Effect of estrus expression or treatment with GnRH on pregnancies per embryo transfer and pregnancy losses in beef recipients synchronized with estradiol/progesterone-based protocols
Two experiments were designed to determine the effect of expression of estrus or GnRH treatment on pregnancies per embryo transfer (P/ET) and pregnancy losses in beef recipients that were synchronized with estradiol/progesterone based protocols for fixed-time embryo transfer (FTET). Experiment 1 eva...
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| Published in: | Theriogenology Vol. 157; pp. 378 - 387 |
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| Main Authors: | , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
United States
Elsevier Inc
01-11-2020
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Two experiments were designed to determine the effect of expression of estrus or GnRH treatment on pregnancies per embryo transfer (P/ET) and pregnancy losses in beef recipients that were synchronized with estradiol/progesterone based protocols for fixed-time embryo transfer (FTET). Experiment 1 evaluated the effect of expression of estrus and GnRH treatment in the absence of estrus on P/ET. Beef cows (n = 729) were treated with 2 mg estradiol benzoate (EB) and an intravaginal device containing 0.5 g of progesterone. Devices were removed 8 d later and all cows received prostaglandin F2α (PGF2α), 400 IU eCG, and 0.5 mg estradiol cypionate (ECP) at that time. Expression of estrus was determined at 48 and 56 h after device removal using tail-paint and cows that did not show positive signs of estrus by 48 h received GnRH or no treatment at random. The overall estrus rate was 76.0% (554/729); 68.0% had positive signs of estrus by 48 h after progesterone device removal and 28.0% of those not in estrus by 48 h showed estrus by 56 h. The proportion of recipients receiving in vivo-derived (IVD) or in vitro-produced (IVP) embryos and P/ET were greater in recipients that showed estrus by 48 and 56 h (94.0% and 48.4%, respectively) than in those that did not show estrus 41.0% and 29.0%, respectively; P < 0.01). However, GnRH treatment of recipients not showing estrus by 48 h did not improve P/ET. Experiment 2 evaluated the effect of expression of estrus on P/ET and pregnancy loses up to parturition in recipients synchronized with two estradiol-based protocols. Beef cows (n = 403) were divided at random to receive the same synchronization protocol as in Experiment 1 (ECP) or a J-Synch protocol (device removal on day 6 and without using estradiol cypionate to induce ovulation). In this experiment, pregnancy was determined at 30 and 60 d by ultrasonography, and all pregnant recipients were followed until parturition to determine pregnancy losses during gestation. Although the number of recipients receiving IVP embryos was greater in the ECP group (90.5% vs. 83.5%; P = 0.03), P/ET did not differ (ECP: 37.0% and J-Synch: 39.0%; P = 0.43). Overall, 88.0% (357/407) of the recipients synchronized showed estrus and a greater P/ET (P = 0.05) was found in the recipients that showed estrus (39.0%) vs. those that did not show estrus (26.0%), regardless of treatment group. Pregnancy losses were lower (P = 0.004) and the calving rate was higher (P = 0.01) in recipients that showed estrus (25.0% and 29.3%, respectively) than in those that did not (88.8% and 2.9%, respectively). In summary, expression of estrus was associated with a greater P/ET in recipients treated with two different estradiol/P4-based synchronization protocols. The expression of estrus was associated with a greater proportion of recipients receiving embryos, P/ET and calving rate. Treatment with GnRH did not improve P/ET in the recipients that did not show estrus, questioning the its use in recipients synchronized with estradiol/progesterone based FTET protocols.
•Expression of estrus was associated with increased utilization and pregnancy rates.•GnRH treatment in recipients that did not show estrus did not improve utilization or pregnancy rates.•Pregnancy losses throughout gestation were greater in recipients that did not show estrus. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 ObjectType-Undefined-3 |
| ISSN: | 0093-691X 1879-3231 |
| DOI: | 10.1016/j.theriogenology.2020.08.023 |