Page 557 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

532 CHAPTER 2

VetBooks.ir dimethlyformamide or DMSO. The extender com- circumstances be kept in a standard freezer. This
may be an area of confusion for horse owners. Two
ponents protect the sperm membrane from phase
transitions and other changes during freezing, and
A dry-nitrogen shipper is a short-term storage and
exert osmotic forces to draw water from the sperm types of container are available for frozen semen.
cell prior to ice-crystal formation. transport vessel. Liquid nitrogen is used to charge
Following routine semen collection and evalu- and cool the vessel, but is not kept within the tank.
ation, the semen is extended 1:1 with a standard When semen is transported by truck or aircraft, it
extender used for insemination or chilling. is imperative that all remaining liquid nitrogen be
Inclusion of a centrifugation cushion reduces removed from the dry-shipper. Couriers and airlines
sperm damage and increases yield, while allow- will not accept a dry-shipper with liquid nitrogen
ing use of higher G force. The extended semen within it. Models vary in capacity and also in the
is centrifuged at 400–900 G to produce a sperm length of time that the temperature is maintained
pellet, allowing removal of the seminal plasma. once charged (from only a few days to 3 weeks). If
Cryopreservation results are generally improved semen is received in a dry-nitrogen shipper, it is rec-
with the inclusion of 5–10% of seminal plasma in ommended that it be moved immediately to a liq-
the final volume. The sperm pellet is gently resus- uid nitrogen tank. When a dry-nitrogen shipper is
pended in freezing extender to the desired final opened, a puff of vapour will be seen from the top
concentration and mixed well. Several packaging if the tank is still charged. If there is no vapour,
methods are available; however, the 0.5 ml plastic then the tank has lost its charge and the semen has
straw is currently the most widely used. Straws thawed. A liquid nitrogen tank is the best method for
should be clearly labelled with the stallion’s name, storage of frozen semen. These tanks are generally
registration number, breed, freeze date and freeze kept on the farm or in the veterinary clinic, and the
location/clinic name. The loaded straws are placed dry-shipper is used for short-term transport from
on a rack for cooling to 5°C (41°F) over a period of one liquid tank to another.
20–120 minutes, depending on the protocol, before Epididymal sperm can be collected from the
being placed over nitrogen vapour. Straws remain testicles of a recently deceased stallion and cryo-
over vapour for 8–15 minutes before being plunged preserved. Testes of a deceased stallion should be
into liquid nitrogen. Once frozen the straws are removed within 4 hours of death and transported
stored in liquid nitrogen until required. at 4°C (39.2°F) to a laboratory capable of perform-
It is important to note that while semen is gen- ing the sperm recovery and cryopreservation, within
erally referred to as ‘frozen’, it cannot under any 24 hours.

ABNORMAL SEXUAL FUNCTION IN THE STALLION

Demands placed on many breeding stallions require POOR LIBIDO
them to function in an environment that is very dif-
ferent from the natural equine herd. The manner in Definition/overview
which stallions are housed and bred, as well as the Poor libido occurs when a stallion takes longer than
demands of performance, may cause extreme stress desired by an owner or manager to obtain an erec-
on certain individuals. Prognosis for behavioural tion and ejaculate. It is reported in stallions used for
problems is good when there is a strong commitment in-hand breeding and artificial semen collection. In
from all the people interacting with the stallion. pasture mating situations, poor libido, as a cause of
Calm and consistent handling is the cornerstone of low pregnancy rate in an otherwise normal stallion,
treatment. has not been reported.