Reproductive technology is progressing all the time and includes more traditional practices such as artificial insemination right through to arguably the most extreme process of cloning. Whilst there are lots of ethical questions relating to reproductive technologies which is why it is still not permitted to be used in any form in the Thoroughbred racehorse, the reduced risk of injury and disease to the breeding animals is indisputable.
For mares, embryo transfer is most commonly used to enable successful competition mares to continue their competitive career whilst not missing out on the opportunity to breed from her whilst she is in her prime. It is also useful for producing offspring from mares that suffer early embryo loss.
Other forms of reproductive transfer include:
● Oocyte transfer: A more specialised technique that is used clinically. This allows the extraction of offspring from mares that cannot provide an embryo for embryo transfer.
● Gamete intrafallopian transfer: The transfer of both sperm and oocyte to the oviduct is currently only efficient when fresh semen is used, and so has limited application at this time.
● Intracytoplasmic sperm injection: This offers a method for in vitro fertilisation of isolated oocytes, as standard in vitro fertilization is not repeatably successful in the horse.
● Nuclear transfer (cloning): This offers a method for preserving the genetics of valuable individual horses.
A horse’s fertility is highly linked to its diet and so the horse feed used is key. The chances of conception can be significantly reduced in mares that are over or underweight and the ideal is to have a mare on a rising plane of nutrition ie gaining weight as she would naturally do in spring which is the normal time a mare would conceive. For horses bred out of season, which is usually much earlier in the year, it may be necessary to feed more conditioning horse feed to replace what spring grass would normally provide.
Just as for humans, a balanced diet with the correct vitamins and minerals is also important. Studies in dairy cows have shown that female fertility is linked to beta carotene. If an animal has access to fresh pasture then they will be consuming plenty but in the winter or for those stabled horses, it may be necessary to provide beta carotene in the supplementary horse feed ration. Green, leafy forages such as alfalfa are a great source and so feeding a couple of kgs a day would be ideal.
Pros and Cons of AI for horses
Semen for AI can either be frozen for later use or chilled for more immediate use. Freezing is a more aggressive process and so increases the chances of poor-quality semen which consequently reduces the chance of conception. However, the process of using chilled semen certainly has its pros and cons too. To successfully breed a mare with chilled semen, all parties involved, the mare owner, stallion manager, and vets, must all communicate efficiently throughout the entire process. This goes from coordinating the semen shipments to timing the mare’s ovulation which, if not being controlled using medication, requires consistent monitoring. Even Brexit has had an impact on the movement of semen from Europe to the UK as the rules have changed which can cause delays and increases the risk of the semen quality deteriorating.
Before the semen is shipped, the mare owner and the attending veterinarian must clarify several points with the stallion manager.
● The cost of stallion collection
● The cost of preparing the semen for shipment, the number of collections provided, the cost of shipping semen tanks by air, and when and how the semen tanks must be returned.
● The days of the week the stallion is collected.
● Times during the breeding season when the stallion will not be available.
● The number of days notice that the stallion manager needs before the semen shipment.
● The latest time one can call to obtain semen (for example-one must call by 9am to receive semen by the next day)
● The longevity of the semen
● First-cycle conception rate of the stallion.
● The method of transport used.
● Number of times the mare can be bred if she does not conceive.
● The breed registry requirements.
If all parties work in unison, the higher the chance of successful conception and the lower the risks will be. It has also been shown that the stallion’s diet can influence semen quality, especially in the context of how well it copes with being chilled or frozen. Using horse feed with higher levels of omega 3 fatty acids has been shown to be beneficial in some cases and the trace mineral zinc has also been linked to male fertility. With all the attention detail required for a successful mating, the horse feed needs to be considered too!
New reproductive technologies have given horse owners and vets a whole variety of options when it comes to breeding. These techniques have improved and widened the gene pool in some breeds. However, it is a costly process and as the saying goes, “only fools breed horses” so it shouldn’t be undertaken lightly.
