Page 542 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.2 The male reproductive tr act 517

VetBooks.ir toward the orifice again before reflecting caudad prostate is lobulated or nodular and firm, distin-
guishing it from the smooth, thin-walled vesicular
to form the internal preputial fold and preputial
ring. It is this additional internal fold that allows
5–9 cm long, 2–6 cm wide and 1–2 cm thick. Multiple
the marked lengthening (approximately by 50%) glands lying next to it. Each prostatic lobe measures
of the stallion’s penis during erection. During erec- ductules from the prostate enter the lumen of the
tion, the preputial orifice is visible at the base of the urethra lateral to the colliculus seminalis. Prostatic
penis just in front of the scrotum, and the preputial secretions appear to contribute to the sperm-rich
ring is visible approximately mid-shaft in the penis. fraction of the ejaculate. The prostate gland is eas-
Located distal to the preputial ring during erection ily identified ultrasonographically, with its two sym-
is the internal layer of the internal preputial fold. metric, homogeneously echogenic lobes distinctly
The penis and prepuce of a breeding stallion are seen (Fig. 2.127). Hypoechoic dilations within the
best examined following teasing with an in-oestrus gland parenchyma of each lobe are usually evident.
mare, when the stallion can be observed to drop the These hypoechogenic spaces are smaller within the
penis and attain a full erection. Removal of smegma isthmus of the gland, and the size of these spaces
accumulations may be required for a complete exam- varies with the frequency of ejaculation and degree
ination of the skin surfaces. of sexual stimulation.

ACCESSORY SEX GLANDS Vesicular glands
The vesicular glands are paired, pyriform, thin-
The accessory glands found in the stallion are the walled structures lying laterally to the ampul-
prostate gland, seminal vesicles, bulbourethral lae, predominantly within the genital fold. Sexual
glands and ampullae (Fig. 2.126). Their secre- stimulation results in dilation and elongation of the
tions produce the seminal plasma that makes up the vesicular glands, up to 12–20 cm long and 5 cm in
majority of the ejaculate volume. diameter. The distal ends of the glands converge,
passing under the prostate as they parallel the
Prostate gland ampullae towards their termination at the urethra.
The prostate gland of the stallion consists of a cen- The excurrent ducts of the vesicular glands open
tral isthmus and two lateral lobes that extend along lateral to the excurrent ducts of the ampullae at
the caudolateral borders of each vesicular gland. the colliculus seminalis of the urethra. Secretions
Although not always palpable per rectum, the of the vesicular glands make up the gel fraction of

2.126

Ampullae Vesicular glands Prostate Bulbourethral glands
Fig. 2.126 Accessory glands of the stallion removed en bloc with cranial to the left. The ampullary glands are
the most cranial of the accessory glands and are glandular dilations of the deferent ducts. The paired vesicular
glands are found on either side of midline, just caudal to the ampullae. The prostate gland lies just caudal to the
vesicular glands and includes a central isthmus and two lateral lobes. The paired bulbourethral glands lie dorsal
to the pelvic urethra, caudal to the prostate, and are embedded within the urethralis and bulboglandularis
muscles.