Page 554 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.2 The male reproductive tr act 529

VetBooks.ir of sperm in the original semen sample is the number 2.137
of sperm × 10 /ml.
6
For example, if the average count of both sides of
the haemocytometer is 195, then:
ACR
Normal sperm
Number of sperm in 0.1 µl volume within the
haemocytometer chamber = 195
and number of sperm in 1 ml = 1,950,000
(195 × 10,000)

Accounting for the 1:100 dilution of the semen, LH
1,950,000 ×100 = 195 × 10 /ml concentration in the
6
original sample. Fig. 2.137 Normal equine sperm. ACR = sperm that
has lost the acrosome cap; LH = loose heads.
Age, season, frequency of ejaculation, testicular
size, sperm reserves and systemic and reproductive 2.138
disease can all influence total sperm count. The total
sperm number is multiplied by the percentage of
progressively motile sperm to give the total number
of progressively motile sperm in the ejaculate.

Sperm morphology
Sperm morphology is determined either by exami-
nation of a fixed-stained specimen under oil immer-
sion bright-field microscopy or by examination of a
wet mount using differential interference-contrast
microscopy (Figs. 2.137–2.141). For the stained
method, the most commonly used stain is eosin-
nigrosin. Other stains that can be used include
modified Wright–Giemsa, Indian ink, Spermac or Fig. 2.138 Complete normal equine sperm with
new methylene blue. A drop of warm semen is gen- whole tail.
tly mixed with a drop of warm stain at one end of
a microscope slide. A smear is made using either a and/or handling technique (tertiary). Specific abnor-
second slide or a glass pipette, similar to the method malities may give insight into the presenting prob-
used to make a slide for a differential blood smear. lem. For example, detached heads in large numbers
Two hundred sperm should be counted under oil indicate stagnation of sperm in the ampullae, ductus
immersion microscopy, recording the number of deferens and epididymis. Coiled tails, by compari-
normal as well as abnormal sperm within each cat- son, are usually associated with significant testicular
egory. Sperm with abnormal morphology are cat- dysfunction even if present in low numbers. Note
egorised as to the type of defect present (i.e. head, that in stallions, abaxial attachment of the mid-piece
mid-piece and tail defects; proximal and distal drop- to the head is common and such sperm are consid-
lets; and loose heads). Morphological defects can ered to be morphologically normal. According to
be further classified according to whether they are the guidelines of the Society for Theriogenology, at
defects of spermatogenesis and testicular in origin least 60% morphologically normal sperm should be
(primary), occurring in the efferent duct system present in the ejaculate for a stallion to be considered
(secondary) or caused by incorrect semen collection a satisfactory breeder.