British Breeder Magazine November 2019

Feature - VET INSIGHT
Timing is
everything
Dominant follicle close to ovulation
In a herd/ wild situation the stallion
would cover the mare repeatedly in
one oestrus cycle, during the period in
which she will stand to be mounted.
This leads to a high probability of
viable sperm being present in the
oviduct at the time of egg release
allowing fertilisation to occur.
In the sports horse where artificial
insemination is the norm; Stallion
availability, semen costs, plus the risk
of increased post mating endometritis
or fluid accumulation from repeated
inseminations means that one
insemination per cycle is usually
preferable. The equine oocyte is only
viable if fertilised a maximum of 6-8
hours after ovulation while Semen
processing for shipping and freezing
reduces the lifespan of the sperm cell.
These two factors mean that accurate
timing of insemination in relation to
egg release is crucial.
Semen Longevity
Fresh and chilled semen should survive
within the oviduct for approximately
48-72 and 12-24 hours respectively.
Good pregnancy rates are therefore
achieved with insemination being
performed within these time periods
prior to ovulation. Frozen semen has a
much reduced survival post thaw and
therefore requires greater accuracy,
with insemination as close as possible
to or up to a maximum of 6 hours
post-ovulation.
Semen Longevity
• Repeated examination of the mare is
necessary by rectal ultrasonography of
the reproductive tract and palpation
the cervix.
• As ovulation approaches, follicles will
reach maximum size (>35mm), begin
to lose their round shape, develop a
thicker wall and soften.
• Uterine oedema increases during
oestrus up to a maximum before
decreasing again in the final 12 hours.
• The cervix dilates and softens
• Some will show ovarian pain on
palpation
• Specialist ultrasound techniques
(Doppler) can highlight changes in
blood flow in the follicle wall.
Ovulation Induction Agents
Products containing either Human
chorionic gonadotrophin or deslorelin
are commonly administered to the inseason
mare. These prompt a hormonal
response, accurately and reliably
controlling the timing of a naturally
occurring ovulation, thus avoiding the
need for repeated inseminations and
reducing the number of examinations
required.
Maximal uterine oedema
What can go wrong?
• Failing to follow a conventional
pattern or formation of haemorrhagic
anovulatory follicles, which fail to
respond to ovulation induction agents
may be a one off or a recurring trait
in the individual. Reproductive history
should always be investigated.
• Endometrial infection may alter the
predictors of ovulation and so must be
diagnosed.
• Semen courier and health paper
issues may force an unpredicted delay
in insemination.
Oakham Veterinary Hospital stud vet Victoria
Marchi scanning a mare
For more information contact:-
Matthew Hecking
01572 722647 or 07976 822903
matthew.hecking@oakhamvethospital.
co.uk
54 | BRITISH BREEDER