Page 552 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Reproductive system: 2.2 The male reproductive tr act 527

VetBooks.ir 2.135 high metabolic activity of spermatozoa, antibiot-
ics to combat the bacterial contamination inevitable
with collection and protection from cold shock dur-
ing cooling. The semen from individual stallions
varies greatly according to which type of extender
it performs best in. Practitioners are encouraged to
test several extenders with every stallion to deter-
mine which best suits each case. All slides, coverslips,
containers, pipettes, etc. that come in contact with
semen should be kept warm.

SEMEN EVALUATION

Once collected, semen is evaluated for colour and
Fig. 2.135 These unusual contaminants found appearance, volume, total and progressive motil-
within a semen sample were determined to be starch ity, concentration and morphology. Stallion semen
granules and were the result of baby powder applied should be white to skimmed-milk in colour and
within the artificial vagina to prevent the rubber appearance. The ejaculate is divided into sperm-
sticking together. Contaminants such as powders, rich (produced by the testes and epididymides) and
soaps, lubricants and water significantly impact on gel fractions (produced mainly by the accessory sex
semen motility and viability. glands) by use of an in-line filter within the collec-

tion bottle. If an in-line filter was not used in the
of the artificial vagina on the stallion’s penis cause artificial vagina, the gel fraction should be removed
ejaculation. Most stallions ejaculate readily with the immediately after collection by filtering, decanting
temperature set in the range of 43–48°C (109.4– or aspiration.
118.4°F). However, the temperature and pressure
may be modified to suit a particular stallion’s prefer- Semen volume
ences. Care must be taken to ensure that the stallion’s The volume of both the gel and sperm-rich fractions
penis is fully within the artificial vagina, preventing of the ejaculate should be recorded. Semen volume
ejaculated sperm from being exposed to the high can be measured using a warmed sterile plastic tube,
temperature of the device and resulting in heat shock. clean dry baby bottle or graduated cylinder. Normal
The artificial vagina is fitted with a collection bottle semen volume varies greatly depending on breed,
or bag, and use of an in-line filter method is recom- age, season, frequency of collection and amount
mended. The filter removes most of the gel fraction of time spent teasing the stallion prior to collec-
as well as dirt or smegma. Immediately following tion. A typical average volume from an adult stal-
collection the semen is moved to an incubator and lion would be 50–70 ml, with a range of 25–300 ml.
maintained at 37°C (98.6°F) for the initial evaluation. The volume varies according to the season: higher
Semen extender should be prepared immediately in the spring and summer, lower in the autumn and
before semen collection and kept at 37°C (98.6°F) in winter. Pre-copulatory sexual stimulation (teasing)
the incubator. Commercially available semen extend- may increase the gel portion and high frequency of
ers may range from simple combinations of sugar and ejaculation will decrease the semen volume. At this
milk solids, to complex buffer solutions. Recently, the time, a small sample of unextended semen is taken
industry has seen the development of defined-media for morphological analysis and determination of
extenders capable of providing considerably longer- sperm concentration. The semen volume multiplied
term, cooled storage of stallion spermatozoa. The by sperm concentration determines the total number
extender provides an energy source to support the of sperm in the ejaculate.