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BREEDING MARES

Mares are usually considered seasonal breeders, that is they will usually show oestrus ('in season') behaviour in the warmer spring/summer months. 'In season' behaviour may include: increased attachment to other horses, increased whinnying to other horses, squatting and urination at the approach of other horses, 'winking' of her vulva when approached by other horses. This behaviour usually lasts for about 5 days.

 

The Equine Reproductive Cycle

Mares usually have an approximately 3 week reproductive cycle. As the mare is about to cycle, one or more follicles develop on her ovaries. During oestrus the follicles grow in size until they are approximately 4-6 cm in diameter, when they ovulate and release the egg into the fallopian tubes. To achieve pregnancy it is desirable to serve or inseminate the mare as close as possible before ovulation occurs. Once ovulation has occurred a structure called a corpus luteum forms which secretes progesterone and stops the mare coming back into season. From there 2 things may occur:

•    If the mare is served or inseminated at the appropriate time, the sperm fertilizes the egg in the fallopian tubes, and the fertilized egg gradually travels down the fallopian tubes until it enters the uterus approximately 5 days after fertilization. If pregnancy occurs the corpus luteum remains as the main hormonal support for the pregnancy for the first 35 days of gestation. 

•    If the mare is not pregnant the corpus luteum disappears approximately 2 weeks after ovulation to and the mare will come back in season. 

Most breed societies in Australia have determined an arbitrary date of 1 August as the birthday for horses (for standardbreds it is the 1 September). To fit with this date it is usual to start serving mares in the first week of September (October for standardbreds). There is pressure on breeders to have their mares foal earlier rather than later in the season, especially if they are planning to sell the foals as weanlings to 2 year olds (for example most thoroughbred foals) as foals born earlier in the season may be bigger by sale time than those born late in the season. This arbitrary date often does not coincide with the peak fertile period for horses, especially in southern states of Australia. There are management practices and medication that may help to encourage mares to breed earlier in the season which may be discussed with you if you choose to breed from your mare.

 

Methods of insemination

There are many ways to inseminate mares. A brief summary will be provided below, further details of the more intensive methods of insemination will be discussed elsewhere. 

 

Natural service (service by a stallion)

'Running with the stallion'

This a common method used in Australia. In this method the stallion is kept with a band of mares for a period of time. During that time it is assumed the stallion will serve each mare and they will fall pregnant. Pregnancy testing may be performed intermittently to determine an estimate of pregnancy status, or the stallion manager may simply elect to wait until the mares foal

The advantages of this method are: 

Little human intervention required

The disadvantages of this method are: 

The need for a suitable block of land to safely contain the herd
The risk of injury to the stallion or the mares
Little control available on when the mares may foal (a degree of control may be imposed by only running the stallion with the herd for a set period of time for example September to December)
Some mares may fail to fall pregnant for a range of behavioral or medical reasons
The possibility of twin pregnancy occurring
The risk of transmissible venereal infections passed between horses

 

'Hand Service'

This method involves supervised service of the mare at a predetermined time. The timing of service may be determined by monitoring the mare for signs of oestrus and serving intermittently during the time she is showing oestrus (commonly every 2 days), or by regular veterinary examination of the mare's ovaries to determine a suitable time for service. Pregnancy may be determined by monitoring the mare for return to service, by manual or ultrasound pregnancy testing by a veterinarian or by hormone assays on blood or urine.

The advantages of this method are:

Reduced risk of injury to the stallion or mare
Does not necessarily require assistance by a veterinarian (although to reduce the chance of twin pregnancy reproductive ultrasounds are strongly recommended)

The disadvantages of this method are:

The need to have mare and stallion in the same place at the same time, which could involve either agistment costs or transport of the mare to the stallion on one or more occasions
Risk of transmissible venereal infections passed between horses

 

'Fresh Semen Insemination'

This method involves collecting the stallion's semen through the use of an artificial vagina and teaser mare or 'dummy'. The semen is then transferred directly into the mare's vagina or uterus.

The advantages of this method are:

Reduced risk of injury to the stallion or mare
Reduced risk of transfer of transmissible venereal infections

The disadvantages of this method are:

The need to have mare and stallion in the same place at the same time, which could involve either agistment costs or transport of the mare to the stallion on one or more occasions
Some equipment and technical expertise required

 

Chilled Semen

Chilled semen insemination involves collection of semen from the stallion using an artificial vagina and teaser mare or dummy mount. The semen is mixed with a special solution to extends its life and is then chilled. This allows the semen to be transported in special containers designed to keep it chilled from the stud where the stallion stands to where the mare is to be inseminated. Ideally the mare should be inseminated within 1-2 days of semen collection, although individual stallion's semen may last longer than that when chilled. Chilled semen is commonly transported across Australia or even from New Zealand to Australia for use. Pregnancy rates using chilled semen should be close to those for single hand service.

The advantages of this method are:

No need to transport the mare to the stallion for insemination
Reduced risk of transmissible venereal disease
More than one mare may be inseminated by a single ejaculate

The disadvantages of this method are:

Some equipment and technical expertise needed at both the stallion and mare end
Additional cost and time involved in arranging transport of the semen
Need for regular reproductive assessment of the mare to determine optimum time for service
If a suitable area for mare reproductive examination is not available the mare may need transporting to another facility
Not all stallion owners offer this service
Pregnancy testing strongly recommended to reduce chance of twin pregnancy

 


Frozen Semen

Frozen semen insemination involves collection of semen from the stallion using an artificial vagina and teaser mare or dummy mount. The semen is mixed with a special solution to extend its life and protect is from damage by the freezing process and is then frozen. It may then be kept indefinitely providing it is maintained under ideal conditions. The mare must have her reproductive cycle closely monitored and is inseminated as close to ovulation as possible, generally within 6 hrs before ovulation.

The advantages of this method are:

No need to transport the mare to the stallion for insemination.
It is possible to use semen from stallions all over the world (providing import restrictions are observed)
The ability to store semen for future use, even if injury or death of the stallion were to occur
Reduced risk of transmissible venereal disease 
The semen may be collected at a time to suit the stallion owner, for example it may be collected in the off season for performance horses and stored rather than needing to collect semen when the mare is ready to be served.

The disadvantages of this method are:

Not all stallions are suitable for frozen semen production
Increased cost for semen collection, processing, storage and transport of semen
Significant decrease in per cycle conception rate for mares bred by frozen semen compared to natural service or chilled semen insemination
Significant increase in cost to mare owner due to increased frequency of reproductive examination and increased technical skill.
Most mares will need to be transported to a suitable facility for reproductive monitoring as ovulation approaches

 

Embryo Transfer

Embryo transfer involves inseminating the 'donor' mare by any of the techniques above, then at 6-7 days after ovulation the embryo is flushed from the uterus and transferred to another ('recipient') mare. The recipient mare needs to be at a similar stage of her reproductive cycle to the donor mare.

The advantages of this method are:

Allows breeding from valuable performance mares with minimal disruption of their performance career
Reduced risk of breeding from valuable mares due to not having to undergo the foaling process. 
More than one foal may be bred from a mare during a breeding season (subject to registration restrictions)
It may be possible to freeze embryos and store them for future use

The disadvantages of this method are:

Substantial cost due to need for equipment and technical expertise
Decreased per cycle pregnancy rate compared to natural or chilled semen insemination
Mare will need to be transported to a suitable facility for embryo collection and transfer
Significant cost involved in maintaining recipient mare (many embryo transfer facilities maintain a recipient mare herd into which embryos are transferred, in the event of successful transfer a fee is payable for the purchase or use of the recipient mare). More than 1 recipient mare needs to be prepared for each donor mare cycle.

 

Our vets have experience in all the reproductive methods listed above so please do not hesitate to give us a call and arrange a consult about the reproductive needs of your horses!

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