The equine ovulation fossa.
Key words: ovary, equine, fossa, probe, mare, anatomy
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A probe inserted into the ovulation fossa of the ovary in a mare. A transected ovary with a probe inserted into the interior aspect of the ovulation fossa.
A probe inserted into the ovulation fossa of the ovary in a mare. A transected ovary with a probe inserted into the interior aspect of the ovulation fossa.
The equine ovary is
unique among those of domestic animals because the tough tunica albuginea
prevents ovulation through the surface of the ovary. Consequently, ovulations
only occur through an ovulation fossa. There is no tunica albuginea in this
area, located in the hilus of the ovary. Equine follicles become so large (~3.5
to 5cm) that one part of the periphery of
the follicle always impinges on the ovulation fossa; this area ruptures and the
oocyte is released into the infundibulum.
Because of the absence of ovulation through the surface of
the ovary, corpora lutea are entirely internal to the ovary and no “crowns” form,
as they do in other animals. This makes it impossible to feel the presence of a
corpus luteum via trans-rectal palpation. Therefore it is impossible to
determine if a mare is having estrous cycles by transrectal palpation alone;
this is one reason why ultrasound is so important in equine stud practice.
A small corpus albicans is present in the ovary, not
palpable but easily identified via ultrasonography.
