2 research outputs found
The biological mechanisms regulating sperm selection by the ovine cervix
In species where semen is deposited in the vagina, the cervix has the unique function of facilitating progress of spermatozoa towards the site of fertilisation while also preventing the ascending influx of pathogens from the vagina. For the majority of species, advances in assisted reproduction techniques facilitate the bypassing of the cervix and therefore its effect on the transit of processed spermatozoa has been largely overlooked. The exception is in sheep, as it is currently not possible to traverse the ovine cervix with an inseminating catheter due to it's complex anatomy, and semen must be deposited at the external cervical os. This results in unacceptably low pregnancy rates when frozen-thawed or liquid stored (>24h) semen is inseminated. The objective of this review, is to discuss the biological mechanisms which regulate cervical sperm selection. We assess the effects of endogenous and exogenous hormones on cervical mucus composition and discuss how increased mucus production and flow during oestrus stimulates sperm rheotaxis along the crypts and folds of the cervix. Emerging results shedding light on the sperm-cervical mucus interaction as well as the dialogue between spermatozoa and the innate immune system are outlined. Finally, ewe breed differences in cervical function and the impact of semen processing on the success of fertilisation, as well as the most fruitful avenues of further investigation in this area are proposed
Ewe breed differences in cervical anatomy and cervicovaginal mucus properties: an international study
In sheep, cervical artificial insemination (AI) involves depositing semen at the cervical opening, as it is
not possible to traverse the cervix due to its complex anatomy. However, internationally this method
yields low pregnancy rates when frozen-thawed semen is used. An exception to this is in Norway, in
which vaginal deposition of frozen-thawed semen to a natural estrus yields pregnancy rates around 70%.
As the cervix and its secretions are the principal factors influencing sperm transport to the site of
fertilization the aim of this study was to characterise the differences in the cervical anatomy as well as
the cervicovaginal mucus properties of six European ewe breeds across three countries known to have
differences in pregnancy rates following cervical AI with frozen-thawed semen. These were Suffolk and
Belclare in Ireland, Fur and Norwegian White Sheep (NWS) in Norway and Ile de France and Romanov in
France (n ¼ 28e30 ewes/breed). Cervicovaginal mucus was collected at the follicular and luteal phases of
both a synchronized and natural cycle and assessed for mucus weight, viscosity and colour. The
anatomical characteristics of the cervix (length of the cervix, number of cervical rings and the appearance of the external os) were assessed post-mortem. There was a type of the cycle by ewe breed
interaction represented by no differences in mucus production between ewe breeds at the natural cycle
for both the follicular and luteal phases of the cycle. However, there were differences between ewe
breeds at the synchronized cycle (P < 0.05). Belclare had the lowest mucus production at the follicular
phase while NWS had the lowest amount of mucus at the luteal phase of the synchronized cycle. Overall,
across all ewe breeds, mucus production was higher at the follicular than at the luteal phase (P < 0.05).
Despite reports of Suffolk and NWS having the most divergent pregnancy rates following cervical AI with
frozen-thawed semen, both breeds had the lowest overall mucus viscosity at the follicular phase of both
types of cycle with no differences between both ewe breeds (P > 0.05). The length of the cervix, number
of cervical rings and the external os type were affected by ewe breed (P < 0.05). Suffolk ewes had longer
cervices but lower number of cervical rings than NWS and Fur ewes (both with higher pregnancy rates).
In conclusion, while mucus production and mucus viscosity was affected by breed, these changes are not
consistent with the known differences between ewe breeds in their pregnancy rates following cervical AI
with frozen-thawed semen