Abstract
Simple SummaryThe foreseeable shortage of equine chorionic gonadotrophin (eCG) for estrus synchronization in sheep will have a huge impact on breeders using out-of-season breeding, artificial insemination, or embryo transfer because there is no other product with similar activity. Hence, there is a strong need for alternative protocols. The aim of the present work was to evaluate the reproductive response of sheep in breeding season to the administration of gonadotrophin-releasing hormone (GnRH) using propylene-glycol as a cosolvent, as well as the most adequate timing for such administration. From the results obtained, protocols based on a short-term treatment with a Controlled Internal Drug Release (CIDR) device and a single dose of GnRH in propylene-glycol at 36 h after CIDR removal may constitute an alternative to traditional protocols based on the administration of a single dose of eCG at CIDR removal.The foreseen shortage of eCG for estrus synchronization in sheep makes necessary the development of alternative protocols. The aim of the present work was to evaluate the reproductive response of sheep in breeding season to the administration of GnRH using propylene-glycol as a cosolvent and the subcutaneous route for slowing and extending the release of GnRH, as well as the most adequate timing for such administration. In the present study, protocols based on a short-term CIDR treatment and a single subcutaneous dose of GnRH in propylene-glycol at 36 h after CIDR removal induced a similar ovarian response to protocols based on administration of eCG at CIDR removal or intramuscular GnRH in distilled water at 56 h after. In such protocol, 80% of the animals developed estrus in a narrow timing (75% between 36 and 48 h after CIDR removal), and all of them also ovulated in a narrow window (87.5% between 72 and 76 h after CIDR removal, with 62.5% between 72 and 76 h) and showed a similar ovulation rate and plasma progesterone concentrations at the induced estrous cycle. Hence, administration of GnRH in propylene-glycol may constitute an alternative to traditional protocols based on the administration of eCG.
Highlights
Induction and synchronization of estrus and ovulation in sheep, in both breeding or non-breeding season and both for natural mating or artificial insemination, mostly rely on the use of protocols including the insertion of intravaginal devices with progesterone or progestagens and a single dose of equine chorionic gonadotrophin at device removal [1]
The banning of equine chorionic gonadotrophin (eCG) will have a huge impact on sheep producers using out-of-season breeding, artificial insemination, or embryo transfer because there is no other product with similar activity [7]
From time of second PGF2α to ovulation in ewes treated with two doses of PGF2α and a single dose of distilled water or 50 μg of gonadotrophin-releasing hormone (GnRH) in either distilled water
Summary
Induction and synchronization of estrus and ovulation in sheep, in both breeding or non-breeding season and both for natural mating or artificial insemination, mostly rely on the use of protocols including the insertion of intravaginal devices with progesterone or progestagens and a single dose of equine chorionic gonadotrophin (eCG) at device removal [1]. Afterwards, was eCG found to be effective for ensuring a narrow window of ovulation among ewes in the same lot and was incorporated into first protocols including fixed-time artificial insemination (FTAI), which was developed in the 1960s [4,5]. These protocols have been carried on for decades, with changes only having been made in the type and duration of the progestative treatments, but always maintaining eCG as an essential component.
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