Page 549 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

524 CHAPTER 2

VetBooks.ir inguinal rings can be palpated along the abdominal within 5 minutes of semen collection. Most normal
stallions have progressive motility of >40%. Higher
wall cranioventral to the pelvic brim and lateral to
the midline. Bending and straightening the index
finger while sliding the hand along the appropriate progressive motility is generally associated with
higher conception rates, although this is not always
area of the abdominal wall will cause the finger to the case. In stallions at daily sperm output, a signifi-
enter the ring. The ring can then be evaluated for cant change in motility between collections often
hernia and adhesions. indicates a semen-handling problem such as cold
shock, heat damage or water contamination. Since
Bacterial culture high sperm concentration and/or sperm agglutina-
After washing and drying the penis, the glans is tion and sticking to the slide may preclude examina-
stimulated to initiate the flow of pre-seminal fluid. tion of individual sperm motion characteristics, it is
The fluid is allowed to wash the urethral lumen normal practice to repeat the motility evaluation on
before the urethra is swabbed with a bacterial cul- an extended sample. Following evaluation of motil-
ture swab; a second swab is taken immediately after ity of raw semen, a small portion of the sample is
semen collection. In addition, an aliquot for bacte- diluted in warmed semen extender to approximately
rial culture is removed from the semen, immediately 30–50 × 10 /ml concentration.
6
post collection, in a manner that minimises the risk
of contamination. In normal stallions, bacteria cul- pH
tured from samples are inconsistent and bacterial pH should be evaluated within 10 minutes of col-
numbers decline after ejaculation. Pure cultures or lection using commercial pH paper with an appro-
increased numbers of bacteria on the post- ejaculation priate range. Normal pH is 7.2–7.8. Elevated
sample are indicative of reproductive tract infection. pH may indicate urine or soap contamination or
In countries with CEM, microaerophilic culture inflammation.
should be performed.
Sperm concentration
Semen collection (see also p. 526) During a BSE, the sperm concentration in the sec-
Prior to a BSE, semen should be collected from the ond semen sample is expected to be approximately
stallion twice daily for 7 days in order to deplete half that of the first sample. If the concentration of
epididymal reserves and reach daily sperm output. sperm is roughly the same as the first collection,
During a BSE, semen is collected twice, with 1 hour consider whether complete ejaculation in both col-
between collections. Normally, the volume and pH of lections has in fact occurred. An excessive drop in
both collections are similar, but the second collection sperm concentration of the second collection may be
contains half the total sperm number. During semen seen in stallions with severe testicular or epididymal
collection, a hand should be placed on the ventral dysfunction or disease.
shaft of the penis so that the strength of the ejacula-
tory pulses can be evaluated. Deviations from normal Sperm morphology
mounting, intromission and ejaculation are recorded. During a BSE it is generally important to determine
It is essential that the ejaculate is collected and handled the percentage of normal sperm in the ejaculate
carefully, avoiding exposure to excessive heat (above in order to calculate the number of progressively
body temperature), direct light and contact with sper- motile, morphologically normal (PMMN) sperm. It
matotoxins, such as lubricants, soaps and detergents. is thought that in most cases abnormal sperm do not
reach the oocyte. However, certain morphological
Semen evaluation (see p. 527 for abnormalities may not impair motility, simply fer-
details) tility. In these cases, defective sperm are competing
Initial motility with normal sperm at the moment of fertilisation,
Using warmed slides and coverslips, the total and and therefore the proportion of defective sperm may
progressive motility of raw semen should be evaluated be significant.