Ed Squires, PhD, an
honorary Diplomate in the American College of Theriogenology
(reproduction), of Colorado State University, presented a lecture at the
2003 American Association of Equine Practitionersí convention on a
simplified strategy for insemination of mares with frozen semen.
Squires said the perception in the industry is that mares must be
examined four to six times per day to use frozen semen successfully. He
said the reasons for frequent examination are because limited semen is
made available and the desire to breed as close to ovulation as
possible. If multiple doses of semen are available, mares could be
examined once a day and treated identically to mares bred with cooled
Perceived negatives to using frozen semen are that it is usually sold
by the dose, it can be difficult to get, and it is often expensive if
imported, he noted. There is also concern about uterine inflammation
with multiple insemination doses with frozen semen and reduced fertility
if mares are not bred close to ovulation. Therefore, there is a need to
have a better method for breeding with frozen semen.
When frozen semen was first introduced, pregnancies were achieved by
checking the mare frequently each day and breeding with a single dose of
semen as close to ovulation as possible. Therefore, this was adopted as
standard operating procedure, said Squires. Veterinarians checked a mare
every six hours once she was in heat and had been given hCG (human
chorionic gonadotropin) or Ovuplant (deslorelin).
The problems with this protocol, said Squires, are the time demands
on the veterinarian, cost to the client, and lower conception rates than
with cooled or fresh semen in spite of this tremendous effort. The end
result was that lots of owners stayed away from frozen semen.
Squires said the emerging protocol for frozen semen is to inseminate
the mare twice with a timed insemination technique. This helps balance
the cost of semen and the cost of veterinary care.
This new protocol for breeding with frozen semen centers around
breeding a mare twice each cycle after administration of hCG or Ovuplant.
If the mare ovulates within 18 and 52 hours of treatment, then viable
sperm should be available within the window of six hours after or 12
hours prior to ovulation.
Squires said two studies compared pregnancy rates for mares
inseminated only once within six hours post-ovulation with mares
inseminated on a timed insemination protocol 24 and 40 hours after hCG
In the first study at Colorado State, one group of mares was given
hCG once they developed a follicle greater than 35 mm. The mares were
scanned with ultrasound every six hours until ovulation was detected,
then they were bred using 800 million frozen thawed sperm post
In the second group, Squires developed a
timed insemination program. Once these mares developed a follicle, they
were only scanned once a day, administered hCG, then bred 24 and 40
hours after hCG administration using 400 million sperm at each breeding.
Pregnancy rates were similar between the two groups, and there was
no difference in the occurrence of post-breeding fluid accumulation.
Squires said data from Italy showed that the pregnancy rates in the
timed insemination group were higher than for mares bred after
Data from Select Breeders Services laboratories in 2002 and 2003
showed that mares bred one time with frozen semen had similar pregnancy
rates as those bred multiple times.
Therefore, said Squires, the optimum window for AI with cooled
semen is 24 hours before ovulation to six to eight hours after. With
frozen semen the optimum time is 12 hours before to six-to-eight hours
Squires said daily exams were sufficient when mares were inseminated at
fixed times after hCG or GnRH (gonadatropin-releasing hormone)
administration. Multiple inseminations did not adversely affect
fertility; there were no detrimental effects to the mares bred more than
once in the cycle with frozen semen.
Therefore, with frozen semen, timed insemination at 24 and 40
hours after giving hCG or Ovuplant resulted in pregnancy rates
comparable to those obtained with single post-ovulatory administration
with the mare inspected via ultrasound every four to six hours.
timed insemination protocol has the advantage that mares can be managed
identically to mares inseminated with cooled semen and examined with
ultrasound only once per day.