A Review of Advances in Artificial Insemination (AI) and EmbryoTransfer (ET) in Sheep, with the Special Reference to Hormonal Inductionof Cervical Dilation and its Implications for Controlled AnimalReproduction and Surgical Techniques

摘要

Artificial insemination (AI) and embryo transfer (ET) play an important role in the genetic improvement ofsheep herds. This review primarily describes the methods that have recently been researched and/or adapted to circumventthe problematic anatomy of the ovine cervix, which prevents the widespread application of transcervical AI and ET in thisspecies. A mechanism of cervical ripening at parturition and the endocrine influences on cervical tone are described as abackdrop to understanding the action of various pharmacological agents used to induce cervical dilation. Although severalcatheters have been designed to penetrate the ovine cervix, and a specific protocol has been developed for TCAI in sheep(Guelph Method), penetration rates and resulting pregnancy/lambing rates are still inconsistent and unpredictable.Hormonal dilation of the cervix may significantly improve the ease with which the ovine cervix can be traversed.Treatment with Cervidil?, a dinoprostone-containing vaginal insert with a slow release mechanism, currently used toinduce labor in women, could significantly improve cervical penetration in ewes without adverse effects on uterinecontractility. This mode of drug delivery holds promise to result in the development of a safe method to induce cervicaldilation for a broad range of transcervical reproductive manipulations in mammalian species including, but not limited to,AI, ET, embryo and oocyte recovery, treatment of ringwomb and transcervical surgical procedures. However, morestudies are needed to evaluate the effects of hormonal methods on cervical morphology/pathomorphology, sperm/embryotransport and viability, and fertility in both cyclic and seasonally anovular ewes.