FEMALE REPRODUCTIVE ANATOMY
OVARY
Mare
- Sexually mature mare has largest ovaries among all domesticated animals (size of dog kidney)
- Bean-shaped in mature mare, oval-shaped in foal
- Located in the dorsal sublumbar area of the abdomen
 Caudal to the kidney
 At about the level of L5 and rectum
- Ovarian bursa is small, shallow, and does not house the ovary
 Ovarian bursa is a “pocket” bounded by the mesosalpinx (laterally) and the mesovarium (medially)
- Lacks true suspensory ligament – mesovarium suspends ovary
- Proper ligament of the ovary is well defined and connects the caudal pole of ovary to the uterine horn
- Most of their surface covered by peritoneum
 Ovary is mostly covered by germinal epithelium in other species
- Ovulation fossa is the only site of ovulation (only place covered with germinal epithelium)
 Located at the indentation of the ovary
 Cannot be palpated per rectum
- Follicles can be large (10 – 70mm, size of a tennis ball)
 Easily palpated per rectum
- Corpus luteum does not project above the surface of the ovary
 Cannot be palpated easily per rectum
Cow
- Ovaries are relatively small
- Mature ovary has follicular projections, immature ovary is oval and flat
- Suspended from the dorsolateral abdominal wall
 Located ventral to the brim of the pelvis
- Found within well-defined ovarian bursa (though this bursa is not 100% complete like in the dog)
- Lacks distinct suspensory ligament
- Proper ligament of ovary attaches to mesometrium
- Entirely covered by germinal epithelium (with exception of attached border)
 Ovulation can take place anywhere on the ovary
- Follicles are much smaller than in horse (2cm)
 Still can palpate per rectum
- Corpus luteum is large and may occupy half of the ovarian mass (only small portion projects above surface)
 Can palpate corpora lutea per rectum
Functional stages of the cow ovary
A. Ovary with small, 2° follicles
B. Ovary with mature follicle
C. Ovary with ruptured follicle
D. Ovary with mature corpus luteum
E. Ovary with regressing CL
Small Ruminant
- Oval to round shaped, surface is uneven due to follicular growth and corpora lutea
- Corpora lutea (1-2) are large relative to size of ovary
- Ovarian bursa is not well-defined
- OTHER FEATURES SIMILAR TO COW
Sow
- Resembles a bunch of grapes
- Very uneven due to numerous follicles and corpora lutea of varying sizes protruding over ovary
- Ovarian bursa is extensive and cone-shaped
- Mesovarium is very extensive
 Many possible attachments to abdominal wall
- Proper ligament of ovary is very muscular and attaches the ovary to the mesometrium
Species Differences of the Ovary
Species
Carnivore
Horse
Cow
Small Ruminant
Pig
Llama
Palpable
Follicles
n/a
X
X
Palpable
Corpora Lutea
n/a
n/a
n/a
X
Well-defined Ovarian
Bursa
(small)
X
X
X
Proper Ligament of Ovary
Attachment
Uterine horn
Uterine horn
Mesometrium
Mesometrium
Mesometrium
Mesometrium
INFUNDIBULUM AND OVIDUCT
Mare
- Ostium abdominale tubae uterinae (abdominal opening of oviduct) is near ovulation fossa
- Fimbrae of infundibulum are well-developed
 Fimbria help “capture” and sweep ova into oviduct
 Some fimbriae are attached within the ovulation fossa
- Isthmus is a significant location of sperm storage
- Abrupt transition in lumen diameter from oviduct to uterine horn
 UTJ is easily-visualized
- Utero-tubual junction (UTJ) exhibits small papillae and sphincter
 Only fertilized eggs exit the oviduct via these sphincters
Cow
- Ostium abdominale tubae uterinae faces the ovary
- Oviducts are quite long and have tortuous (winding) course
- Gradual transition in lumen diameter from oviduct to uterine horn (Same in small ruminants
 UTJ is harder to visualize
Sow
- Oviduct has tortuous course in mesosalpinx
- UTJ is abrupt
- Obstruction of oviduct causes hydrosalpinx (most common cause of infertility in sows)
UTERUS
Uterus-simplex
Paramesonephric ducts are almost completely united, resulting in a single uterine body
with non-fused, paired uterine tubes (primates)
Uterine duplex/
Vagina simplex
Paramesonephric ducts are fused only in the caudal region, resulting in a single vagina with
paired uteri and cervices (rabbit)
Uterine duplex/
Vagina duplex
Paramesonephric ducts are not fused caudally, meaning the uterus, cervix, and vagina are
paired structures (marsupials, monotremes)
Bicornuate
Paramesonephric ducts are fused caudally but are separate cranially, resulting in fused
vagina, cervix, and uterus, but paired uterine horns (carnivores, pigs)
Bicornuate –
Bipartite
Uterine horns are separated by a septum and the body of the uterus is small (ruminants)
Bicornuate –
Cruciform
Uterus resembles uterine simplex in having a large body, but resembles bicornuate uterus
in having separate uterine tubes (horses)
Species Differences of Uterus Type
Species
Carnivore
Horse
Cow
Small Ruminant
Llama
Pig
Monotremes, Marsupials
Rabbit
Primates
Uterine
Simplex
Uterine Duplex /
Vagina Simplex
-
Bicornuate
Bicornuate –
Bipartite
Bicornuate –
Cruciform
X
X
X
X
X
X
X
X
X
Mare
-
Uterine Duplex /
Vagina Duplex
Broad ligament is attached to dorsal
uterus and uterine horns
 This is why the uterus feels
smooth when palpating per rectum
 Attaches uterus and uterine horns
to sublumbar area at level of L5
Body of uterus is very large, cylindrical,
and flattened dorso-ventrally
Uterine horns are entirely within
abdominal cavity
 Normally straight, giving the
uterus a T-shape
 Have large tubular lumen
Cow
Dorsal view of the reproductive organs of the cow
1. Ovary
2. Uterine tube
2’ Infundibulum
3. Uterine horn
4. Inter-cornual ligament
5. Wall of uterus dividing the two horns
6. Body of uterus with caruncles
7. Broad ligament
8. Cervix
9. Vaginal part of cervix
10. Fornix
11. Vagina
12. Position of former hymen
13. External urethral orifice and suburethral diverticulum
14. Major vestibular gland and its excretory orifice
15. Vestibule
16. Glans of the clitoris
17. Right labium
-
-
-
-
Broad ligament of uterus is attached to the ventral uterus and very muscular
 Uterus does not feel smooth when palpating per rectum
Round ligaments of the uterus are well developed
 They can be followed to the inguinal canal, though do not pass through
Body of uterus is short
Uterine horns are long (though appear shorter than body due to common peritoneum)
 Curved to form spiral coil (“ram’s horns”)
 Attached to each other via ligaments composed of muscle and CT
o Dorsal intercornual ligament
o Ventral intercornual ligament
o These ligaments form a fossa (intercornual fossa) that is a palpable per rectum and used to
stabilize uterus during palpation
Endometrium of uterus contains 4 rows of caruncles
 Caruncles vary in size, shape, and presence of pits
 Fuse with fetal cotyledons to form placentomes, forming the cotyledonary placenta during pregnancy
 Typically, maternal caruncles are convex while fetal cotyledons are concave
Myometrium
 Outer, thin longitudinal layer (continuous with broad ligament)
 Inner, thicker circular layer
 Vessels, nerves, and lymphatics are between layers surrounded by CT
Estrogenized uterus
 Uterus engorges with blood (becomes firm) during follicular phase of estrous cycle
Uterine glands become large and secretory during luteal phase of estrous cycle
Small Ruminant
-
Body of uterus is small
Uterine horns resemble those of cow
Caruncles
 Typically, maternal caruncles are concave while fetal cotyledons are convex
 More pronounced in ewe (not doe)
 Immature caruncles of ewe (not doe) are often pigmented
 Mature caruncles of ewe (not doe) are usually less pigmented during pregnancy
Sow
- Body of uterus is very short
- Uterine horns are longest among domestic species (1.5m)
 Length doubles during pregnancy
 Immature uterine horns resemble jejunal coils
CERVIX AND VAGINA
Mare
- Fornix vagina is present due to caudal part of the cervix protruding into vagina
- Mucous membrane of the cervix forms longitudinal folds
 Makes it relatively easy to pass AI instruments
- Vestibulo-vaginal fold is formed by mucosal folds on the dorsal and ventral walls of the vagina
 Separates the vagina from the vestibule, preventing air and potentially-infectious material from
entering vagina and uterus
Cow
- Plica circulares are circularly-arranged annular rings of the cervix (3-4 in number
 Composed of bands of smooth muscle covered with mucosa
 Make the cervical canal tortuous and difficult to traverse
- Fornix vagina is formed by the most caudal plica circulares protruding into the vagina
- Vagina exhibits transverse folds and longitudinal folds
Small ruminant
- Sheep has 4-6 plica circulares that interdigitate
- Goat has 3-5 plica circulares that do not interdigitate
- Cannot be palpated per rectum
Sow
- Cervix is very long, and mucous membrane exhibits longitudinal folds
- Pulvini cervicalis are firm, inter-digitating tubercles of the cervix
 Form a spiral canal that make the cervix difficult to traverse
- Fornix vagina is absent, as the epithelium of the cervix is continuous with the epithelium of the vagina
- Vagina exhibits longitudinal folds
EXTERNAL GENITALIA
Mare
- External urethral orifice is located at the vestibulo-vaginal fold
- Mucosa and vestibular folds line the vestibule
- Clitoris is well-developed and sits within the clitoral fossa of the vestibule
 Clitoral fossa can harbor Taylorella equigenitalis, which transmits contagious Equine Metritis
Cow
- External urethral orifice marks the entrance to the vestibule from the external environment
- Suburethral diverticulum is just caudal to the external urethral orifice (also found in all small ruminants)
 Can be mistaken for the external urethral orifice when trying to pass a urethral catheter
- Clitoris is well-defined and sits within the clitoral fossa
Sow
- External urethral orifice sits on the floor of the vestibule
- Suburethral diverticulum is present
- Clitoris is very well-defined and long, projecting over the clitoral fossa
PLACENTATION
How is placenta classified?
1. Histological structure of placenta (epitheliochorial, synepitheliochorial, endotheliochorial, etc.)
2. Degree of uterine wall encroachment (deciduate, non-deciduate)
3. Shape of hemotrophic exchange (diffuse, zonary, discoid, cotyledonary)
4. Fetal extraembrynic membranes (chorionic, yolk sac, chorioallantoic)
Carnivores
- Endotheliochorial (4 layers due to erosion of uterine epithelium)
- Deciduate, zonary
- Chorioallantoic sac over the fetus that does not rupture at birth (danger of suffocation)
Equine
- Epitheliochorial (least invasive, 6 layers)
- Non-deciduate, diffuse
- Chorioallantoic sac over the fetus ruptures at birth due to standing birth
- Microcotyledons function in histotrophic nutrition (facilitate diffusion of nutrients to fetal membranes)
 Cervical star – region over cervic where chorioallantois microcotyledons
- Umbilical cord is very long
 Amniotic part (visible inside amniotic sac)
 Allantoic part (exposed)
 Umbilicus exhibits a change in epithelium near the fetus – at this junction, the cord easily tears at birth
- Hippomanes are internal amniotic plaques
Ruminant
- Synepitheliochorial (sometimes 5 layers, sometimes 6 layers)
- Partially deciduate, cotyledonary
- Placentomes are formed via association of maternal caruncles with fetal cotyledons
 Large ruminant – caruncles are convex, cotyledons are concave
o Fetus requires 80-100 caruncles for successful nutrition during pregnancy
o Typically a total of 120 caruncles in the uterus (25lbs at birth)
o Caruncles do not regenerate
o Retained placenta is not typically removed. If so, some caruncles may be damaged. If 20-30%
of the caruncles are damaged, cow many become sterile due to inability to sustain fetus
 Small ruminant – caruncles are concave, cotyledons are convex
- Chorioallantoic sac
- Internal amniotic plaques are normal, proteinaceous concretions of unknown function
Pig
- Epitheliochorial (least invasive, 6 layers)
- Non-deciduous, diffuse
- Chorioallantoic sac
- When looking at fresh fetal membranes, there are areolae (white dots) on the chorion. Areolae are the spaced
into which uterine glands secrete nutrients (histotrophic nutrition)
- Right ovary is most active (55% ovulation)
- Embryos become evenly spaced in the uterine horn by peristaltic-type uterine horn contractions
- At parturition, uterine contractions begin behind first fetus, which is expelled. The next contraction then expels
the second fetus, etc. This ensures that all fetuses does not “crash” at the utero-cervix junction
MALE REPRODUCTIVE ANATOMY
TESTES
Stallion
- Oriented horizontally, with the tail of the epididymis pointing caudally
- Mediastinum testis is at the cranial pole of the testis (unique to the stallion)
 It is centrally-located in most species
Testes of the stallion
Testes of the bull
A. Testis
B. Head of epididymis
C. Body of epididymis
D. Tail of epididymis
E. Ductus deferens
F. Testicular vessels
G. Testicular bursa
H. Cremaster m.
I. Parietal vaginal tunic
Bull
- Oriented vertically, with the tail of the epididymis pointing ventrally
- Located far more cranially on the ventral abdomen than stallion or boar testes
Boar
- Located just ventral to the anus, just caudal to the thigh
PENIS AND PREPUCE
Stallion
-
-
-
-
Musculocavernous penis
 Cavernous blood sinuses are lined by smooth muscle and fibrous tissue
 Expanded corpus spongiosum (ventral sinus) caps corpus cavernosusm (large central sinus)
 SNS innervation to smooth muscle maintains penis in prepuce when horse is not erect
 Erection requires engorgement of blood sinuses
Prepuce exhibits unique double-folding of skin
 External prepuce – outer layer that corresponds to the prepuce in other species
o Outer lamina reflects at preputial orifice to become the inner lamina
o Outer and inner lamina are composed of common integument (glandular)
 Preputial fold – inner layer that is unqiue to the stallion
o Outer lamina is continuous with the inner lamina of the external prepuce and is also glandular
o Most cranial point of the fold is the preputial ring
o Inner lamina arising from preputial ring reflects onto penis (mucosal, non-glandular)
Glans penis has several characteristics
 Fossa glandis is a depression on the cranial extremity of the glans
o Houses the urethral process
 Urethral sinus is the deep part of the fossa glandis dorsal to the urethral process
o Dead cells and debris collect in the urethral sinus to from smegma, or “the bean”, which can be
painful during mating and is regularly cleaned in breeding animals
 Corona glandis is an elevated, ridge-like circumference of the glans
 Collum glandis is the circular constriction in the neck of the glands, just caudal to the corona
Muscles
 Retractor penis m. courses ventrally and is unpaired
 Bulbospongiosus m. is ventral to the corpus spongiosum
o Only muscle to courses to the end of the penis
o Only found in the horse
Bull
- Fibroelastic penis
 Contains more CT trabeculae than erectile blood sinuses
- Prepuce is comprised of a single layer
 Outer lamina exhibits numerous longitudinal folds and glands
 Inner lamina reflects onto the penis and is non-glandular
In the non-erect state, ~1/3 of the penis forms a
sigmoid flexure, which is maintained by the paired
retractor penis mm. as well as elastin fibers of the
penis.
The sigmoid flexure is located post-scrotal because
the scrotum is located very cranial on the ventral
abdomen
-
Glans exhibits several unique features
 Raphe penis on ventral aspect. This structure was once the frenulum of the penis, which kept the penis
within the prepuce. During puberty, elevated testosterone levels should causes this frenulum to tear,
allowing the penis to exit the prepuce (surgical intervention if this process does not occur)
 Urethral process is found within the urethral groove (on the right side of the glans)
Small Ruminant
-
Fibroelastic penis (similar to the bull)
Prepuce consists of a single layer (similar to the bull)
Post scrotal sigmoid flexure of the penis (similar to the bull)
Both sheep and goat exhibit a long, worm-like urethral process
-
Tuberculum spongiosum is only present in the ram (not the goat)
 Composed of corpus spongiosum and located behind the glans on the left
Boar
- Fibroelastic penis
- Prepuce is very large
- Prepuce exhibits a preputial diverticulum on
the dorsal aspect
 Collects cell debris and secretions that
give boar a characteristic odor (and
can taint meat)
 Secretions may include pheromones
and play a role in mating
 Boar can masturbate into this
diverticulum, making semen
collection difficult
- Pre-scrotal sigmoid flexure because the
scrotum is located very caudal
- Glans is sprially-twisted with pointed end
- Raphe penis twists along glans