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EQUINE MATTERS
B R E E D I NG
Veterinary Surgeon
Roger Dixon
XLVets Equine practice
Ashbrook Equine
Hospital
Breeding: Ai or Natural Cover
roger dixon BVM&S CertAVP(ESM) MrCVS,
Ashbrook Equine Hospital
Artificial insemination (AI)
Artificial insemination (AI) is a well-established
assisted-breeding technique. It involves a
veterinary surgeon or qualified AI technician
depositing previously collected, frozen,
chilled or fresh semen into the uterus of the
mare at the optimum time to allow fertilisation
of her egg. It is widely used in show-jumpers,
dressage, eventing and pleasure horses.
However, AI is less commonly used in
thoroughbreds because, by convention, the
offspring are ineligible to be registered for
racing. Natural cover therefore predominates
in the thoroughbred industry.
Natural cover
There are several different management
systems that have been adopted for ‘natural’
cover. In the least intensive and most
inexpensive system, the stallion ‘runs’ with a
number of mares in the field and covers them
as they come into season. This mirrors the
situation in the wild and favours those mares
of superior fertility. It may take several oestrus
cycles to achieve conception; indeed, the
average ‘per-cycle’ conception rate in this
situation is surprisingly low at around 40%. A
variation on this system involves visually
monitoring the mares and ‘hand-covering’
them when they are receptive to the stallion;
this at least ensures that mating occurs.
The intensively managed thoroughbred studs
are at the other end of the spectrum. These
stallions may be in very high demand with
just one opportunity per oestrus for mating;
close veterinary management of the mare is
therefore required to ensure she is presented
to the stallion at the optimum time to achieve
conception. Although veterinary costs will be
higher, a well-managed thoroughbred stud
can expect to achieve per-cycle conception
rates of up to 70%.
Selecting natural cover or AI?
A mare owner considering breeding a foal,
may have to decide whether to proceed with
natural cover or AI.
The option of AI will depend on several
factors. These may include:
●
The availability of the stallion:
◦
Many sports horse stallions will only
be available via AI due to competition
commitments or concerns about the
stallion suffering injury during covering.
●
The location of the stallion:
◦
A mare may go to a stud close to
home and the semen can be brought
in from elsewhere in the UK or abroad.
This removes the need to subject the
mare to long-distance travel.
●
The age and breeding history of the mare:
◦
AI is particularly suitable for sub-fertile
mares e.g. older mares or mares with
poor vulval conformation who are
prone to uterine infection (endometritis).