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CHAPTER 1.2
can be induced pharmacologically with a combination of imipramine and xylazine hydrochloride
(McDonnell, 2001), or with xylazine hydrochloride alone, preferably following sexual prestimulation
(McDonnel and Love, 1991).
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In conclusion the final goal for semen collection is to obtain a complete ejaculate with a
single mount and minimal sexual stimulation of the stallion before collection of semen, hereby
optimizing the potential to obtain an ejaculate with relatively low volume and high sperm
concentration (Loomis, 2006).
1.2.2. Preparation of cooled semen
As soon as an ejaculate is collected, the semen should be transported to the laboratory
taking care of minimizing physical trauma, exposure to light, cold shock or excessive heat. In the lab,
the raw, undiluted semen should be processed in an incubator using only materials preheated to
body temperature (37-38°C). If no inline filter was used during the collection, the semen should be
filtered immediately through a non-toxic, sterile filter to remove debris and gel admixtures. The gel
fraction can also be careful aspirated with a syringe. These two methods are associated with a higher
sperm loss in comparison to the use of inline nylon micromesh filters. Subsequently, volume,
concentration, color and possible admixtures should be registered. Independent of the following
procedures, the semen should be mixed with an appropriate preheated extender as soon as possible
following collection to maximize sperm longevity. At this point, a dilution ratio of 1:1 to 1:2 is
appropriate. Stallions with semen that is extremely sensitive to cold shock might benefit from adding
the same volume of preheated extender as the expected volume of semen to the collection bottle
prior to collection (Pickett, 1993; Squires et al., 1999; Brinsko et al., 2011).
Influence of sperm collection
Excessive sexual stimulation prior to ejaculation must be avoided due to two reasons. Firstly,
the increased volume of the ejaculate following excessive stimulation is associated with a reduced
sperm concentration, meaning that the total sperm output is not affected. Secondly, large volumes
of seminal plasma have a negative effect on semen quality after 24h of cooled storage (Sieme et al.,
2002). Moreover, multiple mounts in the same AV without changing the liner or the collection vessel,
will increase the contaminants and the amount of presperm fraction in the collected semen. So if