Page 974 - Small Animal Internal Medicine, 6th Edition

946 PART VIII Reproductive System Disorders

it flows into the clear tubes. There are three fractions in the
ejaculate. The first is clear, from seminal vesicles. The second
VetBooks.ir fraction is white sperm-rich fluid (SRF). The third fraction
is clear and is prostatic fluid. The SRF is usually released at
the end of rapid thrusting after the dog has turned. Semen
evaluation requires the collection of only the first and second
fractions. Evaluation of a small amount of the more volumi-
nous prostatic fluid is adequate. If collecting for fresh artifi-
cial insemination, avoid collecting the clear prostatic fluid.
The total volume of SRF in a large dog is generally no
more than 1 to 2.5 mL. After collection is complete, leave the
AV on the stud until his erection has diminished. This keeps
the penis more comfortable. Apply some water-soluble lubri-
cation to the base of the penis, under the AV, to facilitate
return of the penis within the prepuce. Always check to make
sure the paraphimosis (penis extruded outside of the
prepuce) resulting from artificial semen collection resolves. FIG 54.21
It is not necessary to walk the dog; he will lose the erection Canine spermatozoa, phase contrast microscopy.
in 5 to 15 minutes. Care must be taken to ensure that the
stud dog has adequately recovered from his erection before
he is retired; preputial skin and hair can strangulate the tip
of the penis. Detached
head
SEMEN ANALYSIS
Semen analysis should include evaluation of sperm mor-
phology, motility, and concentration. If the clinician is
uncomfortable with semen evaluation, the sample or a rep- Distal
resentative aliquot can be submitted to a commercial labora- Proximal droplet Coiled
tail
tory for analysis, but motility must be judged immediately droplet
postcollection. Normal canine semen has 70% (or greater)
progressively forward-moving sperm with moderate speed
and good-quality motility. To evaluate motility, place a drop “Dag”
of the sperm-rich fraction (second) on a warmed slide, using defect
a pipette. Top with a coverslip and observe under ×10 to ×40 Bent tail
magnification. Sperm should swim across the slide in a rela-
tively straight path, with minimal gyrations (good-quality Thickened
motility) and brisk speed (moderate to fast motility). No Pyriform midpiece
head
Acrosomal
sperm-to-sperm agglutination should occur, but agglutina- condensation abnormal
tion to egg yolk particles in extenders or other cells in semen midpiece
can be normal. If motility is poor, prepare another drop on
a new slide and double-check. Observe individual live, FIG 54.22
unstained sperm cells under ×40 magnification for morphol- Schematic of sperm morphology showing common
abnormalities.
ogy. Abnormal sperm can have coiled tails, proximal drop-
lets, abnormal shape to heads, double tails or heads, and
altered acrosomes (Figs. 54.21 and 54.22). The acrosome is semen morphology with the previously mentioned catego-
difficult to visualize without phase contrast microscopy. Iat- ries is helpful. If a high number of morphologic abnormali-
rogenic damage can cause detached heads and bent tails. ties occur poststaining, a different methodology may be
Observing fresh sperm before staining permits evaluation advisable. Note the presence of epithelial cells, white blood
for stain-induced morphologic abnormalities. Prepare cells (WBCs), and RBCs as well (record as 1-4+/HPF). Sperm
another slide with the pipette as you would a peripheral counts can be performed by using a hemocytometer and
blood smear, air dry, and stain for morphologic analysis. Unopette. Alternatively, the automated Spermcue (MOFA
Both Wright-Giemsa and eosin-nigrosin stains are com- Inc.) produces a very accurate automated sperm count. Mul-
monly used. At least 100 to 200 sperm should be tallied for tiply the number of sperm per milliliter by the volume of the
morphology, noting both normal cells and sperm cells with SRF to obtain the number of sperm per ejaculate. Normal
head abnormalities (misshapen, double), neck abnormalities dogs have 200 to 400 million (up to a billion) sperm per
(proximal droplets), and tail abnormalities (distal droplets, ejaculate. Normal toms’ average semen volume varies by the
coiled, double). Using a differential cell counter labeled for method of collection (10.5-233 µ/L); sperm count 21 to 57