Traversing the ovine cervix – a challenge for cryopreserved semen and creative science

Abstract

This review brings together research findings on cervical relaxation in the ewe and its pharmacological stimulation for enhancement of the penetration needed for transcervical insemination and embryo transfer. On the basis that the success of artificial insemination is the percentage of ewes lambing, a review is made of recent research aimed at understanding and minimising the sub-lethal effects of freezing and thawing on the viability of spermatozoa, their membrane integrity and their ability to migrate through cervical mucus, as these characteristics have a major influence on fertility, particularly when semen is deposited, artificially, in the os cervix. Milestones of achievement are given for transcervical intrauterine insemination, embryo recovery and transfer and the birth of lambs of pre-determined sex, firstly following intracytoplasmic sperm injection, then laparoscopic intrauterine insemination using highly diluted flow-cytometrically sorted fresh semen and subsequently by os cervix insemination using sexed semen that had been frozen and thawed. Diversity of research endeavour (applied, cellular, molecular), research discipline (anatomy, histology, immunology, endocrinology) and research focus (cell, tissue, organ, whole animal) is embraced within the review as each has significant contributions to make in advancing recent scientific findings from the laboratory into robust on-farm transcervical insemination and embryo transfer techniques.Keywords: ovine cervix, semen cryopreservation, artificial insemination, embryo recovery and transfer ImplicationsIn bringing together the results of recent research on the cryopreservation of ram semen and the relaxation of the ewe cervix, this review provides a basis for identifying opportunities for improving the efficiency of cervical insemination and transcervical embryo recovery and transfer in sheep genetic improvement programmes.

Melatonin Inhibits Formation of Mitochondrial Permeability Transition Pores and Improves Oxidative Phosphorylation of Frozen-Thawed Ram Sperm

“…However, in sheep, <1% of semen is frozen (2), due to extensive structural and functional damage during freezing and thawing reducing sperm quality and fertility (3). Cryopreservation-induced damage to ovine sperm mitochondria reduces energy production and consequently fertility, as the cervix becomes a formidable barrier to sperm transport and sperm have shortened duration of survival in the female reproductive tract (4). However, melatonin protects mitochondria by reducing oxidative stress and preventing mitochondrial permeability transition pore (MPTP) opening (5).…”

Current and Future Assisted Reproductive Technologies for Mammalian Farm Animals

“…There may also be benefi cial components of seminal plasma that are lost when seminal plasma is discarded or diluted during the storage process. Addition of seminal plasma before freezing has been reported to improve sperm survival in the bull, boar, ram, and stallion (Robinson et al 2011 ;Caballero et al 2012 ) and there are reports that addition of seminal plasma after thawing can improve pregnancy rates when ewes are cervically inseminated with frozenthawed semen using the transcervical (Robinson et al 2011 ). Specifi c components of seminal plasma may also interact with sperm cells or in the reproductive tract to enhance pregnancy rates.…”

“…1.3 ) that is based on visualization of the os cervix with a lighted speculum, manipulation of the cervix with a forceps, and manipulation of a pipette through the cervix and into the uterus (Buckrell et al 1994 ). Some authors have reported excellent results whereas results were disappointing in other studies (Robinson et al 2011 ). Efforts to improve the system have relied on hormonal regimens to dilate the cervix such as estradiol, prostaglandin E2, and oxytocin (Robinson et al 2011 ).…”

“…Some authors have reported excellent results whereas results were disappointing in other studies (Robinson et al 2011 ). Efforts to improve the system have relied on hormonal regimens to dilate the cervix such as estradiol, prostaglandin E2, and oxytocin (Robinson et al 2011 ). More information about the biology of cervical relaxation may lead to more consistent results.…”

Collagen, glycosaminoglycans and matrix metalloproteinase‐2 and metalloproteinase‐9 in the cervix of the ewe during prepubertal development

“…The tortuous nature of the ovine cervix restricts the transcervical passage of the cannula (Halbert, Dobson, Walton, & Buckrell, ), and many studies have aimed to understand the endocrine mechanism of cervical dilatation in the adult ewe for transcervical cannulation improvement (Robinson et al, ). In prepubertal lambs, there is evidence that both the ability to respond to the steroid hormones of the cervical tissue and the mechanisms for the recruitment of antral follicles and ovulation in response to the administration of eCG are functional (Rawlings, Evans, Honaramooz, & Bartlewski, ; Rodríguez‐Piñón, Meikle, Tasende, Sahlin, & Garófalo, ); however, little is known about the remodelling of the cervical tissue during the prepubertal development of the lambs.…”