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

Abstract

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.

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

“…The screening of corpora lutea also showed similar ovulation rate and plasma progesterone concentrations to the control groups. The main difference among the groups eCG, PPG36, and WAT56, in agreement with previous studies [8], were mainly determined by the timing of onset of estrus behavior (i.e., the time needed by the preovulatory follicle to reach its maximal estradiol secretion and therefore to induce estrus signs), as the intervals between the preovulatory LH surge and the ovulation were similar among the three treatments. In fact, timing of ovulation in the group PPG36 was intermediate between groups eCG and WAT56, which, besides the narrow range of appearance of estrus and ovulation, indicated a good synchronization of the terminal growth phase of ovulatory follicles.…”

“…Secretion of estradiol during preovulatory stages and secretion of progesterone during the first days of the luteal phase of sheep play an important role on the expression of several hormones and signaling factors in the oviduct and uterine secretions, crucial for early embryo development [27][28][29]. Therefore, according to the results of the present study, the conditions created by the early GnRH administration would not promote adequate conditions for the final follicular growth and the conception in the ewe [8,30].…”

“…However, almost all (83-96%) of the treated sheep were found to be ovulated in spite of the absence of estrus signs. Concomitantly, occurrence of estrus was also slightly affected during breeding season [8]; its onset occurred later in GnRH-treated sheep compared with eCG-treated sheep, although intervals among timing of estrus-preovulatory luteinizing hormone (LH) peak-ovulation were similar with both hormones. Our hypothesis for such absence or delay of estrus signs would be that a single GnRH injection could not stimulate an adequate development and maturation of the preovulatory follicle.…”

The effect of prostaglandin and gonadotrophins (GnRH and hCG) injection combined with the ram effect on progesterone concentrations and reproductive performance of Karakul ewes during the non‐breeding season

“…Dursun (2019) reported that the injection of GnRH or hCG in synchronized ewes (not pregnant after multiple matings) with sponge combined with pregnant mare serum gonadotropin and PGF2α increased the profitability of flocks at the end of the breeding season. During the breeding season, a double administration of GnRH (at device insertion and 56 hr after CIDR removal) instead of eCG had similar P4 concentrations and fertility rate in a protocols based on short‐term (five days) CIDR treatment (Martinez‐Ros & Gonzalez‐Bulnes, 2019). Improved oestrous synchronization and fecundity were reported in ewes receiving GnRH–PGF2α protocol when progestagen sponge was applied during treatment at the beginning of the breeding season (Titi, Kridli, & Alnimer, 2010).…”

The Effect of P4 + eCG Estrus Induction Protocol during the Deep and the Transition Anestrous Period on the Reproductive Performance of Crossbred Dairy Goats

“…Reproductive seasonality is an adaptation mechanism developed in response to environmental changes and food availability across a given year. Estrus and ovulation synchronization in small ruminants can be controlled by different means, such as the administration of progesterone (P4) plus equine chorionic gonadotropin (eCG), to counteract reproduction seasonality [ 1 ], using either artificial insemination or natural mating [ 2 ]. Such a reproductive seasonality occurs in temperate regions of the world and negatively affects products for marketing of sheep and goats [ 3 , 4 ], from regions ≥25° N [ 5 , 6 ] to the higher latitudes >40° N and S; [ 7 ].…”