One Dose Protocol
The most reliable way to use one dose of frozen semen is to inseminate
post-ovulation. Post-ovulation inseminations must be made within 6-8
hours of ovulation due to the lifespan of the ovum within the oviduct.
Obviously, the closer to ovulation the insemination is made, the better
the result, this is true for fresh and frozen semen. The one dose
insemination protocol generally involves single daily ultrasound
examination until a 35mm pre-ovulatory follicle is detected, then
administration of an ovulation agent (hCG or Deslorelin). The mare
would then be checked 12 – 24 hrs after administration of the ovulatory
agent and every 6 hrs (range 4-8hr) thereafter until ovulation is
detected, at which point insemination occurs. Insemination can be
performed pre-ovulation, however it is difficult to accurately predict
when a follicle will ovulate, therefore it is preferable to wait for
ovulation to occur and inseminate within six hours rather than risk
losing a dose on a premature pre-ovulatory insemination.
Two Dose Protocol
SBS has developed and tested a simple and effective two dose timed
insemination protocol for managing mares with frozen semen. This
protocol involves a single daily examination until a 35mm pre-ovulatory
follicle is detected, administration of an ovulation agent (hCG or
Deslorelin), and insemination with two doses of semen; one each at 24
and 40 hours after administering the ovulation inducing agent. Use of
this protocol insures that viable sperm are available for fertilization
in the mare’s reproductive tract during the time of 12 hours before to
6 hours after ovulation for mares ovulating 18 to 52 hours after
administration of the ovulatory agent.
Is Fertility Equal?
When deciding between the 1 or 2 dose protocol, the first consideration
should be whether there is a difference in fertility outcome between
the two methods. In a clinical trial conducted in Italy (Reger et al.,
2003), 26 out of 34 mares became pregnant (76%) after two timed
inseminations versus 15 of 21 (71%) following a single insemination
within 6 hours post-ovulation. In the same paper, the authors also
reported the outcome of a controlled study carried out in Colorado
where they found no difference in embryo recovery rates for mares
inseminated once within 6 hours post-ovulation with 1 dose of 800
million total frozen-thawed spermatozoa (60%) versus mares inseminated
twice at 24 and 40 hours post-deslorelin with a half dose of 400
million total spermatozoa per insemination (55%). Two data sets
collected in the USA during the 2002 and 2003 breeding seasons (Loomis
and Squires, 2005) were examined retrospectively and reported similar
pregnancy rates for mares inseminated once or multiple times in a given
cycle (51.5% versus 51.7% for 2002 and 47.1% versus 46.1% for 2003).
Mares inseminated twice on a cycle, once before and once after
ovulation, became pregnant at a rate similar to mares inseminated once
within 6 hours post-ovulation (48.1% versus 47.3%). Furthermore,
additional studies performed in France (Vidament et al., 1997), Germany
(Sieme et al., 2003) and Canada (Samper 2001) have reported that
pregnancy rates with frozen semen were higher when mares were
inseminated more than once per cycle.
Cost Comparison
Given comparable fertility the next consideration is usually financial.
Obviously the cost of veterinary care across the US and more so around
the world varies significantly, so it is difficult for us to make
generalizations here. Nonetheless, it is fair to assume that the
frequent ultrasound examinations required when inseminating with one
dose of frozen semen results in greater costs for veterinary management
per cycle than the once daily examination utilized for the two dose
timed insemination protocol. For convenience to the veterinarian the
one dose protocol may also necessitate the mare being boarded at a
breeding farm or clinic so that late night checks can easily be
performed to insure that insemination occurs within the critical 6 hour
window after ovulation.
However….The purchase price of the frozen semen also has a significant influence on the anticipated costs for each breeding cycle. Of course, as horse owners and breeders we place just as much value on the selection of the stallion as we do in the consideration of veterinary expenses for mare management, in some cases perhaps more bias towards stallion selection. By choosing that top international stallion, with limited frozen semen available at a significant cost per dose, we essentially limit our choice in insemination protocol. Semen sold on a per dose basis for hundreds or even thousands of dollars imparts a significant pressure on the mare owner and veterinarian to use only one dose of frozen semen per cycle, since the cost of the extra ultrasound examinations incurred when breeding with one dose is generally less than the cost of purchasing an additional dose of semen.
At SBS we recommend to our stallion owners that they sell frozen semen as a breeding and provide at least two doses per cycle, as opposed to selling frozen semen by the dose. This allows mare owners to choose the timed insemination protocol and benefit from the flexibility in scheduling and reduced costs in veterinary management.
For further discussion on purchasing one or two doses of frozen semen, see our recent blog article, Frozen Semen Sell by the Dose or as a Breeding
Does Breeding With
Two Doses Result in More Post Breeding Fluid Accumulation?
The numerous reports on timed-insemination protocols demonstrate that
multiple inseminations in normal mares are not harmful. Insemination
with frozen-thawed semen twice per cycle does not increase the
incidence of fluid accumulation and post-breeding endometritis. All
mares experience a natural inflammatory response within the uterus,
after the deposition of semen. The post-breeding inflammation initiated
by the first insemination is cleared within 12 hours in reproductively
healthy mares. Thus, a second insemination can safely be performed 16
hours later without negatively affecting fertility.
However, use of multiple inseminations per cycle may not be appropriate for all breeding situations. For example, mares that are susceptible to post breeding endometritis are less efficient at clearing the uterine lumen of semen and inflammatory products accumulated after breeding. Fertility is reduced in this group of mares and, unless properly addressed, the condition may aggravate with subsequent matings. These mares may require a more intense management scheme and be bred only once per cycle in order to minimize invasion of the susceptible uterus.
For more information on this subject, see the blog article, The Facts About Frozen Semen and Post Breeding Uterine Fluid
Further
Considerations
Remember, not all semen is created equally. There is a huge variation
in the quality of frozen semen on the market, both in the technique and
standard of quality control applied to the semen processing as well as
in the semen quality itself. Furthermore there is inherent variability
between stallions in the longevity and fertility of their frozen semen.
The industry recommended minimum is 200 million progressively motile
sperm per frozen semen dose. But to complicate matters further the
evaluation of semen quality can vary depending upon the technician and
technique used when performing the analysis. Mare owners should gather
as much information about the quality and fertility of the frozen semen
before purchase.
See the blog article, Questions Mare Owners Should Ask Before Breeding With Frozen Semen and the FAQ Can’t Post-Thaw Motility Vary With the Laboratory Performing The Analysis?
Both the selection of your mare and veterinarian could influence the outcome of your proposed breeding; we plan to review these variables in future blog posts.