Estrous and fertility responses of dairy ewes synchronized with combined short term GnRH, PGF2α and estradiol benzoate treatments

Pharmacological approaches to induce follicular growth and ovulation for fixed-time artificial insemination treatment regimens in ewes

In Experiment I, during the non-breeding season, after intravaginal devices containing progesterone (P₄) were withdrawn (n = 28), estrous rates were greater with treatment with 400 IU eCG (P <  0.05) than with FSH (10 and 15 mg) and no treatment. During the breeding season (n = 147), estrous and pregnancy rates after fixed-time artificial inseminations (FTAI) were similar among groups: 300 IU eCG; 10 mg FSH; and control (P >  0.05). In Experiment II (non-breeding season), ewes of one group were treated with 300 IU eCG (n = 8) and of two groups were treated with 10 mg FSH. In one FSH group, 250 μg estradiol benzoate (EB) were administered after 24 h (n = 9); in the other, 4 μg GnRH were administered after 36 h (n = 10). Serum P₄ concentrations were greater in eCG-treated ewes (P < 0.05). Estrous rates were similar for the eCG- and FSH plus EB-treated ewes (P >  0.05). In Experiment III (breeding season), the treatments were: 300 IU eCG; 250 μg estradiol cypionate; 250 μg EB; or control (n = 22). Follicular growth was greater for eCG-treated ewes within 0-24 h and for control ewes within 48-72 h (P =  0.001). Although estrous and ovulation rates did not differ (P >  0.05), all eCG-treated ewes had ovulations. During the non-breeding season, FSH treatment promoted follicular growth but did not induce ovulations. For FTAI regimens, eCG was more effective than FSH plus GnRH and estradiol esters in inducing estrus and ovulation.

Effect of different protocols for estrus synchronization on reproductive performance of Santa Inês ewes under Amazon environmental conditions

 The objective of this study was to evaluate the effect of different hormonal protocols on the reproductive performance of Santa Inês ewes in Amazon environmental conditions. Twenty-two Santa Inês ewes between 3 and 4 years-old were distributed in a randomized block experimental design, where the treatments consisted of two protocols for estrus synchronization (short and long) with eleven animals each. Data on the occurrence of estrus were described for each protocol. Data of estrus, pregnancy, and prolificity were firstly subjected to ANOVA and a subsequent Tukey’s test. Results were considered significant at p ≤ 0.05. The short-term protocol presented an interesting successful rate, where above 70% ewes tested had estrus. The long-term protocol also achieved a high successful rate, where above 80% ewes tested had estrus. However, comparing the protocols, the long-term protocol presented better results of positive estrus and pregnancy rates in ewes. Thus, it can be concluded that both protocols presented satisfactory results regarding estrus manifestation, and prolificity (lambs produced per ewe). However, under Amazon environmental conditions, the long-term protocol presented better results regarding positive manifestation of estrus and pregnancy rate.

Pregnancy rates in hair sheep after Ovsynch synchronization and a combined intracervical fixed-time artificial insemination and 10-day mating period

Aim:

This study aimed to evaluate the pregnancy rates in hair ewes using an Ovsynch synchronization protocol under a breeding system that combines fixed-time insemination plus a 10-day mating period as an alternative.

Materials and Methods:

Through an experimental study (n=27), ewes were randomly located into one of three treatments: (1) Pre-synch (n=9): Prostaglandin F2α (PGF2α)+Gonadotropin-releasing hormone (GnRH)+PGF2α+GnRH; (2) Ovsynch (n=9): GnRH+PGF2α+GnRH; and (3) control: Ewes bred by natural mating (NM) (n=9). Ewes were fixed-time inseminated (fixed-time artificial insemination [FTAI]) with fresh semen, collected just before the insemination time through vaginoscopy at 16 h after the second GnRH (gonadorelin) injection. Each experimental group was placed separately during 15 days and, after this time, fertile rams were allowed back with ewes for a 10-day mating period. Control group ewes remained with the rest of the herd suitable for breeding and were bred under NM. Pregnancy diagnosis was performed by ultrasound at 28-, 56-, and 84-day post-breeding to differentiate between FTAI and NM pregnancies. Total (FTAI±NM) pregnancy rates at 56-day post-breeding were used to compared Pre-synch, Ovsynch, and control. For this purpose, two-tailed proportions comparison z-test was used with a 95% confidence level, for testing as the null hypothesis whether two proportions were equal.

Results:

Pregnancy rates were higher in control ewes (66.4%) than FTAI (46.6%). When pregnancy rates after a 10-day mating period (40%) were added, the final rate (86.6%) was significantly (p<0.05) higher in Ovsynch-based protocols. The pregnancy rate was significantly lower in FTAI ewes compared to FTAI +10-day mating group (p<0.05). The overall pregnancy rate was 88.0, 85.7, and 67.0 (p>0.05) for Pre-synch, Ovsynch, and control ewes, respectively.

Conclusion:

These results provide evidence on the benefits of combined FTAI protocols for improving the reproductive efficiency of sheep.

Induction of fertile estrus without the use of steroid hormones in seasonally anestrous Suffolk ewes

Objective

To evaluate the efficacy of treatments based on GnRH, GnRH-PGF2α, and/or intense exposure to novel rams to induce fertile estrus without the use of steroid hormones in seasonally anestrous Suffolk ewes.

Methods

In the first experiment, ewes were treated with one injection of GnRH, two injections of GnRH administered 7 days apart, or a sequence of GnRH-PGF2α-GnRH. In the second experiment anestrous ewes were exposed, for 36 days starting on the day of weaning, to groups of four rams of three different breeds that were alternated every day. Besides exposure to the males, the ewes were injected with saline solution (ME group, n=20), with GnRH (ME-GnRH group, n=20) or with a sequence of GnRH-PGF2α-GnRH (ME-GPG group, n=20). The rams used for male-effect were fitted with aprons to prevent mating, and ewes detected in estrus were bred to selected fertile rams. Ovarian activity was monitored by progesterone determinations in both experiments.

Results

In the first experiment sustained induction of ovarian activity was not achieved and no ewe was detected in estrus. In the second experiment induction of sustained ovarian activity was achieved in all groups. Most of the ewes were detected in estrus, 76.7 % of the ewes were mated during a 36-d breeding period and 71.7 % of all the ewes became pregnant during that period. No significant differences between groups were found for any of these variables. However, estrus detection efficiency was higher in the ME-GnRH group than in the ME group (p<0.05).

Conclusion

An intense male-effect, that included the continuous presence and frequent alternation of several rams of different breeds, was sufficient to induce ovarian activity and fertile estrus in Suffolk ewes during the period of deep anestrus without the use of hormones, although addition of GnRH improved the efficiency of estrus detection.

Effects of progestagen exposure duration on estrus synchronization and conception rates of crossbreed ewes undergoing fixed time artificial insemination

Synchronization of estrus and ovulation are of paramount importance in modern livestock improvement programs. These methods are critical for assisted reproduction technologies, including artificial insemination and embryo transfer, that can increase productivity. In the current study, subcutaneous implants containing norgestomet were placed for long (14 days), medium (9 days), and short (5 days) periods of time in 70 crossbred ewes undergoing fixed-time artificial insemination. The resulting effects on estrus synchronization and conception rates were subsequently evaluated. Among the synchronized ewes, 85.7% (60/70) underwent estrus over a period of 72 h after progestagen treatment ceased. The shortest mean interval between withdrawal of the device and onset of estrus (34.2 ± 8.9 h) was observed in the G14 days of P4 group (p < 0.05). The conception rate of the G14 days of P4 group was statistically higher than that of the other groups (83.3% vs. 60.9% vs. 47.8%; p < 0.05). In conclusion, 14 days of norgestomet treatment produced higher conception rates and a greater number of pregnancies at the beginning of the breeding season.

Strategies for rapid rebreeding of lactating ewes in the spring

Rapid rebreeding of winter- and spring-lambing ewes is essential if ewes are to lamb more than once per year, but fertility of lactating ewes is often low and early weaning of lambs may be undesirable in forage-based production systems. Selection to improve fertility in spring matings has been successful and led to development of ewes with a reduced seasonal anestrus. Potential for rapid rebreeding of lactating out-of-season breeding (OOS) ewes was tested in three studies. In Experiment 1, effects of short-term lamb removal on rebreeding was evaluated over 2 years using 71 January-lambing OOS ewes. At an average of 63 days postpartum, 36 ewes had lambs removed for 72 h, and all ewes were joined with rams. Circulating progesterone levels indicated that 74% of ewes ovulated before lamb separation; 91% of ewes mated within 5 weeks of ram exposure, 85% were diagnosed as pregnant and 75% lambed. The average interval between lambings was 225 days. In contrast to results observed in cattle, none of the measured variables was affected by lamb separation (P>0.20). Experiment 2 compared rebreeding performance of 24 OOS and 23 St. Croix ewes that lambed in January and averaged 60 days postpartum at ram introduction. More OOS ewes ovulated, mated and became pregnant during the first 21 days of ram exposure (83.3%, 58.3%, and 41.7%, respectively; P<0.001) compared with St. Croix ewes (26.1%, 0%, and 0%, respectively). After 39 days of ram exposure, pregnancy rates still favored OOS ewes (66.7% v. 39.1%; P=0.06), but the percentage of ewes that lambed did not differ (P>0.20) between OOS (47.8%) and St. Croix ewes (34.8%). In the third study, 34 March-lambing OOS ewes were exposed to rams on May 3 at an average of 40 days postpartum to characterize their reproductive performance. After 39 days of ram exposure, 52.9±8.7% of the ewes had mated, and 38.2±8.5% were diagnosed as pregnant. However, only 20.6±7.0% of the ewes produced viable lambs, suggesting a high level of uterine insufficiency. Spring fertility of lactating OOS ewes in these studies was one of the highest reported in the literature and indicated that selection for fertility in spring mating would improve reproductive performance in accelerated lambing programs. However, exposure of lactating OOS ewes to rams at 30 to 50 days postpartum was associated with high prenatal lamb mortality.

Comparison of prostaglandin- and progesterone-based protocols for timed artificial insemination in sheep

The objective was to compare the reproductive performance of a new PGF(2α)-based timed artificial insemination (TAI) protocol in sheep (Synchrovine®: two doses of PGF(2α), 7 d apart) to a traditional progesterone-eCG (P4-eCG) protocol, considering the effects of seminal state, AI-times, and AI-pathway. Three experiments involving 1297 multiparous Australian Merino ewes were done during the physiologic breeding season (location 32 °S-57 °W). Reproductive performance was assessed as non-return rate to service 21 d after AI (NRR21d), based on detection with androgenized wethers, as well as Fertility (pregnant/inseminated ewes), Prolificacy (fetuses/pregnant ewe), and Fecundity (fetuses/inseminated ewe), which were based on transabdominal ultrasonography 50 d after TAI. In Experiment 1, Synchrovine® treated ewes TAI cervically with fresh semen at 42, 48, or 54 h had similar NRR21d (0.51, 0.46, 0.57), Fertility (0.27, 0.31, 0.26), and Fecundity (0.29, 0.32, 0.27), all of which were lower (P < 0.05) than in a control P4-eCG group inseminated at 54 h (0.61, 0.48, 0.52, NRR21d, Fertility and Fecundity respectively). In Experiment 2, using chilled semen and cervical TAI, Synchrovine® treated ewes inseminated at 42 h yielded lower (P < 0.05) NRR21d, Fertility and Fecundity (0.28, 0.06, 0.06) compared to 48 (0.43, 0.24, 0.24) and 54 h (0.44, 0.22, 0.23). In Experiment 3 with chilled semen, Synchrovine® treated ewes TAI into the cervix at 51 or 57 h were similar in NRR21d (0.16 vs 0.20), Fertility (0.12 vs 0.14), and Fecundity (0.12 vs 0.15), respectively; but lower (P < 0.05) than P4-eCG treated ewes TAI at 54 h (0.34, 0.28, and 0.33 for NRR21d, Fertility and Fecundity respectively). Synchrovine® treated ewes intrauterine TAI at 51 or 57 h yielded similar NRR21d (0.51 vs 0.58), Fertility (0.43 vs 0.51), and Fecundity (0.45 vs 0.56) respectively, but lower (P < 0.05) results compared to P4-eCG treated ewes (0.75, 0.71, and 0.88 for NRR21d, Fertility and Fecundity respectively). In conclusion, AI-time in Synchrovine® treated ewes with fresh semen might be extended (42 to 54 h after the second PGF(2α)), but should be delayed to 48-54 h with chilled semen and cervical AI. Independent of the seminal state, AI-time or AI-pathway, Synchrovine® yielded lower reproductive results than a conventional P4-eCG protocol.