Approaches of estrous synchronization in sheep: developments during the last two decades: a review

Investigation of the effectiveness of ultrasonography in determining pregnancy and the number of fetuses on the 35th day of pregnancy in Awassi sheep

“…In sheep, progesterone or prostaglandins have been used most commonly for oestrus synchronization. Gonadotropins (eCG and GnRH) are often used to increase the efficiency of P4-based protocols (Hameed et al, 2021). In small ruminants, oestrus occurs 24-48 hours after removing the intravaginal sponges for oestrus synchronization (Uçar and Özyurtlu, 2015).…”

“…In sheep, the conception rates for progesterone applications are reported to be around 70-80% (Gordon, 1997). Synchronization studies using different doses of MAP+eCG report pregnancy rates between 20% and 100% in sheep (Hameed et al, 2021).…”

Towards Improving the Outcomes of Multiple Ovulation and Embryo Transfer in Sheep, with Particular Focus on Donor Superovulation

“…Therefore, the synchronization of estrus is an important tool that can enhance the efficiency of ARTs. The traditional protocols for the synchronization in sheep are based on progestogen/progesterone treatment in the form of intravaginal implants, such as sponges and CIDRs [ 17 , 77 ]. Intravaginal sponges are usually inserted for 11–14 days, and ewes usually show estrous signs 24 to 48 h after sponge removal ( Table 1 ).…”

“…Superovulation is an important step in any MOET program, in which the maximum oocyte number can be produced by the same animal through injecting various gonadotropin hormones. During superovulation, intravaginal sponges are inserted for 12 to 14 days, followed by various exogenous gonadotropins, usually starting two days before the withdrawal of vaginal pessary [ 7 , 17 ]. This stimulates follicular growth, which ultimately leads to multiple ovulations.…”

Effects of exogenous GnRH administration on lambing performance of oestrus‐synchronized Kazak ewes during the breeding season

“…A single dose of GnRH given 24 to 36 h after removal of the progestagen pessary synchronizes the luteinizing hormone peak approximately 40 h after pessary removal and ovulation occurs in 90% of ewes within 72 h after pessary removal (Menchaca & Rubianes, 2004). Although GnRH is already widely used in ovine fixed time artificial insemination programmes (Hameed et al, 2021), the effects of GnRH on pregnancy rates are controversial (Menchaca & Rubianes, 2004). Some studies reported that a single dose of GnRH given 24 to 48 h after pessary removal increased the pregnancy rate (Biehl et al, 2017; Kutlu & Dinç, 2021), while some others have reported no changes (Ayaseh et al, 2021; Cavalcanti et al, 2012; Olivera‐Muzante et al, 2011; Reyna et al, 2007; Türk et al, 2008) or even decreased the pregnancy rate (Martemucci & D'Alessandro, 2011; Olivera‐Muzante et al, 2013; Walker et al, 1989).…”