 6) ovulated 1 to 6 days after PGF2alpha, but this did not affect the emergence of ensuing follicular waves (experiments 1 and 2). These ovulations, confirmed by laparotomy and histological examinations of the ovaries (experiment 3), were not preceded by an increase in LH/FSH secretion and did not result in corpora lutea, as evidenced by transrectal ultrasonography and RIA of serum progesterone (experiments 1 and 2). Following the removal of MAP sponges, the mean ovulation rate was 3.1 +/- 0.4 in treated ewes and 2.0 +/- 0.3 in control ewes (experiment 1; P < 0.05). In experiments 1 and 2, the ovulation rate after treatment (3.1 +/- 0.4 and 2.8 +/- 0.4) was also greater than the pretreatment rate (1.9 +/- 0.3 and 1.9 +/- 0.1, respectively). Ovulations of follicles from two consecutive waves before ovulation were seen in five treated but only in two control ewes (experiment 1), and in seven ewes in experiment 2. There were no significant differences between the MAP-treated and control ewes in mean daily serum concentrations of FSH and estradiol, and no differences in the parameters of LH/FSH secretion, based on frequent blood sampling. Treatment of nonprolific Western white-faced ewes with PGF2alpha and MAP at midcycle changed follicular dynamics and increased ovulation rate by approximately 50%. These effects of MAP, in the absence of luteal progesterone, may not be mediated by changes in gonadotropin secretion.     

Comparison of two progestogens during out-of-season breeding in a commercial ewe flock

A comparison was made of the relative effectiveness of subcutaneous ear implants containing 2 mg Norgestomet or vagnial pessaries containing 60 mg medroxyprogesterone acetate (MAP) to induce estrus and conception in dry anestrous ewes. Groups of ewes were treated with one of the two progestogens for 14 d, and 500 IU pregnant mare serum gonadotropin (PMSG) was administered intramuscularly at the time of progestogen withdrawal. No significant differences in estrus induction, pregnancy rate or number of lambs born per ewe lambing were observed. Ewes treated with Norgestomet had 96% estrus, 60% pregnancy rate and 1.4 lambs per ewe lambing. Comparably, ewes treated with MAP had 94% estrus, 65% pregnancy rate and 1.7 lambs per ewe lambing. Norgestomet implants compared favorably with MAP pessaries for estrus induction and breeding of commercial, dry anestrous ewes.     

Effects of repeated removal of large ovarian follicles and treatment with progestin on ovarian function in the ewe

Preovulatory follicles were removed from ewes during estrus to determine hormonal, ovarian and behavioral responses. In Experiment 1, new follicles were recruited and ovulated within 4 days, and a second estrous period was observed in most ewes. In Experiment 2, follicles were removed at Day 0 (estrus), Day 3.5 and Day 7.0 to determine responses to repeated follicular removal in the absence of a corpus luteum (CL). Ewes in two groups were given exogenous progestin at the time of first or second surgery. Each follicular removal was followed by a surge of follicle-stimulating hormone (FSH) and follicular growth, and in many cases, behavioral estrus and/or a surge of luteinizing hormone (LH) was detected around the time of the next follicular removal. Although not necessary for display of estrus, treatment with progestin during follicular maturation increased the number of ewes showing estrus. When the newly developing follicles were allowed to ovulate, resulting corpora lutea produced low levels of progesterone or had a short life span.     

Superovulatory response in anestrous ewes is affected by the presence of a large follicle

Superovulatory response to conventional treatment with eCG (1200 IU) and progestagen sponges (MAP, n = 9; FGA, n = 9; or controls without sponge, n = 6) was studied in Corriedale anestrous ewes. The follicular population just before the administration of eCG and the total ovarian response (large anovulatory follicles plus normal CL and prematurely regressing CL) to treatment were determined after laparotomy. Pretreatment with progestagen did not modify the number or class of follicles greater than 1 mm observed on the ovarian surface at the time of eCG administration (19 +/- 2.2 follicles vs 19 +/- 2.9 follicles, for pooled progestagen-treated groups and control groups, respectively; mean +/- SEM) but significantly decreased the number of large anovulatory follicles (4.7 +/- 1.0 vs 10.2 +/- 2.6; P < or = 0.01) observed following treatment. Progestagen-treated animals were classified according to the presence (n = 13) or absence (n = 5) of a large follicle (LF: > or = 4 mm diameter) on the ovarian surface at the time of eCG treatment; a qualitatively better superovulatory response was observed in ewes without large follicle (large anovulatory follicles: 1.6 +/- 0.7 vs 5.8 +/- 1.3, P < or = 0.05; normal CL: 7.0 +/- 1.4 vs 3.8 +/- 1.0, P < or = 0.1; normal CL/total ovarian response: 78.7 +/- 10.1 % vs 34.9 +/- 8.2 %, P < or = 0.01; for ewes without LF and ewes with 1 to 2 LF respectively). No differences were observed in the individual ovulatory response when comparing ovaries ipsilateral or contralateral to LF in a same animal, indicating that the effect of LF on the superovulatory response would be fundamentally systemic. This work shows that, similar to what occurs in cows, the presence of a large follicle at the time of gonadotropin administration decreases the superovulatory response in anestrous ewes.     

Effect of eCG on early resumption of ovarian activity in postpartum dairy cows

The purpose of the present study was to hasten the resumption of ovarian activity early postpartum in lactating dairy cows, using equine chorionic gonadotropin (eCG), to enhance follicular growth, followed by hCG, to induce ovulation. Primiparous Holstein dairy cows (n=21) were assigned equally into eCG, eCG-hCG and Control groups. Cows in the eCG and eCG-hCG groups received an i.m. injection of eCG (500 IU Folligon?) on Day 6 postpartum. Cows in the eCG-hCG group were also given an i.m. injection of hCG (500 IU Chorulon?), once dominant follicle reached the diameter of 13-16 mm following eCG injection. Cows in Control group did not receive any treatment. Daily blood sampling and ultrasound examination were conducted, starting at Day 6 postpartum until confirming the third ovulation. Follicles ≥10 mm in diameter were detected on Day 11.5±1.48, 10.1±0.52 and 11.1±1.36 after calving in Control, eCG and eCG-hCG groups, respectively (P>0.05). The first wave dominant follicle ovulated in 71.4% of cows treated with eCG and eCG-hCG. In contrast, none of the first wave dominant follicles ovulated in Control cows. By Day 20 postpartum, all cows in eCG group, 6/7 cows in eCG-hCG group and none of the cows in Control group ovulated (P<0.05). Short estrous cycles (≤16 days) were detected in 2/7, 1/7 and 6/7 cows in eCG, eCG-hCG and control groups, respectively (P<0.05). In conclusion, injection of eCG on Day 6 postpartum could assist the early resumption of ovarian activity by enhancing ovarian follicle growth and early ovulation in postpartum cows. In this context, subsequent hCG injection may not provide any more beneficial effect.     

Endocrine and Ovarian Changes in Response to the Ram Effect in Medroxyprogesterone Acetate-primed Corriedale Ewes During the Breeding and Nonbreeding Season

Two experiments were performed to determine the endocrine and ovarian changes in medroxyprogesterone acetate (MAP)-primed ewes after ram introduction. Experiment 1 was performed during the mid-breeding season with 71 ewes primed with an intravaginal MAP sponge for 12 days. While the control (C) ewes (n = 35) were in permanent contact with rams, the ram effect (RE) ewes (n = 36) were isolated for 34 days prior to contact with rams. At sponge withdrawal, all ewes were joined with eight sexually experienced marking Corriedale rams and estrus was recorded over the next 4 days. The ovaries were observed by laparoscopy 4–6 days after estrus. Four weeks later, pregnancy was determined by transrectal ultrasonography. In eight ewes from each group, ovaries were ultrasonographically scanned; FSH, LH, and estradiol-17β were measured every 12 hours until ovulation or 96 hours after estrus. The response to the rams was not affected by the fact that ewes had been kept or not in close contact with males before teasing. No differences were found in FSH, LH, estradiol-17β concentrations, growth of the ovulatory follicle, onset of estrus, ovulation rate, or pregnancy rate. Experiment 2 was performed with 14 ewes during the nonbreeding season. Ewes were isolated from rams for 1 month, and received a 6-day MAP priming. Ovaries were ultrasonographically scanned every 12 hours, and FSH, LH, estradiol-17β, and progesterone were measured. Ewes that ovulated and came into estrus had higher FSH and estradiol-17β levels before introduction of the rams than did ewes that had a silent ovulation. The endocrine pattern of the induced follicular phase of ewes that came into estrus was more similar to a normal follicular phase, than in ewes that had a silent ovulation. The follicle that finally ovulated tended to emerge earlier and in a more synchronized fashion in those ewes that did come into estrus. All ewes that ovulated had an LH surge and reached higher maximum FSH levels than ewes that did not ovulate, none of which had an LH surge. We conclude that (a) the effect of ram introduction in cyclic ewes treated with MAP may vary depending on the time of the breeding season at which teasing is performed; (b) patterns of FSH, and estradiol-17β concentrations, as indicators of activity of the reproductive axis, may be used to classify depth of anestrus; and (c) the endocrine pattern of the induced follicular phase, which is related to the depth of anestrus, may be reflected in the behavioral responses to MAP priming and the ram effect.