Ovulation of aged follicles does not affect embryo quality or fertility after a 14-day progestagen estrus synchronization protocol in ewes

Effects of short and long - term nutrition and progesterone supplementation on the success of fixed - time artificial insemination in the ewe

The success of fixed - time artificial insemination (AI) in the ewe is variable due to poor synchrony of estrus. We examined the effects of long-term nutrition (LTN; low, medium, high - 6 months), short-term nutrition (STN; 1.0 M, 1.5 M - 14 days) and progesterone supplementation (P; single pessary, replacement on Day 9) on synchrony and reproductive outcomes. High LTN advanced (P < 0.05) estrus, increased (P = 0.06) pregnancy (range 71.1 - 81.1%) and improved (P < 0.01) litter size (range 1.30 - 1.50). STN increased (P < 0.05) pregnancy (79.0 versus 72.3%) but not litter size or timing of estrus. A LTN x STN interaction (P < 0.01) for time of estrus indicates that the effects of LTN were moderated by STN depending on the level of LTN. Pessary replacement delayed (P < 0.05) the onset of estrus, improved synchrony but did not affect pregnancy or litter size. High LTN increased (P < 0.05) the number of large (≥ 3.8 mm) and medium - size follicles (2.0 - 3.7 mm) but the diameter of large follicles tended to be reduced (P = 0.08) on Day 12. STN did not affect follicle number or size whilst P reduced (P < 0.05) the diameter of large follicles on Day 12 (4.83 versus 5.10 mm) and increased the number of medium - size follicles (3.56 versus 2.74 mm). In conclusion, both LTN and STN are major sources of variability in AI programs whilst pessary replacement has potential to reduce variability.

Ovarian follicle dynamics in ewes treated with intra-vaginal progesterone pessaries. 2. Factors affecting timing of estrus and reproductive outcomes following artificial insemination

This study extends observations on the effects of intra-vaginal progesterone treatment on the relationships between the time of luteolysis, emergence of the ovulatory follicle, timing of estrus and ewe fertility. Observations were made in progesterone - treated ewes in autumn, the spring equinox and late spring (Experiment 1, Data set 1) and in progesterone - treated ewes and naturally cycling ewes in autumn and the spring equinox (Experiment 1, Data set 2). In Data set 1, the day of emergence of both the first and second ovulatory follicle was positively related to the day luteal regression within each season. In turn, the day of emergence influenced the timing of estrus by means of a season by day of luteal regression interaction (P < 0.001) indicating that the relationship was positive in autumn and the spring equinox but negative in late spring. In autumn, older ovulatory follicles were associated with an earlier onset of estrus compared with younger ovulatory follicles. In late spring, this relationship was reversed and was influenced by whether or not ewes were cycling at the time of pessary insertion. In Data set 2, the relationship between the day of follicle emergence and luteal regression was influenced by a treatment by day of regression interaction indicating the relationship was positive in treated ewes and negative in naturally cycling ewes. Timing of estrus was positively related (P < 0.001) to both the day of luteal regression and the day of follicle emergence (P < 0.05), with both relationships being stronger in naturally cycling ewes than in treated ewes. In Experiment 2, pregnancy rate following artificial insemination in autumn was highest (90.2%) when luteolysis occurred during Days 7-9 of the pessary period compared with Days 1-6 (77.8%, P = 0.16), 10 to 12 (68.8%, P < 0.05) or Days ≥13 (71.2%, P < 0.05). Timing of estrus was not affected. The mean diameter of ovulatory follicles that emerged during Days 7-9 was larger on Day 12 (5.8 ± 0.13 mm) compared with other periods (range 4.7 ± 0.05 to 5.6 ± 0.14 mm). This study provides two potential strategies to improve the success of AI programs. Firstly, appropriately timed treatment with PGF2α to control the time of emergence of ovulatory follicles and, secondly, earlier treatment with eCG to improve the development of ovulatory follicles that emerge late in the pessary period. Each is likely to be influenced by season and the cyclical status of the ewe.

Ovarian follicle dynamics in ewes treated with intra-vaginal progesterone pessaries. 1. Follicle waves and parameters of the estrous cycle

Progesterone treatment for synchrony of estrus is standard in sheep artificial insemination (AI) programs but can be associated with poor outcomes. Potential for improvement exists through a better understanding of the interactions between follicle development, luteal regression, emergence of the ovulatory follicle and timing of estrus. These interactions were examined by comparing progesterone-treated (Day 1 = day of pessary insertion) and naturally cycling ewes (Day 1 = day after estrus) at three times of the year (Autumn, Spring equinox and late Spring). Observations were made from Day 1 until the day of ovulation. Compared with the natural cycle, progesterone treatment (300 mg intra-vaginal pessary for 14 d) reduced the number of follicle waves (2.2 ± 0.18 versus 2.8 ± 0.12; P < 0.05) and increased the length of the ovulatory wave (8.6 ± 0.45 versus 6.6 ± 0.42 d; P < 0.05). The number of follicles per wave, the inter-wave interval and ovulation rate were not affected. However, progesterone treatment induced (P < 0.05) an earlier luteolysis (9.7 ± 0.51 versus 15.4 ± 0.49 d after Day 1), an earlier emergence of the ovulatory follicle (7.5 ± 0.48 versus 11.4 ± 0.46 d after Day 1) and an earlier onset of estrus (26.1 ± 2.95 versus 53.3 ± 2.84 h after Day 14). Time of year also influenced the response to progesterone treatment. In Autumn compared with the Spring equinox and late Spring, there was a reduction (P < 0.05) in follicle wave number (2.4 ± 0.21 versus 2.5 ± 0.29 versus 3.0 ± 0.20 respectively), follicles per wave (2.6 ± 0.27 versus 3.5 ± 0.25 versus 3.2 ± 0.20 respectively), ovulation rate (1.6 ± 0.12 versus 1.9 ± 0.12 versus 2.0 ± 0.10 respectively) and the inter-wave interval was longer (5.3 ± 0.40 versus 4.0 ± 0.32 versus 3.8 ± 0.27 d respectively; P < 0.05). Time of year also influenced (P < 0.05) the time of luteolysis (earliest in late Spring), emergence of the ovulatory follicle (earliest in Autumn) and onset of estrus (earliest in Autumn). It is concluded that (1) the effects of progesterone treatment on follicle waves are relatively minor, (2) the effects of treatment on timing of luteolysis, emergence of the ovulatory follicle and onset of estrus are all significant although the effects on AI outcomes remain to be determined and (3) time of year has a minimal effect on follicle waves but a more significant effect on other parameters of the estrous cycle. A better understanding of these complexities will assist in the development of improved protocols for synchrony of estrus.

Ovarian response to P4-PGF-FSH treatment in Suffolk sheep and P4-PGF-PMSG synchronization in cross-bred ewes, for IVD and ET protocol

BACKGROUND

The success of an embryo transfer protocol in sheep depends on many factors, but the choice of drugs for the desired superovulation as well as the conception rate (CR) are most essential. Reproductive activity in sheep is characterized by a seasonality influenced by several factors such as photoperiod, latitude, temperature, nutrition and breed. Reproductive seasonality and nutritional condition are the main factors that influence embryo production in sheep. In sheep, some anatomical peculiarities limit the application of traditional reproductive biotechnologies used in cattle.

OBJECTIVES

The aim of this study was to conclude on the effectiveness of a wider on farm in vivo embryo transfer development programme in Suffolk sheep by streamlining hormone therapies and optimizing technique.

METHODS

A total number of 60 sheep and three rams were included in this study, divided into two groups (receptors and donors). Donor Suffolk sheep were treated for superovulation using the P4-PGF-FSH multiple ovulation embryo transfer (MOET) protocol, while the cross-bred recipients' group was synchronized with P4-PGF-PMSG.

RESULTS

On the first day after superovulation, all ovaries had more than five dominant follicles, while corpora lutea were later observed in 83.3% sheep. The recovery rate was 83.3%, while 72.9% embryos were transferable. Embryos were transferred directly into recipients. Fertility after 30 days was 68.57%, lambing rate was 91.6% and CR was 62.85%. This study showed that veterinary drugs (P4, FSH, LH, PMSG, PGF) used for superovulation optimized by us were capable of producing by this improved technique the optimization of the reproduction indices at embryo-transfer (ET) and to be able to be used successfully.

CONCLUSIONS

The application of an MOET protocol has a positive effect in the production of in vivo embryo production (IVD) embryos in Suffolk sheep and can guarantee the success of embryo transfer activity to ewes with lower genetic merit. Our research aimed at representing a model for sheep farms for a rapid improvement of productive traits.

Treatments with intravaginal sponges for estrous synchronization in ewes: length of the treatment, amount of medroxyprogesterone, and administration of a long-acting progesterone

We evaluated if alternative treatments achieve at least similar results as traditional long treatments with intravaginal sponges (IVS) in three experiments considering (1) the use of 6-day treatments associated or not with the administration of PGF2alpha at IVS insertion; (2) a reduction of 50% MAP content in short-term or traditional treatments, with or without change of the IVS 6 days after its insertion; and (3) the substitution of IVS for long-time acting injected progesterone associated with the administration of a PGF2alpha. More ewes came into estrus with long than short IVS treatments, independently of the MAP IVS content. Fewer ewes came into estrus if the IVS containing 30 mg was replaced 6 days after its insertion. The length of the treatment did not affect the conception rate, but the pregnancy rate was greater in 12 than 6 days treatments. The administration of long-acting progesterone did not prevent the lower conception rate associated with the use of PGF2alpha and was less effective to synchronize estrus, but the conception rate did not differ from that of 12d IVS treatments. Overall, MAP content could be decreased without affecting the estrous rate; thereafter, the MAP IVS content should be decreased in the commercial devices. Although pregnancy rate was lower using long-acting injected progesterone than with IVS, as the conception rate did not differ, it is interesting to study deeper the use of this treatment, especially if preparations of progesterone with a longer half-life are developed. However considering all the results, the traditional long IVS treatment still provided the best result.

Addition of eCG to a 14 d prostaglandin treatment regimen in sheep FTAI programs

In the present study, there was evaluation of the alternative of adding eCG as part of a long-interval prostaglandin-F_2α (PG) treatment on the reproductive efficiency of Merino sheep during the breeding season. A total of 210 ewes and 182 ewe lambs were randomly assigned to three experimental groups to induce the timing of estrus among ewes in a: Long-interval PG, group being synchronized using two doses of PG 14 days apart; Long-interval PG + eCG group being synchronized using the same treatment regimen as Group PG with the addition of 200 IU eCG to the regimen, administered concomitantly with the second PG administration; and MAP + eCG group being synchronized with intravaginal progestin sponges for 14 days plus 200 IU eCG, administered at the time of sponge removal. The percentage pregnancy rate in ewes of the MAP + eCG group was greater than the ewes of the Long-interval PG and Long-interval PG + eCG groups (76.4 % compared with 52.0 % and 62.5 %, respectively; P < 0.05). The prolificacy rate was greater in the ewes of the Long-interval PG+eCG group compared with the other groups (114 % compared with 100 % and 103 %, respectively; P < 0.05). When considering the fecundity rate, ewes of the Long-interval PG+eCG and MAP+eCG groups had greater values than ewes of the Long-interval PG group (71.2 % and 78.8 % compared with 52.0 %, respectively; P < 0.05). The Long-interval PG+eCG is an alternative to the conventional progestin sponge plus eCG treatment regimen with there being a greater fecundity rate when this regimen is used compared with the Long-term PG and similar to MAP-eCG treatment regimens.

Re-use of intravaginal progesterone devices associated with the Short-term Protocol for timed artificial insemination in goats

Because intravaginal devices impregnated with 0.3 g of progesterone (i.e., CIDR-G) contain remaining hormone after their use in a Short-term Protocol (5 to 7 d of treatment), the reuse of these devices is proposed in goats. Two experiments were designed to study the effects of the reutilization of CIDR-G, establishing serum progesterone concentrations, follicular development, ovulatory response, and fertility. Experiment 1: Thirty dairy goats received a Short-term Protocol for 5 d using CIDR-G of first use (new devices, n = 10), second use (previously used for 5 d, n = 10), or third use (previously used twice for 5 d each time, n = 10). Goats were given (im) prostaglandin F(2α) (10 mg dinoprost) and eCG (300 IU) at device insertion and withdrawal, respectively. Serum progesterone concentrations induced by CIDR-G of first use were higher than CIDR-G of second or third use (P < 0.05); concentrations were consistently > 1 ng/mL in all females treated with reused devices. Estrus and ovulation were synchronized in 100% of goats (no differences among treatments). All females treated with new devices, but only 80% of females treated with re-used devices ovulated a new follicle that emerged after CIDR-G insertion (P = NS). Ovulation occurred between 60 and 70 h after device removal (no differences among groups). Experiment 2: In goats subjected to a Short-term Protocol followed by AI at 54 h after CIDR-G, pregnancy rates with CIDR-G of first, second, and third use were 75.3% (64/85), 67.4% (60/89), and 62.1% (54/87), respectively (devices of first versus third use, P < 0.05). In summary, intravaginal devices originally containing 0.3 g of progesterone appeared effective to synchronize estrus and ovulation after first, second and third use in the Short-term Protocol. Although the pregnancy rate with reused devices was acceptable (i.e., > 60%), it was significantly lower than that achieved with new devices and further studies to ensure adequate follicular turnover are required.

Ultrasonographic imaging in small ruminant reproduction

CONTENTS

Ultrasonography is a simple, reliable and non-invasive imaging technique without secondary effects. Application of ultrasonography in veterinary practice, and specifically in small ruminants, has developed to become the most efficient diagnostic tool for managing reproduction. The objectives of current revision are to offer an overview, after a short reminder of equipment and techniques for imaging genitalia in small ruminants, of the uses and utility of ultrasonography for the evaluation of physiological and pathological conditions in males and females and for the application of assisted reproductive technologies.

Endocrine, luteal and follicular responses after the use of the short-term protocol to synchronize ovulation in goats

The effect of the so-called Short-Term Protocol (5-day progesterone treatment+PGF(2)alpha) on ovarian activity and LH surge was studied in goats. The goats received 250IU eCG at the time of device withdrawal (eCG group; n=7), or 200microg of EB (estradiol benzoate) 24h after device withdrawal (EB group; n=8), or received neither eCG nor EB (control group; n=8). The Short-Term Protocol induced greater (4.1+/-1.1ng/ml) progesterone serum concentrations at 24h after start of the treatment, that declined to 0.2+/-0.1ng/ml at 12h after device withdrawal. In all of the groups, the maximum concentration of estradiol-17beta was reached at about 36h after device withdrawal. Maximum concentration was greater in the EB group (76.9+/-24.6pmol/l) than in the control group (41.8+/-9.0pmol/l; P<0.01), with the eCG group showing intermediate concentration (70.3+/-32.5pmol/l; P=NS). The LH peak occurred earlier in the eCG group (38.4+/-2.0h after device withdrawal) and in the EB group (41.0+/-4.1h), than in the control group (46.3+/-5.1h; P<0.05). Ovulation occurred earlier in the eCG group (5/7) and in the EB group (8/8) (58.8+/-2.7h and 63.0+/-5.6h, respectively), than in the control group (7/8) (70.2+/-8.3h; P<0.05). In summary, the Short-Term Protocol induced similar concentrations of progesterone among treated goats. In addition, eCG or EB resulted in a similar increase in estradiol-17beta and a similar LH surge, which induced ovulation in most females (86.7%) in a consistent interval (about 60h) after the end of progesterone exposure.

Reproductive Performance of Ewes after 5-Day Treatment with Intravaginal Inserts Containing Progesterone in Combination with Injection of Prostaglandin F2alpha

Three experiments were conducted with a total of 1579 ewes to examine reproductive performance in response to synchronization of oestrus during the breeding season, using controlled internal drug releasing (CIDR-G) inserts in regimens designed to provide high concentrations of circulating progesterone. In experiment 1, treatment with two CIDR-G inserts for 12 days produced conception rate (79%) and prolificacy (1.9) to first service equivalent to breeding at natural oestrus (56% and 2.0, respectively). Pregnancy rates to two service periods were 90 and 79%, respectively. In experiments 2 and 3, progesterone was delivered by a single CIDR-G insert for 5 days in combination with prostaglandin F2alpha (PGF2alpha; 5 mg i.m., twice, 3 h apart) the day before (experiment 2), or at insert removal (experiment 3). The combined treatments improved rates of synchronization of oestrus (p<0.01) by 23 and 20% points, respectively, and pregnancy rates to the first service period by 19 (p<0.05) and 13 (p<0.01) percentage points, respectively, compared to treatment with PGF2alpha alone. It is concluded that the combination of treatment for 5 days with a CIDR-G insert and two injections of 5 mg PGF2alpha, the day before, or the day of insert removal, were effective treatments to obtain high fertility at synchronized oestrus in ewes during the breeding season.

Effects of progestagens and prostaglandin analogues on ovarian function and embryo viability in sheep

Current study assessed differences in the response of sheep to estrus synchronization either by the administration of two doses of prostaglandin or by the insertion of an intravaginal progestagen sponge. The preovulatory follicular dynamics and estradiol secretion, the ovulatory response and progesterone secretion and the number and quality of embryos were studied in 27 ewes treated with two doses of 100 microg of cloprostenol, 10 days apart, and in 29 sheep treated with progestagen sponges for 14 days. Percentage of sheep responding to the synchronization treatments with signs of estrus behaviour was similar between both groups (81.5% versus 72.4%, respectively). The use of progestagen resulted in a higher diameter of the largest follicle (6.6+/-0.2 versus 5.9+/-0.2, P<0.05), and a lower number of small (6.7+/-0.3 versus 9.6+/-0.4, P<0.005) and total follicles (10.3+/-0.3 versus 12.9+/-0.4, P<0.005). However, mean plasma estradiol concentration during the follicular phase was higher in cloprostenol treated sheep (P<0.005). The mean ovulation rate was similar in both treatments (1.7+/-0.2 versus 1.7+/-0.3), but progesterone concentration during the early luteal phase was again higher in sheep treated with cloprostenol (P<0.05). The mean number of retrieved oocytes/embryos was very similar in both treatments (1.2+/-0.2 versus 1.4+/-0.2) and showed similar fertilization rates (70.6% versus 66.7%), but, although differences did not reach statistical significance, final viability rate was higher in cloprostenol than in progestagen treated ewes (58.9% versus 46.1%, P=0.07). Current results give new evidences supporting the negative effects of progestagens on the functionality of ovulatory follicles and support the development of new protocols for assisted reproduction including the use of prostaglandin analogues.

The effects of ram exposure during progestagen oestrus synchronisation and time of ram introduction post progestagen withdrawal on fertility in ewes

Three experiments were undertaken to investigate the effect of a pre-mating ram exposure during progestagen synchronisation treatment on time of breeding, ovulation rate, embryo quality and fertility and any interaction with time of ram introduction for breeding post sponge withdrawal. Crossbred ewes in experiment 1a (n = 348), 1b (mule; n = 133) and 2 (n = 58) underwent a 12-14 days synchronisation protocol. Three days prior to sponge withdrawal ewes were divided into Control (ewes in continued isolation from rams) or +Ram (ram-exposed) groups. Rams were introduced to +Ram ewes and remained with ewes until sponge withdrawal. Ewes in experiments 1a and 2 received eCG at sponge withdrawal and were reintroduced to rams at either 36 or 48 h post sponge removal (PSR). In experiment 1b, ewes did not receive eCG and were reintroduced to rams at 24 h PSR. In experiments 1a and 1b time of breeding, date of lambing and litter size were recorded. In experiment 2, ewes were slaughtered 5 days post breeding, reproductive tracts flushed and corpora lutea, ova and embryos assessed. Fewer +Ram ewes were mated by 96 h PSR (P < 0.001) than Control ewes in experiment 1a but not when rams were introduced earlier in experiment 1b. In experiment 1a, ram introduction at 36 h PSR improved conception to first service compared to introduction at 48 h PSR (P < 0.01) in both +Ram and Control groups. In experiments 1a and 1b, +Ram ewes had reduced litter size caused by more single births (1a; P < 0.001, 1b; P < 0.01). In experiment 2, +Ram ewes had fewer corpora lutea than Control ewes (P < 0.001) but embryo quality was similar. However, more good embryos were produced when rams were introduced for breeding at 36 h compared to 48 h PSR (P < 0.001). We conclude that a pre-mating ram exposure during the synchronisation treatment reduced the number of ewes mated at and conceiving to the first service. This was partially overcome by introducing rams for breeding earlier (24 or 36 h compared to 48 h PSR) but the most dramatic decrease in fertility was due to a reduction in ovulation rate in the ram-exposed ewes.

Effect of ram exposure at the end of progestagen treatment on estrus synchronisation and fertility during the breeding season in ewes

Two experiments were conducted to examine the effects of ram exposure during the breeding season, in combination with progestagen treatment on estrus synchronization, fertility the LH surge and ovulation in ewes. Experiment 1 was subdivided into experiments 1a and 1b. In all experiments cross-bred ewes were treated with an intravaginal sponge for 12-14 days and three days before sponge withdrawal ewes were divided into control (no further treatment; n=191, 103 and 50 for experiments 1a, 1b and 2, respectively) or ram exposed (three mature rams per 50 ewes were introduced; +Ram; n=187, 99 and 49 for experiments 1a, 1b and 2, respectively). At sponge withdrawal ewes in Experiments 1a and 2 received 500 IU eCG and rams were removed from all the +Ram groups. In Experiments 1a and 1b, raddled, entire rams were introduced to ewes 48 h after sponge withdrawal. The timing of mating was recorded and ewes were maintained until lambing. In Experiment 2, estrus behavior was determined every 4 h and the time of the LH surge and ovulation were determined from a subset of 10 ewes per group. In Experiment 1a, less +Ram ewes were bred by 48 h after ram introduction (control 98% versus +Ram 89%, P<0.001) and in Experiments 1a and 1b 14% fewer (P<0.05) of the ewes bred in the first 3 h after ram introduction lambed to that service. In Experiment 1a, ram exposed ewes had a lower litter size than control ewes (1.93+/-0.06 versus 1.70+/-0.06 lambs per ewe; P<0.05). In Experiment 2, rams advanced (P<0.05) estrus, the LH surge and ovulation by 2-6 h compared with control ewes. We speculate that exposure of ewes to rams increased LH secretion and that this in turn increased follicle development and the production of oestradiol that led to a more rapid onset of estrus, the LH surge and ovulation compared to control ewes. Unexpectedly, ewes that were bred had lower fertility in the +Ram groups than control groups.

The influence of the corpus luteum on ovarian follicular dynamics during estrous synchronization in goats

Ovarian follicular dynamics and fertility are unaffected by the presence or absence of a corpus luteum during synchronization of estrus with progestins in goats. On day 5 of the estrous cycle (estrus= day 0), a gestagen-containing sponge was inserted in the vagina for 11 days. To remove corpora lutea, one group of goats (CL-, n=41) received 7.5 mg of luprostiol on days 7 and 8 of the estrous cycle. The second group of goats retained the CL (CL+, n=38). Growth and development of follicles > or =4 mm in diameter were measured daily from onset of estrus to 2 days after subsequent ovulation in seven goats from each group, using rectal ultrasonography. Estrus was detected by the use of a reproductively sterilized buck and estrous does were subsequently mated. The number of waves of follicular development (CL- =3.57+/-0.2 versus CL+ =3.14+/-0.14; P>0.05) did not differ between groups. The second wave of follicular development was present at the time of progesterone decline in the CL- group and neither its duration (CL- =4.8+/-0.4 versus CL+=5.6+/-0.7 days; P>0.05) nor the day of commencement of the third wave of follicular development (CL -=11.6+/-0.7 versus CL+=11.8+/-0.6; P>0.05) were altered by the concentration of endogenous progesterone. The pregnancy rate was similar between the two groups. (CL-=68.29% versus CL+=65.79%; P>0.05). Thus, in goats, ovarian follicular dynamics and fertility were not altered by the presence or absence of a corpus luteum during estrous synchronization.

Multiple factors affecting the efficiency of multiple ovulation and embryo transfer in sheep and goats

This review offers an overview of the basic characteristics of in vivo embryo technologies, their current status, the main findings and the advances gained in recent years, and the outstanding subjects for increasing their efficiency. The use of superovulation and embryo transfer procedures remains affected by a high variability in the ovulatory response to hormonal treatment and by a low and variable number of transferable embryos and offspring obtained. This variability has been classically identified with both extrinsic (source, purity of gonadotrophins and protocol of administration) and intrinsic factors (breed, age, nutrition and reproductive status), which are reviewed in this paper. However, emerging data indicate that the main causes of variability are related to endocrine and ovarian factors, and so the number of studies and procedures addressing a better understanding and control of these factors may be increased in the future. The accomplishment of this objective, the improvement of procedures for embryo conservation and for the selection and management of recipient females, will allow further development and application of this technology.

Ultrasound and endocrine evaluation of the ovarian response to a single dose of 500 IU of eCG following a 12-day treatment with progestogen-releasing intravaginal sponges in the breeding and nonbreeding seasons in ewes

A standard dose of 500 IU of eCG is commonly given to progestogen pre-treated anestrous ewes for induction of estrus. Twelve seasonally anestrous and 12 cyclic Western White Face ewes were treated for 12 days with intravaginal sponges impregnated with medroxyprogesterone acetate (MAP). In trials in both the breeding and nonbreeding seasons, six randomly selected ewes were given 500 IU of eCG at sponge removal to determine the effects of low dose of eCG on ovarian antral follicular dynamics and ovulation. Ultrasound scanning and blood sampling were done daily. Treatment with eCG did not have marked effects on antral follicular growth. All ewes ovulated, except for five of six control anestrous ewes. Luteal structures and progesterone secretion were confirmed in all but the control anestrous ewes. In the breeding season, peak progesterone concentrations were greater (P<0.05) in eCG-treated compared to control ewes. Daily serum estradiol concentrations were greater in the periovulatory period in eCG-treated compared to control ewes (treatment-by-day interaction; P<0.05), particularly in anestrus. Progestogen-treated ewes ovulated follicles from several follicular waves, in contrast to ovulations of follicles from the final wave of the cycle in untreated, cyclic ewes. Anestrous ewes exhibited more frequent follicular waves and FSH peaks compared to cyclic ewes after a progestogen/eCG treatment. In conclusion, 500 IU of eCG given after 12 days of progestogen treatment had limited effects on the dynamics of ovarian follicular waves. However, eCG treatment increased serum concentrations of estradiol during the periovulatory period, particularly in anestrous ewes; this probably resulted in the synchronous estrus and ovulation in anestrous ewes.

Ovarian follicle growth and consequences for fertility in sheep

Understanding the pattern of ovarian follicle development is seen as an important step leading to the development of techniques that maximise fertility in sheep. Repeated observations of the growth of individual follicles have led to the understanding that follicles develop in a wave-like pattern during the oestrous cycle, with two to four waves per cycle being the most common. The ease with which follicle waves are described seems to depend on the their frequency and the number of follicles per wave. There is evidence for the largest follicle(s) of a follicle wave inhibiting the development of other follicles; however, in some cases this is not apparent as other follicle waves emerge when a previous large, healthy follicle is still present. Follicle development can be manipulated using exogenous gonadotrophins or progestagens and these have been shown to alter the number or age profile of developing follicles. The ovulation of aged follicles in cattle clearly has a detrimental effect on fertility, but this relationship is less clear and seems to be less critical in sheep. Recent findings at the molecular level show that the bone morphogenetic proteins (BMP) and their receptors are critically involved in the control of ovulation rate, but fully understanding their mechanism remains to be described. This highlights the potential for the integration of molecular and physiological findings to better develop methods to manipulate follicle development and reproduction in sheep.

The pattern and manipulation of ovarian follicular growth in goats

The understanding of the dynamics and regulation of follicle development in the goat has increased in recent years due to the use of ultrasonography. Previous findings observed in other ruminants extend to this species such as: the wavelike pattern of follicular growth with waves emerging every 5-7 days; the presence of follicular dominance, particularly during wave 1 and the ovulatory wave; and the role of progesterone concentrations on follicular wave turnover. However, traditional hormone treatments for oestrus synchronisation and superovulatory programs remain essentially unmodified and without taking into account this new information. The use of long progestogen priming is largely unjustified. Short progestogen priming can be used successfully in both anoestrous and cycling goats (in this case associated with PGF2alpha), and also linked with timed artificial insemination. On the other hand, recent attempts to overcome the deleterious effect of the dominant follicle on superovulatory response using the emergence of the wave 1 have been successful. Overall, using ultrasonography a new field has been opened and surely successful output will be forthcoming in the next years to improve reproductive management of the goat, the fastest growing ruminant population in the world.

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.