Friesian Semen Network
If
you are currently involved in the equine breeding industry, it is obvious
that Artificial Insemination (or 'AI') is set to play an ever increasing
role in the future.
It
is equally apparent that there is a need for Friesian breeders and their
veterinarians alike to understand fully and to be familiar with the
techniques of AI in the horse. This should ensure the welfare of and
success of Artificial Insemination in the horse.
We Can
Help You
by
connecting you with reputable, professional and (inter)national Stud
farms whom provide Chilled and/or Frozen Semen of your favorite Dutch
FPS approved Friesian Stallion of the highest quality.
Here to send us your e-mail
about your requirements.
Breeding
With Chilled & Frozen Semen
- By
Jonathan F. Pycock, BVetMed, PhD, DESM, MRCVS, RCVS Specialist in
Equine Reproduction
Artificial
Insemination (AI) involves the introduction of sperm into the reproductive
tract of the mare without natural mating. AI in the horse was first
practiced long ago. Ancient Arabian texts describe how mares were successfully
inseminated.
In
the late 18th Century, an Italian scientist took the idea up again.
He performed a series of studies in which he placed stallion semen in
the snow and found that he did not necessarily kill the spermatozoa
(or "spermatic vermiculi" as he termed them), but merely made
them inactive. Upon warming, their motility returned. The use of AI
on a regular basis in horse breeding dates back to the beginning of
the 20th Century.
The
first organized AI programs were run on Russian stud farms. During the
past two decades, AI has been accepted by many national and international
breed authorities throughout Europe and America. In some countries,
for example The Netherlands, several thousand mares are inseminated
each year.
There
are some breed restrictions to the use of AI, most noticeably the General
Stud Book and The Jockey Club, which regulate the Thoroughbred. It is
therefore important to know which breed registries permit AI and which
do not.
For
those of us currently involved in the equine breeding industry, it is
obvious that AI is set to play an ever-increasing role in the future.
It is equally apparent that there is a need for breeders and veterinarians
alike to understand fully and to be familiar with the techniques of
AI in the horse. This should ensure first of all the welfare of the
horse and secondly the success of AI in the horse.
A
successful AI program depends upon both the stallion and the mare, and
it involves for the stallion the following components: a thorough examination
for breeding soundness, confirmation that the stallion has semen of
sufficient quality, and appropriate cooling and storage of the semen
sample after collection.
It
involves much more for the mare: a satisfactory breeding soundness examination;
the induction of an ovulatory estrus; the accurate prediction of ovulation;
correct timing of insemination relative to ovulation; appropriate storage,
thawing, and handling of semen; correct insemination technique; post-insemination
examination and treatments as required; and correct pregnancy diagnosis
14 to 16 days after insemination.
There
are two key concepts--evaluation of the semen sample and a well-timed
insemination. It is no use merely collecting a sample of semen; the
sample must be thoroughly evaluated to make sure that it is of sufficient
quality to be used in an AI program. The semen must be processed adequately
to assure that it retains its fertilizing potential. Likewise, the sperm
must be infused at the appropriate stage of the mare's reproductive
cycle.
It
is important to be aware that AI in the horse requires a high degree
of veterinary input and is not a cheap alternative to natural breeding.
It is vital that there is good communication at all times between the
mare owner and stallion owner, and their respective veterinarians.
Advantages
And Disadvantages Of Breeding With Chilled Or Frozen Semen
Although
AI has many advantages, there are some drawbacks to consider.
Advantages
of using AI include the following:
1)
Eliminating the cost and stress of mare (and perhaps foal) transport.
2)
Maximizing the efficiency of stallion usage as more mares can be bred
from one ejaculate.
3)
Increasing the availability of stallions both within and among countries.
4)
Preventing the mare from returning home in poor condition and reducing
the likelihood of mare injuries or of the foal's contracting disease.
5)
Evaluating the semen on a regular basis, which means that any problems
in the stallion's fertility will be identified more quickly.
6)
Using extenders with proper antibiotics to preserve the longevity of
sperm and minimize bacterial contamination.
7)
Enhancing the safety of animals and animal handlers.
8)
Reducing the risk of sexually transmittable and other diseases spreading
through a breeding population or among farms.
Among
the disadvantages of AI are these:
1)
The higher costs due to the considerable technology and skill required
to collect, evaluate, and ship semen properly.
2)
The need for considerable amounts of paperwork and the need for tightly
controlled regulations for the control of diseases to guarantee the
export of healthy semen.
3)
The requirement of adequate infrastructure for transporting the semen.
4)
Semen from some stallions will not tolerate the cooling and/or the freezing
and thawing process.
5)
Mare owners in remote areas might not be able to have the stage of the
mare's cycle determined.
For
an AI program to be successful, strict attention should be paid to health
precautions and hygiene. There should be strict adherence to Guidelines
and National Codes of Conduct for Disease Control appropriate for your
country to reduce the risk of disease transmission. Bacterial cultures
from the stallion's semen, urethra, and prepuce submitted to an appropriate
laboratory to identify any venereal pathogens should be performed. These
samples need to be taken regularly if the stallion is involved in both
a natural breeding and AI program.
The
Stallion: Semen Collection And Handling
Most
stallions easily can be collected artificially using one of several
models of artificial vaginas (AVs; the Hannover model is illustrated
in Figure 1). Although shape and size vary, AVs work with the same principle:
a double rubber liner with a water jacket in between.
The
stallion will ejaculate in response to appropriate temperature, pressure,
and friction of a well-lubricated AV. As a rule, the inner liner temperature
of the AV should be between 43° and 45° Centigrade. Selection
of temperature and pressure will depend on stallion's preference. The
AV should be well lubricated with a sterile, non-spermicidal lubricant.
The
container where the semen is collected should be dry, clean, and at
body temperature in order to prevent damage due to "cold shock"
of the sperm cells. Cold shock will result in premature death of the
sperm and/or abnormal motility patterns. The changes resulting from
cold shock in most cases will severely compromise the fertilization
potential of spermatozoa.
Virtually
all stallions of normal libido will ejaculate into an AV provided it
has an appropriate temperature and pressure and is properly lubricated.
The correct pressure can be achieved by adjusting the amount of water
or air in the AV. It generally is preferable to overfill the AV since
it is easier to remove than add water.
The
optimum temperature of the water immediately before collection is 48°
C. This equates to a Lumina temperature of 45° C. A marginal increase
of water temperature (up to 52° C) might be beneficial if the stallion
will not ejaculate. Depending on the stallion's preference, pressure
and water temperature can be adjusted.
If
the stallion does not mount quickly, it is worth considering the use
of an AV model such as the Colorado, which contains a large amount of
water and thus retains heat better than a lighter model with less water
(Figure 2). On the other hand, this model can be very heavy.
The
Hannover AV has a partial partition at the distal end, and some stallions
prefer to touch this with their glans penis for extra resistance. For
very small ponies, a bull AV can be used.
A
small amount of non-spermatotoxic lubricating gel must be applied before
use. This might not be necessary if the plastic disposable liners are
used. A roll of plastic film, together with a sterilizable bottle (such
as a baby bottle), can be used as a disposable AV liner. These liners
can be used with or without an in-line filter to prevent contamination
of the ejaculate with dirt or gel.
It
is important that the liner is non-spermicidal. If a rubber liner is
used, it is important to clean, rinse in de-ionized water, and air dry
the liner. Plastic liners are easier to use, but a few stallions seem
to dislike their texture and will not readily use them.
The
sterilized collection bottle should be kept in the incubator at 37°
C until just before use, and maintained close to this temperature throughout
the collection process. An insulated cover for the collection bottle
is useful.
Stallions
can be collected either mounting a mare in heat, a breeding phantom
or dummy mare (Figures 3A and 3B), or on the ground with proper manual
stimulation. The "teaser" or "jump" mare should
be of adequate size, should be sturdy, should be placid, and should
be free of contagious diseases and in standing estrus. To keep a mare
in estrus, it is possible to ovariectomize her and treat with estradiol
benzoate (50 mg per week). A tail bandage is applied and her perineal
region and flanks cleaned. It is necessary that she stand still, so
a twitch might be needed.
To
protect the stallion against being kicked by the mare, a breeding hobble
(such as a rope around her hind legs and tied around her neck) can be
used. To protect the mare against biting from the stallion, the mare's
neck and shoulders can be covered with a cloth or shield (Figure 4).
Routine
pre-collection hygiene measures for the stallion include cleansing of
the penis with hand-warm water (40° C) and several disposable cloths.
Cleansing begins at the glans penis, then the sheath and prepuce are
washed. Special attention should be paid to the fossa around the urethral
process with the urethral sinuses and the urethral diverticulum. These
parts often are contaminated with smegma. Dry the penis thoroughly with
a clean disposable towel, although some prefer not to dry the penis.
Antibiotic
or disinfectant solutions should not be used. If the stallion has not
been used for collection or a long period (one to two weeks), the routine
initially should be performed every time before collection. If the stallion
is collected daily, it is suggested that the treatment be performed
once or twice weekly. The majority of stallions accept the treatment
well after they become accustomed to it.
Semen
should be collected into a pre-warmed container, as mentioned earlier,
and maintained at body temperature while in its raw state. Semen should
be filtered to remove the gel fraction and other debris if an in-line
filter was not used (Figure 5) and diluted with an appropriate pre-warmed
extender. The physical characteristics of the ejaculate, including volume,
concentration, color, and motility, should be evaluated. Motility is
checked using a microscope with a warming table at 37° C. (Figure
6).
Semen
Preservation
The
temperature at which semen should be stored depends on the period of
time from collection to insemination. Semen that is to be inseminated
immediately can be used undiluted, but if the semen is to be used after
10 minutes, it is best diluted with pre-warmed extender. Semen to be
used within six to eight hours after collection can be stored at room
temperature (18-22° C) in a dark environment.
Removing
the seminal plasma by centrifugation might be beneficial for certain
stallions. It is preferable that semen stored for such a period should
not be subjected to fluctuations in temperature, and storage in a light-proof,
airtight container (such as a thermos flask) should be considered. If
semen is intended to last longer than eight hours, it should be cooled
down to 5-8° C over a two- to three-hour period to prevent too much
energy loss of the spermatozoa.
The
rate of cooling from room temperature is critical. Approximately 12
years ago, the Hamilton Thorne Company developed a container (The Equitainer)
for transporting chilled equine semen (Figure 7). This consists of a
strong container with a snap-lock that holds frozen canisters, insulation,
thermal ballast bags, and an isothermolyzer. The container is special
in that it has the ability to lower the temperature of the semen package
approximately 0.3° C every minute until the temperature stabilizes
at 4-6° C.
The
semen should remain constant at that temperature for 48 hours. This
cooling rate was designed specifically after trials were conducted to
determine sperm motility after cooling at various rates. If the total
volume of the extended semen and thermal ballast lies between 120 and
170 ml, the semen will cool at the proper rate.
Special
equipment, such as the Equitainer, is required for optimal survival
of semen after transport. In my experience, the Equitainer is easy to
use, durable, and works very well. Disposable containers for shipping
chilled semen are available on the market, at less cost than the Equitainer,
but sperm survival might not be optimal under certain conditions due
to storage temperature fluctuation and reduced storage period.
In
The Netherlands, a polystyrene box in which two 15 ml tubes with chilled
semen can be placed is used to transport chilled semen (Figure 8). The
polystyrene box is packed in a cardboard box, which can be placed in
a refrigerated (at 5° C) transporter. Semen arrives at the insemination
center later that afternoon, i.e., within eight hours of collection.
This is an efficient and inexpensive system, but is only really possible
in a small country such as The Netherlands, where the distances over
which the semen needs to be shipped are smaller.
Some
stallions have semen that transports well in the cooled state, while
others do not. For that reason, it is advisable to test the storage
ability of a stallion before his semen is shipped to a client. An ejaculate
should be collected, diluted 1:2 with an appropriate extender, placed
in an Equitainer, then examined at 12-hour intervals for sperm motility.
Because
one usually packs at least one billion progressively motile sperm per
insemination dose, final dilution rates will vary (1:1 to 1:6) according
to the density of the semen collected. It is generally accepted that
approximately 50% of spermatozoa are nonviable by the time of insemination
due to the process of cooling and shipping the semen, and that is the
reason one billion progressively motile spermatozoa should be shipped.
The
ideal dilution rate for chilled semen is within the range of 25 to 50
million spermatozoa per ml. This means that in most cases, the volume
of shipped extended semen can be kept in the range of 30 to 60 ml, which
would seem optimal. Extended semen that is too dilute will result in
large volumes being lost from the mare's reproductive tract via the
cervix. The low spermatozoa concentrations might not achieve optimal
pregnancy rates.
Each
shipment of fresh or chilled semen has to be accompanied by documents
with information on the stallion (identity and health status), the collection
center, collection date, shipment date, and information about the semen
quality and the number of sperm sent.
If
life expectancy of the semen is longer than 72 hours, cryopreservation
(freezing) seriously should be considered. There are several additional
advantages of frozen semen:
1)
Semen can be transported easily internationally (this also can be done
with chilled semen in some cases).
2)
Semen can be used from stallions which are away competing for long periods
of time or recovering from injury.
3)
Semen can be frozen from potentially valuable stallions and stored indefinitely.
There
are several disadvantages:
1)
Pregnancy rates using frozen semen often are disappointing. Indeed,
pregnancy rates can be 0% if strict stallion selection and careful insemination
routines are not practiced. There is considerable variation among breeds
with regard to the ability of semen to freeze satisfactorily.
2)
Charges for freezing stallion spermatozoa are relatively high.
3)
Frozen-thawed semen has a very short life span, which means that insemination
must take place very close to ovulation. This means repeated and frequent
veterinary examinations are necessary, which further increase costs.
Mare
owners often pay large sums of money for frozen semen of unknown potential.
Post-thaw motility results often are quoted as the basis for selling
frozen semen. It would be better to select stallions on the basis of
fertility (number of live foals produced from frozen semen inseminations)
rather than post-thaw motility because the correlation between fertility
and post-thaw motility of frozen semen could be poor.
Stallion
owners should be encouraged to sell semen only on the basis of confirmed
pregnancies. When substantial fertility data have been accumulated on
a particular stallion, his semen can be sold with an expected pregnancy
rate in mind.
The
Mare
Before
a mare owner begins on a breeding program using chilled or frozen semen,
the difficulties associated with the use of the technique, as well as
an indication of the expected success rates, must be understood. Many
mare owners seem to believe that once they have decide to breed a mare,
she will become pregnant and have a live foal the following year. This
is simply not true, and it is important that they are aware of the likelihood
of success.
For
a typical set of circumstances, i.e., a reasonably fertile mare and
good-quality semen, one can expect pregnancy rates of 55-70% per cycle
with chilled semen and 35-50% per cycle with frozen semen. The overall
pregnancy rates at the end of the season vary between 50% and 90%, with
an average of about 75%. Of course, some mares lose the pregnancy and
the resulting live foal rate ends up around 65%.
It
also is important to realize the costs involved with using AI. Many
mare owners expect costs to be decreased because of no transport of
the mare. They do not realize that there can be considerable costs involved
with the collection and transporting of semen and for monitoring the
reproductive cycle of the mare and inseminating her at the appropriate
time.
Breeding
Soundness Examination
All
mares should have a thorough pre-breeding assessment before breeding
with chilled or frozen semen. This is to identify mares likely to conceive
successfully and carry a foal to term. While unforeseen problems can
occur, there are procedures that can help you and your veterinarian
decide if a mare is suitable for breeding.
The
suitability for breeding does not refer to the quality of the horse
or its temperament; rather it is an assessment of the genital health
of that particular mare. Collectively, these procedures are known as
the breeding soundness examination.
First
of all, a complete breeding history of the mare for the last five years
should be taken. By answering a series of detailed questions, mare owners
will help uncover information that otherwise would remain unknown. Some
relevant questions are as follows:
How
old is the mare? Fertility declines with age once a mare is more than
10 years old. This is not to say that old mares cannot become pregnant
and have a foal, but in general, the older a mare is, the less likely
she is to have a foal.
Has
the mare been to the stallion or inseminated previously? If so, has
she become pregnant and delivered any foals? Mares which have had foals
have at least proven that they are capable of doing so. Maiden mares
which have not had foals are more of an unknown quantity. In many cases,
they are young mares and go in foal relatively quickly and easily.
However,
if the maiden mare is older, she will be less likely to get in foal.
The breeding history should include a record of whether the mare has
ever aborted, conceived twins, suffered dystocia, or failed to conceive.
The
gynecological examination should consist of a thorough and systematic
rectal examination (both manual palpation and ultrasound) of the cervix,
uterus, and ovaries. The vagina and cervix also should be examined using
a speculum (a narrow tube down which you can shine a light), manually
by vaginal palpation, or both.
In
many cases, a swab of the lining of the uterus will be taken to see
if there are any bacteria present or signs of an inflammation of the
uterus (endometritis).
During
estrus, your veterinarian should continue to monitor the cycle by daily
(more frequently when frozen semen is being used) rectal palpation and
ultrasound, and/or teasing, if available. Ultrasonographic examinations
should be done prior to breeding. These exams provide information as
to the number of follicles of ovulatory size, prevalence of uterine
cysts, and any sign of inflammation and/or infection.
In
many cases, mares which are intended for AI often are kept at the owner's
home, where no teaser stallion is available for detection of estrus.
This also could be true if, as is often the case (in England) for ease
of examination, the mare is kept at the veterinarian's premises.
Detection
of estrous behavior in the absence of a teaser stallion usually is misleading
and, therefore, the attending veterinarian must be prepared to induce
and diagnose estrus in the absence of a stallion.
Prediction
of ovulation is not easy and involves taking into consideration several
findings and making a considered judgment. By a combination of daily
rectal and vaginal palpations and ultrasound examination, an experienced
veterinarian usually can make an accurate prediction of when ovulation
will happen. Hormones frequently are used to induce ovulation.
The
most commonly used method is the intravenous administration of 3,000
IU human chorionic gonadotrophin (hCG) once it has been established
that the mare is in estrus with a soft follicle at least 35 mm in size
and an edema pattern (Figure 9) visible in the uterus. Approximately
85% of mares will ovulate in the 24 to 48 hour period following hCG
administration. Recently, use of a gonadotrophin releasing analog, deslorelin,
has been found as effective in inducing ovulation as hCG.
Timing
Of Insemination
Ideally,
the stallion owner should be notified 48 hours prior to the desired
breeding date and a clear communication channel opened between the mare
owner's veterinarian and the stallion owner early in the cycle. Any
application for import permits should have been made well in advance
of the desired breeding date.
Accurate
prediction of ovulation is important because the optimal time for AI
with chilled semen is in the 24 hours leading up to ovulation. Pregnancy
rates generally will decrease if insemination is outside this range.
This time interval is shorter than if fresh semen or natural service
is used.
That
is not to say that pregnancies will not occur when the interval exceeds
24 hours, but differences among individual stallions, different extenders,
and different systems of cooling can cause a wide variation in the longevity
of chilled semen not only in storage, but also in the mare's reproductive
tract.
With
frozen semen, there is evidence that some semen might not remain viable
as long as 24 hours following insemination, so insemination closer to
ovulation is preferable. The regime most commonly used with frozen semen
is to examine the mare every six hours as ovulation approaches. Insemination
should be just before ovulation is anticipated. If semen supplies are
limited, insemination can be withheld until ovulation is detected.
This
system ensures the use of a single insemination dose at a maximum of
six hours after ovulation. In my experience, pregnancy rates do not
begin to decline with frozen semen as long as insemination is within
six hours following ovulation. Ideally, one would prefer to inseminate
the mare in the eight hour period before ovulation. However, it is not
possible to be 100% certain in predicting when ovulation will occur.
Insemination
Technique
The
mare should be identified from a passport or similar identity document
and might need to be matched against an identity supplied with the semen.
The documentation accompanying the semen should be checked and the paperwork
should confirm that the stallion has passed all relevant health checks.
Information on date and time of collection, motility, concentration,
and type and ratio of extender used also should be included with each
shipment.
The
veterinarian carrying out the insemination should certify that the semen
has been received and that the identity of the mare has been checked
and is the same as that described in the nomination agreement. It should
be further certified that only this mare has been inseminated and that
any unused semen has been destroyed.
She
should be prepared for insemination in a clean, well-lit environment;
a crush (stock) for restraint is preferable. Her tail should be bandaged
and tied out of the perineal region. The vulva and perineal area should
be thoroughly cleansed with very dilute povidone-iodine solution or
mild soap. This is then thoroughly rinsed off with fresh warm water
and the perineal area dried with clean, soft, disposable (paper) towels.
If
chilled semen is being used, the semen container should remain unopened
until this stage. No attempt should be made to warm the semen prior
to insemination of the mare. Since there might be a small delay between
cleaning the mare and insemination, it might be helpful to empty the
mare's rectum of feces to prevent contamination of the area after cleansing.
It
is highly recommended that all the semen arriving should be inseminated
as soon as the shipment arrives. Although many breeding farms ship semen
for two inseminations, semen should not be stored for use 12 to 24 hours
later. The oviduct (fallopian tube) of the mare is a far better incubator
of spermatozoa than any transport system available. In addition, the
first insemination might cause some degree of uterine inflammation,
and any subsequent insemination will make this inflammation worse.
The
semen should be gently mixed prior to loading into a sterile plastic
syringe (without a rubber plunger). The syringe then should be attached
to a sterile insemination pipette. The operator should use a "sterile"
obstetric glove (i.e., a glove turned inside out). In certain circumstances,
a sterile surgeon's glove should be placed over the clean rectal glove.
It might be necessary to place a small amount of sterile, non-spermicidal
lubricant on the top of the hand around the knuckles.
The
catheter should be held with the tip behind the finger tip and the hand
brought into the vulva (Figures 10 A and B). The external opening of
the cervix should be located with the index finger, and a finger inserted
into the cervical canal. The catheter is inserted alongside the finger
and the catheter gently pushed forward.
It
is very important that the catheter reaches the mid or cranial uterine
body and does not remain obstructed in the cervix. This passage through
the cervix is not always easy. Deposition immediately cranial to the
cervix should be avoided.
The
syringe should be gently emptied, infusing the semen into the uterus.
During the deposition of the semen, it is important that the tip of
the catheter not be buried in the uterine mucosa or a uterine fold.
Any resistance to the flow of semen should be corrected by a fractional
withdrawal of the catheter.
A
small amount of semen should be warmed to 37° C, after which it
should be examined for progressive motility and gross abnormalities.
Once
the semen has been thawed, the technique for insemination of frozen-thawed
semen is identical to that used for fresh or cooled transported semen,
except that one should use warm instrumentation (catheter and syringe).
No attempt need be made to increase the volume of semen frozen in small
containers. Equine semen can be frozen in 0.5 ml straws like those used
for cattle. In that case, between one and eight of them are required
per insemination (Figure 11).
When
several straws are required for one insemination, the thawed semen should
be pooled, then inseminated. Plastic bags, aluminum sachets, pellets,
1 ml vials, 1ml straws, and 4.5 ml "Maxitubes" with ball seals
at either end also are used for freezing semen.
Each
package has its own thawing method, and if thawing instructions are
absent, the inseminator should obtain them before using the semen because
one cannot assume that because semen is in a particular kind of package,
that it should be thawed by a certain method. Obviously, an optimal
packaging system has yet to be developed. Marking on semen packages
also is variable.
Examination
Following Insemination
The
mare should be checked for ovulation by your veterinarian within 24
hours. It might be necessary to order a second delivery of semen if
the time of ovulation has been miscalculated. It cannot be assumed that
just because sufficient numbers of viable sperm have been inseminated
at the optimum time relative to ovulation that pregnancy automatically
will ensue in a mare.
Breeding
induces an acute inflammatory response, which is normal and beneficial.
The reason many mares, particularly old maiden mares, fail to become
pregnant is defective uterine clearance of this inflammatory "soup."
It is the spermatozoa themselves that elicit the most acute inflammatory
response. (A detailed discussion of the inflammatory response to breeding
and the management of the susceptible mare will be covered in a future
article and only brief details are given here.)
Ultrasonic
examination of the uterus 12 to 24 hours after insemination often shows
collections of fluid (Figure 12). These must be removed if optimum pregnancy
rates are to be achieved. Oxytocin probably is the drug of choice. Subsequent
intrauterine antibiotic treatments can be beneficial in certain cases.
Mares
with defective uterine clearance are better treated in relation to insemination
rather than waiting for ovulation. Large-volume lavage with warm saline
solution in addition to oxytocin might be beneficial. The perineal conformation
of the mare should be checked and a Caslick operation performed if necessary.
Examination
of the mare for pregnancy should take place as early as possible using
ultrasonography. This is best done 14 to 15 days after insemination.
The 14 day pregnancy is 13 to 18 mm in size (Figure 13). The embryonic
vesicle grows at a rate of approximately 3.5 mm/day at this stage of
pregnancy and remains highly mobile, making thorough examination of
the uterus important.
In
the event of twin pregnancies, both vesicles usually can be seen at
14 days, even if the second twin arose from a later ovulation. This
fact, together with the mobility and relatively small size of the concepti,
make 14 to 15 days the optimal stage of pregnancy to diagnose twins
and crush one. Although pregnancy diagnosis is highly accurate even
at this early stage, it is important to be aware of the possible confusion
caused by uterine cysts and the presence of twin conceptuses.
Ideally,
one would have performed an ultrasound examination before breeding the
mare, but this is not always possible. If the first scan is performed
at Day 14 or 15, then it is possible to return the next day in cases
of confusion and see if the pregnancy has changed position or grown
in size. This should allow differentiation from a cyst before the pregnancies
have a chance to become unilaterally fixed.
Following
an initial examination at Day 14, the aim of the examination at Day
24 to 27 should be to assess that the embryo is developing normally
and identify the heartbeat. At this time it can be confirmed that there
is only a single conceptus. If twins were missed at the earlier examination,
it still might be possible to correctly manage them.
Ideally,
a third examination should be performed around Day 33 to 35 to confirm
that a single conceptus is developing normally. If there is failure
of normal development or if twins are detected, it usually is possible
to terminate the pregnancy and re-breed the mare.
In
conclusion, the success of breeding with chilled or frozen semen depends
on the fertility of the stallion, the fertility of the mare, and managerial
practices. The end product (foal) is an interaction among all of these
factors.
The Next
Step
If
you, after reading the info on our Web pages, come to the conclusion
AI might suit your Breeding Program, then here
to get in touch with us.
About
The Author Jonathan F Pycock, BVetMed, PhD, DESM, MRCVS, RCVS Specialist
in Equine Reproduction, is a 1983 graduate of the Royal Veterinary College,
University of London, from where he obtained his PhD in 1988 for his
thesis on breeding problems in the mare.
He
was in private equine practice until 1994, when he took a position as
Associate Professor of Equine Reproduction at the University of Utrecht
in The Netherlands. While there, he developed a special interest in
artificial insemination with both chilled and frozen semen and worked
extensively in those areas. He was awarded his Diploma in Equine Stud
Medicine in 1994, and in 1995 became an RCVS recognized Specialist in
Equine Reproduction.
He
returned to the UK in January 1997 to begin Equine Reproductive Services,
a first opinion and referral private equine practice based in Yorkshire.
He has published many papers and book chapters and recently completed
editing the book Equine Reproduction and Stud Medicine. He is Chairman
of the AI Committee of the British Equine Veterinary Association and
is responsible for organizing the courses for technicians involved in
equine AI.
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