Synchronization Of Oestrus In Sheep Research Articles

Comparing CIDR with progesterone injections and eCG with human recombinant FSH for synchronizing estrous cycle in ewes.

It is desirable in estrus synchronization in sheep to avoid intravaginal devices and to shorten the program from 14 to 6 days. Moreover, replacement of eCG with safe, cheap, and efficient gonadotropin is in worldwide demand. This study investigates the possibility of replacing eCG with human recombinant FSH (hrFSH) and CIDR with progesterone injections for estrous synchronization in ewes. Assaf and Lacaune ewes (n=170) were divided into two groups and synchronized with either progesterone injections for 6 days or CIDR for 14 days. Ewes assigned in the injection group, received progesterone (37.5 mg; SC) and GnRH analogue (7.5 µg Alarelin acetate; IM) on day 0 of the experiment. On days 3 and 6, ewes received 25 and 12.5 mg progesterone (SC), respectively. On day 6, ewes in both groups received prostaglandin F2α (250 µg Cloprostenol; IM), and were divided into two subgroups to receive either hrFSH (75 IU Follitropin alfa; SC) or eCG (400 IU; IM). On day 7, fertile rams were introduced to ewes for 21 days. Data were analyzed using GLM and Glimmix. There was no difference in the respective lambing rates, prolificacy, and fecundity between CIDR (71.1, 1.63, and 1.16%) and injections (66.7, 1.55, and 1.03%); between eCG (71.4, 1.60, and 1.14%), and hrFSH (66.3, 1.58, and 1.05%, P>0.05). In conclusion, 6-day progesterone injection-based protocol produced similar results to 14-day CIDR program and hrFSH could be an effective alternative for eCG during estrus synchronization in ewes.

Application of hormonal subdoses at the Bai Hui acupoint for estrus synchronization in sheep

Here, the efficiency of applying subdoses of equine chorionic gonadotropin (eCG) and prostaglandin F2α (PGF2α) at the Bai Hui (BH) acupoint for estrus synchronization in sheep was evaluated. Thirty Santa Inês ewes received intravaginal sponges containing 60 mg medroxyprogesterone acetate for 7 days. The animals were divided into five treatments (T) (n=6): T1 (control), 132.5 μg PGF2α (100% of dose) and 300 IU eCG (100% of dose), both intramuscularly (IM); T2, 39.75 μg PGF2α (30% of dose) at the BH acupoint and 300 IU eCG (100% of dose) IM; T3, 132.5 μg PGF2α (100% of dose) IM and 90 IU eCG (30% of dose) at the BH acupoint; T4, 39.75 μg PGF2α (30% of dose) and 90 IU eCG (30% of dose), both at the BH acupoint; and T5, 39.75 μg PGF2α (30% of dose) and 90 IU eCG (30% of dose) both at a false acupoint (IM, at the same location as in T1). After 12 h of sponge removal and hormone application, the ewes were subjected to monitoring for estrus and mating and ultrasound assessments of follicular growth and ovulation time every 12 h. The data were evaluated for normality and subjected to analysis of variance, considering a 5% probability. There were no differences in the percentage of animals in estrus (93.3±9.1%), interval from sponge removal to estrus onset (48.1±6.0 h), interval from sponge removal to estrus end (69.6±5.4 h), duration of estrus (24.0±4.7 h), interval from sponge removal to ovulation (73.7±5.9 h), interval from estrus onset to ovulation (26.5±2.3 h), size of the largest follicle (6.7±0.4 mm), follicular growth rate (0.8±0.1 mm•day-1), number of ovulations (1.3±0.1), and plasma progesterone levels 7 days after ovulation (9.6±2.0 ng•mL-1). The cost of the synchronization protocol per animal was US$ 4.37, 4.12, 2.96, 2.71, and 2.71 for T1, T2, T3, T4, and T5, respectively, with 37.99% cost reduction using PGF2α and eCG at 30% of the conventional doses. Therefore, the application of reduced PGF2α (39.75 μg) and eCG (90 IU) doses at the BH or false acupoint effectively synchronized estrus and reduced protocol cost in sheep, indicating that the conventional doses are overestimated.

The Use of hCG for Inducing Ovulation in Sheep Estrus Synchronization Impairs Ovulatory Follicle Growth and Fertility.

Simple SummaryThe present study, in view of the importance of finding an alternative hormone to eCG, aims to determine the response of sheep to hCG-based treatments. The findings indicate that the low fertility rates reported for protocols based on the administration of hCG for inducing ovulation during estrus synchronization in sheep may be related to a high occurrence of abnormal follicular growth patterns, disturbances, and retardments of ovulation and concomitant formation of follicular cysts in the treated females. These results preclude their practical application to induce ovulation concomitantly to estrous synchronization treatments.Currently, there is an intense effort to find an alternative hormone to eCG to induce ovulation after estrus synchronization treatments in sheep. One of the proposed alternatives is based on the use of hCG, but the results are controversial since fertility rates are commonly affected. The present study aims to evaluate, therefore, the adequacy of hCG in protocols for the synchronization of estrus and ovulation. Ovarian follicle dynamics, occurrence of estrus behavior and subsequent ovulation, quality of corpora lutea, and pregnancy rate after controlled natural mating were assessed in two consecutive trials. The findings indicate that the low fertility rates reported for the protocols based on the administration of hCG for inducing ovulation during estrus synchronization in sheep may be related to a high occurrence of abnormal follicular growth patterns, disturbances, and retardments of ovulation and concomitant formation of follicular cysts in the treated females. These results preclude their practical application to induce ovulation concomitantly to estrous synchronization treatments.

Induction and synchronization of oestrus in sheep and goats

Different methods for oestrus induction and synchronization in domestic small ruminants have been developed. Seasonality and female’s status are important factors for choosing the most appropriate treatment. In the case of females during breeding season, prostaglandins can be used since functional corpus luteum must be present in the ovaries, while during non-breeding season females should be treated with progesterone-based treatments, accompanied by equine chorionic gonadotrophin (eCG), releasing hormones and other compounds. Significant spread of oestrus synchronization during and after the breeding season has been achieved by the use of intravaginal sponges impregnated with synthetic analogues of progesterone. However, the effect of hormonal drugs on the female reproductive system may manifest differently depending on the initial functional state of reproductive organs and the hormonal status, and negative consequences can be observed when drugs are wrongly administered. In addition, insufficient knowledge about the patterns of change in the reactivity of the nervous sexual centers and the corresponding reactions of the body to the administration of hormones reduces their effectiveness, which limits the widespread use. In general, the induction and synchronization of oestrus in small ruminants is an currently important direction of scientific research and an urgent problem of sheep and goat breeding, but the proposed methods require further improvement by reducing the costand increasing biosecurity and predictability of the result.

Economic potential of AVIKASIL-S technology for estrus synchronization in sheep

The study captures the economic benefits of AVIKASIL-S, an estrus synchronization technology in sheep using an economic surplus approach in the Rajasthan state of India. The adoption of technology at the field level was at a nascent stage. Study simulated scenarios at different adoption rates of technology and discerned that technology has the economic power to enhance the income of shepherds in the state. To reap the more benefits of technology, the adoption rate needs to increase. The support of government, private sector, and public-private partnership models besides entrepreneurs are the channels for wider adoption of technology amongst shepherds.

Use of Propylene-Glycol as a Cosolvent for GnRH in Synchronization of Estrus and Ovulation in Sheep.

Simple SummaryThe foreseeable shortage of equine chorionic gonadotrophin (eCG) for estrus synchronization in sheep will have a huge impact on breeders using out-of-season breeding, artificial insemination, or embryo transfer because there is no other product with similar activity. Hence, there is a strong need for alternative protocols. The aim of the present work was to evaluate the reproductive response of sheep in breeding season to the administration of gonadotrophin-releasing hormone (GnRH) using propylene-glycol as a cosolvent, as well as the most adequate timing for such administration. From the results obtained, protocols based on a short-term treatment with a Controlled Internal Drug Release (CIDR) device and a single dose of GnRH in propylene-glycol at 36 h after CIDR removal may constitute an alternative to traditional protocols based on the administration of a single dose of eCG at CIDR removal.The foreseen shortage of eCG for estrus synchronization in sheep makes necessary the development of alternative protocols. The aim of the present work was to evaluate the reproductive response of sheep in breeding season to the administration of GnRH using propylene-glycol as a cosolvent and the subcutaneous route for slowing and extending the release of GnRH, as well as the most adequate timing for such administration. In the present study, protocols based on a short-term CIDR treatment and a single subcutaneous dose of GnRH in propylene-glycol at 36 h after CIDR removal induced a similar ovarian response to protocols based on administration of eCG at CIDR removal or intramuscular GnRH in distilled water at 56 h after. In such protocol, 80% of the animals developed estrus in a narrow timing (75% between 36 and 48 h after CIDR removal), and all of them also ovulated in a narrow window (87.5% between 72 and 76 h after CIDR removal, with 62.5% between 72 and 76 h) and showed a similar ovulation rate and plasma progesterone concentrations at the induced estrous cycle. Hence, administration of GnRH in propylene-glycol may constitute an alternative to traditional protocols based on the administration of eCG.

Efficiency of CIDR-Based Protocols Including GnRH Instead of eCG for Estrus Synchronization in Sheep.

Simple SummaryThis study examines the preovulatory and ovulatory events (in terms of the timing of onset of estrus behavior, preovulatory LH surge, and ovulation) and the yields obtained (in terms of ovulation rate, progesterone secretion, and fertility) after insertion of controlled internal drug release (CIDR) devices for 5 days and treatment with equine chorionic gonadotrophin (eCG) or gonadotrophin-releasing hormone (GnRH).The present study examined, for meat sheep (Segureña breed; 2–5-years old, mean body score of 3.5 ± 0.5), the timings of onset of estrus behavior, preovulatory luteinizing hormone (LH) surge and ovulation, and the ovulation rate and fertility obtained after insertion of controlled internal drug release (CIDR) devices for 5 days plus treatment with equine chorionic gonadotrophin (eCG; single dose at CIDR removal, n = 19 ewes) or gonadotrophin-releasing hormone (GnRH, either in a single dose at 56 h after CIDR removal, group CIDR-GnRH, n = 19 ewes; or in one dose at CIDR insertion and another dose 56 h after CIDR removal, group GnRH-CIDR-GnRH, n = 19 ewes). In all the ewes, the appearance of estrus behavior ranged between 84% and 90% and all females showing estrus signs had subsequent preovulatory LH peaks and ovulations. Onset of these events was earlier in the CIDR-eCG group than in the CIDR-GnRH and GnRH-CIDR-GnRH groups (p < 0.05). These differences were mainly determined by the onset of estrus behavior, since timing and intervals of LH peak and ovulation were similar among treatments. In fact, the range of ovulations was narrower in the GnRH-CIDR-GnRH group, which suggests better synchronization of follicular growth (p < 0.05). In conclusion, protocols with two doses of GnRH offer similar yields to eCG protocols.

260 The induction and synchronization of estrus in sheep during the fall and late spring (season and out of season) using controlled internal drug release (CIDR) devices on Delmarva

Changing U.S. demographics have increased lamb demand, which usually follows holidays, changing from year-to-year coinciding with traditions/festivals. In 2013, >80,000 t (metric tons) of lamb were imported to USA. A chief constraint to continuous year-round lamb supply is the influence of season on sheep reproduction. The purpose of this project was not to determine FDA approved CIDRs' (2009) efficacy in sheep but to resolve applicability and practicality of CIDR use in commercial flocks to condense lambing periods and target peak lamb demands. From 2012 to 2015, purebred and crossbred Katahdin ewes (n = 201) were separated into two groups, synchronized (CIDR) or not (CONTROL), for breeding in late Spring (anestrus-season) or Fall (natural-breeding-season). At each breeding event, CIDRs were inserted for 12 to 18 d, and at the time of CIDR removal, ewes were grouped for mating in single sire groups of no more than 6 ewes/group. The FDA approved protocol (12 to 18 d) was followed because pre-trials at this station gave inconsistent results following the label's CIDR insertion and removal time (5 d). At birth, lambs were tagged, weighed, and sexed, and litter size was recorded (LSZ) (lambs/ewe exposed). Data were analyzed using Chi-square and analysis of variance (SAS software package) for effect of synchronization and season on pregnancy rates (PR) (pregnant ewes/exposed ewes) and LSZ at birth. Overall PR did not differ from one year to the other in CIDR or CONTROL ewes. PR was higher (P < 0.0001) in CIDR ewes (63.4%) than in CONTROL ewes (34.3%) but was similar between breeding seasons (62.4% and 37.6% for CIDR and 52.8% and 47.2% for CONTROL in Fall and Spring, respectively). During Spring, PRs were higher (P < 0.0001) in CIDR ewes (71.4%) than in CONTROL ewes (17.6%). During Fall, PRs were similar (58.5% and 49.1% for CIDR and CONTROL, respectively). Overall, ewe LSZ was influenced by season bred and use of CIDRs, with CONTROL Spring-bred ewes having a lower (P < 0.0001) litter size (0.3 ± 0.1) compared to CONTROL-Fall, CIDR-Fall, and CIDR-Spring bred ewes (1.0 ± 0.1, 1.2 ± 0.1, and 1.3 ± 0.1, respectively). The results encourage using CIDRs in commercial sheep flocks to increase pregnancy rate and litter size. Additionally, CIDR synchronization in our station reduced a 60 to 90 d lambing period to 10 d, allowing operators to arrange facilities, labor, and supplies accordingly, enhancing lamb survival and ewe welfare. Project funded by Evans-Allen grant USDA/NIFA MDX-AS1012001.

HORMONAL PROFILES OF BLOOD PLASMA ASSOCIATED ESTRUS SYNCHRONIZATION USING DIFFERENT CONCENTRATION OF MAP AND ECG IN BARKI EWES

The current study aimed to characterize the plateau patterns of plasma progesterone in the peripheral circulation during the application of vaginal sponge impregnated with different concentrations of medroxyprogesterone acetate (MAP) and co-treated without and with different doses of equine chorionic gonadotropin (eCG) and its effects on some items of reproductive performance. Determination the onset surges (time and level) of LH and estradiol-17β were also aimed in the study as a necessary pinpoint to the time of ovulation after MAP sponge-eCG treatment. Forty Barki ewes were randomly allocated into 2 main groups (A & B) of equal numbers (n=20/group). Groups A and B were treated with vaginal sponges containing 25 and 50 mg MAP, respectively. On day of sponge's withdrawal, ewes of each main group were randomly reassigned according to eCG dose into three subgroups (1, 2 and 3). Groups A1 and B1 (n=6 each group), served as control, without eCG injection, while groups A2 and B2 (n=7/subgroup) were injected at sponge removal with 300 IU/eCG, whereas, groups A3 and B3 (n=7/subgroup) were injected with 500 IU/eCG. Blood samples were taken immediately before sponge insertion and after the placement subsequently every 2 days and continued to the end of sponge application to studying the plateau pattern of progesterone in the peripheral circulation. Nine hours after sponge removal to 74h latter, blood samples were also taken every 3h and 6h for determination LH and estradiol-17β surges, respectively. The time to onset estrus (h), estrus duration, pregnancy and lambing rates (%) were recorded as reproductive performance measuring related to the study. The started level of plasma progesterone in group A increased gradually with level reaching to its maximum level on days 6 and 8 of sponge application and then rapidly decreases reaching to minimum level on day of sponge removal. On contrast, the patterns of plasma progesterone changes in group B were forcefully increased but with slightly high level from the beginning reaching its highest concentration on day 6 and day 8, then decline gradually to reach lower level on the day of sponge withdraw. The mean time from sponge withdraw to LH and estradiol-17β surges were significantly shorter (P<0.05) in-group A than B and significantly longer (P<0.01) in group A1B1 than other eCG treated groups. Neither MAP nor eCG have significant effects on LH concentration, while, eCG have positive effects on the concentration of estradiol-17β. Generally, the hormonal plateau patterns of group A were associated with acceleration the time to onset estrus with high pregnancy rate. In conclusion, the protocols used for estrus synchronization in sheep are associated with different plateau patterns of circulating reproductive hormones and subsequently affect reproductive performance.

215 DELETERIOUS EFFECTS OF PROGESTAGEN TREATMENT ON FUNCTIONALITY OF PREOVULATORY FOLLICLES IN SHEEP

The use of progestagen for 14 days in protocols for estrus synchronization has been reported to affect conception rate in sheep. We evaluated the effects of progestagen treatment on the growth pattern and follicular function of preovulatory follicles (PF) and their implication for subordinated follicles (SF). Adult female sheep were randomly assigned to the following estrus synchronization groups: 1) FGA (n = 7), which received an intravaginal device of fluorogestone acetate sponges (Chronogest®, Intervet International, Boxmeer, the Netherlands) for 14 days, or 2) PGF (n = 7), which received 3 i.m. administrations of 125 μg of cloprostenol (Estrumate®, Mallinckrodt Vet GmbH, Friesoythe, Germany) 10 days apart. The third cloprostenol administration in the PGF group was given at the same time of sponge withdrawal in the FGA group (Day 0 = day of sponge withdrawal). Ultrasonographic examinations of the ovaries for assessment of follicular development were carried out daily from Days 0 to 2 by using a scanner (Aloka SSD500) equipped with a 7.5-MHz transducer adapted for transrectal examinations. Follicular function was evaluated in terms of estradiol secretion, and blood samples were taken every 12 h to determine plasma estradiol concentration from Days 0 to 2. Ovaries from all females in both groups were recovered by ovariectomy on Day 2 to determine apoptosis by immunohistochemistry for active caspase-3 in granulosa cells from SF of 3 to 5 mm in diameter. Additionally, SF were histologically classified as healthy, early, or advanced atretic. Data were analyzed by Student t-test and Pearson correlation. The total number of PF observed on Day 2 was 15 and 12 for the PGF and FGA groups, respectively. The 90.9 and 93.3% of PF recorded in the PGF and FGA groups, respectively, on Day 2 was retrospectively identified on Day 0. The 33.6 and 46.6% of those follicles from the PGF and FGA groups, respectively, corresponded to follicles &gt;5 mm in diameter. Although mean diameter of PF was higher in the FGA group than in the PGF group (5.4 ± 0.4 mm v. 4.5 ± 0.4 mm, respectively; P &lt; 0.01) on Day 0, PF diameter was similar between groups on Day 2. Plasma estradiol concentration was significantly higher (P &lt; 0.05) in the PGF group on Day 1 (3.1 ± 0.2 pg/mL v. 1.7 ± 0.2 pg/mL in the FGA group) but did not differ between groups on Day 2. The growing pattern of the PF in the PGF group significantly (P &lt; 0.05) affected the total number of SF, and there was a tendency (P = 0.08) for an increase of the total number of healthy follicles in the same group. In addition, advanced atretic follicles from the FGA group were significantly higher than those observed in the PGF group (P &lt; 0.001). Additionally, caspase-3 immunoreactivity was higher in the FGA group than in the PGF group (P &lt; 0.05) and it was associated with the largest SF in both groups. All of these finding are indicative of the presence of aged follicles with an extended permanence in the ovary. We concluded that the use of progestagen for 14 days in protocols for estrus synchronization in sheep affects the growth pattern and functionality of the preovulatory follicle during the follicular phase and may have a deleterious consequence on oocyte competence. CYCITAGL2005-02669 and DID-D-2007-03 UACh.

Estrus synchronization in sheep with synthetic progestagens

Sixteen female sheep of Degua breed were assigned to receive either the full dose of norgestomet ear implant and injectable solution containing norgestomet and estradiol valerate (n = 8) or half the dose (n = 8). The ear implants were removed in both groups on day 12. All ewes received an intramuscular administration of 500 IU PMSG at implant withdrawal. Synchronized ewes were individually hand mated twice at 48 and 60 hours after implant removal. One ewe in each group however refused mating on both occasions. Pregnancy diagnosis was conducted by bimanual external palpation 90 to 100 days post mating. The conception rates (3/7, 42.85%) and (5/7, 71.42%) were recorded in the two treatment groups, respectively. All eight ewes lambed between 145 to 153 days post mating. In group I ewes carried only singletons (prolificity rate 1.0) whereas in group II two ewes delivered twins, producing 7 lambs with prolificity rate of 1.4 (N.S). From this preliminary investigation it appears that the lower dose of norgestomet ear implants offers better option for estrus synchronization accompanied by higher fertility.

Estrus Synchronization in Sheep and Goats Using Combinations of GnRH, Progestagen and Prostaglandin F2α

The objective of this experiment was to evaluate the effect of GnRH, progestagen and prostaglandin F(2alpha) on estrus synchronization in sheep and goats. Sixty Awassi ewes and 53 Damascus does were used in the study. The experiment started at the beginning of the breeding season (June/July). The same treatments were applied to sheep and goats as follows: no treatment (CON), 14-day progestagen sponges and 600 IU equine chorionic gonadotropin (S), gonadotropin releasing hormone followed 5 days later by prostaglandin F(2alpha) (GP) and gonadotropin releasing hormone, progestagen sponges for 5 days and prostaglandin F(2alpha) on the day of sponge removal (GSP). None of the ewes in the S group lambed from mating during the induced cycle. A greater lambing rate (p < 0.05) was observed in the GSP group compared with the CON and S groups while the GP group was intermediate. The number of lambs born per lambed ewe was similar among the CON, GP and GSP groups. However, the number of lambs per exposed ewe was greater (p < 0.05) in the GSP than the remaining groups. The induced cycle kidding rate was 77% for all treatments combined. Similar kidding rate were observed among treatments. The numbers of kids born per kidded and exposed doe from mating during the induced estrus were also similar among treatments. Greater numbers of multiple births were observed in the GP and GSP than in the S group. In conclusion, a combination of GnRH, progestagen sponges and PGF(2alpha) can be effective in synchronizing estrus and improving fecundity in sheep and goats. Although the use of GnRH-PGF(2alpha) was effective, the addition of progestagen sponges at the time of GnRH administration appeared to improve reproductive parameters.

Use of progestagen–gonadotrophin treatments in estrus synchronization of sheep

The main objective of this study was to investigate the effectiveness of certain progestagen–gonadotrophin treatments on synchronization of estrus in sheep. In Experiment I, 30 Chios ewes were treated at the beginning of the breeding season with medroxyprogesterone acetate (MAP) intravaginal sponges for 12 days and a single i.m. treatment of either FSH (Group 1,10 IU, n=8; Group 2, 5 IU, n=8; Group 3, 2.5 IU, n=8) or eCG (Group 4, 400 IU, n=6) at the time of sponge removal. Ten days after sponge removal laparotomy was performed to record ovarian response. Clinical estrus was observed in more (though not at a significant level) FSH treated than eCG treated sheep (62.5% versus 33.3%). Administration of 400 IU eCG resulted in the highest mean number of CL per ewe ovulating (2.8±0.2), with administration of 10 IU FSH producing the next best results (2.1±0.3). Statistically significant differences in the mean number of CL per ewe ovulating were found only between ewes in Group 3 (1.7±0.4) and Group 4 (2.8±0.2) ( P<0.05). In Experiment II, 53 Chios and 30 Berrichon ewes were treated during the mid-breeding season with MAP intravaginal sponges for 12 days and a single i.m. treatment of either 10 IU FSH (27 Chios and 16 Berrichon ewes) or 400 IU eCG (26 Chios and 14 Berrichon ewes), at the time of sponge removal. Ewes that were in estrus on Days 2–4 and 19–23 after sponge removal were mated to fertile rams. No significant differences were recorded between treatment or breed groups in the proportions of ewes observed in estrus after treatment. In the Berrichon breed, FSH administration resulted in higher lambing rates (93.8% versus 57.1%, P<0.05) and higher mean number of lambs born per ewe exposed to rams (1.4±0.2 versus 0.8±0.2, P<0.05) than that of eCG. After treatment with eCG, the mean number of lambs born per ewe exposed to rams was higher in the Chios than the Berrichon breed (1.4±0.2 versus 0.8±0.2, P<0.05). After treatment with FSH, the lambing rate was higher in the Berrichon than the Chios breed (93.8% versus 63.0%, P<0.05). In conclusion, a single FSH treatment (5 or 10 IU) at the end of progestagen treatment appears to be more effective than eCG for the induction of synchronized estrus in sheep at the beginning of the breeding season, with no cases of abnormal ovarian response observed. During the mid-breeding season FSH (10 IU) appears to be equally as effective as eCG (400 IU) in respect of lambing rate and mean number of lambs born per ewe.

Synchronization of estrus in sheep using progestagen and inseminating with chilled semen during the breeding season

The efficiency of synchronization following the use of halved or whole (60 mg) MAP sponges and 300 IU PMSG during the breeding season was evaluated using 111 Merino ewes. Artificial insemination was performed with chilled semen (stored as 15 °C for 3 h) at 55 h following sponge withdrawal in the progestagen treated ewes and at 12 h following the onset of natural estrus in the control group. Estrous occurrence from time of sponge withdrawal, the interval from sponge withdrawal to estrus (mean of 30.5 vs 27.5 h for the whole and halved sponges, respectively) and the duration of the induced estrous period (mean of 25.1 vs 28.3 vs 35.0 h for the whole, halved sponges and control groups, respectively) was not significantly different in the groups. A high percentage of MAP was still present in the whole (76.6%) and halved (49.3%) sponges following withdrawal after 14 days. The mean serum progesterone concentration during the estrous period was higher ( P < 0.01) in the control group. No significant difference was found in the peak serum LH concentrations and the position of the LH peak relative to estrus. The conception rate was higher ( P < 0.01) in the halved sponges and the control (70.5 and 64.0%, respectively), compared with the whole MAP sponges (54.8%). Similarly the lambing rate was also higher ( P < 0.01) for the halved sponges and control group, compared with the whole sponges (106.8 vs 104.9 vs 85.9%, respectively). Halving of 60-mg MAP sponges is warranted in the breeding season and fertility results obtained with chilled semen are satisfactory.

Evaluation of progesterone controlled internal drug release dispensers for synchronization of estrus in sheep

Three experiments were conducted to evaluate 366 mg progesterone, type S, controlled internal drug release dispensers (CIDR-S) for estrous synchronization. In Experiment 1, synchronization of estrus was investigated in early fall. Of 129 ewes treated for 12 days, 117 (91%) were bred within 5 days of dispenser removal. A total of 118 (91%) ewes lambed with 74% of lambings occurring within 6 days of each other. In Experiment 2, duration of progesterone release from CIDR-S was examined over a 45-day period. In ovariectomized ewes, plasma progesterone levels were 2.8 ng/ml 3 days after insertion and then decreased gradually to 0.3 ng/ml by day 30. In cycling ewes, Day 3 levels were 4.5 ng/ml due to contribution of luteal progesterone. Exogenous progesterone blocked estrus and ovulation for 27 to 31 days, after which ovulation occurred without estrus. Estrus with ovulation occurred by Day 38 to 45. In Experiment 3, cycling ewes were treated for 0, 4 or 12 days and progesterone residue in adipose, liver, kidney and muscle tissues was measured. Residues differed ( P < 0.05) among treatment groups and tissue types with no interaction. Tissue progesterone levels of ewes treated for 4 days were greater than those in ewes treated for 0 and 12 days. Adipose tissue contained over 10 times as much progesterone as other tissues. Progesterone residues were related ( r = 0.5, P < 0.05) to circulating progesterone levels at time of death but with neither total nor peak levels reached during the treatment period. CIDR-S had a 92% retention rate and provided a simple and effective delivery of natural progesterone.

Synchronization of oestrus in sheep: The use of controlled internal drug release (CIDR) dispensers

The use of the CIDR (controlled internal drug release) dispenser as a progestagen-synchronizing agent was evaluated in 37 Karakul ewes during the breeding season, using the intravaginal progestagen sponge as a control (30 ewes). Although there was no significant differences in oestrous response, following intravaginal insertion for 14days, between these two progestagen devices, the time from device withdrawal to the onset of the induced oestrous period (31,2 vs 62,5 h) and the duration of the induced oestrous period (32,7 vs 47,4 h) was significantly (P<0,01) shorter in the CIDR dispenser group. The mean time from device withdrawal to the serum preovulatory LH peak and the interval from the onset of oestrus to the pre-ovulatory LH peak was significantly (P<O,Ol) earlier in the CIDR dispenser group (28,0 vs 78,0 hand 5,3 vs 17,3 h respectively). No significant difference in the serum progesterone concentrations was noted between the two groups. No significant difference in reproductive performance was obtained with conception, lambing rates and fecundities of 72,2 vs 79,3%; 75,0 vs 89% and 103,8 vs 113,0% for the dispenser and sponge treatment groups respectively. Results confirm the potential of the CIDR dispenser as an efficient synchronizing agent and the more concentrated synchrony obtained makes it ideal for fixed-time insemination.

Induction of oestrus in ewes using a controlled internal drug release device and PMSG

A number of methods have been developed for synchronization of oestrus in sheep (reviewed by Maxwell, 1984), but the most successful have been based on the suppression of the oestrous cycle by treatment with a polyurethane progestagenimpregnated intravaginal sponge (Robinson, 1965). A precise synchronization of oestrus and ovulation for artificial insemination (A.I.) is obtained following a 12- to 14-day treatment with the intravaginal sponge and an injection of pregnant mares serum gonadotrophin (PMSG) at sponge removal (Robinson &amp; Smith, 1967). This allows a single fixed time A.I. to be performed on all ewes without the need for detection of oestrus.

Intravaginal Controlled Administration of Flurogestone Acetate I: Development of a Stability-Indicating Liquid Chromatographic Method and Stability Kinetics of Flurogestone Acetate

Flurogestone acetate is a synthetic progestin useful for estrus synchronization in sheep. The estrus synchronization is achieved by inserting the drug‐impregnated vaginal sponge in the sheep for up to 15 d, during which time flurogestone acetate is administered continuously by intravaginal absorption to suppress estrus and ovulation. The sponge is then withdrawn to regain estrus within 2‐4 d. A review of the literature suggests that the analytical methods currently available are not specific, sensitive, and rapid enough. A stability‐indicating high‐performance liquid chromatographic method was developed, which is capable of characterizing the stability kinetics of flurogestone acetate under various environmental conditions and quantifying the release and absorption profiles of the drug from the vaginal sponges.

Fertility following synchronization of oestrus in Romney, Corriedale and Merino ewes.

Abstract Extract Synchronization of oestrus in sheep has been achieved by the use of progesterone and progesterone analogues administered either as an intramuscular injection, or by an impregnated sponge inserted into the the vagina (Robinson, 1958 Robinson, T. J. 1958. Studies in controlled artificial insemination of Merino sheep. Aust. J. agric. Res., 9: 693–703. [Google Scholar], 1961 Robinson, T. J. 1961. The time of ovulation and efficiency. of fertilization following progesterone and pregnant mare serum treatment in the cyclic ewe. J. agric. Sci., Camb, 57: 129–135. [Google Scholar], 1964 Robinson, T. J. 1964. Synchronisation of oestrus in sheep by intravaginal and subcutaneous application of progestin impregnated sponges. Proc. Aust. Soc. anim. Prod., 5: 47–52. [Google Scholar]; Denny and Hunter, 1958 Denny, J. F. and Hunter, G. L. 1958. Synchronisation of the oestrus cycle in sheep. S. Afr. J. agric. Sci, 1: 381–388. [Google Scholar]; Brunner et al., 1964 Brunner, M. A., Hansel, W. and Hogue, D. E. 1964. Use of 6-methyl-17-acetoxyprogesterone and pregnant mare serum to induce and synchronise oestrus in ewes. J. anim. Sci., 23: 32–36. [Google Scholar]; Clark et al., 1966 Clark, J. N., Roberts, E. M., Carter, A. H. and Kirton, A. H. 1966. Hormonal synchronisation of oestrus in Romney Marsh ewes during the breeding season. Proc. N.Z. Soc. anim. Prod., 26: 107–121. [Google Scholar]). Twenty milligrams of progesterone administered every second day appears as effective as 10 mg daily (Robinson, 1958 Robinson, T. J. 1958. Studies in controlled artificial insemination of Merino sheep. Aust. J. agric. Res., 9: 693–703. [Google Scholar]) and provides satisfactory synchronization and fertility to natural service (Lamond and Bindon, 1962 Lamond, D. R. and Bindon, B. M. 1962. Oestrus, ovulation and fertility following suppression of ovarian cycles in Merino ewes by progesterone. J. Reprod. Fertil., 4: 57–66. [Google Scholar]).

Synchronization of oestrus in sheep by orally active progesterone derivative

In a preliminary experiment with 40 Merino ewes of 45 kg liveweight, oral doses of 0, 6.6, 20, and 60 mg 6-methyl-17-acetoxyprogesterone were administered daily for 14 days. The highest dose level completely prevented oestrus during treatment, and all 10 ewes came into oestrus during the 5-day period beginning 24 hr after the last dose; seven of the 10 ewes conceived and lambed. Daily doses of 6.6 and 20 mg reduced the incidence of oestrus during treatment, but produced little synchronization subsequently. In the main experiment 77 similar ewes were treated over 17 days with either 6-methyl-17-acetoxyprogesterone (50 mg orally per day, 39 ewes), or progesterone (10 mg in oil intramuscularly every second day, 38 ewes). There were 19 untreated ewes. Some ewes from each group were marked by rams during the treatment period. In the 6 days following the final dose of progestagen 75% of ewes were marked by rams, with a peak on the third day. There was no difference between treatments. The proportion of ewes that lambed following mating in the 6 days after cessation of treatment was 15/29 and 11/29 for 6-methyl-17-acetoxyprogesterone and progesterone treatments respectively. In the main experiment half the ewes were injected with pregnant mare serum gonadotrophin 24 hr after the last dose of progestagen, and 24 hr later, with human ohorionic gonadotrophin. This supplementary treatment did not further reduce inter-animal variation in time of onset of oestrus, but tended to reduce the proportion of ewes exhibiting oestrus.