Effects of estrus synchronization protocols using prostaglandin and gonadotropins on reproductive performance of Afshari ewes

Introduction: Intravaginal progestagens are widely used to synchronize estrus in sheep, typically resulting in an estrus rate of 90% and a pregnancy rate of 70–80% (Evans et al., 2001). However, these protocols are long-term and expensive. Moreover, there is a need to reconsider these intravaginal devices for social reasons such as animal health, welfare, food safety, and environmental impact (Gonzalez-Bulnes et al., 2020). PGF2α-based protocols produce less environmental pollution compared to intravaginal progesterone devices and are more cost-effective (Fierro et al., 2013); therefore, they may serve as a suitable alternative for estrus synchronization in ewes. To improve PGF2α-based protocols, the administration of gonadotropins has been investigated in several studies. For instance, the studies of Moradi Kor et al. (2012) and Mirzaei et al. (2017) demonstrated that GnRH-PGF2α treatment or GnRH-PGF2α-eCG treatment provided acceptable estrus rates and fertility in ewes. However, the repeated use of gonadotropins, such as eCG, has resulted in low pregnancy rates due to the development of a humoral immune response in small ruminants. In this context, Cox et al. (2024) compared the ability of hCG versus eCG to support follicular growth and fertility. Their results showed that ewes treated with hCG exhibited similar performance to those treated with eCG. The present study was conducted to investigate the effect of GnRH and hCG injections in PGF2α-based protocols on progesterone concentration and reproductive performance in Afshari ewes during the breeding season. Materials and Methods: This experiment was carried out during the breeding season (September 2023) at the Afshari Sheep Breeding Station in Zanjan, Iran. Ewes (n=64) were divided into treatment (GhP and GPP) and control groups. Control ewes (n=24) received intravaginal sponges (contacting 60 mg Medroxy Progesterone Acetate) for 14 days with an eCG injection at the time of sponge removal. The treatment groups were intramuscularly injected with a GnRH analogue at the beginning of the study (Day 0). The GhP group (n=20) was treated with hCG five days later, followed by an intramuscular PGF2α injection seven days after that. The GPP group (n=20) was treated with two doses of PGF2α, administered five and twelve days later, respectively. Blood samples were collected via jugular venipuncture on days -10, 0, and 17 after mating. Results and Discussion: The estrus and pregnancy rate did not differ between treamtments. The interval to estrus was significantly delayed in the GhP group (P<0.01), which may be attributed to the status of the corpous luteum and the stage of follicular development at the time of PGF2α administration (Moradi Kor et al., 2012), as well as the disruption of follicular development following hCG administration (Bruno-Galarraga et al., 2021). The control group exhibited higher progesterone concentrations compared to the treatment groups on day 17 after mating (P<0.01). One possible reason for this observation could be the effect of eCG on the size and weight of the corpus luteum (Silva Filho et al., 2013) and, consequently, on progesterone concentration (Baruselli et al., 2009). A non-statistical comparison of the economic aspects showed that PGF2α-based protocols reduced the duration and cost of treatments. Conclusion: In this study, ewes injected with GnRH and PGF2α exhibited reproductive performance comparable to that achieved with intravaginal progestagene sponges+eCG. Considering the time and cost of estrous synchronization protocols, the GnRH-PGF2α-PGF2α protocol appears to be more efficient and cost-effective compared to conventional intravaginal progestagene sponges +eCG protocol.
Key words: Breeding season, Estrus rate, GnRH, hCG, PGF2α, Sheep reproduction.





Introduction: Intravaginal progestagens are widely used to synchronize estrus in sheep, typically resulting in an estrus rate of 90% and a pregnancy rate of 70–80% (Evans et al., 2001). However, these protocols are long-term and expensive. Moreover, there is a need to reconsider these intravaginal devices for social reasons such as animal health, welfare, food safety, and environmental impact (Gonzalez-Bulnes et al., 2020). PGF2α-based protocols produce less environmental pollution compared to intravaginal progesterone devices and are more cost-effective (Fierro et al., 2013); therefore, they may serve as a suitable alternative for estrus synchronization in ewes. To improve PGF2α-based protocols, the administration of gonadotropins has been investigated in several studies. For instance, the studies of Moradi Kor et al. (2012) and Mirzaei et al. (2017) demonstrated that GnRH-PGF2α treatment or GnRH-PGF2α-eCG treatment provided acceptable estrus rates and fertility in ewes. However, the repeated use of gonadotropins, such as eCG, has resulted in low pregnancy rates due to the development of a humoral immune response in small ruminants. In this context, Cox et al. (2024) compared the ability of hCG versus eCG to support follicular growth and fertility. Their results showed that ewes treated with hCG exhibited similar performance to those treated with eCG. The present study was conducted to investigate the effect of GnRH and hCG injections in PGF2α-based protocols on progesterone concentration and reproductive performance in Afshari ewes during the breeding season. Materials and Methods: This experiment was carried out during the breeding season (September 2023) at the Afshari Sheep Breeding Station in Zanjan, Iran. Ewes (n=64) were divided into treatment (GhP and GPP) and control groups. Control ewes (n=24) received intravaginal sponges (contacting 60 mg Medroxy Progesterone Acetate) for 14 days with an eCG injection at the time of sponge removal. The treatment groups were intramuscularly injected with a GnRH analogue at the beginning of the study (Day 0). The GhP group (n=20) was treated with hCG five days later, followed by an intramuscular PGF2α injection seven days after that. The GPP group (n=20) was treated with two doses of PGF2α, administered five and twelve days later, respectively. Blood samples were collected via jugular venipuncture on days -10, 0, and 17 after mating. Results and Discussion: The estrus and pregnancy rate did not differ between treamtments. The interval to estrus was significantly delayed in the GhP group (P<0.01), which may be attributed to the status of the corpous luteum and the stage of follicular development at the time of PGF2α administration (Moradi Kor et al., 2012), as well as the disruption of follicular development following hCG administration (Bruno-Galarraga et al., 2021). The control group exhibited higher progesterone concentrations compared to the treatment groups on day 17 after mating (P<0.01). One possible reason for this observation could be the effect of eCG on the size and weight of the corpus luteum (Silva Filho et al., 2013) and, consequently, on progesterone concentration (Baruselli et al., 2009). A non-statistical comparison of the economic aspects showed that PGF2α-based protocols reduced the duration and cost of treatments. Conclusion: In this study, ewes injected with GnRH and PGF2α exhibited reproductive performance comparable to that achieved with intravaginal progestagene sponges+eCG. Considering the time and cost of estrous synchronization protocols, the GnRH-PGF2α-PGF2α protocol appears to be more efficient and cost-effective compared to conventional intravaginal progestagene sponges +eCG protocol.
Key words: Breeding season, Estrus rate, GnRH, hCG, PGF2α, Sheep reproduction.