Induction of cervical relaxation for artificial insemination in sheep

Abstract

In general, artificial insemination (AI) in sheep using frozen-thawed (FT) semen in commercial scale is limited due to the fact that the FT semen of sheep needs to be deposited into the uterus to achieve an acceptable fertility rate. Laparoscopic insemination with FT semen gives commercially acceptable fertility rates, however it is not economical and animal friendly. An alternative method is trans-cervical AI (TCAI). However, the unusual anatomy of the sheep cervix is a major limitation to this technique. In ewe, the cervical lumen has a convoluted and tortuous structure that looks like a corkscrew consisting of internal cervical rings. The internal folds of the cervix form a funnel-like shape with a narrow opening projecting caudally into the cervical lumen which limits the passage of inseminating pipette through cervical canal. The induction of cervical relaxation is investigated to allow deeper cervical penetration. The most significant factor in cervical relaxation is the rearrangement of collagen fibresin cervical extra cellular matrix and the changes in smooth muscle function. The application of exogenous substance increases the depth of cervical penetrability. Follicle Stimulating hormone (FSH), Hyaluronan, Misoprostol, Prostaglandin E2 (PGE2) or oxytocin is likely to induce the cervical relaxation during the periovulatory period in ewes. The greater cervical penetrability ensures the success of TCAI.