Estrus resynchronization in ewes with unknown pregnancy status

Abstract

Although fixed-time artificial insemination (FTAI) protocols are available for sheep, estrus resynchronization has not been previously reported. The objectives of this study were to evaluate the effect of estrus resynchronization with exogenous progestogen on endogenous progesterone levels and to compare pregnancy rates after two consecutive estrus synchronizations in ewes. In Experiment 1, ewes (n = 20) received an intravaginal device (IVD) containing 60 mg medroxyprogesterone acetate (MPA) for 10 days. At the IVD withdrawal (D0), ewes received 250 IU eCG and were allocated into two treatments: either no further treatment (Control; n = 10) or estrus resynchronization (Resynch; n = 10) from D12 to D19. Serum progesterone (P4) levels did not differ at D12 and D19 (P > 0.05), but were greater at D15 for the Control compared with the Resynch group (P < 0.05). In experiment 2, ewes (n = 250) were submitted to a first synchronization protocol followed by estrus detection and either artificial insemination (AI) or natural mating (NM). Subsequently, ewes were divided into two groups: Control (n = 104): which received no further treatment and were bred by NM; and Resynch (n = 146): which were submitted to a second synchronization starting on D14 (first IVD withdrawal = D0) and to NM after second IVD withdrawal (D20). Cumulative pregnancy rates did not differ between the Control (67.3%, 70/104) and Resynch (62.3%, 91/146) groups. In a third experiment, ewes (n = 83) were bred by two consecutive FTAI within a 20-day interval. Pregnancy rates after the first (30.1%, 25/83) and the second FTAI (36.2%, 21/58) did not differ (P > 0.05). In conclusion, although exogenous progestogen supplementation reduced circulating levels of P4, pregnancy maintenance was unaffected. Estrus resynchronization in ewes is feasible, resulting in similar fertility after the first and the second services. The use of resynchronization coupled with artificial insemination using semen from genetically superior rams may potentially accelerate genetic improvement in sheep herds by allowing a higher differential selection compared with natural breeding.

Early resynchronization protocols for goats: Progestogens can be used prior to an early pregnancy diagnosis without affecting corpus luteum functionality

“…Miranda et al. (2018) proposed a negative effect of MAP devices on P4 production in ewes (5.8 ± 0.5 ng/ml for control group vs. 4.7 ± 0.5 ng/ml for MAP group on Day 15), although without negative effects on the final percentage of pregnant females. A later study found no effect on P4 values either on pregnancy or luteolysis in sheep species (Cosentino et al., 2019).…”

“…In ewes, even though Miranda et al. (2018) demonstrated a negative effect on P4 production, Cosentino et al. (2019) did not.…”

<p>Oxidative stress and biochemical markers in prenatally androgenized sheep after neonatal treatment with GnRH agonist</p>

“…The animals' cycles were synchronized and then subjected to artificial insemination using a mix of fresh semen collected from adult rams, as previously described. 19 Pregnancy was confirmed at 30 days by intravaginal/rectal ultrasonography. The animals were raised in an extensive farming system, with free access to water supplemented with mineral salts, pellet feed (1.5% of live weight), and alfalfa hay.…”

Koyunlarda Östrus İndüksiyonu Sonrası Ovaryum, Oviduct ve Endometriyumda Folikül Uyarıcı Hormon, Luteotropik Hormon, Östrojen ve Progesteron Reseptör Ekspresyonu

“…Induction of estrus with an intravaginal progesteronereleasing device (IPRD) and GnRH can enhance pregnancy rates in adult ewes, and ewe lambs out of the breeding season [3] . Exogenous gonadotrophins, such as pregnant mare serum gonadotrophin (PMSG), are used to stimulate follicular growth, which increase the estrus response and ovulation rate [4,5] , and also lead to a tighter synchrony of ovulation in out-of-season estrus induction and cyclic ewes [6,7] .…”